Conceptualising difficult physics concepts

Factual Questions
22

This might not be the place to broach this and if it turns out to be irksome, I will drop it immediately.

One of the things I learned studying Buddhism is that we are capable of understanding much more than what can be expressed in language. Under that rubric I would include any strictly deductive system such as mathematics. In fact, given the fact that only a handful of people on the planet probably could be said to actually “understand” quantum mechanics, I think one can safely assume that at the very least, it’s not helping to explain things.

But I’m not suggesting it be dispensed with of course. I’m not suggesting anything at the moment. I will say this however. The sutras I read back then tended to come back to certain core ideas over and over. One of those was the idea that the limitations of language are so profound, that it is so tiny and limited, that it could never be a vehicle of enlightenment. The most you ever hope for in a feverish fit of hallucinations is to use it as a very crude tool that perhaps can suggest a dark reflection of the Truth.

23

Thank you for the compliment.

As a writer with an interest in studying language (one does not always, or usually, imply the other) my primarily conclusion is amazement that we ever get any understanding at all.

Wigner’s famous paper The Unreasonable Effectiveness of Mathematics in the Natural Sciences should be paralleled by one titled “The Unreasonable Effectiveness of Language in Everyday Life.” They exist, although I don’t know of any as concise and approachable as Wigner’s. Most philosophers spend their days explaining why language doesn’t work. And then providing good evidence of it. :slight_smile:

24

There’s actually a very interesting sense in which language is tied up with classical physics, and hence, kind of fundamentally incapable of describing quantum mechanical goings-on beyond somewhat dissatisfying approximations such as ‘wave-particle duality’, etc. The reason for this is that quantum information and quantum correlations cannot be communicated. The most simple example of this is the no-cloning theorem: if you have some quantum state, then you can’t in general just ‘copy’ it, i.e. create another one just like it. But that means you can’t communicate it—since by communication, we typically mean the simultaneous distribution and keeping of information (nobody would ever tell anybody anything if it meant that afterwards, you’d no longer know it yourself).

Somewhat more subtle, having information about something is being correlated with it. If we have two objects that can each assume two states, we can gather information about one object by looking at the other precisely if they are correlated, that is, for example, when one is in the state a, the other is always in state 1, and when one is in state b, the other is in the state 2—it suffices to look at one to know the state of the other. This was purely classical correlation; quantum correlations work similar, without, however, requiring that either object itself be in a definite state.

Now, as it turns out, there is also no way to communicate quantum correlations, just as there is no way to communicate quantum states. While you can do it pretty easily in the classical case—in the example above, you can just set up a third object correlated with either of the previous two, and disseminate that—, quantum mechanics puts a stop to such endeavors (essentially, because you cannot measure a quantum system non-invasively, but I’m not really a friend of that kind of language).

In fact, it turns out that in all cases, only the ‘classical part’ can be communicated, that is, both shared and kept. Thus, in order to describe quantum mechanical phenomena, which simply don’t ‘fit’ within a single classical framework, you have to resort to what Niels Bohr called ‘complementary’ descriptions: that’s why, depending on the experimental context, you have to talk about light either in wave- or in particle-terms, even though these pictures are mutually exclusive.

So there’s a very real sense in which language fails to be appropriate for the description of a quantum world: what’s quantum about it simply can’t be communicated.

25

Perhaps it would help the balloon analogy if you considered the dimension normal to the balloon’s surface as time, with the balloon expanding. Then you’re trapped on the surface of the balloon much as you are trapped in the present. What’s inside the balloon? The past.

This also helps when someone tries to ask where the Big Bang occurred or where the center of the universe is. There is no center of the universe, just as there is no center of the surface of the balloon. And the Big Bang didn’t happen somewhere on the surface of the balloon. It happened in the middle, in the past.

26

Yeah. First ran into the idea in one of Stewart’s books; maybe “Does God Play Dice.” I remember he was very careful about presenting the idea, but it makes sense. I wish I knew where I put that book. Anyway, his basic idea was that if the function behind the Hidden Variables was actually a riddled basin, then Bell’s Inequality would end up looking like there was only randomness behind it.

But I would still like to know what ontic or empistemic has to do with it (really!). I hate having the feeling that I’m missing out on some important bit.

27

Honestly, this article, also in an earlier link here, gives an elegant, precise not to mention seductively comprehensible explanation of these concepts along with the wave function psi and even an important new theorem in QM published in 2010.

