Recently I had a debate with someone who was downright evangelical about the Block Universe (BU) being, absolutely, positively, the way things are. Because Special Relativity. In particular because of what SR says about simultaneity between inertial frames.
Up to that point I’d never given the BU a great deal of thought other than to file it under «Probably Not the Case» (for reasons I’ll get to). But during my morning walks I’ve turned it over in my mind, and after due consideration,… I still think it’s probably not the case.
I get why people feel SR seems to imply a BU, but I don’t see the necessity of that implication. In fact, it almost seems contrary to a basic tenant of SR, that “now” is strictly a local concept.
I’ll get to that, but first it should be clear that belief in the BU — the philosophy of eternalism — is just that, a philosophical belief. It’s an interpretation of physics as we understand it.
There is no way to prove or disprove it, so it amounts to being a metaphysical statement about the nature of reality.
There are a couple of key considerations:
Firstly, the idea of causal determinism, especially superdeterminism. If there is no freedom of choice at any level, then reality, at the least, amounts to a BU. If the future is predetermined, in effect, it already exists.
Secondly, SR seems to suggest that it’s possible to be simultaneous with an event in someone else’s future (according to their notion of simultaneous), so therefore the future must exist.
I have mixed feelings about causal determinism.
On the one hand, it does seem to be the way physics works. (And certainly a lot of physics does seem deterministic.) The reverse of determinism is reduction, and no one has yet shown where reduction fails.
On the other hand is our experience of choice and the idea that the right kinds of systems might be non-deterministic. (Certainly chaotic systems are unpredictable, which might be as good as it gets, but I think the jury is still out when it comes to the true nature of reality.)
In any event, even a superdetermined universe can evolve over time without requiring the future already exist, so there’s no necessity on that count.
(There is an ontological question about the reality of things that must happen even when they don’t seem to have happened yet. Think of the sensation of watching a car accident about to happen. Vivid and real!)
My impression of the BU belief is that it perceives the future (all of it) to exist in a concrete sense. It imagines all of reality as a kind of 4D Lucite spacetime block with embedded bits of matter tracing out 4D world lines.
Here’s my key problem with that:
That Lucite block contains a lot of structure — it’s the entire universe, not just in size, but in time. The matter traces involve a lot of interactions.
How and when were all those computed?
They had to be calculated by something. Those interactions follow patterns, so there must be underlying rules that govern them.
And all that structure must have taken time to calculate, so is there a separate spacetime for the Lucite block to be created? Time seems to need to flow in order to make a calculation of a fact you don’t know. (E.g. What’s two plus three? It takes time to calculate an answer.)
Or does everything — all that vastness of structure — just spring into existence all at once? How? According to what physics? According to God?
On this count alone the BU seems improbable.
Note that, in contrast, if time flows and the universe evolves, then the structure calculates itself as it goes. Each moment generates the next moment of structure.
A question I have is: Does the BU include the Big Bang as part of a larger universe, or does the BU only contain what the Big Bang created?
In other words: BB < BU or BB = BU?
One thing that’s never made much sense to me is the question:
Is time a coordinate or a dimension?
This confuses me, because if something is a coordinate, that means it’s a number along a dimension. And if something is a dimension, then it has coordinates along it.
I think I get what’s being asked, though: Is time something that flows “through” us and “passes,” or is it fixed like a spatial dimension and we, in some sense, move through it.
Perhaps it amounts to the same thing: time flows.
Even in the BU there is a sense of flow that comes from… apparently not time, but something. Another objection I have to the BU is that it needs to account for that sense of flow. (It can’t be tied to consciousness, because chemical reactions and orbits seem to flow without being observed.)
FWIW, I take time to be a fundamental property of reality, related to, but not at all the same as, space. In 4D spacetime, I think time stands alone.
This is obvious when we consider the spacetime interval:
Δs2 = Δx2 + Δy2 + Δz2 – Δt2
Time is taken as, in a sense, opposing space! Distances in 4D Minkowski space are not Pythagorean because time is not a spatial dimension!
Speaking of 4D spacetime, a key premise of the BU is that SR suggests the future exists. Specifically, that an event seen as simultaneous in one frame of reference is seen from another as in the future (or the past).
