On 4 February 2014 23:58, Bruno Marchal <[email protected]> wrote: > On 04 Feb 2014, at 01:55, LizR wrote: > > On 4 February 2014 13:32, Jesse Mazer <[email protected]> wrote: > >> On Mon, Feb 3, 2014 at 6:29 PM, LizR <[email protected]> wrote: >> >>> SR directly demonstrates block time via the relativity of simultaneity. >>> This can be tested experimentally. >>> >> >> The relativity of simultaneity is a claim about physics, not metaphysics. >> Specifically, it's a claim that the laws of physics work exactly the same >> in all inertial frames, which have different definitions of simultaneity. >> If someone agrees that no frame's definition of simultaneity is "preferred" >> in any physical sense, but that one is "metaphysically preferred" in a way >> that is wholly invisible to all possible experiments, this would not >> contradict SR or the relativity of simultaneity as a physical principle. >> > > OK, maybe what I should have said is that no one has come up with an > explanation for the ROS that doesn't include the concept of space-time > being a 4D manifold. > I'm not sure if that leaves us with a physical or metaphysical problem (or > maybe no problem at all!) > >> >>>> That said, if you subscribe to any form of Occam's razor or even a >>>> criteria of "elegance" when it comes to choosing between different >>>> metaphysical hypotheses, it seems a lot simpler to assume that there is no >>>> metaphysically preferred definition of simultaneity, just as I think many >>>> would agree the MWI is the simplest way of interpreting the physical theory >>>> of QM. Adding extra "purely metaphysical" entities to a theory, which don't >>>> correspond to anything that appears in the mathematical formalism of the >>>> theory itself (which would apply to things like a "true present" or to >>>> hidden variables in QM), seems a bit like postulating that there are >>>> invisible intangible elves sitting on each person's head which have no >>>> causal effects on anything we can measure; sure it's logically possible, >>>> but it seems like a very inelegant and arbitrary way for reality to work. >>>> >>>> The MWI is deterministic, however, and hence has hidden variables. >>> >> >> No. The Schroedinger equation which calculates wavefunction evolution in >> QM is already fully deterministic, the MWI just dispenses with the extra >> postulate of "wavefunction collapse" on measurement, which is the only >> random element in QM. Determinism only implies hidden variables if you >> assume each experiment has a *unique* outcome, and that this outcome is >> generated in a deterministic way by the initial conditions. If you assume >> that the physical state at the end of an experiment is a quantum state >> that's a superposition of many possible classical results, then this can be >> calculated from a prior quantum state using just the standard Schroedinger >> equation. >> >> Well, yes, of course. The MWI is defined as QM with no collapse, and the > SWE is deterministic, therefore we have realism....don't we? > > Careful: in this context realism often means "collapse" or "unicity of > outcome", like in Bell's paper. or even in EPR, where realism is thought > only with the implicit assumption of unique universe. > In other context, physical realism means that physics is independent of > us, like in "arithmetic realism" (arithmetic is independent of us). > > Ah, I thought it meant there was no point (in say an EPR experiment) when the values of variables - the polarisation of a photon, say - was genuinely undefined, as opposed to merely unmeasurable.
In that sense, time symmetry and the MWI both preserve what I called realism - all variables are defined at all times - and locality - no FTL. -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/groups/opt_out.
