The Universe is Deterministic

[SezMe]

Yes. I just thought the double-slit was a strange example in a discussion which is basically about the existence of hidden variables.

I don't know that that is what the OP is talking about.

 

[sol invictus]

So why then is the prevaling opinion that the universe nondeterministic?

Because it is non-deterministic according to a huge number of experiments and the theory that describes them. As is being discussed, it might be possible to find a deterministic theory that works, but only by giving up either causality or relativity.

Doesn't non-locality require there to be something which travels faster than light?

But given the restrictions on what that something is in QM it doesn't give you any meaningful time travel that I can see - I think any reasonable definition of time travel should involve transport of an observer or an ability to observe locations at times you 'shouldn't' be able to.

You might be talking past each other here slightly. If you add something to QM to make it causal but non-local (i.e. a non-local hidden variable theory a la Bohm) Dorfl is almost certainly correct that you will introduce causality violation (via time travel type paradoxes) when you incorporate relativity into the theory.

I think edd is referring to the fact that there is an apparent non-locality in vanilla QM without such extra variables, but that it doesn't allow any transport of information or energy.

 

[edd]

You might be talking past each other here slightly. If you add something to QM to make it causal but non-local (i.e. a non-local hidden variable theory a la Bohm) Dorfl is almost certainly correct that you will introduce causality violation (via time travel type paradoxes) when you incorporate relativity into the theory.

Are there nonlocal hidden variable theories that are relativistic and show this then?

 

[Tsukasa Buddha]

I thought Complexity and Chaos Theory showed that a system can be non-deterministic yet non-random.

 

[sol invictus]

Are there nonlocal hidden variable theories that are relativistic and show this then?

I don't know if anyone has ever bothered to write one down, since it would be obviously wrong.

Actually I think much of the literature on this topic is seriously misguided. People (many of whom aren't physicists, they're philosophers or mathematicians) write papers and hold conferences where they discuss all sorts of bizarre versions of non-relativistic QM that resolve this weirdness in one way or another, and not one of those proposals is consistent with relativity. It's as if the last century of particle physics data didn't exist for them.

 

[sol invictus]

I thought Complexity and Chaos Theory showed that a system can be non-deterministic yet non-random.

Chaos is non-deterministic only in practice. By definition, a chaotic system is one where if you take two initial states that differ only slightly, that difference grows exponentially with time. Hence after not very long any uncertainties you had about the initial state become enormous, so it's extremely hard to predict the system's behavior very far into the future.

But nevertheless the equations describing the evolution of the system are perfectly nice causal differential equations, so it's deterministic.

(The word "random" is best avoided here, because it means too many different things to too many different people. "Deterministic" in physics means "past and future are fully determined by the state of the system at some time".)

 

[Cynic]

Because quantum events are stochastic.

How do you know?

 

[sol invictus]

How do you know?

It's called "science"; specifically, "physics".

There's theory and there are experiments. If the experiments support the theory, you keep it. If they don't, you don't.

In this case we're discussing the best-tested theory in the history of science.

 

[Cynic]

So what you're saying is basically that events on one scale appear to be deterministic, and assuming that this therefore has to be true on all scales. I don't think that's a reasonable assumption.

There are two major issues with this topic for me. One is that I don't feel existing experimental evidence in any way necessitates a non-deterministic universe. The second is what what you just said, which represents how, in the absence of hard evidence one way or another, people seem content to make the "odd" choice.

Rarely do we see this happen because experience biases us to expect what we're used to. You go to a place you've never been to (on Earth) and you expect gravity, relative temperatures, etc to remain the same. No one had to you tell you to expect it -- you just do because generally, that's how things work. Airplanes function the same in Pennsylvania as they do in Belgium. The rules for curing cement remain constant, even if the prevaling conditions must be adjusted for.

And it's not like "cause and effect" is some obscure notion here. It always works, on planet or off, on every scale that has been tested. (We're going to discuss tests that people interpret has showing that it does not, but I intend to show that such interpretations are not necessitated.)

So why, when we don't routinely expect to open a door we've never opened and discover a portal to Oz, would we expect to find something equally strange and unusual behind the door of a level of reality we've never seen before. I mean, allow for the possibility sure -- though I think that would defy logic -- but to just assume that it will be the case? Something is wrong with that. A genuine violation of causation is most certainly and obviously the "extraordinary claim" here.

 

[Cynic]

There's theory and there are experiments. If the experiments support the theory, you keep it. If they don't, you don't.

In this case we're discussing the best-tested theory in the history of science.

Please demonstrate an experiment that you feel necessitates a non-deterministic universe.

 

[sol invictus]

Please demonstrate an experiment that you feel necessitates a non-deterministic universe.

Every experiment that supports quantum mechanics, which is just about every physics experiment ever done.

 

[Cynic]

Every experiment that supports quantum mechanics, which is just about every physics experiment ever done.

Well then, since I'm obviously flying in the face of so many physicists, can you do better than arguing from authority by simply citing their opinion as a way of settling the matter? This is a matter of interpretation of observations. If I didn't already know the prevaling opinion, I would not have created this thread...

 

[sol invictus]

Well then, since I'm obviously flying in the face of so many physicists, can you do better than arguing from authority by simply citing their opinion as a way of settling the matter? This is a matter of interpretation of observations. If I didn't already know the prevaling opinion, I would not have created this thread...

I can't figure out what it is you're asking for. Why don't I list some facts and you can pick the one you don't accept?

1) quantum mechanics is a non-deterministic theory.

2) specifically, when one measures a state in a superposition of two eigenstates, the result is random with probability determined by the norm square of the coefficients.

