Light travelling backwards is faster than light.

[FrostyBoy]

http://www.rochester.edu/news/show.php?id=2544

In the past few years, scientists have found ways to make light go both faster and slower than its usual speed limit, but now researchers at the University of Rochester have published a paper today in Science on how they've gone one step further: pushing light into reverse. As if to defy common sense, the backward-moving pulse of light travels faster than light.

So there.

[Zkribbler]

Sorry, but this doesn't make any sense.

Speed (including light speed) is non-directional. If it had direction, then it would be velocity, not speed.

For example, a train going 50 m.p.h. north is going the opposing velocity of a train going 50 m.p.h. south, but both trains are travelling at the same speed.

Speed goes from zero to "C" (according to Einstein) ...but there is no negative speed. Light cannot travel backwards... If it tried, it would just be light going in the opposite direction.

Q.E.D.

[Vince278]

Doesn't make sense. A photon traveling at the speed of light is not traveling in time by its own frame of reference. Therefore, it can be anywhere in the universe. Its vector becomes irrelevent. Things get even weirder at speeds above light (theoretically speaking, of course). The would photon then appear to travel backwards in time.

[Seeker]

How can you go slower than slow?

[KrazyHorse]

Re: Light travelling backwards is faster than light.

Originally posted by Sn00py

http://www.rochester.edu/news/show.php?id=2544

So there.

Yet another example of people not understanding the difference between phase velocity and group velocity.

[Kuciwalker]

KH beat me to it

This same stupid story, along with a number of variants on it, gets reported every month or two. I suppose it's a great way to get grant money or something.

[KrazyHorse]

I suppose there's probably some useful work to be done in optics using these types of experiments. But there's no fundamentally new physics here.

[KrazyHorse]

Originally posted by Kuciwalker
KH beat me to it

That's why they pay me the big bucks.

[Kuciwalker]

[Ted Striker]

Yeah it still can't beat my time in the 40 though

[KrazyHorse]

Originally posted by Kuciwalker

[Seeker]

"But he's now taken what was once just a mathematical oddity—negative speed—and shown it working in the real world."

What is this pre-existing 'mathematical oddity' called negative speed?

I've never heard of it. Is this a reporter created term?

[Vince278]

Originally posted by Seeker
I've never heard of it. Is this a reporter created term?

That happens alot.

[KrazyHorse]

Originally posted by Seeker
"But he's now taken what was once just a mathematical oddity—negative speed—and shown it working in the real world."

What is this pre-existing 'mathematical oddity' called negative speed?

I've never heard of it. Is this a reporter created term?

Probably not. I've never heard it used either (in this context), but then again I've never worked on modern optics. Getting a phase velocity moving in the opposite direction of the group velocity is an interesting trick, and people who specialise in the field might well have developed a term for the previously-unobserved (but solidly theoretically-based) phenomenon.

[Agathon]

Who cares?