# Best Laid Plans

One of my favorite lines of poetry comes from the great Robert Burns poem, “To A Mouse, On Turning Her Up In Her Nest With The Plough” (not to be confused with his similarly titled “To A Louse (On Seeing One On A Lady’s Bonnet, At Church)”).

The line in question is, “The best-laid schemes o’ mice an’ men; Gang aft agley,” (go often astray), and — as you see — it applied to my plan to capture the last sunrise of summer this morning.

The sky was nice and clear… except in the east where I needed clear sky. The Sun is definitely just rising (according to my justified true belief) behind that bank of clouds (I took the photo at 7:02:38). It should be peeking up right at the end of the road, like a pot of molten gold.

Drat. I was so looking forward to the picture.

A small compensation: As I was walked down the sidewalk on the right I saw what I first thought was a large dog crossing the road. It was actually a mother deer, and she was leading her doe. (And there I was with a camera in hand just staring at them. I take some small consolation in that they were too far away for a good picture, but I still wish I’d reacted just a little quicker.)

The sky got a little prettier by 7:08 (now the Sun is behind the clouds behind the trees):

The foreground is the edge of a local park that winds for a mile through a wooded valley. Lots of elevation changes, so it’s a bit of a workout, but the upside is the strong sense of being in the woods. Really nice (I should do a photo essay like this one).

By the time (7:30) I’d walked a mile south (paralleling, but not down in that park), the Sun had finally gotten above the cloud bank:

On the right is my local library. (I wrote not long ago about the Cloud Library app that gives me access to their online catalog. I’ve read a lot of books that way this past year.)

If we could see the stars, we’d see that the Sun is now well-centered in the house of Virgo, although, in fact, today is the last day of the Virgo sign per the Tropical Zodiac (see Slowly Slipping Zodiac for details).

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Ah, well, best laid plans, so it goes, it is what it is. At least I got what was, for another hour, a shot of the summer Sun. As I write this, that same Sun is now the fall Sun (even though, at the moment, it’s still rising).

I don’t usually take my phone with me on walks (just my iPod), but sometimes I think I really should. (There is such great scenery here.) Yesterday I missed what could have been a some great shots of huge flocks of Canadian Geese flying overhead in canonical “Vee” formation.

Today, camera in hand, I got a pale imitation of that shot:

But it would have been so much better with them flying almost directly overhead like they were yesterday. Still it does show how large the flock is. That’s a lot of geese!

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As I’ve said, this is my favorite time of  year here. The weather cools off and dries out, the bugs go away, and (best of all) the leaves turn. I just love the riot of fall color — I’ve always favored earth tones.

The maple trees are some of the best, although they aren’t quite at their full glory around here, yet. The wild sumac, however, goes bright red pretty soon once summer starts to fade:

Some years I see the sumac go in late August. You see long-needle pines behind them. I love the long-needle pines — they put such a hush in the sound of the wind. (There are a lot of them in the Cathedral of Pines where I disposed Sam’s ashes.)

Birch tree leaves generally just yellow rather than turning red, but there is something about birch trees I just love:

For one thing, a stand of them in the distance seems to shimmer. The trees have smallish roundish leaves, and birch wood is very springy, so the leaves act as if they were on springs. The breeze makes them all vibrate, and the way the leaves reflect the sunlight makes the trees look like they’re shimmering. It’s not an effect I’ve noticed with other trees.

And then there’s that cool white bark that’s so much fun to peel off. I’ve never made a canoe of it, though.

In my little suburb there are some city-maintained walking paths that wind through a wooded buffer zone along the freeway. Long stretches of the chain link fence between the path and the freeway contain wild grapes:

Back when I first started walking those paths I couldn’t believe what I was seeing. But there is such a thing as (grape) wine from Minnesota, so people apparently do grow grapes here. Not that I have a clue, but I always thought grapes required warmer climes.

On the other hand, those are pretty pathetic little grapes. I don’t have the courage to try one, but they look pulpy, not at all juicy, and somehow perhaps vaguely poisonous for all I know. (I’ve noticed the birds don’t seem interested in them.)

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Since I was planning on a photo walk, I thought I’d get out a bit earlier and see if I could capture a shot of Venus:

The photo (taken at 6:19) doesn’t really do it justice. Venus was closer to Earth earlier in the month — it felt close enough to reach up and touch, in fact. Right now it’s roughly 90° from Earth relative to the Sun.

It moves faster than the Earth, so it will continue to pull ahead until it disappears from our view behind the Sun. After a while, it’ll be visible again as the Evening Star (Mercury, which is also about 90° from us right now, but on the other side, is visible in the evening after the Sun sets).

As you see, Mars is behind us, so it’s visible at night. It rises late and is still visible in the early morning before the Sun rises. I tried to get a shot of it, too:

But this doesn’t capture it at all (it’s hardly even visible). There’s no apparent red color in the photo although it’s readily apparently to the eye. It’s much more interesting (and very red) at night.

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So welcome to fall (it officially happened a bit over an hour ago as I type this line).

To see oursels as ithers see us!
It wad frae mony a blunder free us,
An’ foolish notion:
What airs in dress an’ gait wad lea’e us,
An’ ev’n devotion!

Stay safe, my friends! Go forth and spread beauty and light.

The canonical fool on the hill watching the sunset and the rotation of the planet and thinking what he imagines are large thoughts. View all posts by Wyrd Smythe

#### 79 responses to “Best Laid Plans”

• Wyrd Smythe

The first time someone told me about “To A Louse” I was sure they were kidding me and looked it up. That Burns was quite a character! 😀

• Wyrd Smythe

A friend with more tree knowledge corrected me. That stand of “birch” trees is, of course, aspen trees. A common name for which is “quaking aspen” — exactly because of the behavior of their leaves in the breeze.

I’ve always wondered how to tell birch trees from aspen (they are actually entirely different plants). Aspens have smooth-edged flat leaves, and their bark doesn’t peel. Birches have saw-tooth edged leaves with a slight “V” shape and their bark famously peels off easily.

So, hooray, I learned something about trees today!

• SelfAwarePatterns

Pretty nice walking environs. I’d have to drive somewhere to get that, so it doesn’t happen. Maybe once the pandemic is over. At least the temperature is getting milder, although we’re getting a lot of rain right now, which seems to always correspond with my walking times. (I’ve been doing a lot of indoor walking back and forth throughout the house.)

• Wyrd Smythe

Turns out I live in a pretty great spot. Elevation compared to the surrounding area means I never worry about flooding, although lightning strikes are more of a concern (the year after I moved here one blew a hole in a neighbor’s roof; this summer a big one took out the neighborhood’s power until the next morning). Tornadoes are maybe a potential concern, but there’s no history of them in this part of the Twin Cities (a benefit, I think, of being in the urban area’s heat shadow).

We’re a suburb that’s right on the edge between city and farmland, so there’s more elbow room than closer to the cities, and we have a lot of local wooded parks. Enough woods and lakes to support a local population of deer, not to mention foxes, rabbits, and other smaller wildlife. (If I were that into fishing, there’s a fishing spot I could walk to.) Enough out of the city that there’s no sense of urban “rat race” — very relaxed place. Not exactly Mayberry, but not all that far from it.

I’ve thought of getting a treadmill — the walking gets tough in the winter until they shovel and plow the various walkways (it can be several days before the city gets around to doing their bits; some people never shovel their sidewalks, even though it’s required by statute; I shovel my driveway as a form of playing outside). I was thinking I could use a treadmill while watching baseball games (which are usually at least 2.5 hours, more typically 3).

Instead, lately, I’ve been watching an online MIT quantum mechanics undergrad course during ballgames. Physicists talk about how truly understanding QM requires understanding the math, and I’ve gotten to the point I need that to progress. But this course is making it clear I need to go back and bone up on calc and then take the course again — perhaps actually doing the coursework, which is available online. The lectures are very good — excellent teachers — and I’ve managed to begin picking up things, so it’s really fun.

• Wyrd Smythe

I started listening to my Steely Dan albums on today’s walk. Those were also soundtracks to my younger days — a lot of memories. I haven’t really listened to Becker and Fagen in a long time, and I realized I’d have to give their catalog honor mention for Perfect Albums, too.

They’ve never done a tune I don’t like, and some of their major tunes will tell you. And musically they’re just awesome. That was the thing about Steely Dan — the musicality was so rich and complex.

Of course the downside is I’ve had Steely Dan tunes running through my head for two days now…

• Wyrd Smythe

I need to research the following idea, because I’m pretty sure it’s wrong, but if it isn’t there might be an experiment that can test this. I think it works the same way regardless of interpretation.

Imagine we prepare a quantum system Ψ and split it into spin-entangled halves Ψ1 and Ψ2. Part of the splitting involves setting the X-axis spin such that Ψ1(L) and Ψ2(R) (left and right). We give Ψ1(L) to Alice and Ψ2(R) to Bob. They take their respective halves to separate locations separated by a significant space-like interval.

If Alice measures her half, {X}Ψ1(L) — that is, on the X-axis — she always gets LEFT. Likewise, if Bob likewise measures his half, {X}Ψ2(R), he always gets RIGHT. Neither measurement changes the shared Ψ or causes any branching.

Note that, for both of them Ψ is a superposition of UP+DOWN.

If at time t1 Alice measures on the Y-axis, {Y}Ψ1(U+D), she gets UP or DOWN with equal probability. Under MWI, she branches into Ψ1(U) and Ψ1(D).

At this point there are three scenarios:

1. Copenhagen; non-local: Alice’s Y-axis measurement changes Ψ for her and Bob. The change is instantaneous. Depending on her 50/50 result, Ψ becomes Ψ1(U) for Alice and Ψ2(D) for Bob, or vice versa if Alice got a DOWN result.

Crucially, if Bob continued to make X-axis tests — constantly seeing a RIGHT result — Alice changing Ψ makes his test undetermined. Ψ2 is now in a superposition of LEFT and RIGHT. If Bob made a Y-axis measurement, he would get a DOWN result (assuming Alice got an UP) with 100% probability.

The bottom line is that, after t1 Bob has a 50% chance of seeing a (surprising) LEFT result rather than the expected RIGHT. (Once gets any result, he invalidates Alice’s Y-axis measurement, and now she might get an unexpected DOWN result if she repeats her measurement.)

The main test is whether Bob can ever get a (surprising) LEFT result demonstrating non-locality. (I believe Bell’s Inequality tests work somewhat along these lines.)

2. MWI; non-local: Basically the same thing happens, except that each measurement with an unknown outcome results in a branch. Assuming non-locality, Ψ changes simultaneously for both Alice and Bob, so all the same logic applies, except that we end up with lots of copies of Alice and Bob. (Who all go on to lead fruitful lives.)

The branching goes like: Alice:{Y}Ψ1(U+D) branches to Alice:Ψ1(U) and Alice:Ψ1(D). Because Bob’s Ψ2 is correlated (inversely), his half changes, too. Take your pick on whether there now two Bob’s (to match the two Alices). There definitely will be if he tests {Y}Ψ2, since Bob:Ψ2(D) and Bob:Ψ2(U) are required to compliment the two Alices.

3. MWI; local: If MWI (or any theory) is local, then Bob cannot ever get a LEFT result until the information about Alice reaches him. (Either because Alice informs him or because the wave-function is spatially limited to c.)

If Bob ever does get a LEFT result (after ALICE does a Y-axis measurement) before the change could reach him, then locality can’t be true.

So it seems like a feasible experiment that might falsify locality (in any theory). As I said, I think that’s ultimately what Bell’s Inequality experiments are doing, so it may be this has been done. The logic here illustrates non-locality can apply to MWI.

My problem is that this seems to potentially allow FTL communication, so there must be a flaw to the experiment or the logic. It wouldn’t be reliable — which might be enough — because there is only a 50% chance of seeing an unexpected result. But still, if Bob did see an unexpected LEFT result, he’d instantly know Alice had done a Y-axis measurement. (He’d have no idea what result she got, just that she’d changed the wave-function.)

((Wouldn’t it be weird if I just invented the Ansible? 😀 😀 😀 ))

• Wyrd Smythe

Note that Ψ(R) = Ψ(U+D) and Ψ(L) = Ψ(D+U), which is to say that the known eigenstate (R) or (L) is equally validly described as a superposition between (U) and (D).

Ψ(R) and Ψ(L) are eigenvectors with opposite eigenvalues (+1 and -1), so the superpositions they see have a sign reversal, hence the (U+D) versus (D+U) for them respectively.

• SelfAwarePatterns

Everything I understand about entanglement is that you can’t use it to alter the state of the remote particle, except by doing a measurement that causes it to take on a definite value. Along those lines, you also can’t use it to communicate. (There actually an annoying theorem call the “no-communication theorem.”)

I think the answer is this from the Wikipedia on entanglement:

Entanglement is broken when the entangled particles decohere through interaction with the environment; for example, when a measurement is made.[39]

If that’s right, then the issue ends with the first measurement.

So when Alice does her measurement of the Y axis, the entanglement has been broken. It puts the X axis of her particle in superposition, but has not effect on Bob’s, even under Copenhagen.

Of course, under MWI, the correlation was set at the entanglement, but was only relevant until the first measurement, and then only if the measurement was done on the right axis.

It would be nice if we could find ourselves to an ansible. But it seems unlikely with entanglement.

• Wyrd Smythe

Well, I was kidding about the Ansible (because I know communication is ruled out), and if the first test does break entanglement from then on that rules out experiments based on repeated tests.

The thing about the Wiki article is in invokes decoherence as what breaks entanglement, and I’m considering a system where the halves remain environmentally isolated and coherent. The question is whether certain properties, such as spin, might be measured without destroying the coherence. What I’m describing about Ψ(U+D) and Ψ(L+R) being orthogonal superpositions with regard to a single particle is basic quantum mechanics.

The question is whether we can apply it to a two-particle entangled system. Does measuring that system necessarily break entanglement? It might, but this is one question I have for an expert.

Regardless those first tests Alice and Bob make are correlated. Bell’s Inequality tests are based on that fact. Which is why I think the basic scenario I’m describing is along the lines of what such tests do. Alice measures along one axis; Bob measures along another. Certain alignments return classical results, but others return strictly quantum results. And seemingly demonstrate non-locality in the process.

