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)
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.