On Tuesday, April 9, 2019 at 12:05:11 PM UTC-6, Brent wrote: > > > > On 4/9/2019 7:52 AM, [email protected] <javascript:> wrote: > > > > On Monday, April 8, 2019 at 11:16:25 PM UTC-6, [email protected] wrote: >> >> In GR, is there a distinction between coordinate systems and frames of >> reference? AG?? >> > > Here's the problem; there's a GR expert known to some members of this > list, who claims GR does NOT distinguish coordinate systems from frames of > reference. He also claims that given an arbitrary coordinate system on a > manifold, and any given point in space-time, it's possible to find a > transformation from the given coordinate system (and using Einstein's > Equivalence Principle), to another coordinate system which is locally flat > at the arbitrarily given point in space-time. This implies that a test > particle is in free fall at that point in space-time. But how can changing > labels on space-time points, change the physical properties of a test > particle at some arbitrarily chosen point in space-time? I believe that > such a transformation implies a DIFFERENT frame of reference, in motion, > possibly accelerated, from the original frame or coordinate system. Am I > correct? TIA, AG > > > You're right that a coordinate system is just a function for labeling > points and, while is may make the equations messy or simple, it doesn't > change the physics.?? If you have two different coordinate systems the > transformation between them may be arbitrarily complicated.?? But your last > sentence referring to motion as distinguishing a coordinate transform from > a reference frame seems to have slipped into a 3D picture.?? In a 4D > spacetime, block universe there's no difference between an accelerated > reference frame and one defined by coordinates that are not geodesic. > > Brent >
Suppose the test particle is on a geodesic path in one coordinate system, but in another it's on an approximately flat 4D surface at some point in the transformed coordinate system. Doesn't this represent a change in the physics via a change in labeling the space-time points? How is this possible without a change in the frame of reference, and if so, how would that be described if not by acceleration? AG -- 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 https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