What I’d like to demonstrate is that a claim of simultaneity is virtual and can only be validated after the fact.
It’s similar to, while you’re driving over the river and through the woods to grandmother’s house, thinking that “right now she’s baking the turkey!”
Maybe she is, maybe she isn’t. You won’t know until you get there. (Maybe she’s been playing Cribbage with her friends all afternoon and thought you were bringing pizza.)
To make sense of this we need to take a close look at what we mean by simultaneity.
Take a look at diagram 1. (I apologize for the crude diagrams. I’m feeling pretty casual and lazy about the topic.)
I’m going to assume you are familiar with spacetime diagrams. If not there are resources on the web, or you can try my SR series where I explored both the diagrams and simultaneity in detail.
In diagram 1, the dark black vertical line (x=0) is the observer, Al, in his frame of reference.
At point A (x=0, t=-4) Al fires a laser (red line) which crosses space to point B (x=8, t=+4) and is reflected back across space to Al at point C (x=0, t=+12).
Al can then (and only then) subtract the departure time from the arrival time to see that the round trip took 16 clock ticks.
Since both legs of such a trip must be symmetrical, it takes light half that time (8 clock ticks) to go one way. That means point B is 8 space clicks away (because time clicks and space clicks are normalized in these diagrams).
More importantly, Al can tell that point B occurred at t=+4. That is, it was simultaneous with Al’s point D back when his clock read +4. (Currently it reads at least +12 or more.)
Crucially, D can only be deduced after point C.
Note that if Al knows where point B is, and (as in this case) point B is in his frame of reference, it’s possible to claim at point D that point B will turn out to have been simultaneous (once confirmed at point C).
That would be like predicting what grandma is doing before you get there. The point being, since she’s roughly in your frame of reference, that you can assume she’s doing something while you’re driving there. But you still can’t make any factual statements about it until you get there.
Now let’s consider that scenario with Barb, who passes by (from left to right) at 0.5 c.
Diagram 2 illustrates how this appears as rendered from Al’s point of view!
(To Barb things appear very similar to how they appeared to Al in diagram1, but the distance appears foreshortened and therefore the light takes less time to make the round trip.)
The dark vertical line is still Al. The dark green line is Barb’s world line as she passes Al.
The dotted lines (in both diagrams) are the lines of simultaneity as seen by Al. (In Barb’s frame, her dotted lines would be horizontal, and Al’s would be angled. To her, Al’s situation looks like diagram 2, except Al seems to be passing from right to left, so his lines are slanted the other way.)
As in the first scenario, once Barb reaches point C she can say that point B occurred simultaneously with the origin point. (Which I forgot to label in both diagrams! Oops!)
So it appears that Barb sees, as simultaneous with her t=0 line, something that Al sees as simultaneous with his t=+4 line.
Barb appears to almost see into Al’s future!
But does she really? She certainly can’t make any use of supposedly knowing Al’s future. In fact, she doesn’t know anything about that future (yet).
By definition, any spacetime event that occurs on your surface of simultaneity is outside your causal influence. That is, outside your light cone:
Which is why you don’t know what grandma was really up to all afternoon while you were driving.
Barb can’t know anything about Al’s supposed future events until the light from those events reaches her.
Just above I used the term surface of simultaneity rather than (line of).
In 2D spacetime diagrams (such as shown here), because there is only one spatial dimension (x), there is a line of simultaneity.
If we make 3D spacetime diagrams, there are two spatial dimensions (x and y), so there is a plane of simultaneity.
Which we can at least visualize (diagram 4).
In 4D spacetime, with three spatial dimensions, there is a 3D surface of simultaneity — a 3D volume that, in moving frames, seems angled in four dimensions. (Which we can’t visualize!)
The point is that this surface can only be probed remotely because, by definition, it’s outside your causality (your light cone).
You can’t make any statements about events in that surface until their light reaches you.
In a very real sense, that surface of simultaneity is virtual. As such, it doesn’t speak to the reality of “future” events you can’t say anything about until after they’ve happened.
SR teaches us that the concept of “now” is a strictly local concept with no real meaning over distance. Believers in the BU treat simultaneity as if it reifies the “now” throughout all of spacetime.
