On 04 Feb 2014, at 21:47, LizR wrote:
On 4 February 2014 23:58, Bruno Marchal <marc...@ulb.ac.be> wrote:
On 04 Feb 2014, at 01:55, LizR wrote:
On 4 February 2014 13:32, Jesse Mazer <laserma...@gmail.com> wrote:
On Mon, Feb 3, 2014 at 6:29 PM, LizR <lizj...@gmail.com> 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.
OK. But time symmetry still asks fro special boundary condition, and
seems to me to still look like using ad hoc information to select one
reality against others. I agree with Deutsch's idea that Cramer
transactional theory is still a MWI, + initial conditions selecting a
reality.
Bruno
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