I just finished reading Beyond Weird: Why Everything You Thought You Knew About Quantum Physics Is Different (2018) by science writer Philip Ball. I like Ball a lot. He seems well grounded in physical reality, and I find his writing style generally transparent, clear, and precise.
As is often the case with physics books like these, the last chapter or three can get a bit speculative, even a bit vague, as the author looks forward to imagined future discoveries or, groundwork completed, now presents their own view. Which is fine with me so long as it’s well bracketed as speculation. I give Ball high marks all around.
The theme of the book is what Ball means by “beyond weird.”
Colloquially, someone might say (and they have), “Oh, Wyrd, you’re acting beyond weird right now!” By which they mean I don’t seem just weird to them but weird-magnified — weird-to-the-power-of — a weird too far.
Ball is punning this colloquial usage. He actually means it in the original sense of going beyond something. In this case, going beyond the simple acceptance of “weird quantum physics” to trying to understand what Mother Nature is really saying.
So this is a book about trying to figure out what quantum mechanics tells us about reality. Ball explores the various aspects of the quantum world that have earned its weirdness reputation: superposition, interference, and entanglement. A key question throughout is: what (if anything) divides the “classical” world from the quantum one?
In one of the last chapters, Ball mentions Jeffrey Bub (Univ. Maryland), who has some interesting quantum mechanics books himself. Bub is one of many theoretical physicists working on what’s called quantum reconstruction. The idea of which is to start with what we observe and try to build a completely different quantum theory — one that isn’t weird.
Or rather, since it seems the quantum world will always present a counter-intuitive side to us classical beings, a theory in which the mechanism of that weirdness is well understood and grounded.
I mention Bub because, as Ball puts it, “Bub believes that non-commutativity is what distinguishes quantum from classical mechanics. This property, he says, is a feature of the way information is fundamentally structured in our universe.” I like this notion a lot. It doesn’t necessarily explain anything, but it hits to the heart of the true difference.
Simply put, for a non-commutative system: A×B ≠ B×A
One illustration of this is that measuring a particle’s momentum and then its position gives different results from measuring its position and then its momentum. In quantum mechanics, in many cases, a measurement invalidates a previous related measurement (this is readily apparent in spin measurements).
This non-commutative relationship is true for all conjugate variables (such as position-momentum, time-energy, spin axes, and others). The notion is reified in what’s called a (mathematical) commutator.
In classical mechanics: A×B = B×A
One can measure the height, the width, the depth, the mass, the temperature, the electrical charge, the surface properties, and more; and these measurements can be done in any order. The results are the same regardless. The properties of classical objects don’t change upon being measured — they all commute.
That means we can measure (in any sequence) and know all these properties at once. Knowing the object’s height does not preclude knowing its width. In quantum mechanics we can never know all of an object’s properties.
Note that there are classical examples of operations that don’t commute. A common example is rotations of a cube. I like the example of getting dressed. First underwear then outerwear gives quite different results than putting underwear on last.
[For that matter, there are classical examples of spin ½ systems that take two full 360° rotations to return to their original state.]
The punchline, if there is one, is that many in this game wonder if it doesn’t all boil down to information. In their view the fundamental particle is an information bit of some kind (which aligns them with Wheeler’s “it from bit” view).
What’s interesting about this view (and I’m by no means sold) is that it accounts for a lot of the quantum “weirdness” we experience. The quantum world seems to be a world in which we’re only allowed to extract a certain amount of information. Knowing spin on one axis means we can’t know it on any other.
Ball illustrates with what I think is a compelling example:
Imagine a special version of Twenty Questions. I’ll present it the way Ball does, where you, dear reader, are the guesser or questioner. You’ve left the room, and the group has decided on how to puzzle you.
When you return, you begin asking questions: For example, “Is it alive? Yes! Is it human? No! Is it animal? Yes! Four legs? Yes! Fur? No! Sharp teeth? No! […]” Obviously the goal is to determine the secret with 20 questions (or less). Members of the group will alternate in answering.
At first you notice the answer come quickly, but as the game wears on, it seems to take each person longer and longer to answer. Which is weird, right?
Finally you guess, “It’s an elephant?” At first there’s no reaction, you notice some exchanged glances (and are now really wondering what’s up), and then everyone starts laughing and agreeing that, yes, it was an elephant.
What you learn later is that elephant wasn’t the secret. No object was. Instead, the first answers (especially the very first) are essentially random, except that each answer must be consistent with previous answers. There must be some object those answers identify.
