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Speed-of-light experiments yield baffling result at LHC

bbc.co.uk

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

#11

Post by smallblacksun »

steverb wrote: post #4

I desperately want to believe that this will somehow enable us to live in a Star-Trek future, even though I'm sure it won't. Would someone with some knowledge of physics care to break down the ramifications of this (if it's not some sort of measurement error)? Please?

It would mean that the theory of relativity is not 100% correct (in much the same way as Newtonian physics are not 100% correct). It wouldn't have any direct impact on anything (because relativity still makes correct predictions the vast majority of the time), but it would create the opportunity for new theories which can explain everything that relativity does plus this new experiment to be created. That new theory could have significant ramifications, or it could be a minor adjustment to current theory that changes nothing.

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

#12

Post by DenisM »

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 particles is more dense and so they are visible to equipment. Hence, it is deemed that the light has "entered" the material when the second group has entered, long past after the first one actually did. Having entered the material the first group has triggered release of energy from the material, and the second group was partially consumed by the material (energizing it for the next time around). The outgoing bunch looked like this: ...::: And this time it was the first group of photons that was detected. So the apparent speed of the beam was higher than the speed of light. However that's not because the same particles traveled faster than light, but because the peak energy of the entire bunch has shifted forward during travel. If you try hard enough, the light will have "exited" the material before it has "entered".

Similar thing could be happening here.

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

#13

Post by beej71 »

coffeenut wrote: post #5

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

Excellent question. Doesn't seem like "must faster", but if the speed of light isn't the limit, what is the limit?

All this reminds me of the beginning of Mostly Harmless: "One of the problems has to do with the speed of light and the difficulties involved in trying to exceed it. You can't. Nothing travels faster than the speed of light with the possible exception of bad news, which obeys its own special laws. The Hingefreel people of Arkintoofle Minor did try to build spaceships that were powered by bad news but they didn't work particularly well and were so extremely unwelcome whenever they arrived anywhere that there wasn't really any point in being there."

I doubt the experiment will be repeated, but it sure would be awesome if it broke Einstein.

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

#14

Post by nickolai »

coffeenut wrote: post #5

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

> Practical implications?

Print out 90% of physics articles from the century. Get big trash can. Put printout in trash can.

Of course i'm exaggerating, but if the story is true, this is going to be big.

Speed of light is the main block for things like time travel and a hard limit on communication speed.

It doesn't matter that it is only 0.0025%, what matters is that it can be done(if it is confirmed). As a(very poor) analogy, the first CPUs were probably about 0.0025% the speed of the modern ones, yet look where we are today, in no small part thanks to them. The point is, if true, this may well open a whole new realm in physics, and who knows what we will find there.

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

#15

Post by dholowiski »

coffeenut wrote: post #5

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

I'm not smart enough to explain it properly, but basically if information can be transmitted faster than the speed of light, it makes time travel possible. Read "Black Holes and Time Warps" By Kip S. Thorne for a 624 page explanation of why.

More likely, it's experimental error.

.0025% is meaningless compared to the scale of the earth, but over hundreds of light years it's huge.

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

#16

Post by dholowiski »

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.

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

#18

Post by Terretta »

coffeenut wrote: post #5

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

> Practical implications?

Using ion propulsion and gravitationally assisted slingshot trajectories, you'd get to Proxima Centauri about 173 days 12 hours sooner, which sounds pretty cool if you ignore that that's 173 days of a 19,000 year trip.

By nuclear pulse propulsion (EDIT: invented, but still theoretical, thanks adrianN) taking 85 years, you'd get there about 18 hours sooner.

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

#19

Post by jxcole »

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. Due to their very humble attitude, I bet they examined the literature and ruled this particular possibility out very early on.

I bet you there is a systematic error, but I don't think it's this one.

My general rule with physics is that if I can think of it, then a real physicist will laugh at it's triviality.

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

#20

Post by Florin_Andrei »

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 in between. Then the "superluminal" illusion is created by quanta created before t=0.

TLDR: I find it bizarre that seasoned professionals could be fooled by phase velocity or a similar effect.

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