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Light so Fast it Travels Backward
An anonymous reader writes "Slowing down light used to be considered a neat trick for physics wonks. But researchers in New York now say they've pushed light into reverse. And as if to defy common sense, the backward-moving light travels faster than light." While there's not much use to come of it yet, it will be interesting if Einstein himself is proved wrong.
"Einstein said information can't travel faster than light, and in this case, as with all fast-light experiments, no information is truly moving faster than light," says Boyd.
Way to read the article, CowboyNeal.
A slashdotter who didn't build his own computer is like a Jedi who didn't build his own lightsaber.
Quantum mechanics generally include special relativity (for example, the Dirac equation). It is general relativity and gravity that is the problem. Speed of light being the maximum speed of information travel is accepted, as far as I know, in all QM. This is just one of those phase velocity vs group velocity things that pop up every so often here, I would wager.
I have freaks! I did something right...
light traveling backwards, wtf
The main problem is that physics research is being more and more geared towards being appealing to people who don't know physics, hence all the BS taking advantage of phase/group velocity confusion, wanking about various string theories, etc. Sure, it's nice to let people know what's going on in physics, but in the end if they get the impression that most physicists are excited or even remotely interested by simple tricks like this, I don't think it bodes well.
You see I can picture a car going forward and back. It has a front and a back. This plus the convention of designation means that one is forwared and one is Reverse. However with light this seems a bit odd. I mean if you had a perfect mirror and held it at exactly 90 degrees to the beam of light would it be going backwards or forwards to where it came from. I suppose if I think of it as obsorbtion, in that the origination source takes back the energy it pushed out it could be considered backwards. But then wouldn't this make a black hole a reverse Sun? In short. This is most likely why I'm in applied Physics (EE) not Theoretical Physics.
I'm sorry, I'm to tired to be witty at the moment so this message will have to do.
Folks, let's PLEASE keep in mind that you don't actually change the speed of light. What you're changing is the _apparent_ speed of light. Light appears to slow in a medium because stuff is absorbing and re-radiating it, holding it for a short while and changing its apparent speed. You never actually make photons move any slower.
I honestly don't know if the receiving prior to sending thing is bunk or what, I am not a physicist.
However, I believe it would be safe to assume that the prior to sending beam could only appear if you were in fact going to send the beam, as in whatever dimension that allows this to happen, the beam is a single thing moving all at once through space and time, and not travelling unusually at all. It still has to be sent from the one time point to appear at the next. Or previous in this case. I think what I'm saying is the information would have velocity through time only if granted its equivilent of force.
If we were able to receive and then not send, it would be an odd inconsistancy in things.
They're there affecting their effect.
The light from the flashlight will appear to be travelling at c to both the observer holding the flashlight (and travelling at 0.999c) and a stationary observer.
This is because of time dilation, which would result in making everything, from the flashlight holder's perspective, appear to be moving really really fast (including the light). A velocity that would normally be measured as 0.001 c will instead be measured as c due to this time dilation.
The stationary observer would, of course, measure the speed of the light as c.
Now, if two flashlight wielders were travelling towards each other in opposite directions, both at 0.99c in their respective directions, I have no idea how to explain what they observe.
Aaah... see now instead of the people displaying how big their brains are, someone actually thinks to post to a link with a picture of why something can "appear" to travel faster than light. WITHOUT the need for stupidly complex formulae! Thanks!
I refuse to have a sig... dammit!
Wait a second - if we make light go faster than the "speed of light", then doesn't that just mean we miscalculated something!? If I can run faster than I can run, its because I thought I was slower than I actually am.
Seems to me that inside of a speed for light, its just variable speed and we have calculated its speed in a normal situation and labeled it the speed of light.