This is why the game takes longer and longer. The person responding to the question has to find an object that fits all the properties so far named, and give an answer that fits the new question. (People don’t confer during this, each is on their own to come up with an appropriate reply.)
This, Ball suggests, is similar to how the quantum world appears to us.
We can ask questions and get answers (and the more information we gather, the more effort those answers do take), but it is a mistake to think there was ever a specific answer to begin with.
Effectively, measurement weaves reality over time.
(Note that asking questions doesn’t imply a mind or experiment. That infamous cat is being constantly questioned by its environment and its own body: Are you alive or dead? In fact the questioning goes on at an extremely high rate.)
What I’m maybe a bit askance at is, far from seeking a physical grounding, an axiomatic (and so far undefined) “bit particle” is exactly the sort of speculative physics I shun.
That said, maybe there simply isn’t any physical grounding for the quantum reality without some new basic axiom.
(It would have to be new, since what we see as elementary particles, such as the electron, photon, and quark, would have to contain multiple information bits. That said, I have long wondered about the ontology of an invisibly small elementary “particle” with multiple properties, even if some of them are mutually unknowable. String theory was attractive for providing that ontology.)
One thing I appreciated a lot about this book is that Ball resists the temptation to cover either the basics or quantum mechanics or its very interesting history (and hence the temptation).
But if I have to read about Planck discovering the quantum one more time…
This book delivered big time on what I wanted: a recent overview of leading edge quantum physics.
It’s an interpretation-free overview in the sense that Ball is generally agnostic about interpretations given this is a book very much about different interpretations. One of Ball’s key points is that he doesn’t like any of them and, per the idea of reconstruction, would scrap them all.
Also per reconstruction, apparently I’m a fan, since I’ve long wondered if QM went down a very successful, but basically wrong, path. (The canonical example is Epicycles.)
Ball does single out the “shut up and calculate” flavor of the Copenhagen Interpretation as, albeit is very successful, an unacceptable, and ultimately untenable, position. That we can’t just accept quantum weirdness is the point of the book.
A notable exception to his agnosticism is the MWI, which Ball devotes an entire chapter deconstructing. He and I see eye-to-eye on this. The MWI is an attractive brainstorm idea, but it seems to lead to an incoherent view. In narrowing the view exclusively to the Schrödinger equation, it becomes too simple to rationally account for our observations. Further, it’s actually giving in to quantum weirdness, not solving it.
(I would prefer to avoid debating the MWI here. (Mention as context is fine.) Let’s try to focus on established (by experiment and math) physics and the information ideas Ball raises. I have a post planned, MWI: Objections (or maybe just MWI: Questions) to summarize issues I’ve accumulated in recent discussion, reading, and thought. We can debate there, if desired.)
Some interesting bits from the book:
Speaking of the notorious wave-function “collapse” Ball dismisses the Copenhagen approach that makes it axiomatic while noting Bohr saw it as “emblematic” of the quantum-classical divide. Ball asserts that the collapse is just a name we give the process that turns quantum states into observations. He goes on to say (emphasis his):
Wavefunction collapse is then a generator of knowledge: it is not so much a process that gives us the answers, but is the process by which answers are created. The outcome of that process can’t, in general, be predicted with certainty, but quantum mechanics gives us a method for calculating the probabilities of particular outcomes. That’s all we can ask for.
From the POV of our mathematics and our observations, that seems to be the case. At least, so far.
I highlighted that paragraph and added the note: “Reality weaves itself each moment.” I like the notion that the universe it constantly measuring itself. When we isolate a tiny system, that measuring stops and the underlying quantum reality emerges.
Ball illustrates the quantum-classical divide with a great metaphor:
The quantum-classical transition is then like an ocean crossing between two continents: drawing a border somewhere in the open sea is an arbitrary exercise, but the continents are undeniably distinct.
Which reflects what I’ve been saying for a while now. The divide isn’t a hard line, but due to many contributing factors. (Which we may someday be able to fully understand.)
There are many other bits just too meaty to share here (as my word count approaches 1800). There is much to be said about entanglement, for instance.
In particular, entanglement with regard to experiments testing Bell’s Inequality. These turn on notions of inseparable states and quantum non-locality. I have some issues with Ball’s Bell’s analogy — and I’ve had issues with other analogies, too; it seems a difficult experiment to explain clearly.
The topic is more than deserving of its own post, and I’ve long been planning to explore and post about those experiments.
There is also more to be said about how the classical world emerges from the quantum one. That, too, is a topic big enough to handle in future posts.
Stay beyond weird, my friends! Go forth and spread beauty and light.