(That MIT class I’m watching will be dealing with Bell’s in a few lectures, and I’m looking forward to seeing the mathematical analysis. The professor has already introduced a cool example that I’ll reproduce separately below. (Given a minute to write it up.))

Back to Alice and Bob. (I keep trying to introduce the gender-vague players Alex, Blair, Chris, and Drew, but even I keep forgetting to use them. And no one knows who I mean. Change is hard. 🙂 )

If, as described, Alex and Blair have, respectively, Ψ(L) and Ψ(R), and at t1 Alex measures on the Y-axis, let’s say she gets Ψ(U), then after t1 Blair’s X-axis measurement has a 50% chance of showing Ψ(L). Before t1 it was 100% of Ψ(R).

One flaw might be the assumption we can have Ψ(L) and Ψ(R) to give Alex and Blair to begin with. Maybe entanglement requires completely unknown states. Maybe we can’t split states that way.

In any event, the main question was locality, or lack thereof. I don’t see that MWI needs it to be one way or the other, and (as I mentioned) I have a sneaking suspicion all interpretations turn out to be non-local. Or at least the correct one does. My guess is reality has non-local aspects. We can’t leverage them — it’s like operating system level stuff — but reality does.

I’ll get around to that Tipler paper, I’ve got it bookmarked.

• Wyrd Smythe

In case you don’t see what I said to James: The more I think about it, the more I think a basic premise of the experiment is incorrect. It’s not possible to give Ψ(L) and Ψ(R) to Alex and Blair in the first place. My thinking now is that two entangled particles cannot be in a known eigenstate (or they wouldn’t be 100% entangled with each other). If that’s true, the conundrum is resolved and any hope of communication is out the window.

That doesn’t change the apparent non-locality these experiments display. It just means Blair never gets an unexpected Ψ(L). (And it means I have to try to think of an example that can’t be explained by decoherence between branches of reality. The way MWI “explains” locality so far seems worse than epicycles to me.)

• SelfAwarePatterns

I don’t think MWI’s locality is that complicated. It might seem complicated due to all the scenarios we ran through, but locality scenarios in special and general relativity are also always complicated mind benders.

But it’s funny you mention epicycles. I’m increasingly starting to see the idea of an ontological collapse as a giant epicycle-like kludge, and quantum non-locality as a nested epicycle-like kludge to make the big one work.

The nonlocality here is seen nowhere else in science and can’t be used for anything. It only seems to exist to plug a hole in the collapse view (also seen nowhere else in science). If it were real, I’d expect to see convergence on it from other places.

I suspect the collapse paradigm is the Ptolemaic model of quantum physics.

• Wyrd Smythe

“…but locality scenarios in special and general relativity are also always complicated mind benders.”

I’m reading a book about Einstein and Schrödinger — about how they developed their key theories and about how they interacted with each other. Upon finally getting GR, Einstein looked at his SR work as child’s play. I agree; SR is just geometry. GR, with its tensors, is actually more complicated mathematically than quantum mechanics, which is just calculus and trig. (Which is why I’ve realized I’ll figure out QM before GR. In contrast, I understand SR enough to presume to teach it. Because it’s just geometry.)

My point being that scenarios in SR are trivially easy. Finding mathematical solutions in GR is extremely hard, and even the experts struggle over it. QM is much closer to SR — both are undergrad topics.

That said, I can’t think of any GR thought experiment that doesn’t make sense — GR is a very physical theory, so scenarios make sense. The idea that Alex and Blair make independent measurements creating independent branches that either “meet up” or “pass by” because of being coherent or not is just as much of a hand-wave. It, too, is a kludge tacked on by those who’ve decided a theory must be right and are trying to make it work.

(Truth is, as in many unresolved topics, both sides have strong points and weak points, which is why the topic is unresolved!)

“But it’s funny you mention epicycles. I’m increasingly starting to see the idea of an ontological collapse as a giant epicycle-like kludge,”

Okay. (I think you should learn the math before you decide, though.)

“The nonlocality here is seen nowhere else in science and can’t be used for anything.”

Quantum phenomenon are seen only in quantum circumstances. Why would it be otherwise? Where would you expect it to be seen? That it can’t be leveraged by us is one reason I’m comfortable with it. As I said, it’s like operating system stuff we can’t access. A lot of our theories hint at an extended dimensionality to reality, and non-locality fits comfortably among such ideas.

I think we both need to take a careful look at Bell’s Inequality experiments, since that’s where non-locality really comes into play. (I suppose I’ll have to look at that Tipler paper sooner rather than later. I just hate line-cutters in my TO-READ list. 🙂 )

• SelfAwarePatterns

On the math, from everything I’ve read, the collapse shows up nowhere in it. It’s reportedly a postulate bolted on the explain observations. That’s an observation going all the way back to the original debates and observed again by John von Neumann in the early 30s. As an epistemic strategy in 1928, it made sense as a placeholder. But as alternatives started to become available, it seems increasingly difficult to justify.

On me personally learning the math, I’d like to, but my math skills aren’t there, and learning it enough to have any unique insights on advanced uses of it like entanglement and decoherence, doesn’t strike me as a productive use of my time. It seems like a multiyear journey, one difficult to do outside of a physics PHD program. (Not that I think you shouldn’t if you’re curious enough.)

My thoughts on the details of the Bell experiments are similar. From what I’ve read, the key thing is that they conduct a large number of measurements of a large number of entangled particles, to see if Bell’s statistical constraints are violated, which of course they are. But Bell assumes one set of outcomes, not a branching set of outcomes. Many MWI advocates take these experiments as evidence for MWI. (Of course, they view non-locality as a non-starter.)

• Wyrd Smythe

My point about collapse is that while, yes, it’s an unexplained assumption, so are the contortions necessary for locality in MWI. The deeper point is that both interpretations have pros and cons. (If they didn’t, it wouldn’t be a debate. There’s no clear winner here.)

My point about the math is that as long as I’ve been studying this I’ve heard over and over about how at some point one just has to turn to the math. The assertion has been that it’s not really possible to understand quantum mechanics through words.

I’ve always been interested in math, and since I retired in 2013 I’ve applied myself to digging into the math for quantum mechanics. That effort is starting to pay off, some of the puzzle pieces are falling into place. For example, I wrote Beautiful Math almost exactly five years ago. I’m planning an anniversary post about how naive that post is and how much I’ve learned about Euler’s formula since.

It turns out ei2πkx — which describes a plane wave — shows up everywhere in wave mechanics. Not just quantum wave mechanics, but any wave mechanics. For instance, it’s the basis of the Fourier Transform:

$\hat{f}(k)=\int_{-\infty}^{+\infty}f(x)\; e^{-i2{\pi}kx}\;dx$

So it’s true what they say. Learning the math opens a lot of doors to understanding. The words really don’t carry the necessary concepts. It’s maybe kinda like i, which some people find really hard to even accept as real. As I’ve tried to show in some past posts, from a mathematical understanding, it’s not just real and necessary — it’s almost obvious. There are things in QM that, once you begin to work with the math, become equally obvious rather than mysterious.

Which is not to say any expert view determines what’s real here. Even people who’ve spent years studying and learning at much higher levels disagree, and no one has the right answers. Or, more accurately, if they do, we don’t recognize them as the right answers so far.

“But Bell assumes one set of outcomes, not a branching set of outcomes.”

The thing is, one still has to explain the results of those experiments in our branch. Why do we see the results we see? The reason for using large numbers of particles is the same as in two-slit experiments. One particle, or even a handful, doesn’t show the interference pattern. That only appears with lots of particles. But, in both cases, the combined results seem to demonstrate something.

This lecture series I’m watching will discuss Bell’s Inequality, and I’m looking forward to a mathematical dissection of it!

• Wyrd Smythe

From a practical point of view it requires that Alice and Bob can maintain their halves of the quantum system for a period of time so they remain fully spin-entangled. And it requires creating those halves in the first place (although preparing them in a known state isn’t required — the first measurement either makes puts the system in a known state).

• JamesOfSeattle

Here is my naive understanding of what’s going on, which understanding I will NOT defend, because maths:

I think there are two ways of looking at the equations: epistemically and ontologically(many worlds),ignoring collapse.

Epistemically, the equations do not tell you what is really happening. They tell you a probability of what will happen if you or any system outside the system described by the equations interact with the system. Thus, there is no physical “superposition”. Superposition is just a way of keeping track of what happens inside the system before you interact with it. “Entanglement” is just a word for keeping track of certain information, specifically, mutual information, between parts of the system. In certain cases you can separate parts of the system such that if you interact with one part, then you will know (to some extent) what will happen when you interact with the other part.

So, epistemically, Alex is given a particle which has mutual information relative to the particle given to Blair. When Alex measures Left they know Blair will measure Right. Now, when Alex measures in the up/down direction, that interaction scrambles whatever they knew about the left/right direction. Thus, the particle is no longer entangled with Blair’s particle. The mutual information is lost. But Blair doesn’t know this yet.

Ontologically, so, many worlds, says Alex, with a Left particle, is in the same world with Blair and their Right particle. The particles are in an up/down superposition. When Alex measures up/down, a world splits off (either newly created a la Carroll or preexisting but identical a la Deutsch) so there is an Alex|up, Blair|right world and an Alex|down, Blair|right world. In both of these worlds, Alex’s particle is now in a left/right superposition and is no longer entangled with Blair’s. Alex’s particle has decohered with respect to Blair’s.

So I prefer the epistemic version, but I expect the argument will be that Bell’s theorem says the epistemic version doesn’t work. Bell’s theorem relies on Bell’s inequality, which inequality you so nicely explained in the other reply. My inclination is that the requirements for Bell’s Inequality will not be met. Specifically, that the different axes (plural of axis) of measurement will not be independent, in that measuring along one axis will change the later measurement of a different axis. Kinda like the act of counting the doors on the car actually changes the license plate (sometimes).

Now that I think of it, I’m not sure the epistemic version cares about Bell’s theorem. I need to look up how Rovelli handles Bell, but I think it might get handled the same way Carroll deals with it.

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• SelfAwarePatterns

The epistemic (antireal) strategy is a common one in this realm. I think it’s fine as long as we’re honest about what we’re doing. Because it’s not a complete account, and doesn’t try to be, it’s not subject to things like Bell’s theorem.

But it also doesn’t provide much of a foundation for further theoretical work, nor inspire experimental work. That tends to come from theories that at least take a shot at describing reality. Those theories could be wrong, and they come with metaphysical costs, but if any of them are right, the costs are already there, whether we acknowledge them or not.

I’m reminded of Andreas Osiander’s preface to Copernicus’ book, arguing that heliocentrism should only be viewed as a mathematical contrivance, not physical reality.

• JamesOfSeattle

Philosophically, there *cannot be* a complete account. Not from inside the system anyway, which is where we are. All we can get is better accounts. So string theory seems to be one such attempt. I don’t know what the current state of that is. What’s your take on string theory?

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• Wyrd Smythe

re the current state of string theory: Its star seems to be falling. It’s turned out some interesting mathematics, but no one has been able to make it into a physical theory. (I was an enthusiast at first, but then it got weird and overly complex, so it’s in my “Meh, Whatever” bin now.)

• SelfAwarePatterns

It depends on your definition of “complete.” I’m looking for a causal account. I’m becoming skeptical of the notion that we need to drastically overhaul what we expect of a theory just because of quantum mechanics. Bohr and company had to erect placeholders in the late 1920s, but I think their mistake was failing to admit that’s what they did. (I wonder if Einstein’s challenges didn’t drive them into more of a dogmatic position.)

My take on string theory is it seems to keep needing additional assumptions. First, it assumed that particles were loops of string. That was promising because it reportedly gave them the ability to derive both quantum mechanics and general relativity. But then they had energy conservation issues, so they assumed extra dimensions. But we don’t perceive those dimensions, so they assumed that the dimensions were microscopic and curled up. There were many different versions, which they reconciled with yet another dimension. I lose track after that.

My understanding is that all the assumptions are tightly motivated to fit the data. It’s not just a bunch of guys dreaming. But with that many, it seems like a house of cards. It’s still possible something comes out of it someday, and some physicists still characterize it as the least problematic approach, but it sounds like someone will need to have as big an insight with it as they would with GR and QM themselves.

• JamesOfSeattle

What do you require of a “causal account”? Because every causal account will look like input->[blackbox]->output. You might be able to pry your way into the blackbox, but that only gives you
input->[subinput->[bb1]->suboutput->[bb2]->…[bbn]->suboutput]-> output.
You will always have black boxes (bb’s).

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• SelfAwarePatterns

That may be true, but it’s the nature of the black box that is the issue. I want an account, at some level of abstraction, that explains why we see what we see. We don’t need to get down to particle physics to see the laws of thermodynamics as a complete causal account, an a priori account of a posteriori facts.

Again, I’m fine with incomplete accounts, if necessary, as placeholders. But like Newton, we should be clear what we’re bracketing and why. And that should be an open invitation for people to keep exploring.

• Wyrd Smythe

I agree with pretty much all of that!

The main issue is that I no longer believe Alex and Blair can be given Ψ(L) and Ψ(R) in the first place, so experiments that depend on their knowing a state can’t work. The best we can do is give them Ψ1 and Ψ2 — the first measurement of which gives the measuring party immediate knowledge and which then (depending on scenario)…

Copenhagen (non-local): …alters Ψ for the other party such that the first (and only meaningful) measurement they make reflects that change.

MWI (non-local): …splits reality into, for instance, Alex(U)+Blair(D) in one branch and Alex(D)+Blair(U) in the other. One of them knows this, the other would find it out upon making a Y-axis measurement. Note that if the other makes an X-axis measurement, they get LEFT or RIGHT with equal probability (and create new branches), just as the first one got UP or DOWN with equal probability (and branched).

MWI (local) [AIUI]: …the first measurement splits, for instance, Alex into Alex(U) and Alex(D), but Blair is unaffected. If Blair measures the Y-axis, Blair independently splits into Blair(U) and Blair(D). Both measurements create branches that expand as light cones, and when those light cones meet, the Alex(U)+Blair(D) one and the Alex(D)+Blair(U) one interfere constructively (?) while the Alex(U)+Blair(U) one and the Alex(D)+Blair(D) one interfere destructively (?). [I’m not sure what to make of language that says these branch cones either “pass by” or “meet up” so I’m winging it on saying they interfere.]

