4 ms·

> charged particles traveling faster than the speed of light in water What did I just read?

lumberjack 9y ago
Speed of light in water is slower than speed of light in vacuum
mgsouth 9y ago
https://en.wikipedia.org/wiki/Cherenkov_radiation https://en.wikipedia.org/wiki/Cherenkov_radiation The particles are still moving slower than Relativity's limit, the speed of light in a vacuum.
toufka 9y ago
Cherenkov Radiation [1]. It's not because the particles are going faster than 300M m/s, but because light in the medium is going less than 300M m/s. The unbreakable "speed of light" is actually, the "speed of light (in a vacuum)". Outside of a vacuum, the light is slowed by the materials it travels through (see prisms, angles of refraction, Snell's Law [2] etc.). But it's still a very special condition when the medium slows light to some large fraction of C, while particles are going faster than that (but still less than C). [1] https://en.wikipedia.org/wiki/Cherenkov_radiation https://en.wikipedia.org/wiki/Cherenkov_radiation [2] https://en.wikipedia.org/wiki/Snell%27s_law https://en.wikipedia.org/wiki/Snell%27s_law
- Florin_Andrei 9y ago
  Yup. Whenever you see that blue glow surrounding a reactor core submerged in water, that's the Cherenkov radiation. If the blue glow happens in your own eyeballs, you've probably just witnessed your own death sentence.
  - pitaj 9y ago
    It is dangerous? Nuclear subs have cherenkov radiation outside the hull which implies they have it inside the hull as well, but you don't hear about sailors getting radiation poisoning all the time.
mhluongo 9y ago
That phrase can be parsed in two ways
- hexane360 9y ago
  To the downvoters: This is technically correct. #1: (charged particles traveling faster than the speed of light) in water #2: charged particles traveling faster than (the speed of light in water)
  - itcrowd 9y ago
    Technically, it is technically incorrect. There is no "speed of light", there is only "speed of light in [medium]".* Therefore, interpretation #1 doesn't make sense. Maybe colloquially people refer to the speed of light in vacuum as "the speed of light", but again, that is technically incorrect. *And more technically there's group and phase velocity which may or may not be equal.
    - btilly 9y ago
      This is BS. Go to 10 physicists and say, "Is c the speed of light?" Odds are that most will say, "Yes." And while some may suggest more exact terminology, not one will fail to understand what you meant. Furthermore at the subatomic level, light always goes at c. Even if you're in water. It has no other actual speed. Thanks to interactions between light and a medium it looks like photons go slower through the medium. But that's no different than the fact that current traveling through metal acts approximately like it is being carried by electrons of some other mass and velocity. (Or even, in some cases, like the absence of an election. This fact is critical to the operation of a transistor.) But "acts approximately like" and "is" are two different things.
    - mhluongo 9y ago
      It is technically correct in that there are two parsings (syntax). One of them clearly isn't true (semantics)
  - 21 9y ago
bronson 9y ago
Precedence problem. Read it like this: (charged particles traveling faster than) (the speed of light in water) not this: (charged particles traveling faster than the speed of light) (in water)
thomastjeffery 9y ago
I would have phrased it, "charged particles traveling faster than light through water" or some way that did not include "the speed of light" which people quickly assume to be 1c, rather than .75c (the speed that light travels through water).

Speed of light in water is slower than speed of light in vacuum

https://en.wikipedia.org/wiki/Cherenkov_radiation https://en.wikipedia.org/wiki/Cherenkov_radiation The particles are still moving slower than Relativity's limit, the speed of light in a vacuum.

toufka 9y ago

Cherenkov Radiation [1]. It's not because the particles are going faster than 300M m/s, but because light in the medium is going less than 300M m/s. The unbreakable "speed of light" is actually, the "speed of light (in a vacuum)". Outside of a vacuum, the light is slowed by the materials it travels through (see prisms, angles of refraction, Snell's Law [2] etc.). But it's still a very special condition when the medium slows light to some large fraction of C, while particles are going faster than that (but still less than C). [1] https://en.wikipedia.org/wiki/Cherenkov_radiation https://en.wikipedia.org/wiki/Cherenkov_radiation [2] https://en.wikipedia.org/wiki/Snell%27s_law https://en.wikipedia.org/wiki/Snell%27s_law

Florin_Andrei 9y ago
Yup. Whenever you see that blue glow surrounding a reactor core submerged in water, that's the Cherenkov radiation. If the blue glow happens in your own eyeballs, you've probably just witnessed your own death sentence.
- pitaj 9y ago
  It is dangerous? Nuclear subs have cherenkov radiation outside the hull which implies they have it inside the hull as well, but you don't hear about sailors getting radiation poisoning all the time.

mhluongo 9y ago

That phrase can be parsed in two ways

hexane360 9y ago
To the downvoters: This is technically correct. #1: (charged particles traveling faster than the speed of light) in water #2: charged particles traveling faster than (the speed of light in water)
- itcrowd 9y ago
  Technically, it is technically incorrect. There is no "speed of light", there is only "speed of light in [medium]".* Therefore, interpretation #1 doesn't make sense. Maybe colloquially people refer to the speed of light in vacuum as "the speed of light", but again, that is technically incorrect. *And more technically there's group and phase velocity which may or may not be equal.
  - btilly 9y ago
    This is BS. Go to 10 physicists and say, "Is c the speed of light?" Odds are that most will say, "Yes." And while some may suggest more exact terminology, not one will fail to understand what you meant. Furthermore at the subatomic level, light always goes at c. Even if you're in water. It has no other actual speed. Thanks to interactions between light and a medium it looks like photons go slower through the medium. But that's no different than the fact that current traveling through metal acts approximately like it is being carried by electrons of some other mass and velocity. (Or even, in some cases, like the absence of an election. This fact is critical to the operation of a transistor.) But "acts approximately like" and "is" are two different things.
  - mhluongo 9y ago
    It is technically correct in that there are two parsings (syntax). One of them clearly isn't true (semantics)
- 21 9y ago

bronson 9y ago

Precedence problem. Read it like this: (charged particles traveling faster than) (the speed of light in water) not this: (charged particles traveling faster than the speed of light) (in water)

thomastjeffery 9y ago

I would have phrased it, "charged particles traveling faster than light through water" or some way that did not include "the speed of light" which people quickly assume to be 1c, rather than .75c (the speed that light travels through water).