-1

Exclaimer, I am in the high school physics range, in no way do I claim to know anything, nor expect to be right, this is just an idea I had when thinking about the one way speed of light

so I was watching some physics YouTube, specifically "Why No One Has Measured The Speed Of Light" by Veritasium, and then started to think about it, and I had an idea

there are 3 positions A,B,C, with A on the left, C on the right, and B directly in the middle. In position A and c are two clocks that will start to count when they receive a light pulse, and in position B is a button connected to two lasers, each one pointed at the clocks, when the button is pressed, and the one way speed of light is constant, then the clocks will be synchronized. If the one way speed of light was different, then they would be unsynchronized.

My question is if, theoretically, the speed of light was different in different directions, could this detect that difference?

Qmechanic
  • 201,751
DuckSupreme
  • 7

2 Answers2

2

How can you tell if the clocks are "synchronized?"

The problem is that what Physicists mean when they say "speed of light" isn't just the speed of light. They're really talking about the speed of "cause and effect." It's the fundamental speed limit of the universe.

Any attempt to find out whether the two clocks received the light pulses at the same time, means moving something back to the starting point. Maybe a light signal, maybe some other signal, maybe you move the clocks themselves; but you can't complete the measurement until you have sent something back. Whatever the something is, it's still a "cause" that has an "effect." The experiment no longer is "one way."

Solomon Slow
  • 14,534
0

The guy in "Veritasium" is technically right that the speed of light has always been measured from a round trip, i.e. it is the two-way speed, and the one-way speed has never been exactly measured. Einstein said in his theory that he stipulated that the one-way speed must be assumed to be the same as the two-way speed. However, he then formulated the Special Theory of Relativity and you could say that it is as well established now as Newton's laws of motion were in 1905, and no one has ever conducted an experiment that showed it to be wrong or that showed that a one-way speed was different from c.

When I watched the video I noticed that he suggested a one-way speed experiment where two atomic clocks were synchronised and then one of them was moved 1km away from the other. Subsequently a laser beam pulse was fired from the first to the second to measure the one-way speed. He then said that the two clocks would not really be synchronised because one would have been moved and "moving clocks run slow". I was amazed to hear him say this because it is so obvious that the time dilation would be incredibly small and could not possibly be measured. Try calculating it using almost any sensible speed.

Regarding your experiment, I cannot see why it wouldn't measure the difference in speeds (or demonstrate that no difference existed) but it is not as symmetrical as it is intended to be. If the Earth was indeed moving in an objective way through space at a high relativistic speed (as suggested in the video) then the time dilations would be different for clocks A and B when they were moved.

After you've finished thinking about all of this it is important to remember that two clocks A and C, which have been carefully synchronised in one inertial frame would not be seen to be synchronised by an observer moving at a high relativistic speed in the direction of separation of the clocks, and this is a fundamental part of the Special Theory. If you simply look at the two clocks from position B through telescopes, you will see them to be synchronised. However, to be consistent with the theory, an observer who is moving at high speed in the direction C to A (and sees you moving from A towards C) will see you moving towards the light from C, giving an earlier time and away from the light from A, giving a later time.

Rob Tristram
  • 597