B The One-Way Speed of Light: Speculation of a Tired Mind

[Matthew_p]

TL;DR Summary

could we not mathematically prove a non-zero one-way speed of light relative to the speed of electrical transmission? (send a signal one way, turn a light on, and attempt to determine differences in transmission speeds?)

I perfectly understand that we cannot, as of our current methods, determine the one-way speed of light - I was, however, wondering if we could determine a relative speed using electrical transmission. the basis of which would be sending a laser light across a field into a sensor, starting a clock, and then waiting for an electrical signal to stop said timer. if we repeated the experiment with different orientations would it be possible to detect a shift, and - if present - use said to shift to determine the one-way speed of light relative to electrical transmission? (assuming electricity either suffers the same theoretical problems to a different degree or does not experience a speed change at all)

 

[Matthew_p]

the video that peaked my interest into said topic -

 

[Ibix]

No, the one way speed of light is a value you can choose and it cannot be measured without assuming your answer. If you pick an anisotropic one way speed of light you pick everything else to have anisotropic speeds too, including electric signals, in such a way that it makes no difference to your experimental results.

This isn't a thing that you can work your way around by sneaky experimental design. The problem is that "space" and "time" aren't truly separate things, they are both aspects of spacetime. How you choose to divide spacetime into space and time is just that - a choice. And the choice you make affects your definition of distance travelled and time taken, and hence your definition of speed (of anything, not just light) in such a way that the choice cancels out of measurements and remain in how you interpret your measurements. So in your proposal there is some fixed time for "light travel time plus electrical signal travel time" that is independent of the choice of light speed, but how you divide that total into its two components is your choice.

As long as you don't travel very fast, the flexibility in defining speeds doesn't make much difference. For example if you do a 100m race, I can only vary your time by about $0.3\mathrm{\mu s}$ by messing around with my definition of "space". That's in "who cares" territory for a 100m sprint, or even the fastest planes or cars, which is why we don't notice this stuff in every day life.

 

[PeterDonis]

Moderator's note: Thread moved to the relativity forum.

 

[Dale]

TL;DR Summary: could we not mathematically prove a non-zero one-way speed of light relative to the speed of electrical transmission? (send a signal one way, turn a light on, and attempt to determine differences in transmission speeds?)

I perfectly understand that we cannot, as of our current methods, determine the one-way speed of light

It has nothing to do with our current methods. The one way speed of light is something that we define through our simultaneity convention. We fully determine it by making an arbitrary choice. It is not that it is unknown, but that it is something we are free to decide.

 

[PeroK]

the video that peaked my interest

The word you are looking for is piqued:

https://www.dictionary.com/browse/pique

 

[Matthew_p]

As long as you don't travel very fast, the flexibility in defining speeds doesn't make much difference. For example if you do a 100m race, I can only vary your time by about 0.3ms by messing around with my definition of "space". That's in "who cares" territory for a 100m sprint, or even the fastest planes or cars, which is why we don't notice this stuff in every day life.

okay, speed dilation is then a major issue, but all in all this really doesn't matter in an applied physics sense then?

 

[Orodruin]

okay, speed dilation is then a major issue, but all in all this really doesn't matter in an applied physics sense then?

It doesn’t matter in any physics sense.

 

[Ibix]

okay, speed dilation is then a major issue, but all in all this really doesn't matter in an applied physics sense then?

The maths is easier if you assume the one way speed of light is the same in all directions, and you don't have to keep track of which way you decided was the fast direction. But apart from that it really doesn't matter at all.