On Mon, Feb 3, 2014 at 7:55 PM, LizR <lizj...@gmail.com> 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. >
What do you mean by "explanation" for ROS, though? It's normally assumed that the fundamental laws of physics have various symmetries, like rotational invariance and CPT-symmetry, and the ROS is just a consequence of Lorentz-symmetry. Do we need a meta-explanation for why the laws of physics have any particular symmetries? I suppose here on this list we do play around with the possibility that the laws of physics themselves could be derived from some more basic assumptions, but physicists normally take fundamental laws as a stopping point that can't be explained in terms of anything more basic (unless they turn out to not be "fundamental" laws after all). And when you say the "concept of space-time being a 4D manifold", again I think you have to distinguish between the idea that it's useful to *model* it in that way from some more ontological statement that all points on the manifold "exist" in the same sense. While modern physics certainly models spacetime in that way, again I don't see how physics can lead you to any definite ontological claims, though those of us who favor Occam's razor might say that the fact that there's no physically preferred definition of simultaneity makes it seem more "natural" to assume there's no metaphysically preferred simultaneity either. > 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? OK, I may have > used the wrong terminology here. Maybe "hidden variables" means something > different from what I thought. I assumed the MWI, being completely > deterministic (a "block multiverse") had a definite state at all times, and > that therefore there is stuff that we can't measure but is there, even so - > which I thought meant hidden variables. But I may have messed up. > > (That said, time symmetry could also be termed hidden variables, I think?) > As I said in my comment to you at http://www.mail-archive.com/everything-list@googlegroups.com/msg46130.htmlI think there are various conceivable ways a theory could be time-symmetric--the conventional one is just that you can use the same equations to "retrodict" a system's earlier state as you used to predict its later state, given some set of conditions at a particular time, and I don't see how that could be said to involve hidden variables. But the other type of possible time-symmetric theory I discussed in that post, where to determine physical states at a given point in spacetime you must take into account both its future and its past, might perhaps be said to involve a sort of hidden variable since we don't have direct knowledge of the future events that may be influencing things in the here and now. Jesse > > -- > 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 everything-list+unsubscr...@googlegroups.com. > To post to this group, send email to everything-list@googlegroups.com. > Visit this group at http://groups.google.com/group/everything-list. > For more options, visit https://groups.google.com/groups/opt_out. > -- 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 everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/groups/opt_out.