Not only do I think that doesn’t follow from SR. I think it’s contrary to it!
So, in summary:
- How and when was the BU structure calculated?
- What makes time appear to flow in the BU?
- Relative simultaneity is virtual; “now” is strictly local.
In short, the BU is BS! 😀
Stay unblocked, my friends!
October 30th, 2019 at 6:50 pm
I view the block universe as an interesting metaphysical possibility, but one that is utterly irrelevant to our lives. Even if it’s true, it does me no good in my daily life, or even for scientific theories. I can’t perceive the future and I’m still separated in time from lost loved ones.
I am open to time possibly being emergent, although what it emerges from would need to be identified. Can’t say I find entropy a convincing answer.
“How and when was the BU structure calculated?”
The turtles did it, and remember, it’s turtles all the way down. 🙂
“What makes time appear to flow in the BU?”
That’s the thing. I’m actually somewhat open to consciousness being involved since “now” is part of our model of reality. Would “now” be a thing without consciousness? If so, what would make it a thing? There would still be time, but would there still be anything dividing the past and the future?
October 31st, 2019 at 1:34 am
“I view the block universe as an interesting metaphysical possibility, but one that is utterly irrelevant to our lives.”
Yeah, exactly. (Hence not bothering to make better diagrams. 😀 )
“Can’t say I find entropy a convincing answer.”
No, I’ve never thought so. To me, thermodynamics is the consequence of the behavior of particles over time. (IOW, basic physics + time = thermodynamics.)
“The turtles did it, and remember, it’s turtles all the way down.”
😀 What’s cute is that, in the programming language Logo, “Turtles” draw the graphics, so one has the fanciful idea of Meta-Universe-Logo® with Turtles that draw the 4D Lucite block of reality.
You see the problem, right? If all that structure exists, something had to calculate it.
“There would still be time, but would there still be anything dividing the past and the future?”
Cute questions, but if we define what we mean the question is more clear.
Was there a configuration of the universe where our Sun hadn’t formed? Clearly there’s a configuration where it has. Is there a timeline involved in the change of configuration? If so, then any point along that timeline can be defined as a “now” in terms of what comes before and what comes after.
The terms “past” and “future” are normally self-centric. The terms “before” and “after” aren’t, and if you accept, at the least, history as a timeline, then “before” and “after” have meaning.
The terms “past” and “future” can be related to them with the understanding the reference is in terms of some point in the past. Likewise, one can talk about the “past” and “future” in terms of some point in the future (assuming one grants time progressing into the future in at least some sense).
But how is consciousness involved in the 13.8 billion year apparent history of the visible universe (let along the putative part we can’t see)?
((Let alone multi-verses, but let’s let those alone.))
October 31st, 2019 at 7:43 am
Wow, Logo and turtle graphics. Now those are terms I haven’t seen in a long time. My dad used Logo to learn programming, writing a simple game in it.
“You see the problem, right? If all that structure exists, something had to calculate it.”
I understand the sentiment, but I think you might be applying standards from within the universe to the universe itself. If the block universe is true, then it just is. It was never calculated. It’s just a timeless structure. Asking when it was formed might be a category error.
That’s the problem with cosmology. Eventually, no matter what you do, you get to a point that seems absurd: a beginning of reality, no beginning, an edge to reality, infinite reality, etc.
I agree “before” and “after” have objective meaning relative to any particular event. But aside from a system remembering past events and planning future ones, where does the concept of “now” come in? What made the collision of the original Earth and Theia, which went on to form the moon, a “now” event, rather than just a convergence of certain patterns along a timeline?
On the 13.8 billion year history, no consciousness is required for events in time. It’s only the concept of “now” that might require it.
October 31st, 2019 at 8:51 am
“If the block universe is true, then it just is.”
Sure. I’m saying it seems the biggest leap of faith among major cosmologies. In decreasing order of the amount of structure required to simply exist:
The first one requires everything in a completely expanded universe, all that structure from beginning to “end” (whatever that amounts to in a block), has to simply exist eternally.
The second one confines the structure to some creator with the power to create a cosmos. Traditionally that’s God, but could be hyper-beings creating a virtual reality. (Or, worse, it’s some kid with a build-a-universe kit.)
