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Uncaused events?

KingMerv00

Penultimate Amazing
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I've heard people say that in quantum mechanics, particles appear without reason or that electrons "decide" their spin without cause.

Why is this the consensus? Why have physicists decided that there are uncaused quantum events when these phenomenon could just as easily be explained by an undiscovered clockwork mechanism of the universe?

Why MUST they be uncaused?
 
KingMerv00 said:


Why is this the consensus? Why have physicists decided that there are uncaused quantum events when these phenomenon could just as easily be explained by an undiscovered clockwork mechanism of the universe?

The Bell inequalities. Basically, if you measure properties between two related particles, the measured properties will agree some of the time and disagree some of the time. (The formal term for the degree of agreement is, of course, "correlation.") Bell showed (1964, I believe) that if there is an undiscovered clockwork mechanism of the universe (the usual term is "hidden local variables"), then various inequalities must hold. Experimentally, they don't. Therefore, hidden variables are out.
 
They don't have to be if you assume an entirely unknown class of causal event. It's one of the few situations where Occam's razor is too blunt. Which is simpler- hidden variables or acausality?

Edit to add- This was a response to the OP, not to DRKitten. The posts crossed in the mail.
 
Soapy Sam said:
They don't have to be if you assume an entirely unknown class of causal event. It's one of the few situations where Occam's razor is too blunt. Which is simpler- hidden variables or acausality?

I'm not sure I understand what you're saying. Are you suggesting a new class of causal event could potentially violate the Bell inequalities? If so, how?
 
Bell just made predictions in the 1960's. The technology to verify it wasn't available until the mid 1980's. I don't remember the names of the two individuals who experimentally verified Bell's work but Brian Greene covers it well in his new book Fabric of the Cosmos.
 
Re: Re: Uncaused events?

new drkitten said:
Bell showed (1964, I believe) that if there is an undiscovered clockwork mechanism of the universe (the usual term is "hidden local variables"), then various inequalities must hold. Experimentally, they don't. Therefore, hidden variables are out.

The distinction between local and nonlocal hidden variables theories is important. Bell's inequality disproved the former, but has nothing to say about the later. Local hidden variables theories were attractive because they could, in principle, eliminate much of the "strangeness" of quantum mechanics. But, being "hidden", the only appeal they ever held was aesthetic, since you could hope that things weren't really so strange underneath it all. They never had any practical use for anything.

Nonlocal hidden variables theories are still quite possible under Bell's inequality, but they don't really get you anywhere. They are still "strange," (nonlocality is a little hard for me to explain, but it's very non-classical) so they have no aesthetic appeal, and they're just as useless from a practical standpoint. So they've been abandoned, since they don't appeal to people's sensibilities and they have no practical benefits either. But they're not actually categorically ruled out.
 
Cause and effect

WHAT IS Fate?” the Mulla Nasrudin was once asked by a scholar. “An endless succession of intertwined events, each influencing the other,” he replied. The scholar raised a sceptical eyebrow: “I can’t accept that. I believe in cause and effect.” “Very well,” said the Mulla and drew his attention to a procession of people, leading a man to be hanged. “Is that man going to die because someone gave him the money that let him buy the knife he used for murder, or because someone saw him do it, or because nobody stopped him?”

Not exactly quantum mechanics, but I think it is a lovely quote from some Nasrudin book :)
 
KingMerv00 said:
I've heard people say that in quantum mechanics, particles appear without reason or that electrons "decide" their spin without cause.

Why is this the consensus? Why have physicists decided that there are uncaused quantum events when these phenomenon could just as easily be explained by an undiscovered clockwork mechanism of the universe?

Why MUST they be uncaused?

It's simply human preference.

Many physicists just found it easier to believe things are fundamentally determined by chance than by undiscovered causes, so indeterminism was adopted as the way the universe is.

However, it's not hard to imagine that the universe is like a simulation running in a computer and it appears indeterministic to any artificially intelligent person inside the simulation but is in fact deterministic and following a set program with only one possible past, present and future.

If the program was written so that there was no way for any AI person inside the simulation to tell if it was determinisitic or not, than that is that as far as the AI person's investigation goes.

We could be in a similar situation, not in the sense of being in a computer but in the sense that the causes for events might simply be something that we can never know.
 
Re: Re: Uncaused events?

new drkitten said:
The Bell inequalities. Basically, if you measure properties between two related particles, the measured properties will agree some of the time and disagree some of the time. (The formal term for the degree of agreement is, of course, "correlation.") Bell showed (1964, I believe) that if there is an undiscovered clockwork mechanism of the universe (the usual term is "hidden local variables"), then various inequalities must hold. Experimentally, they don't. Therefore, hidden variables are out.

Would this be a bad time to bring up the maxim "correlation does not equal causation"?
 
Re: Re: Re: Uncaused events?

TeaBag420 said:
Would this be a bad time to bring up the maxim "correlation does not equal causation"?