If Blair measures the X-axis, that would independently split into Blair(L)+Blair(R), and it would seem random which two of the possible four Alex+Blair pairings would “meet” or “pass” — in the other two scenarios it would be random.

One can certainly take an epistemological view of the wave-function. Or of any math describing reality — because that’s all math is, a description. (That’s why, on Mike’s post, I said I think it’s good to separate the actual Schrödinger equation from the putative physical wave-function. The former is just math describing the situation. The latter is a (putative) physical reality that can be described by other maths.)

On the epistemological view, a solution to the Schrödinger equation gives an amplitude, the norm-squared of which is the probability of getting that particular reading making that particular measurement at that particular spot (x,y,z) and that particular time (t). On this view, “collapse” is just finding a solution.

As you say, Bell’s Inequality experiments seem problematic for the epistemic view.

“Specifically, that the different axes (plural of axis) of measurement will not be independent, in that measuring along one axis will change the later measurement of a different axis.”

You, I take it, believe in something along the lines of a hidden variable theory there?

I have speculated that something like spin might be physically grounded in something that spins or wobbles. I see it as related to the quantum phase of the particle. (String theory seemed so attractive to me at first because, hey, there it is, a thing that spins and wobbles.)

So imagine that, unmeasured, it’s wobbling all over the place such that any initial measurement returns a “random” result. In reality, at the instant the interaction begins, the physical state of the wobble determines the outcome. The wobbling is at very high frequency (Planck level wavelengths here) so measuring it is effectively random.

Once measured, the wobble is constrained. For instance, if it was measured vertically, it’s now forced by the measurement into wobbling in a mostly vertical manner. But it still wobbles, so measuring it on an orthogonal axis produces a “random” result, but measuring it on the same axis reliably returns the same result.

• JamesOfSeattle

So yeah. My current best understanding is pretty much your wobble theory.

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• Wyrd Smythe

Great! If it flies we’ll call it Wobble Mechanics. 😀

• JamesOfSeattle

Sorry for jumping in here, but if Alex is given a spin-left particle and Blair a spin-right particle, there is nothing Alex can do to their particle (like measuring up/down) which would change Blair’s left/right measurement. Blair’s left/right measurement would always have to measure right. Otherwise, faster than light communication would be possible by giving each a hundred particles instead of just one. Alex could choose to make all the measurements or not, and if Blair makes all the measurements they will get 100 rights, or about 50 rights, depending on Alex’s choice.

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• Wyrd Smythe

Do you agree that is how it works in the single particle case? That, given Ψ(R), measuring {Y} gives either Ψ(U) or Ψ(D) with 50/50 odds and that both outcomes are now superpositions of (L+R) such that measuring {X} now gives either Ψ(L) or Ψ(R) with 50/50 odds?

So the question is why an entangled system that acts like a single particle system (in virtue of having a single wave-function) doesn’t show the same behavior.

The more I think about it, I think the answer might be that 100% entangled particles cannot be in a known eigenstate. If that’s true, it would completely eliminate any possibility of communication. And it eliminates the apparent conundrum involving Blair’s unexpected Ψ(L) — it can’t happen because Blair cannot have any expectations.

• Wyrd Smythe

There’s a reason I deliberately picked the “Best Laid Plans” post for this idea. I knew there had to be a plow that would overturn the nest. Just couldn’t see it any better than the wee beastie did. Not until it was right on top of me! 😀

• Wyrd Smythe

Think of a set of things: books, cars, food, whatever. Then think of three independent binary properties all members of the set have.

For example, if you have a library of books, you might pick {Books} as the set, and [A] Hardback (or not), [B] Sci-Fi (or not), [C] More than 200 pages (or not). These are independent properties; any book can have any combination of them.

If a book is a 350-page SF paperback, we say: [~A + B + C] is true. (~ means “not”)

If a book is a 42-page art hardback, we say: [A + ~B + ~C] is true.

As another example, if you have a view of a parking lot filled with cars, you might pick {Cars} as the set, and [A] Red (or not), [B] Four-door (or not), [C] Out-of-state plates (or not). These properties are, again, binary and independent. There can be a red two-door car with foreign plates [A + ~B + C] or a green four-door local car [~A + B + ~C].

Regardless of the set or properties you pick, the following is true:

n(A+~B) + n(B+~C) ≥ n(A+~C)

The function n(…) is “number of” — it returns the number of items matching the logical clause it takes as a parameter. As a trivial example, using the {Books} set, A is the subset of all hardbacks and n(A) is the count (or cardinality) of that subset.

Putting the above in words in terms of the {Books} set, the equation says: The number of books that are hardbacks and not SF, plus the number of books that are SF and not over 200 pages is always greater-than or equal to the number of books that are hardbacks and not over 200 pages.

There are various ways to demonstrate this logically (I’m planning a post that gets into this in detail). For now, define a {Set} with independent binary properties [A], [B], and [C], that all members share, and try it with some random population. Do the counts, see what you get.

Here’s the punchline: That equation is called Bell’s Inequality, and it’s necessarily logically true regardless of the {Set} and [A]-[B]-[C] properties (so long as requirements are met).

It’s necessarily logically true… except in the quantum world.

• JamesOfSeattle

Just wanted to say thanks for this. That’s a really good explanation of Bell’s inequality.

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• Wyrd Smythe

Oh, thanks! It’s due to Professor Allen Adams at MIT. I’m watching one of their online courses, 8.04 Quantum Physics, which is mainly about working with the Schrödinger equation — something I’ve always wanted to understand better.

Prof. Adams did it live during the lecture using the class {Students} although I forget what the A, B, and C, properties were. He did a poll, taking a count of hands for each property and then did the math. It was fun to see in action like that. He then showed a logical proof, but I’ve always liked the Venn diagram version. When I get around to writing a post about Bell’s Inequality I’ll show both proofs. And how quantum experiments violate it. I want to watch Adams lecture on the topic first.

• Michael

Wyrd,

I think you already figured this out, but if you start the experiment knowing each particles’ spin in a definite way, then I think you had to measure them in some way after the down conversion event to know this, and so that measurement would have broken their entangled state. At that point they would no longer be entangled with each other, right?

Michael

• Wyrd Smythe

Right. Certainly if they were measured after the split and before giving them to Alex and Blair. I was imagining that they could be prepared in such a way that they would be known to be Ψ(L) and Ψ(R), but I think that turns out to not be possible if the two are to be 100% entangled.

It’s reassuring, actually. I knew the idea couldn’t work; I just wasn’t sure why.

• Wyrd Smythe

A general sociological observation popped into my head while I was making lunch.

Many topics have good arguments pro and con but no resolution — the answer just isn’t known at this time. They’re debated so much because there are such good arguments either way (but no resolution — failed arguments or a resolution would end the debate conclusively).

The thought that occurred was that, knowing both sides have pros and cons, we tend to see a given side as having (unanswered) questions (which are okay) and objections (which aren’t). My thought is that we tend to side with a view that we see as having questions, but not one that we see as having objections.

For example, I see collapse and non-locality as questions that might be answered. I’m not sure I even have objections to Copenhagen so much as seeing it as incomplete (and having questions). On the other hand, I have objections to things like MWI, MUH, BUH, etc.

If I’m being fair to Mike’s view, he may have questions about MWI, but he has objections to collapse. (And non-locality also?)

The difference being that an objection is a question with the implication of disbelief. “I don’t think that can be right — can you prove it?” On the other hand, a question is neutral. “I don’t understand that — can you explain it?”

So the interesting sociological question might be why we see some questions as objections. I can’t and won’t speak for others, but I know enough about myself to see why collapse and non-locality don’t bother me whereas aspects of MWI do. (I’ve posted thoughts about collapse, and non-locality just fits in with my sense of the richness of reality.)

It strikes me as an interesting meta-question of self-awareness. Why do I believe the things I believe? What makes an unknown an objection rather than just a question?

• Wyrd Smythe

The Block Universe Hypothesis is a good example. I have serious objections to that one!

• SelfAwarePatterns

I think it comes down to your philosophical priors. The collapse, inherent randomness, and non-local aspects never sat easy with me. I was willing to accept them as brute empirical facts. Particularly since, when first reading about quantum physics, the alternatives sound nuts, especially in those introductory books that only devote a paragraph or two to each one.

(One of the things I’ve learned over the years is that ideas that sound obviously wrong in a short summation, but continue to stick around, are almost always more plausible when described by someone who buys it.)

But QM seems to require that we throw away centuries of physical principles that had guided us well from the scientific revolution until the 1920s. Now it’s always possible that’s still necessary. General relativity challenged many of our preconceptions, but it didn’t challenge logic itself. (By explaining gravity, it actually restored a hole in the causal view of the universe.)

One of the reason I think so many physicists are attracted to the MWI is because it gets us back to determinism and localism, aspects of the old mechanical philosophy. It does exact a heavy metaphysical price, but that price is unseen (at least for now), so it’s easy to ignore from a strictly scientific perspective, if not from a philosophical one. (In fact, many accept core Everettian physics but stay agnostic about the long term reality of the other branches.)

I was listening to Richard Brown’s podcast the other day. He was talking with Philip Goff and Bernardo Kastrup. (Listening to Goff and Kastrup debate each other and their skepticism toward each other’s ideas, BTW, was interesting.) Anyway, I was struck by the intense disdain Kastrup has for the MWI. Listening to him, I realized it takes away all the metaphysical idealism conclusions he derives from QM. It’s a reality he wants to be true, so he rejects a possible obstacle to it.

Myself, I want to understand the universe, so given alternatives, I’m going to gravitate to the one that seems to provide a more causal account, a less magical seeming one. Part of that comes from a life where the magical explanations have all turned out to be bunk. But I’ll also admit that the idea that just following the mathematics of QM, not only solves the measurement problem, but leads to something so unsettling and groundshifting, an expression of the Copernican principle to an extent previously unfathomable, is bracing and enticing.

But as I’ve noted before, it’s possible all the interpretations are wrong, and the reality is so unimaginably strange that our brains can’t model it. But it doesn’t seem productive to assume that.

• Wyrd Smythe

“I think it comes down to your philosophical priors.”

Yes, definitely. My pondering has to do with how those priors cause us to frame things as mere questions to be answered or as objections to things we see as problems. What underlying views account for disbelief versus an open mind? (You touched on this in a post recently, and it’s been on my mind a lot in the current political climate.)

“But QM seems to require that we throw away centuries of physical principles that had guided us well from the scientific revolution until the 1920s.”

QM sure has aspects that challenge our intuitions! (Just to be clear, though, this question versus objection thing exists in many (most? all?) human endeavors. As I say, I’ve been pondering it with regard to politics and society.)

So, for that matter, does something as simple as SR. Or, for some, even just math itself.

It does seem that science leads us into understandings far beyond our daily experience. I think I’ve talked before about the notion of “informed intuition” — that the more one knows about a topic, the better one’s intuitions about it are. I recall we’ve also touched on the Dunning-Kruger effect — that one needs a certain level of base knowledge to even understand the questions.

I think here I’m mainly focused on informed intuition. When we’re informed on a topic, what aspects of our, as you put it, philosophical priors causes us to be sympathetic, neutral, or opposed? You suggest, as in the case of Kastrup, it’s vested interests, which I’m sure is one reason. (I have to admit, it would be kind of funny to watch Kastrup and Goff, two guys whose ideas I very much object to, object to each other.)

But in the average discussion there aren’t really vested interests (other than one’s ego, I suppose). It just seems weird to me that some questions have that extra layer of being objections. It makes me ask myself what exactly I’m objecting to.

“I want to understand the universe, so given alternatives, I’m going to gravitate to the one that seems to provide a more causal account, a less magical seeming one.”

I think that’s generally true of all of us who pursue science. The confounding thing — what I’m getting at here — is how we frame and sort ideas as physical (causal) versus magical. To some, collapse is magical; to others, multiple worlds is magical. (It’s another form of question versus objection.)

“I’ll also admit that the idea that just following the mathematics of QM,”

As an aside, one of the most annoying aspects of science to me is how \$&%#@ well the math of GR and QM predict our experiences. Especially the latter, since I view it as more incomplete compared to GR. We know absolutely and for sure that neither is a correct theory. They are, at best, incomplete. Both of them.

But, damn, they work so well to so many decimal places. Drives me crazy. Why can’t we reconcile them?

• SelfAwarePatterns

In the case of Kastrup, maybe it’s being too harsh to suppose vested interests instead of just his own strong priors. Although now that I’m thinking of it, Kastrup characterized the MWI as a desperate move by the physicalists (he singled out Carroll) to preserve their worldview. So he sees it as vested interest in the other direction. (Which is strange since a lot of physicalist shun MWI, and it seems like there were more idealists in the 19th century when determinism was more firmly entrenched.)

In the case of QM, it often seems to come down to which aspect of reality being overturned bothers us the most. I think that’s why antireal interpretations are popular. They allow people to just not think about it, a way to seemingly dodge the weirdness tax.

Strangely enough, if the non-local effects were more robust, I’d actually be more willing to accept them, thinking maybe there’s a tiny wormhole or something between the particles. It’s the very tenuous nature that makes me doubt it.

In the case of the collapse, I think what bothers me about it is its abrupt nature, and the idea of things just disappearing from reality. I’ve always found the idea disturbing, and that we simply have to be missing something. Just accepting it as some kind of fundamental thing feels like giving up.

I think I mentioned that Philip Ball’s articles attacking the MWI actually strengthened it in my eyes. But I have to admit that Ball channels what I think disturbs a lot of people about the MWI. Many interpret it as rendering our sense of self, and our understanding of the world, meaningless. It seems to say the self and perceived reality are illusions. I think that’s looking at it wrong, that the self and classical world are emergent, but it seems people have a visceral reaction and struggle to see it that way.

There’s a lot to be said for keeping all theories at arm’s length. Hakwan Lau argued that theories can become their own dogmas if we’re not careful. In that sense, while I think MWI is viable and promising, it remains for me just a candidate for reality. I need to understand the energy issue better, but also would like to see evidence for remnant interference between decohered branches.

