4 ms·

Nah. The speed of light is slower in water, yes, which is why Cherenkov radiation exists -- that's basically the photon equivalent of a supersonic shockwave. T

Nah. The speed of light is slower in water, yes, which is why Cherenkov radiation exists -- that's basically the photon equivalent of a supersonic shockwave. The speed of causality doesn't change, and it's easy to demonstrate that by throwing particles through it at superluminal speeds; nuclear reactors do it all day long.

TeMPOraL 6y ago
Wait. Isn't that entirely explained by the light being repeatedly absorbed and re-emitted after a short delay? But otherwise travelling at c?
- emikulic 6y ago
  Good Fermilab video explaining how the slowdown works: https://youtu.be/CUjt36SD3h8 https://youtu.be/CUjt36SD3h8
- andreareina 6y ago
  Absorption and re-emission are probabilistic, so you'd expect experiments to show a spread distribution of propagation times, deflection angles, etc that aren't actually observed. The explanation gets into looking at light as a wave. https://www.youtube.com/watch?v=CiHN0ZWE5bk https://www.youtube.com/watch?v=CiHN0ZWE5bk https://www.youtube.com/watch?v=YW8KuMtVpug https://www.youtube.com/watch?v=YW8KuMtVpug
scarygliders 6y ago
I'm not convinced by that. Cherenkov radiation is still light/electromagnetic energy, and it still must obey the speed of light (Causality) through the water, which means it will still be slower to arrive from source to observer at a slower speed than it would have had it been travelling through a vacuum.
- Dylan16807 6y ago
  You're mixing up what Cherenkov radiation is. Cherenkov radiation is light that is emitted by particles going faster than the local speed of light. You're not supposed to measure the speed of the Cherenkov radiation. You're supposed to measure the particles that are causing Cherenkov radiation. If you measure those fast particles, you'll see that they will cross a tank of water just as fast as they will cross a tank of vacuum. They can cross faster than a beam of light will.
visarga 6y ago
> it's easy to demonstrate that by throwing particles through it at superluminal speeds I am confused, what particles could reach superluminal speeds?

TeMPOraL 6y ago

Wait. Isn't that entirely explained by the light being repeatedly absorbed and re-emitted after a short delay? But otherwise travelling at c?

emikulic 6y ago
Good Fermilab video explaining how the slowdown works: https://youtu.be/CUjt36SD3h8 https://youtu.be/CUjt36SD3h8
andreareina 6y ago
Absorption and re-emission are probabilistic, so you'd expect experiments to show a spread distribution of propagation times, deflection angles, etc that aren't actually observed. The explanation gets into looking at light as a wave. https://www.youtube.com/watch?v=CiHN0ZWE5bk https://www.youtube.com/watch?v=CiHN0ZWE5bk https://www.youtube.com/watch?v=YW8KuMtVpug https://www.youtube.com/watch?v=YW8KuMtVpug

scarygliders 6y ago

I'm not convinced by that. Cherenkov radiation is still light/electromagnetic energy, and it still must obey the speed of light (Causality) through the water, which means it will still be slower to arrive from source to observer at a slower speed than it would have had it been travelling through a vacuum.

Dylan16807 6y ago
You're mixing up what Cherenkov radiation is. Cherenkov radiation is light that is emitted by particles going faster than the local speed of light. You're not supposed to measure the speed of the Cherenkov radiation. You're supposed to measure the particles that are causing Cherenkov radiation. If you measure those fast particles, you'll see that they will cross a tank of water just as fast as they will cross a tank of vacuum. They can cross faster than a beam of light will.

visarga 6y ago

> it's easy to demonstrate that by throwing particles through it at superluminal speeds I am confused, what particles could reach superluminal speeds?