Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Speed-of-light experiments yield baffling result at LHC

bbc.co.uk

Post reply on HN
Print view View original

21–30 of 255 posts

Re: Speed-of-light experiments yield baffling result at LHC

#21

Post by fleitz »

Couldn't it be that the lack of interaction with the electro-weak force allows neutrinos to exceed the speed of a photon in a non-vacuum environment? Or is the article saying that the neutrinos exceed c?

edit: More questions, since photons are massless they should be unaffected by gravity except in the sense of following the curvature of spacetime. Could the non-zero mass of the neutrino mean that if you changed the experiment so it fired away from the earth mean that the neutrinos would travel "slower" than photons?

Re: Speed-of-light experiments yield baffling result at LHC

#22

Post by sorbus »

fleitz wrote: post #21

Couldn't it be that the lack of interaction with the electro-weak force allows neutrinos to exceed the speed of a photon in a non-vacuum environment? Or is the article saying that the neutrinos exceed c ? edit: More questions, since photons are massless they should be unaffected by gravity except in the sense of following the curvature of spacetime. Could the non-zero mass of the neutrino mean that if you changed the…

The article seems to be saying that the neutrinos appear to have exceeded c. If it were just neutrinos moving faster than photons through some non-vacuum environment, that would be completely non-notable - experiments have already succeed in slowing light down to almost nothing, after all.

Re: Speed-of-light experiments yield baffling result at LHC

#23

Post by Florin_Andrei »

gaika wrote: post #2

It wouldn't break current theory, it would just mean that photons travel slower than "speed of light" and have non-zero rest mass. Constant c in relativity instead of speed of photons would just mean fastest speed possible.

No.

Non-zero rest mass photons will break a lot of theories.

Plus, the "speed of light" is not merely an experimental result coming out of an interferometer. It's also a theoretical result, e.g. from Maxwell's equations - that's the one referred to by special relativity.

Re: Speed-of-light experiments yield baffling result at LHC

#24

Post by hardtke »

gaika wrote: post #2

It wouldn't break current theory, it would just mean that photons travel slower than "speed of light" and have non-zero rest mass. Constant c in relativity instead of speed of photons would just mean fastest speed possible.

An alternative is that neutrinos and photons travel a different distance because there are extra dimensions that affect the two types of particles differently. These are the so-called space-time foam models.

Re: Speed-of-light experiments yield baffling result at LHC

#25

Post by doctoboggan »

dfranke wrote: post #8
jasonkolb wrote: post #6

Earlier quoted context omitted.

Isn't the speed at which photons travel, by definition, the speed of light? And as for the "c" in e=mc^2, doesn't this suddenly make "c" an unknown constant? Doesn't the fact that "c" changes suddenly change the values of the other variables in that equation as well? That seems pretty fundamental to me...

Isn't the speed at which photons travel, by definition, the speed of light? Photons speed up and slow down routinely, depending on what medium they're traveling through. c , as it is used in the equations of relativity, is currently believed to be equal to the speed of light in a vacuum. But, with my limited knowledge of GR, my understanding is that gaika is correct and that the rest of the theory can still stand if…

This isn't technically correct. Photons always travel the same speed but in certain materials they are absorbed and emitted by atoms, causing their apparent speed to slow down.

A photon's instantaneous speed is always the speed of light.

Re: Speed-of-light experiments yield baffling result at LHC

#26

Post by monochromatic »

gaika wrote: post #2

It wouldn't break current theory, it would just mean that photons travel slower than "speed of light" and have non-zero rest mass. Constant c in relativity instead of speed of photons would just mean fastest speed possible.

It wouldn't break current theory for photons to have nonzero rest mass?

Re: Speed-of-light experiments yield baffling result at LHC

#27

Post by felipemnoa »

dfranke wrote: post #8
jasonkolb wrote: post #6

Earlier quoted context omitted.

Isn't the speed at which photons travel, by definition, the speed of light? And as for the "c" in e=mc^2, doesn't this suddenly make "c" an unknown constant? Doesn't the fact that "c" changes suddenly change the values of the other variables in that equation as well? That seems pretty fundamental to me...

Isn't the speed at which photons travel, by definition, the speed of light? Photons speed up and slow down routinely, depending on what medium they're traveling through. c , as it is used in the equations of relativity, is currently believed to be equal to the speed of light in a vacuum. But, with my limited knowledge of GR, my understanding is that gaika is correct and that the rest of the theory can still stand if…

>>Photons speed up and slow down routinely, depending on what medium they're traveling through

Do they really? As far as I know their speed is always constant in any medium. They just seem to slow down because they get absorbed and re-transmited. That is where the lost of velocity comes from. When traveling between one atom and another, which is a vacuum, they are always traveling at the speed of light.

Re: Speed-of-light experiments yield baffling result at LHC

#28

Post by sp332 »

coffeenut wrote: post #5

If I calculated correctly, that's only about .0025% faster than c. Practical implications?

It should be impossible to accelerate a neutrino to 100% of the speed of light. It would take an infinite amount of energy. So getting it to go even faster is really impressive :)

Re: Speed-of-light experiments yield baffling result at LHC

#29

Post by felipemnoa »

dholowiski wrote: post #16
gaika wrote: post #2

It wouldn't break current theory, it would just mean that photons travel slower than "speed of light" and have non-zero rest mass. Constant c in relativity instead of speed of photons would just mean fastest speed possible.

Don't forget... c is the speed of light 'in a vacuum'. Light travels slower through gas, water or glass. Light has even been slowed down to walking speed in a laboratory. The speed of light is not constant. The speed of light in a vacuum is. We assume.

>>The speed of light is not constant

I think this is wrong. Regardless of the medium the speed of light is always constant. It seems to slow down because the photons are getting absorbed and re-transmited by atoms. But the speed of light is always the same regardless.

Post reply on HN