On QM and GR, do we know both are wrong? My understanding is it could be both wrong, or just one of them. Although I think GR breaks down in black holes anyway (singularities).

• Wyrd Smythe

“Which is strange since a lot of physicalist shun MWI,…”

I’ve been wondering about the breakdown on the backgrounds of those who shun vs support MWI. For example, are those who are primarily mathematicians more or less inclined towards it. I know some disciplines seem to lean more towards it. In Kastrup’s case, MWI is goring his ox, so he would naturally oppose it. Carroll certainly wants his book (and career) to succeed. But even those of us with no ox or dog in the hunt seem strong in our views. (Funny how polarizing it is. You’d think we were talking politics or religion.)

“It’s the very tenuous nature that makes me doubt [non-locality].”

The effect is robust, so by “tenuous” I assume you mean the inability to leverage it? The irony is that’s the very property that makes me comfortable with it (as I’ve described above). How does the tenuous nature of non-locality compare with what many might call the tenuous nature of MWI?

“In the case of the collapse, I think what bothers me about it is its abrupt nature, and the idea of things just disappearing from reality.”

Yeah, that’s generally the main objection. Mathematically it means a discontinuity in the Schrödinger equation — it jumps from one form to another form (or vanishes entirely).

For me the conundrum here isn’t solved by MWI. The question I need answered involves the apparent reality of the particle’s momentum wave-function being spread out everywhere the particle could travel. The momentum is well-defined, but the particle could be anywhere. Then it interacts with another particle — now we know exactly where it is (and nothing about its momentum). It’s that spread out momentum wave-function that seems to “collapse”. If the wave-function is real, what spread out, and what vanished?

My first question (not objection, BTW) for MWI is: Exactly what is the ontology of the wave-function. Most supporters of MWI deny the view is Tegmarkian, so what actually is the wave-function? To some it’s just math, but MWI insists it’s real. So what is it? (Another way to put it: What’s reality actually doing when it does this stuff?)

(Then we get to my energy objections. 😀 )

“I think I mentioned that Philip Ball’s articles attacking the MWI actually strengthened it in my eyes.”

Ha, yes. I think I mentioned how Sean Carroll’s book had a similar, but opposite, effect on me. I think that probably says more about our views than anything else. 😉

“Many interpret [MWI] as rendering our sense of self, and our understanding of the world, meaningless.”

So I’ve heard. I can honestly say that aspect has never crossed my mind! As you say, I’m just a tiny emergent piece of a fascinating reality I want to try to understand.

“On QM and GR, do we know both are wrong?”

As you said, GR breaks down in BH singularities and also in the first instants of the Big Bang. There is also that it’s background independent and assumes a smooth spacetime continuum. The former is kinda nice, but both conflict with a quantum view. (It’s exactly the continuum that’s the problem with singularities and the BB.)

QM (or QFT for the fullest description we currently have) has all sorts of holes, of course. (That might make an interesting post.) No description of gravity, dark matter, or dark energy; background dependent; all the issues we’ve been discussing re measurement; why only three families of matter; why no right-handed neutrinos; etc. Quantum is actually kind of a mess, but it’s the best thing we’ve got and, as I mentioned above, it’s proven annoyingly effective.

• SelfAwarePatterns

MWI seems to get a good deal of support from cosmologists and quantum computational theorists, both groups that do seem very math oriented. Interestingly, a lot of the stuff I’ve read on quantum computation tends to be in terms of Heisenberg type matrices rather than Schrodinger. And Deutch in one of his papers remarks that it’s easier to see important details with matrices (particularly for locality), although I’ve read they’re harder to work with overall, but in the age of computers, maybe it’s less of an issue.

On non-locality, as I mentioned above, it seems like if the universe allowed that kind of interaction, we wouldn’t see it in just one place. Now, maybe this is the canary in the coal mine, and in the future we will see it in lots of other places. Of course, if we do, then it becomes more of a threat to GR. Honestly, even in the limited way it’s supposed to exist to support the collapse postulate, I think it challenges GR, and that many physicists are just in denial about it. Einstein’s concern strikes me as rational.

On the tenuous nature of MWI, I think the difference, at least for me, is that the other worlds come about as logical consequences of just letting the dynamics play out. I’d feel different if, like string theory, it required lots of additional postulates. It is a radical expansion of our ontology, and so caution is warranted (we might have implicit assumptions), but our ontology has been expanding throughout the history of science, from an Earth centered universe, to a sun centered one, to the sun just being one of billions of stars, to our galaxy just being one of trillions. (Maybe another reason for cosmologist support.)

“If the wave-function is real, what spread out, and what vanished?”

My understanding of MWI’s answer is that what appears to now be the particle is the fragment of the wave our environment is now entangled with. What vanished are the other parts of the wave that are now decohered from each other, each entangled with their own branch of the environment.

On what the wave actually is, I don’t think MWI addresses that, other than accepting it as something real whose evolution is modeled by the math. What is matter? What is energy? What are fields? It seems like fundamental physics is always in terms that we have to accept as brute entities, but that may be pierced in the future.

On GR and QM, when you say “background independent” and “background dependent”, what do you mean?

• Wyrd Smythe

GR doesn’t assume any underlying manifold — it defines the manifold. As is often said about GR, “Matter/energy defines how spacetime curves, spacetime curving tells matter/energy how to move.” The metric tensor in GR defines the background.

QFT exists within some manifold (spacetime). It assumes a background.

I long wondered if there isn’t just another duality similar to wave/particle or other conjugate pairs (like position/momentum). Maybe reality simply has two descriptions. But stuff I’ve learned in the last decade or so suggests that’s naive.

I’ve also long thought spacetime might be smooth, a true continuum (whereas we know matter/energy is quantized), but things I’ve learned recently are making that increasingly unlikely. And if spacetime isn’t smooth, then GR is, at best, an approximation. (An astonishingly accurate one.)

• Wyrd Smythe

“Interestingly, a lot of the stuff I’ve read on quantum computation tends to be in terms of Heisenberg type matrices rather than Schrodinger.”

Whoa, triple synchronicity! Yesterday evening I watched the lecture on S-matrices. Last night, in that book about Schrödinger and Einstein (Einstein’s Dice and Schrödinger’s Cat, Paul Halpern, 2015), I read about how and why Heisenberg developed the S-matrix, and now here you mention it. Weird!

Yeah, it’s an alternate way of working with certain quantum situations, and I think qubits would definitely be in that category. AIUI, the matrix contains coefficients that are similar to those used in creating superpositions.

According to Halpern, the Schrödinger equation won out as the most commonly used because the wave function is closer to physicality whereas the matrix is entirely abstract. Schrödinger apparently campaigned vigorously in favor of his version over Heisenberg’s on that reason. 🙂

“On non-locality, as I mentioned above, it seems like if the universe allowed that kind of interaction, we wouldn’t see it in just one place.”

I’m finding it hard to separate litigating the issue from the meta-question of why we pick those litigation positions. Maybe it can’t be separated. OTOH, I want to continue the debate about locality, but (OTOH) I also want to try to force myself to stick to the meta-topic.

WRT the meta-topic, you may have helped me see a thread to pick at. I just realized I (rightly or wrongly) perceive aspects of what you just said about non-locality as a misunderstanding. That generates the urge to clear up the misunderstanding, and when I thought about it I realized that urge underpins a lot of my debate participation. It’s the sense that we could reach agreement — we’d see it the same way — if we both understood it the same way.

So maybe at root a lot of the more persistent debates (speaking for myself) come from a desire to figure out why there is a misunderstanding.

Always implicit is that the misunderstanding could be mine, but I generally don’t pursue a topic I don’t understand. (There’s a Dunning-Kruger aspect to that, though. It’s always possible think one understands a topic far better than one actually does. Most education should be an exercise in finding out how much more there is to learn.)

Perhaps an approach based on mutual understandings would produce interesting results. Something to think about.

“I think [collapse] challenges GR,”

Can you give me a scenario?

“On the tenuous nature of MWI, I think the difference, at least for me, is that the other worlds come about as logical consequences of just letting the dynamics play out.”

Can’t that idea be applied to many aspects? Something is a logical consequence of the dynamics? That’s really what I’m getting at here. We structure our thinking to support ideas we’ve accepted (and to reject those we haven’t). What seems a logical consequence to one may not to another. Even views of what the dynamics are can vary.

The thing about additional postulates is that that’s selective, too. MWI ends up with additional postulates that are implicit in its dynamics. Imposing a locality requirement, as I mentioned, bolts on a huge additional postulate in assuming that entire branches of reality can cohere or not. (And we know there are assumptions about energy that don’t match our experience.)

But if one favors MWI then one largely waves away these as mere questions to be answered. If one doesn’t, one sees them as serious objections.

Conversely, if one favors String Theory, one can claim everything is a (mathematically!) logical consequence of the dynamics. As I mentioned, that’s one reason I got off the ST bus. The simple idea that particles are strings, when examined closely, led to a vast swampland. Not just the landscape issue, but the theory went from strings to branes in various dimensions and then onto multiverses. The whole thing blew up into a mathematical fantasy land. NeverNeverLand for mathematicians.

“My understanding of MWI’s answer is that what appears to now be the particle is the fragment of the wave our environment is now entangled with.”

Fragment of the wave? Okay, but isn’t this an additional assumption? In any event, I have deep questions about the ontology of the WF. I think a clear-eyed look at any interpretation reveals assumptions and axioms. That the wave-function is ontologically real is a very large assumption and, clearly, the central axiom of MWI.

(I’ve realized one thing that sets me against MWI is the faint sense of evangelicalism. There is a slight sense to me of MWI being somewhat cult-like or group-think bound. I tend to have antipathy towards anything like that. (Plus I think it’s based on a misunderstanding. 😀 ) As you said above, there is something to be said about keeping all our theories at arm’s length.)

• SelfAwarePatterns

On GR, I think Brian Greene said it best, quantum non-locality preserves the letter of GR, but violates the spirit. He described it as GR remains intact, but just barely. No equations (yet) have been violated. But the philosophy behind those equations have, which is why I think Einstein was unhappy about it.

It’s tough to explore why we hold certain positions without it sounding like arguments for those positions. Although there’s something to be said for focusing on why rather than just making points and counter-points.

My understanding is that locality is not a postulate of MWI. MWI is supposed to just be QM without the collapse. If those mechanics were non-local, then MWI would be non-local too. I know you do see them as non-local, so from that standpoint would tend to see MWI as non-local. I don’t know the math enough to discuss it intelligently. I just know that the physicists I’ve read see the collapse as the thing that brings in non-locality.

One question someone on the other thread asked me about the energy question is, in Copenhagen, what happens to the energy of the other branches when they disappear? I have no idea what the answer is. I read that objective collapse theories actually add new equations (new postulates) into the mix. I wonder if they address it.

On string theory, I think the question would be, logical consequences of which theory? As I understand it, nothing in GM or QM leads to it. You have to add in additional assumptions. But it’s the number of assumptions that I think is really the issue, not that they have any at all.

“Fragment of the wave” is my (possibly very poor) way of describing it. But it’s supposed to fall out of the math.

MWI is definitely a realist theory. It assumes the math models something real out there. My reasoning is that something seems to cause the interference pattern, and that if it isn’t a wave, it seems to produce wave-like consequences.

I know what you mean about the cult like aspect. It seems like part of a bigger issue. Reading about the history of QM, I’m struck by how dogmatic many people were throughout that history. For a long time, those proposing alternatives to Copenhagen were treated with hostility. Anyone who worked in quantum foundations risked their career. John Bell reportedly told graduate students who wanted to work with him to think carefully before doing so since they’d be marked afterward. It’s like reading the history of a religion.

In the case of MWI, I suspect it would have withered away in obscurity if there hadn’t been people like Bryce DeWitt who were aggressive advocates. The reason for that evangelicalism is they feel like they’ve found the answer to quantum mechanics, the one that banishes most, if not all, of the paradoxes. In its darker form, many feel like it’s obviously the right answer and people who won’t accept it are just unwilling to face the truth.

My take is we should regard it as a promising prediction of quantum mechanics we can’t test yet.

• Wyrd Smythe

“But the philosophy behind those equations have, which is why I think Einstein was unhappy about it.”

Yes, he hated “spooky action at a distance”. But, as you say, there’s no violation of the math, so the objection is strictly philosophical. Isn’t that similar to people’s reaction to MWI? It follows the math but raises philosophical hackles?

“My understanding is that locality is not a postulate of MWI.”

Yep. 😀 😀

“I just know that the physicists I’ve read see the collapse as the thing that brings in non-locality.”

That’s true, and I can see why one might think that means non-locality goes out the window. The problem might be that it requires a view from outside — one that can see more than one reality — to perceive the locality. From inside a single branch, things still appear non-local.

That may be because all interpretations ultimately must explain what we see, so they can’t escape certain consequences of our observations. Our observation is that, when Alex alters a Ψ shared with Blair, that wave-function changes for both of them regardless of spatial separation.

The question is, which is more acceptable (and per this thread why?): [A] The wave-function has “magic” properties that allow it to (without violating causality) transcend spacetime; or [B] The wave-function has “magic” properties that allow it to create new realities that apparently share our space but are inaccessible to us.

“…about the energy question is, in Copenhagen, what happens to the energy of the other branches when they disappear?”

That touches on one of the points I made there about the energy accounting in the measuring device.

Detecting a single particle isn’t easy. In fact, I want to learn more about how it’s actually done in various types of experiments, but we can talk about photomultipliers, which can detect single photons. They leverage the photoelectric effect to generate an electron that is cascade amplified to a large enough current to be detected by a high-impedance amplifier.

Essentially a series of energy amplifications to develop a classical signal, but it starts when a single photon strikes a (vapor-thin) metal cathode. Per the photoelectric effect that won Einstein his Nobel prize, that photon ejects an electron from the metal. Crucially here, there is a full accounting of the energy, from the photon to the output signal.

So consider Sean Carroll’s beam splitter. A single photon source sent through a half silver mirror to two detectors.

The Copenhagen story is that there is a superposition between two possible paths, and that superposition “collapses” when — apparently randomly — one or the other detector decides it has seen the photon. The important bit is that it sees all the energy of the photon. The energy of the photon was never “split” between branches; it was effectively spread all throughout the space it might be reasonably found if looked for.