3) quantum mechanics is the best-tested theory in the history of science

4) some predictions of QM are inconsistent with those of any local, deterministic theory.

5) those specific predictions have been experimentally confirmed many times over.

 

[Cynic]

I can't figure out what it is you're asking for. Why don't I list some facts and you can pick the one you don't accept?

By the numbers then. Hopefully my position will become more clear.

1) quantum mechanics is a non-deterministic theory.

This is in dispute. Whether or not the underlying reality of the universe is deterministic or not is a matter of interpretation of the experimental observations, not a consequence of the theory -- regardless of how well it is able to make predictions.

2) specifically, when one measures a state in a superposition of two eigenstates, the result is random with probability determined by the norm square of the coefficients.

Which one of these sequences is random?

1011010101110100011111001 --or-- 0000011111001110000101001

Can you tell? While uncertainty necessitates the use of probability to predict outcomes, it does not imply that there was no cause, only that the cause cannot be determined because of the nature of uncertainty.

It's circular to be forced to use a probalistic approach to solving a problem and then declare that since you used it, it's random.

3) quantum mechanics is the best-tested theory in the history of science

I wouldn't dispute that, but then, it's not in dispute. Quantum mechanics is also universally regarded as incomplete and incompatible with other very well-tested theories that have yet to fail on their own terms either. However well it works, interpretation on the results is somewhat subjective. It's that interpretation -- the more common interpretation regarding "randomness" -- I dispute.

4) some predictions of QM are inconsistent with those of any local, deterministic theory.

Can you detail one that specifically demonstrates the necessity of a non-deterministic universe?

5) those specific predictions have been experimentally confirmed many times over.

Granted. But have their interpretations, such that a non-deterministic universe is necessitated?

 

[Dorfl]

I don't know that that is what the OP is talking about.

Isn't a discussion about whether QM is deterministic necessarily a discussion about the existence of hidden variables?

 

[Dorfl]

You might be talking past each other here slightly. If you add something to QM to make it causal but non-local (i.e. a non-local hidden variable theory a la Bohm) Dorfl is almost certainly correct that you will introduce causality violation (via time travel type paradoxes) when you incorporate relativity into the theory.

I think edd is referring to the fact that there is an apparent non-locality in vanilla QM without such extra variables, but that it doesn't allow any transport of information or energy.

Thanks. I think that clears things up.

 

[Cynic]

Isn't a discussion about whether QM is deterministic necessarily a discussion about the existence of hidden variables?

As far as I can tell, yes -- that what seems random ultimately has a cause, some consequence or relation we haven't caught onto yet.

 

[Dorfl]

There are two major issues with this topic for me. One is that I don't feel existing experimental evidence in any way necessitates a non-deterministic universe. The second is what what you just said, which represents how, in the absence of hard evidence one way or another, people seem content to make the "odd" choice.

Rarely do we see this happen because experience biases us to expect what we're used to. You go to a place you've never been to (on Earth) and you expect gravity, relative temperatures, etc to remain the same. No one had to you tell you to expect it -- you just do because generally, that's how things work. Airplanes function the same in Pennsylvania as they do in Belgium. The rules for curing cement remain constant, even if the prevaling conditions must be adjusted for.

And it's not like "cause and effect" is some obscure notion here. It always works, on planet or off, on every scale that has been tested. (We're going to discuss tests that people interpret has showing that it does not, but I intend to show that such interpretations are not necessitated.)

So why, when we don't routinely expect to open a door we've never opened and discover a portal to Oz, would we expect to find something equally strange and unusual behind the door of a level of reality we've never seen before. I mean, allow for the possibility sure -- though I think that would defy logic -- but to just assume that it will be the case? Something is wrong with that. A genuine violation of causation is most certainly and obviously the "extraordinary claim" here.

I agree that the default should be to expect things to work as usual in a new situation. But this expectation should become weaker the stranger the new situation is. Like, if I walked through a door and found myself suddenly falling onto the ceiling, I would avoid stepping near the windows, even though I never normally wonder about falling out of windows.

Anyway, I think you're wrong to describe physicists as "content to make the odd choice". Historically, the assumption of non-determinism is based on physicists being forced to pick one of two odd choices: non-determinism or violated causality. For whatever reasons, most found the former the least odd. But it is not a choice that they were at all content to make, to claim otherwise ignores a lot of history.

I hope you agree that the idea of information travelling backwards in time is also very, very much against all other experience.

 

[sol invictus]

This is in dispute.

You're mistaken.

There is no dispute that according to standard QM the results we obtain from doing experiments are non-deterministic. There is a dispute (although not much of one) over whether it's possible to augment or replace QM with something else that is deterministic and reproduces its results. However, Bell proved in the 1960's that no such local theory exists.

Which one of these sequences is random?

1011010101110100011111001 --or-- 0000011111001110000101001

Can you tell?

Of course not. But we're not talking about randomness, we're talking about determinism. The word "random" does not appear in the OP, and I'd rather not go there, because it's not a very well-defined word and we will inevitably fall into useless semantic arguments.

Can you detail one that specifically demonstrates the necessity of a non-deterministic universe?

Google "bell's theorem" and look up the associated experiments.

Granted. But have their interpretations, such that a non-deterministic universe is necessitated?

Yes, unless you abandon one of the assumptions necessary to prove the theorem.

 

[Molinaro]

The double-slit experiment doesn't rule out there being hidden variables determining the distribution of the particles, does it?

The double slit experiment can be explained by the transactional interpretation of QM, without needing hidden variables, or non-locality.