Anyway, the highly abridged version is (I hope) that an ontic explanation is one that acknowledges the completeness of QM as an explanation of whatever phenomena are governed by the wave function. It doesn’t necessarily posit the absolute “reality” of Psi (the wave function) but, fine. We didn’t get you to come to Jesus (yet) but we got you to the church.

An epistemic explanation is one that compares the randomness of QM to things like the weather or other complex/chaotic systems. It’s saying just as in those cases, the randomness isn’t “real” but an illusion and if only you had better/complete information about a) the mechanics of the system and b) all of the interactions, its behavior would be as predictable as a clock’s

28

Hm, do you know how the argument went? Is it just that if you’ve got a riddled basin, you basically can’t say that you have repeatability of experiments?

What’s the connection between psi-epistemicism/onticism and Bell’s theorem? It’s important regarding the PBR theorem which you’re referring to, but it seems no matter which of the horns of Bell’s dilemma (non-locality/value indefiniteness) one grabs, one can still be either psi-ontologist or psi-epistemicist.

29

Yes. I was briefly tempted to launch into a stream of consciousness accounting of the twists and turns down that particular rabbit hole, but . . . yeah. I’ll just stop there. :smack: :slight_smile:

30

edit: oh, for clarification, that would have been for the amusement value - it’s funnier when you see it from “Alice’s” perspective . . . although then again . . .

edit2: see, this is why I didn’t do it.

31

It’s a bit foggy, but I believe you’re right. Because even a slight deviation in what was measured could lead to wildly different results AND you do not have any regions in your experimental phase-space that are “safe” by which I mean converging on a single answer, you ultimately have a breakdown in the repeatability of even theoretical experiments. A deterministic function behaves like pure randomness whenever you physically attempt to measure something.

And now it gets real foggy: I seem to remember that this repeatability was a necessary assumption in order to get to Bell’s Inequality. And I wonder if anyone has been able to close that loophole yet.

32

My university’s library stocks the book, I’ll have a look if I remember.

33

So I did remember, and it turns out that Stewart uses an argument of Tim Palmer, which I actually somewhat vaguely was familiar with.

The gist is that using a riddled basin, you can construct a function that is effectively non-computable; if we use this function as the system’s response function, i.e. the function which determines what outcome a measurement produces, then it follows that measurement outcomes are non-computable. Palmer now uses this to effectively argue against counterfactual definiteness: i.e. since we can’t compute what outcome would have occurred if a certain measurement had been performed, then there is no fact of the matter regarding this outcome (i.e. it makes no sense to say 'if I had measured this-and-that, I would have observed such-and-such). From there, he argues that one can’t obtain Bell inequalities.

I think there’s a couple of issues with this. First of all, I’m not sure the argument is not a category error: since nature, for any given measurement, seems perfectly capable of determining an outcome, us not being able to do so does not entail a failure of counterfactual definiteness, but merely a failure of our predictive powers—if the answer depended on some complicated problem nobody knew how to solve, that doesn’t mean there’s no answer. So I think Palmer’s inference from the non-computability of measurement outcomes to their non-existence (which he explicitly proposes as an interpretive principle) isn’t warranted.

Furthermore, even if it were, this isn’t really a way out of the conclusions of Bell’s theorem, or at any rate, it’s a bit of a matter of taste: ultimately, Bell’s theorem says that absent a measurement, you can’t attach a definite value to certain physical quantities (or if you want to do so anyway, these values would have to be subject to non-local influences). But Palmer basically says the same thing—‘unperformed experiments have no results’, as Asher Peres’ famous dictum goes. If non-computability entails the non-existence of definite values for unmeasured physical observables, then the condition Bell called ‘reality’ is explicitly not met, and the theory is trivially not constrained by Bell inequalities.

34

the ballon analogy is often poorly explained, or set up incorrectly. You’re supposed to start by imagining a completely 2-Dimensional universe where everything exists on a single plane (a “sheet of paper”), and there is no perception of depth. Then you move to the surface of a balloon. Then you move to the inflating balloon.

Often the first part of the analogy is missing, which inevitably leads to confusion.

35

I like the raisin bread analogy [Homer Simpson] Mmmmm, raisin bread . . . [/HS]

Our galaxy is a raisin in loaf of bread that is rising. As it does, the other raisins move away, but not because of any velocity relative to the bread, but because the bread or space itself is expanding.

36

What happens if you’re on the crust of the bread and look outwards? What do you see? Would there even be a CMB? :stuck_out_tongue:

(d&r)

37

At that point you have to go with the classics:

a) turtles
b) dragons
c) Cthulhu