Only if you believed that it was relevant.

More generally -- correlation does not equal causation, but causation can certainly (and provably) cause correlation. So a lack of correlation can be proof of a lack of causation. (Think about clinical trials in medicine. If there's no correlation between whether or not you get the drug and whether or not you get better, then the drug doesn't cause you to get better.)

If quantum properties were caused by "hidden local variables," then we would see a higher degree of correlation than we do on the various EPR experiments.

As Ziggurat pointed out, the Bell inequalities don't rule out hidden NONLOCAL variables (whatever the hell that means), but that ends up being just as flakey and newage as the idea of uncaused events, and just as incompatible with the idea of a hidden clockwork universe.
 
Re: Re: Uncaused events?

wipeout said:
It's simply human preference.

Many physicists just found it easier to believe things are fundamentally determined by chance than by undiscovered causes, so indeterminism was adopted as the way the universe is.

However, it's not hard to imagine that the universe is like a simulation running in a computer and it appears indeterministic to any artificially intelligent person inside the simulation but is in fact deterministic and following a set program with only one possible past, present and future.


I believe you are mistaken. Most physicists, especially of the era in which most of the interpretations of modern physics were hammered out, would vastly have prefered that the universe was determined by as-yet undiscovered causes. That's the way the rest of science works, after all. Shroedinger's famous cat parable, for example, was originally intended as a rebuttal to the now-mainstream squishy interpretation of an unresolvable mixture of quantum states. After all, we know how cats work -- and the point is that a cat simply can't be a mixture of both dead and alive. A concept like that doesn't make sense applied to a cat, so why should it make sense applied to an electron or an atom.

Modern scholarship has simply reversed the parable, stating (in the teeth of common sense, I might add), that it does make sense to talk about a cat being a mixture of alive and dead, and if you don't see it, you don't understand quantum mechanics. But the reason that modern scholarship has taken that path is because the experimental evidence is so firmly against underlying unknown causes.

Bell's inequalities directly address this question. A "deterministic" universe where quantum fluctuations were determined by unknown local variables would not be compatible with our experimental evidence. The situation you describe :


If the program was written so that there was no way for any AI person inside the simulation to tell if it was determinisitic or not, than that is that as far as the AI person's investigation goes.

We could be in a similar situation, not in the sense of being in a computer but in the sense that the causes for events might simply be something that we can never know.

is not accurate precisely because we can determine that, whatever the causes for events are, they're not simply an unknown conventional universe with a conventional set of hidden properties. They're either genuinely non-determininstic causeless events, or they're something even stranger.
 
new drkitten said:
I'm not sure I understand what you're saying. Are you suggesting a new class of causal event could potentially violate the Bell inequalities? If so, how?


NDRK- As I said in my edit, I responded to the OP, but your response arrived first, so it looks like I'm responding to you. Not so.

I'm not postulating such a class, no. I just meant that it was initially a toss up which was less probable- an unknown cause or an absence of cause. In 1930 I think I would have plumped for the unknown.

After the work of Aspect et al, I agree that would seem by far the less probable choice of most scientists. I thought the OP referred to the historical choices of scientists, which have changed (as scientific opinions do and should) with the evidence.
 
Soapy Sam said:

I'm not postulating such a class, no. I just meant that it was initially a toss up which was less probable- an unknown cause or an absence of cause. In 1930 I think I would have plumped for the unknown.

So would I. In my less rational moments, I still do -- I keep wandering around the Bell inequalities looking for a flaw that would permit me to believe in the pretty clockwork universe. Haven't found one yet, but no one ever said that Nobel-caliber physics was easy....
 
Re: Re: Re: Uncaused events?

new drkitten said:
Bell's inequalities directly address this question. A "deterministic" universe where quantum fluctuations were determined by unknown local variables would not be compatible with our experimental evidence. The situation you describe is not accurate precisely because we can determine that, whatever the causes for events are, they're not simply an unknown conventional universe with a conventional set of hidden properties. They're either genuinely non-determininstic causeless events, or they're something even stranger.

With EPR experiments, if every possible event in the history of the universe was determined in advance and the universe was following a set program from the start, then Bell's inequalities would work just the same as they do.

You were always going to get that correlation because you were always going to look for that correlation and it was always going to be waiting for you when you looked.

There is no demonstration that the universe is random, only that we have either nonlocal hidden variables or the usual quantum theory with its lack of realism for particle properties (with "realism" obviously being in the technical sense).

With Schrodinger's cat, while it's quite likely impossible to attach any real meaning to a superposition of dead and alive states, there's no reason not to suggest that the cat was always going to be in whichever state you find it in. The wavefunction was always going to "collapse" in the way it does when you look in the box.

As you can hopefully see, I don't mean a underlying classical universe following a set series of events, I mean a purely quantum universe following a set series of events.

Telling random from pseudorandom is quite possibly impossible. :)
 

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