Q & indeterminism

In the workshop I attended last week, an important question was raised: does quantum physics imply indeterminism? We have all been told this in the basic lectures, but… how do we know? I addressed this question partly in another post, to which I refer for more details; but I prefer to devote a new specific post to this important and often asked question. So here is my answer:

With one-particle phenomena, we can’t know: hidden variable descriptions, however hated and non-orthodox they may be, are possible. This means that it is possible to keep a deterministic view of such phenomena. So, if you have been told that the double slit or the Stern-Gerlach experiments necessarily imply indeterminism, think again.

When one goes to two particles, the violation of Bell’s inequalities implies that either of the following three assumptions is wrong (see other post):
1. Determinism (or outcome independence)
2. No-signaling
3. “Free will”, or more precisely, the fact that the choice of the measurements are not correlated with the source.
Adepts of Bohmian mechanics give up 2 (their “quantum potential” is a signaling hidden variable); adepts of many-world interpretations will give up 3 in a complicated way. If you want to keep 2 and 3, then indeed quantum phenomena imply indeterminism. An important remark: it is not quantum theory (i.e. a mathematical construction), but the observed violation of Bell’s inequalities (i.e. a fact) that implies indeterminism.


About valerio

Principal investigator at Centre for Quantum Technologies and professor at National University of Singapore

Posted on September 28, 2011, in Common knowledge, Latest topics, Philosophy. Bookmark the permalink. 3 Comments.

  1. I don’t agree that many worlds is complicated. It just says quantum physics applies to everybody, including you and me.

    • I see your point. What I wanted to convey is: if I would like to save determinism (I don’t), I would just assume that everything is determined in a single universe, that we and all the other particles are playing a single pre-established script (and no need to assume any “intelligent designer” to have “written” that script). This is a vision that cannot be falsified, and I would find this option simpler — just a matter of taste, of course.

  2. What I like personally about many worlds is not that it is deterministic, but that it is a unified description of everything. I suppose one could see the determinism as an added benefit. But of course it is not deterministic for each individual observer.

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