[Bill S]

Edit found this link https://phys.org/news/2014-05-does-light-experience-time.html

Interesting link, but it reiterates the line of reasoning that (unjustifiably?) extrapolates relativity beyond its actual scope.

[jeffreyH (OP)]

This raises the possibility of the detector being in the middle of the room and photons being fired at it from each end along the direction of travel. The problem is clock synchronization. There is no way to synchronize effectively since you would have to measure the one way speed of light.

[PmbPhy]

All particles, photons included, move on geodesics. A geodesic is a curve of extremal length. Its quite possible for a two photons to start out at the same point in space and one return before the other one. A perfect example is on the photon sphere of a black hole. Its like two people standing at one location and to end up one mile away. One takes the route which is the shortest while the other is the route taken along a great circle which is thousands of miles apart.

[Tomassci]

"With respect to whom?", you ask. Is that the wrong question?
[/quote]
Yes, it is. Particuraly. It has travelled the same distance in any view. If you will hold light years stick, then you will mesaure it's still right.

[guest4091]

Bill S #13

1. Is the curvature of spacetime only a mathematical factor, used because it describes gravity better than does Newton's law?

Relativity Theory is a geometric interpretation of physics, via Minkowski 4D mathematical modeling. Perspective requires treating the curvature the same as orbits or trajectories, ficticious histories of positions. If all statements in theory using metaphors, were prefixed with "as if", it might help eliminate the literal interpretations.
The Relativity descriptions of the Mercury orbit and the 1919 eclipse prove to be more accurate than those of Newton.
Hopefully the graphic will help clarify the idea of spacetime curvature.
On the right, light (blue) moves from a source S in a straight line path to observer A.
On the left, a mass M is introduced near the original path. The line x-x is an axis of symmetry relative to B and S. As the light moves toward A, the g-field of M continuously directs it to its center (light gray lines). Observer B to the left of A receives the light, AS IF it originated at S'. (The 1919 eclipse with exaggerated offset for clarity.)
The varying direction of the g-field determines the position of the light/particle, but is  interpreted as a particle following a predetermined curved path, but is being formed in the present!
To state, "space is curved", only generates another question. How/why is it curved?
The lack of understanding how the energy of a mass generates a g-field, for me, does not justify substituting an obscure curvature of space..


g-lensing.gif (6.91 kB . 602x706 - viewed 2421 times)

[guest4091]

JeffreyH

This raises the possibility of the detector being in the middle of the room and photons being fired at it from each end along the direction of travel. The problem is clock synchronization. There is no way to synchronize effectively since you would have to measure the one way speed of light.

Only if you focus on one of the light paths.
Examine the graphic and notice the light paths are skew-symmetric , which means, the path segments are equal length but have a different order, i.e. a 180 deg rotation about t', transforms the forward path into the rearward path. This is also equivalent to mirroring the points of one path through the origin t' an equal distance in the opposite direction.  Based on that alone, one-way light speed is not an issue. Eg., if the forward speed was <c, it would extend the time for the longer segment equally for both directions, and not be detected. There is much experimental evidence limiting any directional variation of c to small fractions of a meter. There has not been any experimental evidence to challenge the 'light speed is independent of the source' rule.

Clock synchronization is a simple procedure.
The setup is clocks c1 and c2, equal distances from a central master clock, moving on the Bt timeline.
1. Simultaneously send signals to clocks c1 and c2, divide the return time in half, resulting in t'.
2. Simultaneously send signals to clocks c1 and c2, setting each to t'.
The axis of simultaneity s1-s2, is the basis for the Bx axis, a mathematical device as part of the 'lines on paper' theory. The B frame is moving parallel to the A frame along the Ax axis.

clock synch.gif (6.17 kB . 661x529 - viewed 2428 times)
clock synch.gif (6.17 kB . 661x529 - viewed 2428 times)

[jeffreyH (OP)]

You are not synchronising your clocks since you are not able to determine the path difference in the asymmetry. You are catering for the asymmetry the only way possible. This is not true absolute synchronisation since that is not possible. Which is what I said in the first place. No amount of spacetime diagrams are going to change this.

[jeffreyH (OP)]

BTW If you could determine the one way speed of light you could also determine that an inertial frame of reference was actually moving in a preferred direction.

[Bill S]

  No amount of spacetime diagrams are going to change this.

Admit it, Jeffrey, they look impressive.  Seriously, though, working them out in the first place is probably a valuable exercise.

BTW If you could determine the one way speed of light you could also determine that an inertial frame of reference was actually moving in a preferred direction.

A bit more about that, please?

[PmbPhy]

one way speed of light

Its been measured already to be c.

[guest4091]

JeffreyH #26

You are not synchronising your clocks since you are not able to determine the path difference in the asymmetry. You are catering for the asymmetry the only way possible. This is not true absolute synchronisation since that is not possible. Which is what I said in the first place. No amount of spacetime diagrams are going to change this. 

First, step 2 should have said:
Simultaneously send signals to clocks c1 and c2, setting each to t' + current time.

The total path length is the same for both directions and the path segments are equal, but in a different order. If the time varied in the long segment, it would do so for both trips, thus go undetected. The speed is irrelevant in this scenario. There is no logical reason why light speed would vary in a particular direction, unless the universe as an integral thing, rotated. The universe cannot have a translational motion since there is no external reference. In the 1905 paper, Einstein, aware of the MM experiment, referred to any ether effect as superfluous. (In case you favor that idea.) He also defined the outbound and inbound paths as equal, since that is what an observer in a pseudo rest frame would expect to measure.
Clock syncronization is relative to the reference frame. This eliminates absolute/universal time.