The third puts the structure in a set of laws, maybe a set of fields, and those laws (and fields) would be the simplest structure (the fields have no structure).
So while I agree any cosmology eventually gets to turtles — requires something that just is — the way I see it, the BU has the largest requirement for stuff that just is. A whole timeless universe of very structured stuff representing an unimaginable number of decision points.
It would require everything humans have ever done or will do, and we’ve added a lot of structure to the universe (just Wikipedia alone represents a lot of structure). All of that has to just be.
In terms of ontological demands, the BU is a Big Ask. 😉
“What made the collision of the original Earth and Theia, which went on to form the moon, a ‘now’ event, rather than just a convergence of certain patterns along a timeline?”
Well, how do you define “now” such that it does not mean “some moment in time”?
What do you mean when you say “now”?
“On the 13.8 billion year history, no consciousness is required for events in time.”
Agreed. This goes back to your original statement and question:
“I’m actually somewhat open to consciousness being involved since ‘now’ is part of our model of reality. Would ‘now’ be a thing without consciousness? If so, what would make it a thing? There would still be time, but would there still be anything dividing the past and the future?”
On the one hand the notion that events occur in time, which presumably flows from one event to the next, but on the other hand the notion that consciousness plays any role in that.
Is there any difference between the presumed flow of time of the Earth orbiting the Sun billions of years ago and the flow of time we experience watching it orbit? Does consciousness make those two different?
Or do you only mean that the notion of “now” by definition means “from a mind’s point of view”?
October 31st, 2019 at 10:21 am
“Well, how do you define “now” such that it does not mean “some moment in time”?”
It seems like all moments in time but one are not “now”. (Relative to a time and place since there is no universal “now”.)
“What do you mean when you say “now”?”
I mean the moment in time between the past and the future. Of course, all three concepts are relative to each other.
“Is there any difference between the presumed flow of time of the Earth orbiting the Sun billions of years ago and the flow of time we experience watching it orbit? Does consciousness make those two different?”
I can’t see that it does, except perhaps for the perception of a “flow”, which might imply a “now” moving along a timeline. But events in time exist regardless.
“Or do you only mean that the notion of “now” by definition means “from a mind’s point of view”?”
Is there a conception of “now” that is not from a mind’s point of view? If so, how would you describe it?
October 31st, 2019 at 1:20 pm
“Is there a conception of ‘now’ that is not from a mind’s point of view? If so, how would you describe it?”
As I said in my first reply to you:
Put another way: If we imagine a person at any random moment (and location) in the past we care to name, is there, at that moment, a local “now” for that person? (Presumably so?)
If there isn’t a person, was there still a local “now” at that moment in the past?
I’m asking if that random past moment can be retrospectively considered “now” for purposes of picking out what came before (the “past” to the “now”) and what came after (the “future” to the “now”). (Given that we’re talking about a time and a location — literally a spacetime event.)
OR do you see “now” as applying only to the “current” moment experienced by an observer (such as a clock or person). It’s not possible to speak of “now” in the past?
Both suggest an ontological reality to now — that time flows. That there are moments along any timeline and each moment was, at some point, the “now” moment.
There is also a more epistemological view that “now” is what consciousness experiences and, to some extent, that’s all that matters or that we can talk about.
In the post I wrote:
In what seemed a reply to that, you started this sub-thread by asking:
And I’ve been trying to understand exactly what you mean by that.
We certainly have a personally experienced “now” — the question is whether time flows the same regardless if some consciousness is experiencing it. You agree orbits are the same regardless of observers, which means you agree time ticks or flows at a constant rate (“proper time”).
But then you qualify it with:
“…except perhaps for the perception of a ‘flow’, which might imply a ‘now’ moving along a timeline.”
Which makes it seem like you don’t agree there was a flow of time for the orbits without an observer?
So I’m not really clear on what effect you think consciousness has on time. (I’m saying, per a favorite quote from Hitchhiker’s Guide to the Galaxy, “none at all.” 🙂 )
October 31st, 2019 at 2:42 pm
I don’t really have any doubt that time itself exists without consciousness. The earth’s formation was not interfered with by the big bang, despite the former happening with some of the energy from the latter, because they were separated by vast stretches of time, presumably despite no conscious entity being around to experience either one.
