Time dilation and the photon clock

[NtroPunDfeetd]

Does the photon actually travel at light speed? When your on a flatbed truck traveling down the highway at 70mph with a photon clock in hand, does the photon for you on the truck still travel at the speed of light and count your seconds accurately? To an observer on the ground does the photon look as if it's going slower? Has this ever been tested and proven?

Please answer my questions shortly and staying on track completely with what I'm asking; do not diverge from my question into other explanations.

 

[Doc Al]

Does the photon actually travel at light speed?

Yes. According to everyone.

When your on a flatbed truck traveling down the highway at 70mph with a photon clock in hand, does the photon for you on the truck still travel at the speed of light and count your seconds accurately?

Sure.

To an observer on the ground does the photon look as if it's going slower?

No. The photon travels at light speed. The clock ticks slower, since for the ground observer the photon travels a greater distance.

Has this ever been tested and proven?

No one has ever done experiments with photon clocks, but the effect it illustrates--time dilation--has been tested.

 

[Austin0]

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Originally Posted by NtroPunDfeetd
Does the photon actually travel at light speed?

Yes. According to everyone.

.

To an observer on the ground does the photon look as if it's going slower?

No. The photon travels at light speed. The clock ticks slower, since for the ground observer the photon travels a greater distance.

What is the interpretation in the case of a photon clock at a location of low gravitational potential?
Is it traveling slower or traveling a greater distance due to the geometry at a small Scwarzschild radius?
Thanks

 

[yuiop]

What is the interpretation in the case of a photon clock at a location of low gravitational potential?
Is it traveling slower or traveling a greater distance due to the geometry at a small Scwarzschild radius?
Thanks

To keep it simple take the case of a short horizontal light clock. (Horizontal rulers are not length contracted by gravity.) To an observer higher up, the clock lower down is running slow and the speed of light lower down is slower than the speed of light higher up. These two effects conspire in such a way, that to a local observer co-located with the light clock at a small Schwarzschild radius, the speed of light appears normal. This slowing down of clocks and light, deep in a gravitational well is not an optical illusion, because by lowering a clock down and bringing it back up again, it can be demonstrated that the lowered clock really does run slower than a clock that remained higher up.

It follows that if the clock lower down is really running slower than the clock higher up, then the speed of light lower down must really be slower than the speed of light higher up, in order for a local observer lower down to measure the local speed of light as c.

 

[Austin0]

To keep it simple take the case of a short horizontal light clock. (Horizontal rulers are not length contracted by gravity.) To an observer higher up, the clock lower down is running slow and the speed of light lower down is slower than the speed of light higher up. These two effects conspire in such a way, that to a local observer co-located with the light clock at a small Schwarzschild radius, the speed of light appears normal. This slowing down of clocks and light, deep in a gravitational well is not an optical illusion, because by lowering a clock down and bringing it back up again, it can be demonstrated that the lowered clock really does run slower than a clock that remained higher up.

It follows that if the clock lower down is really running slower than the clock higher up, then the speed of light lower down must really be slower than the speed of light higher up, in order for a local observer lower down to measure the local speed of light as c.

Thanks for your very clear explanation. It was pretty much what my own logic arrived at but I no longer have the implicit faith in "logic" I once had.