In flight, undetected, the photon is entirely described by its momentum (energy), which means there is no description available of its position. It is literally everywhere it could be. When it does interact, we know its position, and the interaction that causes something to happen (an electron is ejected in this case). Note that in localizing the photon, we lose the description of its momentum — that energy has been transferred to whatever the photon made happen.

I don’t know how helpful this is: In a wave mechanics, momentum and position are Fourier transforms of each other. As such they cannot exist simultaneously. (It’s why the Heisenberg Uncertainly relationship exists.)

So what’s spooky in Copenhagen is how the photon is described by a momentum wave that’s spread out, and the energy of the photon is contained in that wave. So how does the energy in a wave wave suddenly “collapse” into a single point-like interaction? That’s the non-locality part. Somehow all that spread out energy has to collect at the interaction because all the energy of the photon is accounted for in that interaction. And it appears to do so instantly.

So, Bell’s distance experiments aside, there’s a weird non-locality to every quantum interaction. But under Copenhagen, there’s no issues with energy accounting.

“On string theory, I think the question would be, logical consequences of which theory? As I understand it, nothing in GM or QM leads to it.”

No, and part of the issue is that, since string theory is a base-line axiomatic theory, GR and QM have to fall out of it. In fact, one reason for its initial success is that the graviton did fall out of it.

“MWI is definitely a realist theory.”

Yeah, so they say. I find the term a bit dicey applied to any multiverse theory, though. 🙂

“My reasoning is that something seems to cause the interference pattern, and that if it isn’t a wave, it seems to produce wave-like consequences.”

I find the MWI way of producing interference very weird. I don’t think Everett’s original version produces it at all (although I could be wrong; there are entire sections of that paper I can’t parse).

Consider, on the one hand, the Sean Carroll beam splitter. Here two paths are available to the photon, under MWI it takes both, reality branches, and both detectors detect. But we don’t see any of that because they’ve decohered. There’s no sense of interference here.

But in a two-slit experiment, what? Immediately upon leaving the laser, the photon splits, reality branches — but doesn’t decohere — so the photon goes through each slit in a different branch, and each one goes to the same apparently random spot? That’s the only way to get interference — the two paths have to end at the same spot.

The beam-splitter reading of MWI would suggest that, once the photons branch, reality branches. Why do separate branches of reality conveniently interfere when needed, but not otherwise?

“It’s like reading the history of a religion.”

I think there’s a lot of truth to that. Einstein believed in Spinoza’s god. Many scientists don’t admit to any kind of god, but I think everyone craves something to believe in. For many it’s science, and it has to be disconcerting to have one’s beliefs challenged, let alone invalidated.

“The reason for that evangelicalism is they feel like they’ve found the answer to quantum mechanics, the one that banishes most, if not all, of the paradoxes.”

Yeah, it’s exactly what I was saying before about seeing an opposing view as a misunderstanding of the facts. Correcting that feels like being helpful. 🙂

• SelfAwarePatterns

On MWI and realism, I was careful not to say “realistic” since I knew you’d object. 🙂

More precisely, as an instrumentalist, I think MWI aims for realism, which makes it more complete than the antirealist theories. But it’s the nature of such theories that they make a stronger statement, and so have a higher chance of being wrong. For me, there’s no guarantee any theory is actually realist, but I like them to aim for it.

On MWI and the two slit experiment, in my mind, there’s no absolute point when reality splits. You’re right that the split exists right from the beginning, but it has a limited scope. For anything outside of that scope, it’s still a superposition. For anything within the scope, reality has split. Decoherence could be seen as the superposition cascading into the environment, resulting in progressively less interference between the branches, until it’s no longer detectable. So we only see interference very early in the process (unless the system is kept isolated and the superposition can’t cascade).

David Sloan Wilson, in an old ScienceBlogs post, once remarked that truth is his god and science his religion. It’s not a statement most scientists are comfortable making, but I suspect it represents a view many implicitly hold. Of course, to really hold to that, means holding all theories as provisional, easier in theory than in practice.

• Wyrd Smythe

“For me, there’s no guarantee any theory is actually realist, but I like them to aim for it.”

I’m with you on that. In terms of this thread, I think we can sometimes see what’s realist or not in terms of those priors. (The obvious example being that I don’t see MWI as being at all real, despite the claims.)

“For anything outside of that scope, it’s still a superposition. For anything within the scope, reality has split.”

What is inside and outside the scope of the wave-function that is a superposition of two paths? Thing is, it’s the superposition inside that accounts for the interference pattern.

Copenhagen: Ψ describes two paths in superposition. What that means is that there is Ψ1 and Ψ2, each of which is a solution, representing a path through one or the other slit. Adding two solutions creates a new solution, Ψ, which is a superposition with coefficients for each contributing part.

Recall the above about how a photon in flight is described by a momentum wave with a precise energy and no position. Both Ψ1 and Ψ2 are such a description. Their superposition is also a description, but it’s one that interferes. (This is what I mean by the interference and superposition being inside.)

What’s actually interfering is the phase of the energy. A photon in flight has constant energy, but the phase of that energy rotates. (Above I mentioned ei2πkx. Among many things, it describes the rotating energy phase.)

The final solution for Ψ(t,r) involves a time, t, and location r. That’s where the interference determines the final result. The phases rotate for so long over such a path to point r. The solution combines them for an observable.

MWI: Honestly, per Everett, I’m not entirely sure any branching occurs in the two-slit experiment. What exactly constitutes different outcomes here? The two paths through the slits merge. It’s not at all like a beam-splitter experiment with two definite outcomes.

One view might be that MWI says each possible electron the photon could interact with constitutes a branch. In this case, the interference is still a result of wave mechanics, and there are a vast number of branches for each possible electron. (If MWI branches on this order, then walking down the street wearing polarizing sunglasses creates zillions upon zillions of new worlds.)

Another view might be the branch happens immediately (but there is still the problem of zillions of paths available and zillions of final interactions) and then, despite branching they can interfere with each other until the photon lands and they merge? I really don’t see how MWI applies, let alone helps, with the two-slit experiment.

This conversation is getting superposed between this thread and Michael’s down below. Feel free to reply to this below.

• Michael

Mike and Wyrd (and James),

Greatly enjoyed this exchange.

I wanted to chime in with one point that Wyrd already explained, but express how it “really hit home” to me, just in case that is helpful to Mike. That is the background independence of GR. And the light bulb went on for me when it was pointed out that Newtonian mechanics occurs in a universe in which time and space are absolute. They are basically the stage on which the actions occur, but are utterly unaffected by those actions. This is how quantum mechanics works, at least that is my understanding. Wyrd, who has taken the course now, can let me know if that is mistaken. But GR removes COMPLETELY the notion of an absolute space and time. There’s just no such thing, as their properties are variable, and included in the theory. That’s the background independence thing, and my understanding is that the mathematical basis of GR and QM are ultimately irreconcilable because of this fundamental difference in their starting points. You just can’t take a theory that is based on absolute time and space coordinates and jam it into one in which those simply don’t exist. And vice versa.

Second thing… Mike once posed a question on his blog about whether or not someone could think of something that was real but immeasurable. And I think that’s the other worlds of MWI… One question for me is this: if all these worlds are “decoherent” but occupy the same physical space essentially, what the F is going on?

I think of the radio station analogy, where maybe different branches have a different fundamental frequency, but it’s something different than that because if they were waves in the same medium they would interfere continuously right? And they don’t. So other branches are really a wild thought experiment: They branch from the same point in physical space and physical time, and then we say they are equally real to what is here now and observable, but for all intents and purposes they disappear completely and do not interact with any other elements of the branch of reality we occupy. But they’re just as real as ours. And they’re not just distinguished by different frequencies or something… They’re just ghosts altogether. How do you explain what the hell that is!?

The only “logical” explanation is that decohered branches are physically disconnected universes. Right? How else could that be viewed?

Michael

• Wyrd Smythe

Thanks, Michael.

“Wyrd, who has taken the course now, can let me know if that is mistaken.”

You are correct throughout. With the tiny caveat that Wyrd is taking the course (and will probably have to take it again after brushing up on calc skills to actually do the coursework). It’s 24 90-minutes lectures; last night I just watched #14, “Resonance and the S-Matrix” (later, reading Einstein’s Dice and Schrödinger’s Cat, I read how Heisenberg created them, and then this morning Mike mentioned them in his comment — triple synchronicity).

Anyway, yes. As you say, (and AIUI) the Schrödinger equation (or S-Matrix) assumes a background x, y, z, and t, that are unaffected by quantum interactions. Those are always external variables representing some manifold.

GR has a metric tensor, which essentially defines x, y, z, and t.

The difference absolutely is a huge part of the problem reconciling them. (And led to my wondering if that was just another duality we might be stuck with.)

“I think of the radio station analogy, where maybe different branches have a different fundamental frequency, but it’s something different than that because if they were waves in the same medium they would interfere continuously right?”

Absolutely. The electron movement in any antenna reflects all the radio wave photons impinging on it (given the antenna’s resonance increasing some frequencies and decreasing others).

You’re hitting on what’s grown to my #1 question about MWI: What exactly is the proposed ontology? As you say, “what the F is going on?”

If I understand the wave-function per the Schrödinger equation (and I’m not saying I do yet), the general expression ÔΨ refers to applying an operator (Ô) — it could be an energy operator, a position operator, or a momentum operator, for example — to the wave-function, Ψ, which I understand to be just a multi-dimension vector in an appropriate Hilbert space.

(One thing I’m not yet clear on is whether Ψ comes with math that controls its evolution, or if that evolution is strictly due to applying an operator. I’m thinking the former, since it’s common to see Ψ(t) or Ψ(x,t) notation, which makes Ψ literally a function that, given some time (and/or location) returns a vector. I think that’s a pre-req topic I’ll have to go back and cover, since the lectures and exercises seem to assume the student knows exactly what Ψ is.)

Anyway, (AIUI) one defines the desired operator and solves ÔΨ=oΨ — where o is a real number. And solving it is what “collapses” the wave-function, because the solution selects an eigenvector (physicists call it an eigenstate) where the real number o is the measurement value. So Ψ goes from all possible superposed values to only those values matching that eigenstate (times some constant).

So (assuming I have any clarity on this at all) how does that translate to MWI ontology? What is supposedly happening? What does it mean for reality itself to be superposed like that? (This is why I think it might be a good idea to separate the Schrödinger equation from the ontology of MWI and focus on the physicality of it.)

Just consider Schrödinger’s notorious cat. The one that’s both dead and alive. (And Schrödinger’s whole point was how ridiculous this is physically.) How are there two superposed cats? What does that mean? Is each individual particle entangled with a matching one in the other cat? Normally when two things are entangled, we see two of them. If they decohere, there’s still two of them. So how is there a second cat, and where does it go?

• SelfAwarePatterns

Hi Michael,
Supposedly decoherence is not an absolute process. Under MWI, there actually is interference between worlds, but it is extremely difficult to detect. Many physicists think it might be possible in the future. It might be in the femtoseconds after decoherence, where the experimenter could still predict what that interference might look like, but that would let us know the decohered branches were still there.

A macroscopic object held in superposition would also provide evidence for MWI, although there’s far less confidence that could be done.

Deutch also talks about the possibility of a quantum computer AI that could take in information from multiple worlds (all descended from the one it started its current quantum run in). If so, such a system may be able to demonstrate the existence of those other worlds.

As counter-intuitive as it is, the quantum formalism is supposedly clear that the worlds are all right here. It’s just that we can’t interact with them in any meaningful way.

Think about dark matter. It doesn’t appear to interact with the electromagnetic force. If it didn’t interact with gravity, we wouldn’t even know it existed. Now consider if there were a type of matter that didn’t even interact with gravity. That type of matter wouldn’t exist for us at all, even if it could interact with itself. It would pass through us, and us through it, with no effect on either. There could in fact be an infinite number of different types of matter that can’t interact with any of the other types, but they could also exist in the same space.

Under MWI, the other worlds are not far from that type of matter. As noted above, there is limited interference, but for all practical purposes, we can’t interact with them, nor they us, and so we don’t exist for each other. But they’re all right here. Supposedly there are enough degrees of freedom via Hilbert space states that this isn’t an issue.

If spacetime is quantum and branches, that might make things more interesting in terms of how many worlds are actually “right here”, but from what I understand, it isn’t required.

• Michael

Good stuff, Mike. Please understand the question was posed in the spirit of what Wyrd suggested above–not as a detraction but as a curiosity. It’s a real head-scratcher.

There could in fact be an infinite number of different types of matter that can’t interact with any of the other types, but they could also exist in the same space.

There could be–and this is profoundly hypothetical, of course–but wouldn’t there need to be some physical property that distinguishes one from another? And if this were so, wouldn’t that property be an entirely new quantity in our understanding of the universe? This feels extremely speculative to me, (and intriguing), (but still extremely speculative).

As to decoherence, both of you please correct me if I am wrong, but the window in which we might observe the interaction between worlds is really the moment when a system is just emerging from superposition right? And in MWI superposition IS the interaction of the various branches if I understand it correctly. I was thinking that in Deutsch’s view, the “worlds” all already exist and a quantum system in superposition IS those worlds interacting. But the notion that the branches ever interact after that “decoupling” despite continuing to exist in the same space is the real mind-blower here. What I think you’re suggesting is that the emergence of a quantum system from superposition creates an infinite variety of new forms of matter that are subsequently utterly “immaterial” to one another.

I must say that I’m surprised the skeptic in you is on board with this, Mike!

Michael

• SelfAwarePatterns

Thanks Michael. As I noted above, decohered branches aren’t completely isolated from each other. So it’s never a case of being absolutely immaterial to each other, although for all practical purposes it might as well be.

Deutsch does take the interference between branches in a superposition as interference between already existing worlds. As I noted in my post, I’m not wild about his ontology, since it seems to raise as many questions as it answers. And it amounts to additional postulates.

I have to admit that while physicists talk about detecting other branches, the idea of detecting the other branch shortly after the superposition is my own speculation. But I’m thinking that, right after the superposition has spread to the measuring equipment, but before it’s spread any further (an extremely short period), might be a period when future equipment could detect remaining interference from other branches. Maybe.