The only question is whether the concept of “now” itself is meaningful without a conscious system. And the idea of time “flowing” only seems to make sense if it’s flowing past a “now”.
Does “now” show up in any scientific formula? Not an event in time, but “now” in particular? “Now” makes sense to a conscious creature because it separates what is remembered from what can only be predicted, and indicates what has to responded to immediately.
As conscious creatures, we can imagine a past or future “now”, but it doesn’t seem like that makes those events “now” in the same manner as the current event. (At least not anymore than imagining over there is “here”.)
Anyway, this feels like it’s turned into a debate, and I really haven’t thought this out enough for that.
October 31st, 2019 at 4:25 pm
“Anyway, this feels like it’s turned into a debate,…”
I apologize if it feels that way. I’m not trying to debate anything, just trying to understand if you’re objecting to the assertion consciousness is not responsible for the actual flow of time.
I think there’s no disagreement…
“I don’t really have any doubt that time itself exists without consciousness.”
Okay, great, that was my question. No disagreement there!
“The only question is whether the concept of ‘now’ itself is meaningful without a conscious system.”
Right, and I’m trying to get a clear understanding of what you mean by “now.”
“As conscious creatures, we can imagine a past or future ‘now’, but it doesn’t seem like that makes those events ‘now’ in the same manner as the current event.”
I quite agree!
Would you agree that, if there had been a past observer, they would have had a “now” moment they would view as a current event?
Would you further agree that observer or not, events took the same time to happen (i.e. that time flowed in the absence of the observer)?
We don’t have to debate your answer. I just want to know what it is.
October 31st, 2019 at 6:05 pm
On “now”, I see it as the instance in time between the past and future, the border between what we can remember and what we can only predictively imagine.
“Would you agree that, if there had been a past observer, they would have had a “now” moment they would view as a current event?”
“Would you further agree that observer or not, events took the same time to happen (i.e. that time flowed in the absence of the observer)?”
But without the observer, I’m wondering what might mark that event at the time as “now”. In other words, is “now” like color, a convenient concept concocted by the mind? Or more like sizes and shapes with an objective existence?
October 31st, 2019 at 7:37 pm
“But without the observer, I’m wondering what might mark that event at the time as ‘now’.”
Well, that’s what I’ve been trying to explain. 🙂
You asked earlier, “Does ‘now’ show up in any scientific formula? Not an event in time, but ‘now in particular?”
No. I’m not aware of any physics that explains the metaphysical “now” that we experience.
But there are, as you say, events in time, and each them them has a personal “now.” Agreed?
What marks any given event in spacetime as “now” is that it has a personal “now” along its world line that could be experienced by a conscious being present at that event. Such a being would remember the past of that world line and could try to predict its future. Still agree?
So to say a given point in spacetime is “now” is to speak as if you were at that point.
“In other words, is ‘now’ like color, a convenient concept concocted by the mind? Or more like sizes and shapes with an objective existence?”
I think those are interesting questions. What actually accounts for that sense of time flowing?
To me it seems objective because non-conscious processes apparently flow on their own: chemical reactions occur, plants grow and die, objects follow orbits. Assuming an objective reality to such objects and their dynamics, the idea of a “now” evolving from “time zero” to the present and then into the future does seem objective to me.
I’ve mentioned that I think thermodynamics emerges from time plus particle behavior. Likewise I think our conscious perception of now is based on time plus brain activity.
But I am fascinated by the question: What is that metaphysical now? That single clock hand that seems to sweep out the life of the cosmos. Why are we at this point in our brain’s activity?
As I said in the post, even the BU has to account for why that clock hand seems to exist. Why do «I» only seem to exist at one point in time — a point that evolves serially through time. If my entire existence already exists, why aren’t I remembering the whole thing? Why do I appear to live it from start to finish? Why does humanity seem to share that timeline?
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I think taking the BUH seriously just might be a stupidity litmus test. At the very least an indicator of Dunning-Kruger. (And, as I learned, per Bonhoeffer, such people are immune to logical argument. They’re willful in refusing to be educated or led outside the cave.)