# Argument for quantum indeterminism

1. May 8, 2013

### alpha358

If any application of probability and statistics dosen't imply that particular proces dosen't have deterministic laws, then how quantum physicists come up with an idea that determinism is false ?

P.S.
I am second year bachelor student of applied physics and I will have quantum physics course next year.

2. May 8, 2013

### Staff: Mentor

I don't think I get all those negations.
Experiments show that determinism does not work together with other reasonable things, like locality and causality.

3. May 8, 2013

### alpha358

If we can't find deterministic laws at some scale this dosen't mean that world is indeterministic. Is there any formal proof of indeterminism ?

4. May 8, 2013

### Staff: Mentor

Bell's theorem
Kochen–Specker theorem
You cannot prove indeterminism, but you can prove that it does not work together with other features you would like to have in a theory.

There are deterministic interpretations/variants of quantum mechanics like the De Broglie–Bohm theory, but they do not have other features like locality.

5. May 8, 2013

### alpha358

So we are in interesting situation when neither indeterminism nor determinism can be proved ? Than why does some physicists in the media say that Einstein was wrong about God playing dice ?

6. May 8, 2013

### Staff: Mentor

The mathematical formalism of quantum mechanics is non-deterministic but, as you say, that doesn't prove that the world is really non-deterministic, it just means that this particular theory refuses to give us non-probabilistic answers.

However, if you google around for "Bell's Theorem" (and you could do worse than our own DrChinese's page at http://www.drchinese.com/Bells_Theorem.htm) you will find a very convincing argument: Any theory that is both local and deterministic must in some cases make different predictions than quantum mechanics; and these predictions have been tested experimentally and the results agree with QM, disagree with the local realistic prediction.

Note the qualifier "non-local" above. It is possible to construct deterministic theories that match the quantum mechanical predictions as long as they are non-local. There is also superdeterminism, but as it is carefully defnined to be indistinguishable from the nondeterminism that we observe in Bell-type experiments it doesn't much advance the discussion).

Disclaimer: I am playing a bit fast and loose here with words like "realistic" and "deterministic". The above is, IMO, a fair answer to your question, but if you want to seriously dig into the philosophical issues here (google for "interpretations of quantum mechanics") you'll want to be more rigorous in your terminology.

7. May 8, 2013

### Naty1

The following quote is from Roger Penrose celebrating Stephen Hawking’s 60th birthday in 1993 at Cambridge England.....An interesting insight into quantum/classical relationships:

8. May 8, 2013

### alpha358

Thank you for your time and effort, I will study quantum physics soon and very carefuly (checking what is really proved). Now I see that we don't have formal proof of indeterminism.
I am interested in truth no matter how it looks like - deterministic or not.

9. May 8, 2013

### Staff: Mentor

That's it.

But just to give a slightly different take another way of looking at it is via Gleasons theorem (Kochen-Sprecker is a simple corollary to that theorem):
http://en.wikipedia.org/wiki/Gleason's_theorem

You can't define a measure of 0 and 1 on a vector space which means you cant have determinism in the formalism of QM - it inherently is a probabilistic theory. There is an out - contextuality - ie what you measure is dependent on whatever else you are measuring at the same time.

Don't be too worried if you don't understand it right now - you will be able to grasp it better when your math and physics is a bit more advanced. Just take it that your question is quite deep and there is an answer - namely the formalism - with a bit of an out - implies it must be probabilistic - but you need to have a bit more of a background in math than you probably have right now to understand it.

But in case you have the background check out:
http://kof.physto.se/theses/helena-master.pdf

Thanks
Bill

Last edited: May 8, 2013