People often wonder why, as a skeptic, I entertain a concept they consider implausible. An important question for any skeptic is what would convince them. If the answer is nothing, that’s more dogmatic denialism than scientific skepticism. I can be convinced by evidence and logic.

But to be clear, I’m not convinced yet of the MWI. But I am convinced it’s plausible.

• Wyrd Smythe

“An important question for any skeptic is what would convince them.”

I think the opposite question is being asked. The thing that puzzles is why you aren’t more skeptical.

A better way to frame it, per my questions/objections thread, might be to ask why embrace some notions (like different kinds of matter) without much skepticism, but show a lot of skepticism towards other notions. Above I’d asked which was more tenuous, non-locality or invisible multiple worlds. (Only one has been demonstrated in experiment.) What makes one an objection and the other a question?

• Wyrd Smythe

BTW, I don’t mean that as a challenge but as food for thought. I’m pondering the same question.

• Wyrd Smythe

@Mike:

“Under MWI, there actually is interference between worlds, but it is extremely difficult to detect.”

LIGO is detecting spacetime warping 1/10,000 the width of a proton, and SQUID devices are also extremely sensitive, so the interference is normally all but invisible. Yet, if it’s responsible for the interference pattern in two-slit experiments, in that case it’s very blatant. I don’t understand why it’s so blatant in the one case.

“Under MWI, the other worlds are not far from that type of matter.”

I have to echo Michael’s surprise at that ontology. As he says, this suggests every branch creates a new type of matter, but that change isn’t in any way apparent to us. Even if one branch stayed the same, the other one needs to be some entirely other type of matter.

@Michael:

“And if this were so, wouldn’t that property be an entirely new quantity in our understanding of the universe?”

“…the window in which we might observe the interaction between worlds is really the moment when a system is just emerging from superposition right?”

AIUI, yes. Let’s talk about Carroll’s beam-splitter for definiteness. (I’m not convinced MWI has anything to do with two-slit experiments — see my reply to Mike above.)

The MWI picture is that reality branches. I think, in Everett’s version, the split happens when the photon interacts with the half silver mirror. That’s where the quantum decision is made. AIUI, the photon will either interact with an electron in the mirror or not. If it doesn’t it passes through. If it does, that electron quickly releases a new photon that, because of the momentum involved, flies off at the incident angle. In this case, typically 90° to the original path.

At the moment the photon reaches the mirror, MWI suggests it generates a superposition of transmissions and reflections. At this point reality has to branch because the Schrödinger equation mathematically requires one-particle-in-one-particle-out purely on energy conservation grounds. That’s if the mirror interaction counts as an observation, which I think it does.

So two photons exiting the mirror requires a superposition that treats them as a single state (because there’s only one photon’s worth of energy). MWI claims the detectors join this superposed state; both detect a photon. As such, the energy of the transaction is still conserved and shared in the superposition. This wave of superposition extends outwards eventually to Wigner’s friend.

Maybe there might be some way to detect superposition in the mirror, but it seems that, once the photons go their separate ways from the mirror, reality has to have separated.

FWIW, here’s what I believe is “really” happening:

Everett was a little bit right. A measured particle interacts with the measuring device, and there may be some superposition that goes on with the first few particles of that device. The wave mechanics alone suggest this.

I watched Prof. Allen use a graphic app to demonstrate a particle’s interaction with an energy gradient (what’s formally called scattering). Classically, a particle hits the boundary and bounces back, but in wave mechanics it interacts with the barrier and the probability wave extends into the barrier slightly (Heisenberg also requires the interaction not be precise).

So think about the photon’s wave packet approaching the wave packets of the electrons in the mirror. Some will have favorable energy levels for an interaction, and it’s possible entanglement and superpositions occur (rather than some definite interaction with a specific electron).

But the environment of the mirror, at the very least, consists of a wave-function for the mirror that’s comprised of the momentums of all particles of the mirror (a mind-blowing huge Hilbert space). I believe any superpositions in the initial interactions are very quickly swamped out by the overall wave-function of the detector (mirror in this case). Humanity is probing the atto-second range without unexpected surprises, so the time range here has be less than that.

It might be close to Planck length. If the math made it sub-Planck, it would effectively rule out superposition in macro devices. That’s probably not the case since we’re putting larger and larger objects into superposition.

At the risk of repeating myself, I think fully understanding superposition in quantum systems is a major key to the puzzle (and I don’t see MWI playing any role in that). The other major key, I’m convinced, is understanding why there is classical and quantum. What determines the boundary? I think the measurement problem might fall out of that understanding.

• SelfAwarePatterns

On MWI and the two slit experiment, my understanding is that the splitting is constant and pervasive. We often talk as though it only happens according to noted experimental outcomes, but under MWI, it’s happening constantly.

I think it’s important to realize that none of the major interpretations are going to be dismissed on the cheap. If they could be, they would have been ruled out long ago. If we think an interpretation is failing at the two slit experiment, or any other basic scenario, I think our response should be to learn more.

On skepticism, when I discuss something I find plausible, I describe the reasons I see it as plausible. When I think it isn’t, I also discuss my reasons. I frequently ask if I’m missing anything, and try to learn from or address the feedback. I don’t know what else to do.

It’s interesting that my skepticism, or other aspects of my psychology, always seem to come up after a lot of discussion on those reasons, which may say more about the psychology of the person pushing the issue than mine.

All food for thought and in no way a challenge, of course. 🙂

• Wyrd Smythe

Ha! I thrive on food for thought! 😀

“…but under MWI, it’s happening constantly.”

Indeed. Above I mentioned, depending on exactly what constitutes a branch, walking down the street wearing polarizing sunglasses creates zillions of branches. For that matter, so does just shining a flashlight at a wall.

Depending on exactly what constitutes a branch. MWI doesn’t seem to have a clear account of that. We agree, in some views, it’s constant and infinite and beyond counting, but there are other views that limit it. In his book, Carroll says our decisions in life don’t result in branches because (in his view) no quantum interactions are involved.

So what constitutes a quantum interaction that results in a branch? MWI doesn’t seem to have a clear answer. But yeah, it could be essentially infinite.

“I think it’s important to realize that none of the major interpretations are going to be dismissed on the cheap.”

No one has suggested otherwise. I said much the same above.

“If we think an interpretation is failing at the two slit experiment, or any other basic scenario, I think our response should be to learn more.”

To be clear, I’m not saying MWI fails any scenario, in particular the two-slit experiment. (As we’re both clear on, it’s not that easy.) I’m saying I don’t see where it applies because MWI is so vague on what constitutes a branch. Specifically, since I’m not clear on what multiple outcomes implies here, I’m not sure where any branching actually occurs.

Or if it does, it seems only to occur during the photon’s flight. Which produces the situation that multiple worlds do interfere. Quite blatantly so. But then the photon lands and the branches merge? No more interference? I have no idea. OTOH, in the beam-splitter, it seems certain two branches emerge but that experiment shows no interference effects.

The beam-splitter case seems pretty clear under MWI, but I just don’t know how to apply it to the two-slit experiment. Or if it does apply.

And I completely agree that, when faced with a question (or objection!), the first response should be to learn more.

“I frequently ask if I’m missing anything,”

The question from my point of view has been whether you really believe you might be and on how open you actually are to feedback that disagrees with your views. That’s a tricky thing for everyone, especially for someone who identifies as a skeptic. And for the highly educated — who indeed aren’t missing much — it can be an extra challenge.

FWIW, I identify as critical (in the analytical sense). It amounts to nearly the same thing, but the term has different weight to me — kinda reminds me I might be wrong or missing something. I see a skeptical stance as almost pre-objecting rather than questioning (implying the other side is probably wrong), if that makes sense.

As an aside, I subscribed to Michael Shermer’s Skeptic magazine for years but finally gave it up, not because I disagreed with him, but because I couldn’t take that level of skepticism, that level of certainty in the correctness of his own views and in the complete invalidity of the opposing views. That’s the thing about extreme skepticism. It can turn into certainty and dogma.

“It’s interesting that my skepticism, or other aspects of my psychology, always seem to come up after a lot of discussion on those reasons, which may say more about the psychology of the person pushing the issue than mine.”

It may. I’m definitely reactive and often irascible. Newton’s Third Law, though. A tango takes two.

FWIW, I do react to a skeptical stance I see as overly certain of its correctness. That extends all the way to those (Shermer is almost a canonical example) who are convinced science is the one and only answer. A fundamental fact about me is that I oppose gnosticism (confident certainty), and I see an overly strong skeptical stance as form of certainty. To me it’s all contingent. And fuzzy.

• SelfAwarePatterns

Lev Vaidman, in his SEP article on the MWI, notes that it involves two components:
1. The mathematics of QM, which describe the evolution of the quantum universe.
2. A description mapping 1 to our experience of the classical world.

1 is precise. 2 is more ambiguous because it hinges on how we choose to talk about things. We could choose to say reality split at the initial formation of the superposition, or when interaction with the environment reduces the interference between the branches of the superposition to an undetectable level (in the double slit experiment, this is when the photon is detected, that is, when information about it leaks into the environment). Or we could say it doesn’t split for any person or entity until they go into superposition (Wigner’s friend scenarios). Under Everettian physics, I don’t think there’s a fact of the matter answer on which is right.

On whether I believe I’m missing anything, obviously when I take a particular stance, I don’t think I am, since it would have been factored into my stance. But I’m open to the possibility. Can I rule out that I’m unconsciously not really open? No. All I can do is try to be on guard against it, and put myself in situations where people will put pressure on me if I am. Of course, for many who disagree, I’ll never be open minded enough unless I change to their position.

Some skeptics are dogmatic, or inconsistent, or exhibit many other human failings. No one’s perfect. And I find the quality of Skeptic itself pretty uneven. My skeptical ideal is closer to Carl Sagan. But it seems like every prominent skeptic gets accused of dogmatism. I find most generally more open minded than their critics allow. But I don’t know a single one I don’t have disagreements with.

• Wyrd Smythe

“1. The mathematics of QM, which describe the evolution of the quantum universe.”

Let’s be precise. The mathematics of QM describe quantum systems. That much we’ve observed. The extent to which it makes sense to talk about the wave-function of a detector, let alone the wave-function of the universe, is an open question. We haven’t observed any wave-function there.

“2 is more ambiguous because it hinges on how we choose to talk about things.”

All I want is a clear description of the proposed ontology. How do multiple worlds coincide? What constitutes branching? When do branches interfere or not interfere? Copenhagen has its issues, but at least it’s a clear description.

“Of course, for many who disagree, I’ll never be open minded enough unless I change to their position.”

Speaking for myself, I’m fine with ending on disagreeing on a topic. In a vigorous debate, I think it’s important to grant points when possible and to acknowledge valid arguments. I try to start responses with, “That’s true” or “That’s a good point” as much as possible, especially when I know I’ll disagree with a bunch of other stuff.

There are disagreements that come from misunderstanding, and those can be cleared up if the misunderstanding can be cleared up. There are disagreements that come from two people wanting different things. (Relationships have those a lot. Resolution requires give and take.)

Then there are disagreements that come from different worldviews — different philosophical priors, as you said. Those are the ones that make debates interesting. It’s usually not possible to come to agreement. The real goal is for both to say, “Yeah, I see what you mean; I just see it differently.” I don’t always feel you see what I mean. People can agree or disagree with me, but either way I hope they understand me!

• Michael

Being understood is when it transcends debate, which is so often fruitless, however entertaining, and becomes a meaningful exchange. Couldn’t agree more, Wyrd.

@Mike, to the point about your skepticism that I noted, this isn’t about right or wrong or whether or not you have justifications. It’s about that it just doesn’t make sense based on who you’ve presented yourself to be in the past. That’s all. This advocacy on your part strikes me, based on previous exchanges, as a departure from the norms you’ve presented. And the reason is that you are going to some length to defend a notion of the universe that is in many ways extravagant, and also that seems to undermine views of reality I would have thought you hold dear. And only because you think it is plausible. That’s just surprising to me. This notion of the universe involves infinite copies of ourselves, this decoherence thing few seem able to explain, inexplicable forms of matter, and the assumption that the Schrodinger Equation represents the probability that we–macroscopic observers–will find ourselves in a particular world. The latter is itself a statement that could be argued makes little sense if there is nothing but the wave equation.

Anyway, let me ask a question about something you’ve touched on several times that I don’t think I’ve fully understood. You’ve suggested that if macroscopic objects can be held in a state of superposition, that collapse theories would be disproven in some sense. I said that horribly, but I’m sure you’ll know what I’m talking about. Can you explain that?

Thanks!
Michael

• SelfAwarePatterns

Michael,
You’re judging things by the analogies I tried to use. There are far more rigorous explanations of everything I tried to relay above.

I think the MWI is plausible because it’s simply QM without the collapse. Decoherence is a mathematically rigorous concept. And what we call “other worlds”, the superpositions spreading into the environment, are a prediction of the mathematics of quantum mechanics, the same mathematics with a century of validation. It’s a prediction we can’t test right now, but it’s still a prediction, similar to the prediction of black holes in general relativity made several decades before their detection (for which Roger Penrose and a couple of other scientists won the Nobel Prize today).

And it’s worth noting how strange the collapse postulate itself is, including randomness and non-locality, something I think we’ve gotten too used to, and which has to be weighed in the skeptical balance.

In Niels Bohr’s version of Copenhagen (there are actually numerous Copenhagen interpretations), a distinction is made between quantum objects and classical macroscopic ones, with any interaction with a macroscopic object causing a collapse. “Macroscopic” is never well defined (on purpose per Bohr’s explicit instruction).

Some of the objective collapse theories do get a bit more precise, positing that every particle randomly and spontaneously collapses every 10^8 years or something, which in a macroscopic object would happen continuously.

So, the larger an object held in superposition, the more pressure it puts on collapse interpretations. Right now, scientists are getting to ever larger molecules with thousands of atoms, and there have been experiments proposed to go much larger. Then there’s this: https://www.scientificamerican.com/article/quantum-microphone/
Not sure how valid these results are. If they’re real, it seems like a bigger deal should have been made of it.

Deutsch talks about it being possible someday to do an actual Wigner’s friend experiment, but many other physicists are far less optimistic that will ever be possible.

