Do physicists really believe in true randomness? • Hacker News Board

Re: Do physicists really believe in true randomness?

#21

Post by cwzwarich » Fri, Apr 04, 2014, 2:31 AM UTC

ngoldbaum wrote: post #10

cwzwarich wrote: post #8

Earlier quoted context omitted.

There are deterministic interpretations of quantum mechanics, under which the usual randomness in quantum mechanics is not truly random.

But Bell's inequality says that these hidden variable theories are incompatible with the results of experiments. Real experiments. Like these: http://en.wikipedia.org/wiki/Bell_test_experiments It may be the case that there really is a hidden variable, but it would need to communicate it's value nonlocally, which I'd argue is stranger than the universe just being somewhat random.

The Copenhagen interpretation is arguably the most popular interpretation of quantum mechanics and is nonlocal.

Re: Do physicists really believe in true randomness?

#22

Post by avalaunch » Fri, Apr 04, 2014, 2:31 AM UTC

pvnick wrote: post #19

I love the idea of true randomness because it seems, to my uninformed mind, to allow us the possibility of free will. Without true randomness, while we may enjoy the illusion of free will, our decisions are ultimately left to deterministic hidden variables. That makes me sad. But given true randomness, we may in fact have some mechanism whereby we are truly autonomous. How that might work is way beyond me and probabl…

I'm not sure random will is equivalent to free will. Is a choice still a choice if it's made randomly? Couldn't you say that the photon in the experiment has free will then? What's the difference?

Re: Do physicists really believe in true randomness?

#23

Post by dllthomas » Fri, Apr 04, 2014, 2:34 AM UTC

Grieverheart wrote: post #15

ngoldbaum wrote: post #10

Earlier quoted context omitted.

But Bell's inequality says that these hidden variable theories are incompatible with the results of experiments. Real experiments. Like these: http://en.wikipedia.org/wiki/Bell_test_experiments It may be the case that there really is a hidden variable, but it would need to communicate it's value nonlocally, which I'd argue is stranger than the universe just being somewhat random.

Bell's theorem is based on the assumption of free will, see eg http://en.wikipedia.org/wiki/Superdeterminism

Eeeeh, not quite "free will", but "choices that are not structured relative to the thing being measured", which is a much weaker assumption (though still an assumption).

Re: Do physicists really believe in true randomness?

#24

Post by kzrdude » Fri, Apr 04, 2014, 2:36 AM UTC

nanidin wrote: post #16

> If, on the other hand, you try to predict something like the moment that a radioactive atom will radioact, then you’ll find yourself at the corner of Shit Creek and No I love it!

I had the opposite reaction.

Re: Do physicists really believe in true randomness?

#25

Post by ced » Fri, Apr 04, 2014, 2:37 AM UTC

John Bell himself wrote an entertaining paper railing on the orthodox perspective: Against Measurement.

http://www.tau.ac.il/~quantum/Vaidman/IQM/BellAM.pdf

Re: Do physicists really believe in true randomness?

#26

Post by moyix » Fri, Apr 04, 2014, 2:38 AM UTC

avalaunch wrote: post #22

pvnick wrote: post #19

I love the idea of true randomness because it seems, to my uninformed mind, to allow us the possibility of free will. Without true randomness, while we may enjoy the illusion of free will, our decisions are ultimately left to deterministic hidden variables. That makes me sad. But given true randomness, we may in fact have some mechanism whereby we are truly autonomous. How that might work is way beyond me and probabl…

I'm not sure random will is equivalent to free will. Is a choice still a choice if it's made randomly? Couldn't you say that the photon in the experiment has free will then? What's the difference?

There's a pretty good essay from Scott Aaronson [1] that tries to disentangle the question of randomness from unpredictability, by saying that unpredictable events (which he says are the only things we know of physically that might permit something like free will) are events to which we can't assign a probability distribution.

It separates out the notions of "random" events like coin flips, which we know will go heads with p=.5 and tails with p=.5, from truly unpredictable events, where we can't say even in principle what the probabilities of the outcomes might be. These latter events are where he finds some wiggle room for free will.

[1] http://www.scottaaronson.com/papers/giqtm3.pdf

Re: Do physicists really believe in true randomness?

