[Jay-qu]

I was amazed to learn the other day that particals can travel faster than light... under certain conditions. These been that light has been slowed by traveling through a more dense material, such as air.
The example i was given was that high energy cosmic rays collide with and shatter atoms in the upper atmosphere and rain down subatomic particles. some of these particles travel at 99.9999% of c, and this is faster than the amount that light gets slowed to in our atmosphere , dont know about you but i was blown away on hearing this.
So what is the light equivilent of a sonic boom? are there any profound implications of this?

[Qfwfq]

Originally Posted by Jay-qu

So what is the light equivilent of a sonic boom?

It's called Cherenkov radiation. Way back in the '80s I visited the CERN labs in Geneva, trip organized by the physics dep't, and one of the guys told us about a Russian colleague that was in the habit of making fine adjustments by looking into the glass that the beam came out of, while the beam was on. He was deliberately circumventing the safety system to have the beam on while he was inside the chamber. His explanation was simple: he was exploiting the Cherenkov light to see exactly where the beam was.

Originally Posted by Jay-qu

are there any profound implications of this?

Depends on what you mean by profound.

Actually, I'd say "no".

[HydrogenBond]

The speed of light is the limit of the physical universe. Light traveling through the atmosphere stops to smell the roses along the way. It still buzzes at C from molecule to molecule and spends a little time. The cosmic particles are in a rush and use their less than C to reach the surface first.

[Tormod]

Originally Posted by HydrogenBond

Light traveling through the atmosphere stops to smell the roses along the way.

This wins the coveted "unexpected explanation of laws of nature" award. Good one!

[alxian]

all i can say at first is that sonic booms are a consquence of atmosphere, not much [matter] can get from point to point [at c] within earths atmosphere without setting it ablaze.

in space though transcending the 'light barrier' (going at c of faster) as it were of space... creating some form of buffer layer of something (light or radiation) building up on a ships hull which dissipates after a ship goes translight, equivelant to transonic.. um, i can't help but think there would be several such barries before that of c and that once light starts becoming a drag issue (like air causing friction on a shuttle during reentry) whatever materials a translight space craft are made of they'd have to deal with the friction caused by light itself.

that is to say any ship trying to get anywhere close to that fast has to first of all displace the universe (any kind of matter bigger than a photon able to be charged and deflected (lest it impact the hull))

thankfully light can be affected by gravity so once we can harness gravity we can deflct light, in the meantime interstellar dust will be a much bigger problem than a barrier at c, evetually you will be trying to deflect the matter in your path so fast that it might become impossible to do so, even using light (shining a powerful laser ahead of your craft to move those particals or charge them so that they can bounce off you ships very large electromagnetic feild (deflector dish) you are still limiting yourself to c. even the light being emmited by the laser would be at c, the benefit of a ship travelling near c may not cause light to escape it at relative acceleration making it leave the ship any faster than c.


unless c isn't a universal constant but a physical one (and why in some situation where normal matter isn't concerned there seems to be evidence of faster than c travel), where in the physical universe has a viscocity that nothing can transcend, passing from one molecule to the next can only be done so fast?

[Jay-qu]

Originally Posted by alxian

all i can say at first is that sonic booms are a consquence of atmosphere, not much [matter] can get from point to point [at c] within earths atmosphere without setting it ablaze.

in space though transcending the 'light barrier' (going at c of faster) as it were of space... creating some form of buffer layer of something (light or radiation) building up on a ships hull which dissipates after a ship goes translight, equivelant to transonic.. um, i can't help but think there would be several such barries before that of c and that once light starts becoming a drag issue (like air causing friction on a shuttle during reentry) whatever materials a translight space craft are made of they'd have to deal with the friction caused by light itself.

that is to say any ship trying to get anywhere close to that fast has to first of all displace the universe (any kind of matter bigger than a photon able to be charged and deflected (lest it impact the hull))

thankfully light can be affected by gravity so once we can harness gravity we can deflct light, in the meantime interstellar dust will be a much bigger problem than a barrier at c, evetually you will be trying to deflect the matter in your path so fast that it might become impossible to do so, even using light (shining a powerful laser ahead of your craft to move those particals or charge them so that they can bounce off you ships very large electromagnetic feild (deflector dish) you are still limiting yourself to c. even the light being emmited by the laser would be at c, the benefit of a ship travelling near c may not cause light to escape it at relative acceleration making it leave the ship any faster than c.

...dont think so, you cant pass the light barrier, you mass increases with speed until it becomes infinite and hence requires an infinite amount of work to futher accelerate. also think of time dilation effects, at c time dilation becomes infinite. so forever would pass once you reach c, dont ask what would happen if you now slowed down as the question is meaningless - you cant go the speed of light...

[Qfwfq]

Originally Posted by Jay-qu

you cant go the speed of light...

You can if you're a photon in the vacuum! Or any other massless particle.

Remember: c isn't the speed of light, it's the speed of light that's c.

c is a property of space-time. Historically it was discovered from the velocity of light (in vacuo), that's why it's always called in this way.

[Jay-qu]

Originally Posted by Qfwfq

You can if you're a photon in the vacuum! Or any other massless particle.

so photons are massless...? momentum = planks constant / lamda ; yeah - so dont you need a mass to have a momentum?

[Qfwfq]

Originally Posted by Jay-qu

so dont you need a mass to have a momentum?

No, you don't. The word 'mass' is now understood to mean just rest energy. A massless free particle only has kinetic energy. The appropriate equation, using c = 1, is:

m^2 = E^2 - p^2

With zero mass, you have E = p. If you don't like using c = 1 you have E = pc.

[Jay-qu]

so the stuff they teach us in school about the mass of a photon is not entirly correct... it is the energy that is the mass.
You said that 'mass' is now known to be rest energy, I understand how this works with matter - as an object reaches c it gains mass, how does this work with light I have not heard of a photon at rest?