• Wyrd Smythe

“Not sure how valid these results are. If they’re real, it seems like a bigger deal should have been made of it.”

It fascinating, but doesn’t move the needle hugely. It confirms that:

“Yup, quantum mechanics still works,” says U.C.S.B.’s Andrew Cleland, O’Connell’s co-author and adviser.

This highlights a question I have about superposition. We observe it in myriad ways in the branch we inhabit — quantum superposition is a workable property of our experienced reality. But it apparently also involves multiple coincident realities that we can’t access.

More generally I want to understand how we perceive anything — have any reality at all — when MWI says measurement never happens. As Michael touched on, everything we perceive is the result of an observation, a measurement. If we’re just evolving wave-functions, what does perception mean?

• SelfAwarePatterns

There’s actually an interpretation called “many minds”, which in the summarized descriptions sounds like some kind of dualistic or idealism account. But David Deutsch, in his critique of many minds, makes clear that it’s actually a 100% physical theory, that it’s just an alternate way of talking about Everettian physics.

Apparently the creators of that interpretation want to avoid the multiverse terminology. So instead they describe everything as one universe, but with all the superpositions. There is a superposition of our minds which they call “Mind”, and the individual branches called “mind”, with each “mind” having its own unique experience of the superposition universe.

Deutsch acknowledges the view as coherent, but pushes back on its necessity, noting that referring to actual worlds or universes also remains coherent. Focusing on minds and their perceptions implies there isn’t an emergent mind-independent classical world that minds inhabit. I think that’s right. The MWI doesn’t rip the objective world ground from under our feet, just the underlying continental substrate.
http://www.daviddeutsch.org.uk/many-minds-interpretations-of-quantum-mechanics/

All of which is to say, under the MWI, the classical account, including how our minds interact with it, remains coherent. It just has to be seen as something that is emergent from the quantum reality.

• Wyrd Smythe

“There’s actually an interpretation called ‘many minds’,”

I’m sure there is, although my speculation involves the kind of not-decohered-out-of-our-experience superpositions we apparently see and deal with in our single branch.

I think what’s becoming clear to me is that MWI has too many of the properties of a cult for me to ever be comfortable with it. Your abiding confidence in its correctness, I confess, is too much for me.

• Michael

Hi Mike,

I’m not saying it’s irrational to be a proponent of MWI. As may or may not shine through my posts, I am at minimum agnostic to the notion. I’m agnostic to all the QM interpretations really, because I do think there’s more to be understood ultimately. So they’re all interesting and it’s fun to try and solve this confounding puzzle… but I’m not convinced any of this will stand as it is now for the duration.

So I wasn’t saying that being a proponent of MWI was crazy. I was just saying it surprised me that you yourself were. That’s all. Yes the Copenhagen Interpretation(s) are crazy, too. It’s all crazy! So you’re right that we don’t exactly have any really good options to choose from if we hold dear our previous concept of universe.

The mathematics of MWI are the mathematics at the root of every QM theory, I agree. It just doesn’t have the second step. Most interpretations begin with the assumption there is only a single objective world, and that forces the second step of relating the wave function to probabilities for a given result. MWI removes that assumption, and restores locality within a given branch, but says everything that can possibly happen does happen somewhere, and then adds a density function to predict with some probability what branch you’re on.

When I say I’m surprised I don’t mean it’s nuts to consider this plausible. I just mean I’m surprised that you do. When at times I’ve sent you links to scientific papers in the past, for instance, you’ve generally written them off as being below the standard you’ve set for credibility. But none of them postulate the sorts of things that are postulated in MWI, (at least in my opinion). They’re quite tame by comparison. So it seems a great deal of this is a matter of taste…

Michael

• SelfAwarePatterns

Hi Michael,
I think the distinction is in what is being postulated, that is, assumed. Consider the black hole example I mentioned above. If we had never heard of black holes, and someone came up to us and simply postulated them out of thin air, then worked on the physics to justify them, I think we’d have grounds to be skeptical, even if their guess might turn out to be a lucky one, because with that postulate, it would only be a guess.

On the other hand, when someone takes the mathematics of GR, already thoroughly validated through observations of normal phenomena, and then discovers that they predict something like a black hole, it’s something to be taken seriously.

If the first step of the MWI were, assume lots of worlds, I wouldn’t be interested. But it’s important to understand that the only postulate of the Everett interpretation is that the heavily validated mathematics of QM model something real, and removal of the collapse postulate. Those seem like very modest assumptions. It’s the resulting consequences, the predictions, that are shocking, not the assumptions. The “many worlds” name refers to its consequences, not its assumptions.

But another factor that has to be considered, is I have no illusions about my own expertise, or more precisely, my lack of it. I’m crucially dependent on which propositions are taken seriously by the relevant scientific fields, because, frankly, the rest of us are kidding ourselves if we think we have the knowledge to assess radical new theories.

So when someone comes to me with a theory that either has questionable assumptions, or just lots of them, or that has no substantial following among the scientific community, I’m going to be leery of it.

Hope that helps.

• Wyrd Smythe

“The ‘many worlds’ name refers to its consequences, not its assumptions.”

That’s a key argument I just don’t understand. Why don’t both the assumptions and the consequences of a theory matter? It feels like a dodge to avoid those consequences.

• SelfAwarePatterns

The assumptions are the concessions a theory needs to get off the ground.

The consequences, that is the predictions, matter to the extent they agree or disagree with observations, or other more well established theories. The immediate predictions of MWI agree with observations.

The broader predictions can’t currently be compared to observations, that is, tested. It’s very possible some unknown factor prevents them from being accurate. But until any such factors are identified, or the predictions can be test, they’re irrelevant. Of course, people have strong emotions about them anyway.

• Wyrd Smythe

“When I say I’m surprised I don’t mean it’s nuts to consider this plausible. I just mean I’m surprised that you do.”

Michael has elegantly put his finger on what I was trying to find the words to say. I’ve known you a long time and have some model of who I think you are. The things you embrace or reject sometimes don’t seem to fit that model.

Of course, everyone is at least a little paradoxical. That was my point about superposition of thoughts.

• Michael

Hi Wyrd,

Two quick points. Maybe three.

You noted above that non-locality has been demonstrated by experiment but the interference between worlds has not… but if you come at this from an MWI perspective then what has been demonstrated is the interference between worlds, and not non-locality. Each interpretation claims the data as evidence for their perspective, which is rational in both cases. It’s not rational that both interpretations are true, but it’s rational that the data we have does not favor one over the other. So both non-locality and the interference between worlds have been shown in experiment. It just depends on which interpretive axioms you bring with you to the review of the data.

The second thing is that I’m not following your objection to the notion that branching occurs in a double-slit experiment. The weird part of that experiment is not the interference pattern, but the fact that the interference pattern is built of individual photons (or electrons, or whatever you’re flinging at the screen). If a torrent of photons were going through the slit at once interference could be explained classically. But when you have just one quantum of light fired at a time, and yet they land nowhere near the straightline trajectory through either slit, then the notion is that the particle interfered with itself. Whatever that means. But this I think is the branching: that one particle could have landed anywhere within the interference pattern, but it showed up in a particular place. So in MWI, all the possible points where the particle could be absorbed by the detector are realized as separate branches. When the branching occurs is hard to say I suppose. To Mike’s point, I think all the possible trajectories for this experiment that are possible in the wave equation branch from the moment the photon is released from the source.

The third thing is that if MWI is correct, we don’t really know what the classical world is. Let’s stick to the basics of all these branching realities superposed, of which we only perceive one at a time because of decoherence. What we call classical reality then is nothing but our perception of those branches of the wave equation that are identical under repeated interactions with the environment. So… say we have all these trillions of photons shooting down from the sun, and they are hitting a basketball. Each photon that is reflected contains information about the basketball; it is essentially a “measurement” of the basketball. And some are repeated millions or billions or trillions of times more than the measurements of outcomes that are not unchanged by interactions with the environment. (This goes to Zurek’s decoherence ideas.) So it could be there’s a few outcomes in there that differ, but our brain doesn’t bother with those. Maybe the brain is a filter that sticks to the consensus version, which is the dominant information broadcast in the environment.

Hell if I know. That’s just a story, right?

If it’s at all true it’s great for vision, but not for physical contact. Because we bump into the things we see, and not into things in other branches. That simply requires a resonance or coupling between the elements of matter in certain branches that distinguish them from other branches. And I could get on board with that if we understood the least bit about what the hell that coupling was. This is Mike’s infinite forms of matter. We just have no analogues in our experience that I can think of that could create a coupling between a vast wilderness of matter and energy, and not with a trillion trillion trillion copies interwoven that are somehow different.

We call this “phasing” in QM, but that’s NOT the same as phase relationships in water waves–at least I don’t believe so. That’s more to do with what is entangled in a given instant and what is not. And entanglement is just a measure of what we don’t know, in a sense, right?

I’m going to hypothesize that when we have a grip on how all these worlds do and don’t interact, we’ll have discovered an equally radical truth about consciousness. I think what we call consciousness could be related to the construction of consistent paths through this teeming web of information… I think it’s plausible, I mean. 🙂

Michael

• Wyrd Smythe

Hey Michael-

“So both non-locality and the interference between worlds have been shown in experiment.”

By “interference between worlds” you mean Alex and Blair both branch independently, creating two superposed states: A(U)+A(D) and B(U)+B(D). Those states expand, limited to c, and if they meet A(U)+B(D) and A(D)+B(U) will constructively interfere (and be real) while A(U)+B(U) and A(D)+B(D) destructively interfere (and vanish). Yes?

I do understand the basic idea, but I have issues with it (I realize that probably hasn’t been obvious 😀 ).

I’ve pondered the situation: A(U)+A(D) and B(L)+B(R). That is, Alex measures the Y-axis while Blair measures the X-axis. In that case, I think we end up with four branches, because all four outcomes are possible. A(U)+B(L), A(U)+B(R), A(D)+B(L), A(D)+B(R). (It’s even more interesting if Blair measures a diagonal axis. Then the four outcomes become differently weighted rather than equally.)

Certainly I agree that one’s axioms frame how one see all this!

“The second thing is that I’m not following your objection to the notion that branching occurs in a double-slit experiment.”

Yeah, might be better to call it my confusion. Before I get to that:

“The weird part of that experiment is not the interference pattern, but the fact that the interference pattern is built of individual photons (or electrons, or whatever you’re flinging at the screen).”

Yes, that’s exactly what’s weird. AIUI, we’re up to buckyballs in terms of what we throw through a grating and see interference with. (With larger objects they use a fine grating rather than two slits.)

It can be demonstrated that all four classical options are false: It doesn’t go through the first slit. It doesn’t go through the other slit. It certainly don’t go through neither slit. And it cannot be said to go through both slits. That last one is where the brain explodes and is why I say fully understanding superposition is a major key to figuring out quantum. What the heck is going on there?

So back to the two-slit and branching. Under Copenhagen we understand this as the particle in flight being described only by its momentum. The energy is constant, therefore so is its momentum. As you mentioned, what evolves in time is the phase of that energy eigenstate. Charted it looks like a pebble dropped in a still pond. In this case the pond is the 3D space of the experiment.

The ripples of the momentum wave-function interfere. Under Copenhagen, there is a Ψ1 describing the wave passing through one slit (as if the other didn’t exist) and a Ψ2 describing it passing through the other (also as a single-slit scenario). The sum of those gives us Ψ, a wave-function describing both, and how they interfere.

So, yes, absolutely, under MWI, Ψ1 and Ψ2 would represent branches that merge back together. I contrast that with beam-splitter experiments that involve branches that can’t ever merge. Or Alex and Blair experiments where some branches must merge and others can’t.

Lotta questions about the what and how. Not to mention the question of incident realities.

“But this I think is the branching: that one particle could have landed anywhere within the interference pattern, but it showed up in a particular place.”

Spot on. 😉 Above I said, “…creates zillions of branches. For that matter, so does just shining a flashlight at a wall.” Exactly because each photon might land anywhere reasonable.

We can make this concrete by extending the beam-splitter. Imagine a two-slit experiment that fires single photons. The screen in this case is a fine grid of photodetectors. Let’s make it 2000 wide by 1000 high; two megapixels. Each detector is connected to a detection circuit (two-million of them) and those are wired to a giant billboard with two million LEDs. In a stadium with 50,000 people watching. (They all have cell phones and send messages to all their friends.)

Each photon fired ultimately lights up one LED and 50,000 people cheer and text. (Let’s say the LEDs stay on so the crowd can watch the interference pattern appear.)

Under MWI, I think it’s definitely the case that each photon causes a branch because, within the interference pattern, there are many pixels the photon might trigger. Under Copenhagen, it’s randomly selected (which is weird). Under MWI, all the likely detectors detect a photon (and lots of superposed crowds cheer, but each at a different LED).

Absent all that machinery to pick out where the photon lands, is it still the case that, given the photon could interact with a vast number of electrons, the wave-function branches to accommodate all those interactions? Or does the aggregate being an indistinguishable macro-state either mean no branching or that all those branches merge?

I have a similar question about walking down the street wearing polarizing sunglasses. 😎

“The third thing is that if MWI is correct,…”

But it’s not, so that doesn’t matter. 😀

Sorry, I just couldn’t resist. I’m kidding, of course! One can’t take these things too seriously.

I’m not sure I follow. Are you saying our consciousness picks among branches?

“Because we bump into the things we see, and not into things in other branches.”

Did you see the first season of HBO’s Westworld by any chance? (The first season was really good.) They use an interesting device: The robots have programming that prevents them from seeing or thinking about things outside their environment.

“And entanglement is just a measure of what we don’t know, in a sense, right?”

I’m not sure what you mean by that. I’d define it as two systems sharing a quantum state.

“I think what we call consciousness could be related to the construction of consistent paths through this teeming web of information… I think it’s plausible, I mean.”

😀 I’m essentially a realist (as opposed to an idealist), so I tend to see consciousness as emerging from whatever reality is. I have been pondering whether, at least metaphorically, our minds aren’t a superposition of thoughts and ideas. Maybe it turns out consciousness is a quantum state with superpositions. It would certainly explain why we can so easily hold contrary and paradoxical ideas in our heads. Maybe the real secret to AGI is designing a system that can hold two opposing ideas without a divide-by-zero error. 🙂

• Michael

Under MWI, all the likely detectors detect a photon (and lots of superposed crowds cheer, but each at a different LED).