#27

Post by analog31 » Fri, Apr 04, 2014, 2:39 AM UTC

livingparadox wrote: post #9

Can someone explain this a bit better? As far as I can tell, the argument is basically "these particle effects should be predictable. I can't predict them, therefore they're impossible to predict". That sounds like nonsense to me... And I don't understand the cos equation. The argument seems to assume that the experiment is perfectly controlled, and given that we're still figuring out quantum effects, this seems to b…

Forgive me, but I'm reaching back into my recollection of this subject from when I was a physics student. The presence or absence of true randomness has to be turned into a testable hypothesis, or it's not a scientific question. I think the point of the experiment as described is to find such a test, where randomness, or its absence, produce different outcomes. Whether it achieves that goal is for people smarter than me to figure out.

Re: Do physicists really believe in true randomness?

#28

Post by tedsanders » Fri, Apr 04, 2014, 2:42 AM UTC

pavpanchekha wrote: post #3

j2kun wrote: post #2

Isn't this just a question of whether they believe in quantum mechanics?

Believing in quantum mechanics is much like believing in gravity or relativity—it is definitely a part of the universe we live in, and no mainstream physicists disagree on its correctness.

However, there is a degree of belief in the interpretation of quantum mechanics that you choose. It's odd that the author of this article espouses the Many Worlds interpretation without pointing out that it's not a consensus viewpoint. Also oddly, the Many Worlds interpretation is known for being a deterministic interpretation yet the author promotes it as a non-deterministic interpretation.

Re: Do physicists really believe in true randomness?

#29

Post by yk » Fri, Apr 04, 2014, 2:42 AM UTC

livingparadox wrote: post #9

Can someone explain this a bit better? As far as I can tell, the argument is basically "these particle effects should be predictable. I can't predict them, therefore they're impossible to predict". That sounds like nonsense to me... And I don't understand the cos equation. The argument seems to assume that the experiment is perfectly controlled, and given that we're still figuring out quantum effects, this seems to b…

There are two different kinds of randomness [1], one is lack of knowledge, the dice you could calculate or the precise times of keystrokes which could be easily measured. The other is 'true' randomness, that is the claim that no experiment or calculation could predict the value of the random variable. Bells inequality can (sometimes) distinguish between the two. And it turns out that quantum mechanics allows to measure Bells inequality. The result of these experiments is, that there is no straight forward way to introduce 'hidden' variables such that the randomness would just be a lack of knowledge. And it does so in a way that allows for experimental errors. (Sorry for being quite vague, it is quite late here and it would take some time to remind myself of the details.)

So if you want to claim that there is no such thing as true randomness, then you are essentially calling for another revolution of physics on a similar scale as the quantum revolution at the start of the last century. It is entirely possible that this happens, but it contradicts the most fundamental theories of physics we have.

[1] Actually three, it is not obvious what optimal strategies have to do with either of the definitions above.

Re: Do physicists really believe in true randomness?

#30

Post by pvnick » Fri, Apr 04, 2014, 2:44 AM UTC

avalaunch wrote: post #22

pvnick wrote: post #19

I love the idea of true randomness because it seems, to my uninformed mind, to allow us the possibility of free will. Without true randomness, while we may enjoy the illusion of free will, our decisions are ultimately left to deterministic hidden variables. That makes me sad. But given true randomness, we may in fact have some mechanism whereby we are truly autonomous. How that might work is way beyond me and probabl…

I'm not sure random will is equivalent to free will. Is a choice still a choice if it's made randomly? Couldn't you say that the photon in the experiment has free will then? What's the difference?

That's a good point, I'm not quite sure how to answer that. I know almost nothing of quantum mechanics. My logic is simply that if you had a large enough calculator and nothing was truly random that you could predict us having this conversation from the moment of the big bang. That's incompatible with true freedom of will (which someone is sure to ask me to define, I swear metaphysics suffers from death by definitions). But given true randomness:

1) Person faced with ethical decision

2) Random events somewhere in the brain

3) _____________

4) Unpredictable autonomous decision!

Or something like that.

Edit: moyix's is a much better response than mine