On Tue, Aug 6, 2013 at 12:04 PM, Dan Asimov <dasimov@earthlink.net> wrote:
These two things ("free will" and "determined by causes I can't perceive") are not almost the same, but instead are almost opposites. Of course, "determined by causes I can perceive" would also exclude free will. Ultimately, "free will" per se is precisely the opposite of "determinism".
That's a "libertarian" view of free will; there's also the "compatibilist" view: http://en.wikipedia.org/wiki/Compatibilism
Speaking of determinism, can someone please clarify a confusion I've had about the consequences of quantum mechanics:
1) I used to believe in determinism, but then learned that QM implied some things happened ultimately by chance with no underlying mechanism.
The mathematical content of quantum mechanics is entirely deterministic. There are various interpretations of that content; the Copenhagen interpretation asserts that the wave function collapses when it is "observed" (whatever that means), and that collapse is instantaneous and random. Penrose says that the wavefunction collapse is deterministic but uncomputable. The many worlds view says there's no collapse and quantum randomness is an illusion due to postselection. Bohmians follow deBroglie and say there are real point particles guided by pilot waves; the dynamics of this system are entirely deterministic but the evolution of the pilot wave is nonlocal.
2) Then I believed there must be hidden variables until I heard of Bell's Theorem, which is said to prove the non-existence of hidden variables in QM.
3) Then I heard that Bell's Theorem is valid only if non-locality is excluded.
Right; Bell himself became a Bohmian.
QUESTION: Does QM exclude the possibility of determinism?
No, only certain interpretations.
Is some kind of non-locality consistent with known physics?
As above, Bohm's pilot wave is nonlocal, but it only works with Schroedinger's equation. It has trouble with relativity because the number of particles you see depends on your acceleration. There can be nonlocal correlations, but information has to travel at the speed of light. You can't compare two correlated systems without bringing them together, and that "bringing together" action is restricted to c or less.
--Dan
On 2013-08-06, at 10:07 AM, Dave Dyer wrote:
Unless you are a philosopher, the difference between "free will" and "determined by causes I can't perceive" is meaningless.
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