And none of the cheering crowds can actually hear or see the other cheering crowds once their LED lights up…

And agreed we can’t take this stuff too seriously! We just don’t know what we don’t know.

And entanglement is just a measure of what we don’t know, in a sense, right?”

Well there’s a couple ways of looking at this, Wyrd. But I thought one way was that the reason–or perhaps it’s better to say an attribute of–two “particles” being entangled is that their properties are unknown to us. Two particles collide and we don’t know how they shared their energy levels or momentum so until we pry open that little bubble and inspect, they could be in any of a number of states. And each particle’s state depends on the other mutually to preserve something like conversation of momentum or energy or spin. Isn’t there an “information theory” form of QM that would postulate something like this?

Now I get that based on Bell’s Inequality Tests, it’s not simply our ignorance. At least in the Copenhagen Interpretation. It’s the fact that the particles truly don’t abide in one state or the other yet. In MWI that wouldn’t be the case, though, and it would be about our ignorance of which world/branch we occupied… So all I meant was referring to was the notion that in some perspectives entanglement is a measure of what we don’t know, like any probability. Mike actually wrote about this on his site, and in MWI I can see his point.

And I was talking about MWI I think, so this would be consistent with that vein of thinking.

Maybe it turns out consciousness is a quantum state with superpositions.

I truly have no idea. I was just spit-balling that perhaps all these branching worlds are indeed equally real and in the same physical space and what distinguishes them from one another is not that they are completely different forms of matter, but a filtering process that is somehow related to what we call consciousness. Like reading a palimpsest. All sorts of words are there, but your brain navigates a path based on what makes sense…

Michael

• Wyrd Smythe

“And none of the cheering crowds can actually hear or see the other cheering crowds once their LED lights up…”

True dat!

“Two particles collide and we don’t know how they shared their energy levels or momentum so until we pry open that little bubble and inspect, they could be in any of a number of states.”

Ah, I see, got it. There are measures of what we don’t know in many systems, so I just didn’t see it as a property exclusive to entanglement. (And therefore not really a property of entanglement — just the way my mind works — weirdly!)

“It’s the fact that the particles truly don’t abide in one state or the other yet. In MWI that wouldn’t be the case, though, and it would be about our ignorance of which world/branch we occupied…”

Yeah,… there’s still a can of worms there in my eyes, though. It’s not clear to me, under MWI, that anything ever can have a definite state (because that requires measurement). Say Alex measures spin on the Y-axis. That action (AIUI) creates a branch with A(U) and A(D) — both versions think their system is in a definite state now, but under MWI it’s just that Alex has entered superposition.

But is Alex also superposed with a version where the device broke? Versions where all possible failure modes of the device occurred? MWI seems to say yes. The superposition involved is vastly more complicated than just A(U) and A(D) because the wave-function is an ever-expanding environment bubble. It necessarily must contain all possible reasonable paths within that expanding bubble.

Odds are most copies of Alex end up in very similar “ordinary” branches that have successfully obtained either A(U) or A(D) “measurement” (whatever that exactly means in MWI). But all the copies have no idea what will happen if they now make an X-axis measurement. Roughly half of them will get A(L) and roughly half will get A(R). Some fraction will get all the other possible weird results. In all cases, more branches. (Because each measurement breaks entanglement with the copies, yes?)

If all those now double-branched (respective to making “measurements”) copies of Alex make a third measurement back on the Y-axis, a third set of measurement-based branches occurs because the X-axis measurement destroys all knowledge of the Y-axis.

So I’m confused, firstly, about how there can ever be a definite state in MWI. Secondly, Alex can always be seen as a superposition of possible states that could be measured, so I don’t see MWI as resolving our ignorance due to superposition. In a quantum system, there is always more ignorance to be had.

(BTW: I’m using “confused” as short-hand for “question I have I wish someone would give me a precise answer for” and not as a code for “objection”. I don’t object to my confusion; just want it cleared up!)

“I truly have no idea. I was just spit-balling…”

No more do I, and likewise!

“…that perhaps all these branching worlds are indeed equally real and in the same physical space and what distinguishes them from one another is not that they are completely different forms of matter, but a filtering process that is somehow related to what we call consciousness.”

What I wonder about in a case like that is our instruments. Our senses take in what they can about physical reality, and our brains process that natural input data as they can. Our instruments take in very different aspects of reality — things we can’t perceive — and shows us their results in ways very different from the original data but which we can perceive.

So it seems like two very different ways of looking at reality that confirm each other. A view that suggests our perceptions are filtered needs to account for them being either filtered the same way for all our instruments or that our brains consistently filter two different types of input.

It makes me lean towards the idea that our senses, our analysis, and our instruments, are converging on an accurate view of nature. Like a wireframe model that we’re slowly filling in with solidity, textures, and shading. The model may never fully reflect reality, but I think it’s getting closer all the time. Kind of a Zeno’s Paradox for the progress of science. 🙂

• Michael

Our senses take in what they can about physical reality, and our brains process that natural input data as they can.

You make a good point here about what we perceive directly vs our instrumentation. And I really don’t wish to press a point that was merely spit-balling to start with. But what our consciousness would be choosing in the scenario I’ve completely gone-off half-cocked and postulated, is between branches of reality, all of which have instruments. So maybe it’s not wholly rejectable on the notion that our instruments afford us a secondary view from another perspective.

This is not a quote from you, but a move to return to the MWI questions you provided, which spurred a question from myself:

I think a tenant of the plain vanilla QM is that once a measurement is made it should be repeatable. So if you measure spin up, and you don’t go off and do something crazy, but just put another measurement apparatus right after it, and measure spin in the up/down direction, you’re going to just keep getting spin up as many times as you measure… UNTIL, you ask a different question of it, and measure momentum or something, at which point all bets about spin are off.

So I don’t really know how MWI handles the notion that a particle should reliably return the same value on repeated measurements, other than to say that in MWI it was spin up all along. But then in MWI if you measure spin up six times, great–but then you choose to measure momentum next, or spin left-right, then the various world branches entangle briefly and spit you onto a “new” branch. I think we’re saying the same thing now. I’ve just realized that.

Okay, so I think the point is sort of that without collapse, how does the wave function “just keep going” such that it is repeatable until you ask a different question? I guess the truth is the wave equation is up to us to a certain extent, based on the questions we choose to ask, and that remains the case whether it’s MWI or CI…? in which case, how does the universe know when to branch and when not to branch if there are countless wave functions in play to start with?

Michael

• Wyrd Smythe

Yes, that’s the question I’m asking! (Or one of them.)

“So maybe it’s not wholly rejectable on the notion that our instruments afford us a secondary view from another perspective.”

I’ll go along with that. FWIW, my sense is it makes the requirements a bit more twisty, but [A] that could just be my framing of it, and [2] sometimes reality is twisty.

“I think a tenant of the plain vanilla QM is that once a measurement is made it should be repeatable.”

Yep. As you worked out, Alex branches (respective to the measurement) when the outcome is unknown, but repeating the same test on a previously measured system always returns the same (eigen)value. (“Eigen” just means “proper” with, I believe, a similar meaning as “proper time” or “proper length” in Special Relativity. I take it as sort of like “real” or “actual” without strictly claiming either reality or actuality.)

“UNTIL, you ask a different question of it, and measure momentum or something, at which point all bets about spin are off.”

I believe it’s possible to measure a property that is not a conjugate of spin without disturbing the spin measurement. Momentum is not a conjugate of spin so my opinion (but not certainty) is it might be possible to measure momentum and spin simultaneously. That is, to make measurements that give definite repeatable values for spin on a given axis and momentum.

What we can’t do is have definite simultaneous measurements of two spin axes, or of both momentum and position. Above I’ve described how a particle in flight is described by its momentum and during that flight we can’t say where it is. Once it interacts, we know where it was (we can, in some sense, say what path it must have taken), but it no longer has a momentum (momentum is mass times velocity, and it no longer has a velocity).

I don’t know if your background makes the following meaningful: Mathematically, in quantum wave mechanics, the description of momentum and position are Fourier transforms of each other. As such, it’s not possible mathematically to have precise values for both. (This is the same math that underpins the Heisenberg Uncertainty relationship — it’s exactly what we’re seeing here with pairs of conjugate properties.)

So what you’re saying is true with the caveat that measuring disturbs conjugate properties.

The reason is “collapse” — a “measurement” puts the wave-function into an eigenstate with an eigenvalue representing the measurement. In that eigenstate, repeated measurements of the same property necessarily return the same value — the wave-function is already in that eigenstate.

But the eigenstates for other possible measurements are in superposition.

Alex starts with Ψ(?) and measures on the Y-axis to get, let’s say, Ψ(U). (Under MWI, there’s a branch and a mirror version of the following occurs.) If Alex repeats the same measurement on Ψ(U), of course the result is Ψ(U).

The thing is, because Ψ is a quantum system, it’s equally valid to see Ψ(U) as Ψ(L+R) — that is, as a superposition of Left/Right spins. (The other Alex sees something like Ψ(L-R) but it’s still a superposition.) Under MWI, that means Alex(U) is also Alex(L+R) and will branch accordingly in the event of an X-axis measurement.

“I guess the truth is the wave equation is up to us to a certain extent, based on the questions we choose to ask, and that remains the case whether it’s MWI or CI…?”

Exactly so. Tests of Bell’s Inequality involve carefully chosen measurements along non-orthogonal spin axes, which makes the space-separated measurements correlated, but not 100%.

After making, say, an Y-axis measurement, Alex knows something about the quantum system, and that system has a definite state (but one that doesn’t rule out superposition of unmeasured properties).

What I need clarity on, since MWI says “measurement” and “collapse” never happen, is what (precisely) does happen when Alex interacts with the quantum system? How do we observe anything if measurement never happens? Exactly what does MWI supplant experience with?

It seems the wave-function representing Alex before the experiment must itself include the dynamics of Alex going and doing the experiment and then branching. In some sense, Alex’s entire existence has to be a superposition of all the possible things Alex can do.

This is probably where Deutsch gets the notion of pre-existing realities, since, in some sense, if measurement never happens, then all the things that look like measurements must be built into the wave-function from the beginning. It’s almost a kind of superdetermination.

And what we think of as (observation-based) experience is just a moment along the universal wave-function, which is why MWI seems like a Tegmarkian idea to me. If everything really is just math, then MWI makes perfect sense.

• Wyrd Smythe

Wasn’t it Feynman who said that if one understood why the two-slit experiment was so weird one understood why quantum mechanics was so weird? It’s all bundled up in that one experiment.

I was just sitting here thinking about how the interference means there are spots the photon just don’t go (or are highly unlikely to go). It’s not like classical waves canceling — in that case there is energy in the nodes, but its superposed value is zero. In quantum we deal with probability, so the nodes mean zero probability. All the particles that make it through the slits land somewhere and are detected. It’s not the case that a particle vanishes due to destructive interference. It’s that where they can land is constrained.

• Wyrd Smythe

I don’t ask questions I’m not willing to answer, so why do I see non-locality as a question or acceptable axiom but object to multiple worlds? More importantly, do I apply a critical view to both.

I’ve gone on at great length, in posts and comments, about my objections to and questions for MWI. I won’t recite them here. Obviously, I’m skeptical. My claim is that my skepticism is the result of my critical analysis — the end point of some of which appears in comments above.

At this point, I have formed a contingent conclusion that MWI is an incorrect answer. I have too many unanswered logical objections to accept it. As such, no doubt I’m harder to convince than I was. (At one point long ago I found MWI quite acceptable. My view has changed over time.) That said, I’d like to believe that convincing answers to my objections, let alone experimental evidence, would change my view. (In the past my views have changed given new evidence, so I claim a history.)

So I acknowledge I’m skeptical to the point of disbelief with regard to MWI. As I say, I’ve explained why in rather great detail. 😀 😀

But why is non-locality just an open question? Why am I comfortable about that? Am I critical or skeptical? That turns out to be a harder question. Have to think about that. Why is that a form of magic I’m cool with? […goes away for a while to think about it…]

[…jeopardy music…]

So it goes to my basic philosophical views. I’m firmly in the realist camp, and essentially a physicalist (with pronounced dualist suspicions). As such I believe there is a way reality really is, and that we can discover at least some of it. I consider that Heisenberg, Lorenz, Turing, Gödel, and Cantor, have all demonstrated that we cannot ever discover all of it.

Many physical views imply a superset of physics. String theory claims 10 dimensions. There are a number of physical theories that use five (four space, one time). The notion of extra dimensions, either extended, curled up, or otherwise invisible, can imply non-locality when perception is limited to 3+1. (Consider the experience of creatures in Flatland. The notion of extended dimensions is old.) Importantly, these are all single-reality views.

Science fiction, the comics, some physical theories, and MWI, offer some form of many worlds notions, which are distinctly different ontologies than extended reality. Some multiverses are spatially separated, so they are (given the assumption of vast or infinite space) physically plausible. No laws of physics seem violated or in need of extension. Mathematical views (such as Tegmark’s) offer coincidental realities, but that doesn’t offend (on that count) because pure math allows multiple solutions with no penalty.

So, as I see it, that leaves science fiction, comics, and MWI, as theories that posit coincident actual physical realities that don’t interact. Shades of Mister Mxyzptlk. When Jim Baggott referred to it as “fairy tale physics,” I couldn’t help but agree. (Sorry, I’m litigating again. But I want to fully contrast my view of extended realities versus coincident ones.)

The point is extended (single) reality is a notion physics already explores and which has some physical basis. Coincident realities, outside of MWI, just don’t exist.

Bottom line, non-locality, as I see it, fits with a general notion of extended reality. It’s really weird, but reality is weird, and the way it works doesn’t seem to break any rules. It may be an axiom of reality we just have to accept. Given the single wave-function it actually makes sense — it almost has to be that way.

All of that is an opinion. For me the winning card is that we observe it. There is consistent experimental data — and no conflicting results — that say, hey, reality appears non-local, ain’t that a hoot!

• Wyrd Smythe

Interesting discussion, gentlemen, thank you! I may summarize the main points in a post one of these days.