3 ms·
There is a cool video by Veritasium about the specifics of how the speed of light is actually measured (1). I wasn’t aware that only the two way speed of light
by baxtr 3y ago
There is a cool video by Veritasium about the specifics of how the speed of light is actually measured (1). I wasn’t aware that only the two way speed of light was measured so far, not the one way. Which is probably very irrelevant but still quite interesting.
(1) https://www.youtube.com/watch?v=pTn6Ewhb27k https://www.youtube.com/watch?v=pTn6Ewhb27k
- ndsipa_pomu 3y agoCame here to see if someone had mentioned this. It's interesting because it's just unbelievable that light would go at different speeds in different directions, but there's no way (that we can think of) to verify it. It's like the structure of space-time is conspiring against being able to measure one-way light speed.
- gumby 3y agoSure: the Michelson-Morley interferometry experiment: https://en.wikipedia.org/wiki/Michelson–Morley_experiment https://en.wikipedia.org/wiki/Michelson–Morley_experiment
- ndsipa_pomu 3y agoDoesn't that rely on synchronising the detector with the emitter though? That's the issue that makes one-way measurements effectively a round trip measurement. Edit: looks to me like mirrors are used and it is comparing two-way speeds in different directions.
- mikewarot 3y agoIf you look at the folded light path used in the Michelson–Morley interferometer (figure 5), you'll see that the X and Y distances traveled on both paths add to the exact same value. Thus, it would be completely insensitive to changes in the speed of light in the X or Y directions, no matter how it were rotated.
- gumby 3y agoThe whole point of that experiment was that it would show a difference, if such a difference existed, by projecting an interference pattern.
- ShamelessC 3y agoI don’t trust that guy. Is there another source?
- ndsipa_pomu 3y agohttps://en.wikipedia.org/wiki/One-way_speed_of_light https://en.wikipedia.org/wiki/One-way_speed_of_light > When using the term 'the speed of light' it is sometimes necessary to make the distinction between its one-way speed and its two-way speed. The "one-way" speed of light, from a source to a detector, cannot be measured independently of a convention as to how to synchronize the clocks at the source and the detector. What can however be experimentally measured is the round-trip speed (or "two-way" speed of light) from the source to a mirror (or other method of reflection) and back again to detector.
- ShamelessC 3y agoThanks!
- ahazred8ta 3y agoActually we can measure the frequency of light in both directions, and the wavelength of light in both directions, and calculate that it's going the same speed in both directions. It's just that if you try to measure the elapsed time in each direction you run into a chicken and egg problem trying to define what 'elapsed time' really means in a relativistic environment.
- girishso 3y agoYou can also measure speed of light with your Microwave Oven and pizza https://youtu.be/acwF1ubdENo?t=122 https://youtu.be/acwF1ubdENo?t=122