Speed-of-light experiments yield baffling result at LHC • Hacker News Board

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

#51

Post by DougBTX » Thu, Sep 22, 2011, 7:31 PM UTC

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.

> Light travels slower through gas, water or glass.

There is a good description of what is going on in this Stack Exchange post:

http://physics.stackexchange.com/questions/13738/propagation...

It explains why saying "c is the speed of light" makes sense, because when we say light is traveling more "slowly" through a material, we are including the time spent interacting with the material, being absorbed and re-emitted.

I'm bristling a little at your statement that "the speed of light is not constant". Imagine two men walking at the same speed from A to B. But one of them is walking in a straight line, while the other is zig zagging. It would be fair to say that the one walking in a straight line is travelling from A to B faster, even though they are both moving at the same speed. The speed of light is a constant, it is just that light travelling through a medium doesn't necessarily spend all of its time travelling in one direction.

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

#52

Post by felipemnoa » Thu, Sep 22, 2011, 7:33 PM UTC

devijvers wrote: post #49

felipemnoa wrote: post #29

Earlier quoted context omitted.

>>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.

No, it's correct. The light actually gets slowed down in material (anything else than a vacuum.) That has nothing to do with observation, it's an actual physical effect. The speed of light in a vacuum is constant and so is the speed of light in any particular pure material (like a pure gas.) It's just that those constant speeds are different.

I say you are incorrect. Read this: http://physlink.com/Education/AskExperts/ae509.cfm

Here is a relevant piece:

When light enters a material, photons are absorbed by the atoms in that material, increasing the energy of the atom. The atom will then lose energy after some tiny fraction of time, emitting a photon in the process. This photon, which is identical to the first, travels at the speed of light until it is absorbed by another atom and the process repeats. The delay between the time that the atom absorbs the photon and the excited atom releases as photon causes it to appear that light is slowing down.

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

#53

Post by olihb » Thu, Sep 22, 2011, 7:33 PM UTC

DanielBMarkham wrote: post #3

A news article where both the scientists and the reporter understate the claims, publish the data, and ask other teams to please prove them wrong. I like this. Most of the time the reporters overstate the research, the scientists keep the data secret, and the general public is left scratching their heads.

Scientist rarely keep the data secret. It's the basis of peer review. There's a reason why open access journals (PLoS One) are getting so popular, scientists want to be known and publish. In my experience, ego is a currency much more valuable than money in academic circles.

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

#54

Post by jholman » Thu, Sep 22, 2011, 7:34 PM UTC

Why does the link title claim that the result is at the LHC? The LHC is not involved in this story at all.

Edit: other than the obvious reason of "linkbait", I mean.

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

#55

Post by sliverstorm » Thu, Sep 22, 2011, 7:35 PM UTC

foob wrote: post #50

If this result is valid then it would mean that neutrinos are capable of traveling .0025% faster than light. There was a supernova that we observed in 1987 (SN 1987) that occurred 168,000 light years away from us. A neutrino burst was observed in 3 different labs about 3 hours before the light was observed. If neutrinos are capable of traveling .0025% faster than the speed of light then why would we observe these neu…

The result would tear apart well established theories that have been tested time and time again in thousands of different ways.

That's what makes this so exciting!

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

#56

Post by Jach » Thu, Sep 22, 2011, 7:35 PM UTC

devijvers wrote: post #49

felipemnoa wrote: post #29

Earlier quoted context omitted.

>>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.

No, it's correct. The light actually gets slowed down in material (anything else than a vacuum.) That has nothing to do with observation, it's an actual physical effect. The speed of light in a vacuum is constant and so is the speed of light in any particular pure material (like a pure gas.) It's just that those constant speeds are different.

"Material" is made of smaller things, which I think the GP is getting at. The actual photons that travel from electron to electron and such don't get slowed down; they effectively travel through a vacuum that is the tiny spaces inside molecules and atoms.

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

#57

Post by sliverstorm » Thu, Sep 22, 2011, 7:38 PM UTC

jholman wrote: post #54

Why does the link title claim that the result is at the LHC? The LHC is not involved in this story at all. Edit: other than the obvious reason of "linkbait", I mean.

Well, the LHC is at CERN and this happened at CERN.

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

#58

Post by DenisM » Thu, Sep 22, 2011, 7:40 PM UTC

Florin_Andrei wrote: post #20

DenisM wrote: post #12

There was an experiment where an impulse of light came out the other end of a material faster than light could have traveled through vacuum in the same space. The eventual explanation was as follows - imagine that your outgoing bunch of photons looks like this: :::... The first three photons are "invisible" because there is so few of them that they are below the equipment sensitivity. The second group of six particle…

Phase velocity vs group velocity. But it's pretty easy to check that everything is alright with group velocity. If there is zero neutrino production at t=0 (in the reactor's frame of reference), and then the production jumps up, there can be no doubt about the group velocity. Bizarre effects relative to superluminal phase velocity only appear when you start generating particles before t=0 and you mess with the medium…

Phase velocity vs group velocity.

Yes, thank you. Why did it take me so many words? :)

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

#59

Post by sliverstorm » Thu, Sep 22, 2011, 7:41 PM UTC

sp332 wrote: post #36

tsycho wrote: post #33

"...the researchers noticed that the particles showed up a few billionths of a second sooner..." I am impressed that their measuring instruments have a precision that is (statistically significant-ly) smaller than a billionth of a second.

How do you think gigabit ethernet works?

I don't have the specs, but 100Mbit operates at 31MHz. Remember, quad-twisted pair. So it is likely 1Gbit operates at ~300MHz.

Now, 10Gbit probably does operate with a period less than 1ns. (1 billionth of a second)

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

#60

Post by DenisM » Thu, Sep 22, 2011, 7:43 PM UTC

jxcole wrote: post #19

DenisM wrote: post #12

There was an experiment where an impulse of light came out the other end of a material faster than light could have traveled through vacuum in the same space. The eventual explanation was as follows - imagine that your outgoing bunch of photons looks like this: :::... The first three photons are "invisible" because there is so few of them that they are below the equipment sensitivity. The second group of six particle…

That is such a well known result in physics that the likelihood of it occurring here is almost zero. I remember first reading about it and the scientists basically said "we broke the speed of light" without looking for further explanations. These guys seem like they generally don't believe that they have broken the light barrier, but they need help figuring out what they actually did do from the broader community. Du…

I have used the word "Similar" in the most loose meaning of this word, merely to suggest to the audience that "faster than light thing has been observed" does not have to mean that the existing model is broken.