I heard in the news about 6 months ago that a group of physicists had succeeded in making a particle travel faster than light. I also heard that this did not invalidate special relativity. Can anyone explain this to me or provide a website address of someone who can? I have a layman’s grasp of physics, so if the explanation involves something really esoteric, please simplify. Thanks!
Just go to google and do a search on “faster than light experiments”. You’ll get more hits than you can shake a stick at. And, you’ll be able to come back here and fill us in.
They didn’t make a particle travel faster than c (the speed of light in a vacuum). There’s two things that they might have done: First, they might have made a particle travel through a medium faster than light travels through that medium: Light is slowed by passing through a medium, and it’s possible that some other particle might be slowed less. This isn’t actually too hard to do, and has been known for decades. When this happens, you get something called Cherenkov radiation, which is similar to a sonic boom, but with light.
The second possibility is that they made something appear to travel faster than c. There’ve been several experiments which have done this recently, mostly with light pulses. If you amplify the front of a light pulse, and diminish the center of the light pulse, then the point of maximum amplitude will travel faster than c. This doesn’t really do anything, though, since you still had to have something there to amplify, and there aren’t any particles moving faster than c.
Without a little more information, it’s hard to say which experiment it was that you heard of, but rest assured, it’s nothing extraordinary… The media just made it sound that way. Never trust the non-scientific media to get anything scientific right.
I’ve seen this question asked before and, as Chronos explained, the answer is always that nothing special or weird is happening here.
As a hijack but along the same lines of faster than light travel what would happen if you were to close something like a pair os scissors really fast?
Suppose I make a pair of scissors that are really long…say 1 light year in length. The pivot point is 1/10[sup]th[/sup] of the way up the scissors (so 90% of the scissors extend beyond the pivot).
I now have a machine (a very special machine) snap the scissors closed at nearly the speed of light (say .99999999c). Shouldn’t the pointy end of the scissors now be moving faster than the speed of light?
I’m sure there is some way that they wouldn’t actually move faster than light. My guess is the scissors would bend, break or resist the movement such that I couldn’t close the handle fast enough to make the long ends move too quickly.
Still, I’m curious as to the real answer. I know people don’t like ‘magic’ in hypotheticals since it establishes false premises to work from but if making the scissors of some unbreakable and/or unbendable material helps then go ahead and assume that (or not…whatever works for you).
To answer your hijack, you are correct: the blades must bend. The bond between any atom and its neighbor is not infinitely rigid, and it cannot transmit force faster than c.
It has been sometimes pointed out that it is possible, even without infinite rigidity, for the point where the blades meet to move faster than c when a very large pair of scissors is closed. This doesn’t violate relativity, since that point is not an actual object, merely the projection of two objects that are moving much slower than c. Sort of like how a theoretical shadow can exceed c, even though no actual object is moving that fast.
Thanks for the link dqa.
That’ll learn me to search the board beforehand. I know I had heard about the scissor thing before and it popped into my head when reading this thread so I started typing before thinking about it some. Something I unfortunately do too often.
From this site.
I originally heard this on Coast to Coast AM with Mike Segal, I was hesitant at first, because I did not know Michio Kaku’s credentials. He apparently checked out, though I can’t find a site for what he said. His take on it was that Princeton had indeed found a case of FTL travel, 300 times the speed actually. The details were above me, but he mentioned something about packets (quanta) inside the light beams that were sped up 300 times the speed(but not the light beam itself). (quantum mechanics perhaps?) he also stated that there was no way that information could be passed using this message. So might as well forget using it to propel matter this way.
I wish I could supply more links, but most of the ones I found through google were dead links. (might be my ISP though)
Thanks for all of your responses. I ended up finding a pretty good link for this. http://physicsweb.org/article/world/13/9/3
It’s fairly technical and loses me in the section that talks about how the acceleration is accomplished. I also don’t understand the distinction between group velocity and velocity of an individual photon.
-LabRat