Light so fast it goes backwards

[ironduck]

I'm having a little trouble understanding this properly, can someone explain it to me?

http://www.spacedaily.com/reports/Light_So_Fast_It_Actually_Goes_Backwards.html

 

[blackheart]

Well if the world's experts are scratching their heads over this one, then I don't know!

 

[GenMarshall]

The man in the art department are too confused too draw up the animation for this - Mythbusters



Translation: I dont even know how to explain this?

 

[bhsup]

Man, I think I just hurt my brain trying to read that and keep it straight. That TV analogy was not helpful in the least.

 

[BasketCase]

We're probably all familiar with the dealie about how time slows down as you accelerate towards light speed. Which leads some people to take the next step and wonder if time starts going backwards above light speed.

If that's true, then an object travelling above light speed would appear to a stationary observer to be moving in the other direction; a pulse of light would enter the fiber at X o'clock, move through the fiber, and exit the other end at, say, X - 3.

So, who knows? Maybe they finally broke the Big Barrier.

But it's also possible the observers screwed something up.

 

[blackheart]

We're probably all familiar with the dealie about how time slows down as you accelerate towards light speed. Which leads some people to take the next step and wonder if time starts going backwards above light speed.

If that's true, then an object travelling above light speed would appear to a stationary observer to be moving in the other direction.

Lightspeed travel is incredibly insane. So if you went above lightspeed, you'd get to your destination before you left!

 

[Fox Mccloud]

Isn't it impossible for anything to travil faster then light?

 

[Chieftess]

Maybe it's sort of an implosion of the Space-Time Continuum?

 

[skadistic]

Isn't it impossible for anything to travil faster then light?

Apparently light can go a multitude of speeds beyond the slight diffrence between colours. So if light can go faster then the 'base' speed of light in theory anything can.

 

[Xanikk999]

Since im already super sucky at chemistry and physics i cant make heads or tales of this!

 

[BasketCase]

You mean tails or heads.

 

[Bluemofia]

What the heck???

How do you speed up light to begin with? You slow down light by having it be absorbed by an object, and then it releases it. (why light moves slower in the air than in a vacume)

c is always c. Constants stay constant (at least, by deffinition).

Methinks something is fishy here...

 

[Tenochtitlan]

It probably just appears to be going backwards, you know similar to how a spinning car wheel would appear to be rotating the other way around at certain speeds.

 

[Birdjaguar]

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," Boyd explained. "The pulse of light is shaped like a hump with a peak and long leading and trailing edges.”

He said the leading edge of the pulse carries all the information about the pulse and enters the fiber first. “By the time the peak enters the fiber,” he continued, “the leading edge is already well ahead, exiting. From the information in that leading edge, the fiber essentially reconstructs the pulse at the far end, sending one version out the fiber, and another backward toward the beginning of the fiber.

It seems to me that the question is why the leading edge sends a backward pulse; since erbium seems to be the variable, that might be the cause.

 

[Bill3000]

Hooray for people not understanding the differences between group velocity and phase velocity!

 

[Erik Mesoy]

I don't see the problem.

Here's the limitation:

Information cannot be transmitted faster than c.

"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," Boyd explained. "The pulse of light is shaped like a hump with a peak and long leading and trailing edges.”

He said the leading edge of the pulse carries all the information about the pulse and enters the fiber first. “By the time the peak enters the fiber,” he continued, “the leading edge is already well ahead, exiting. From the information in that leading edge, the fiber essentially reconstructs the pulse at the far end, sending one version out the fiber, and another backward toward the beginning of the fiber."

Here's a trick - if I point my laser pointer at one side of the Moon, and then twist my hand so that it points at the other side, an observer on the Moon's surface will see the red dot from the laser pointer traveling across the Moon's surface at faster than light speeds.

 

[Fifty]

koo koo kachoo

 

[Birdjaguar]

Here's a trick - if I point my laser pointer at one side of the Moon, and then twist my hand so that it points at the other side, an observer on the Moon's surface will see the red dot from the laser pointer traveling across the Moon's surface at faster than light speeds.

Why? .......

 

[Sims2789]

Mathematically I understand it but conceptually, no.

 

[History_Buff]

Well, he could be right.

The Diameter of the Moon is 3476 km according to the internet. Thus, his laser dot will be forced to travel this distance in the exact same amount of time it takes him to rotate the laser pen here on earth. Assuming he can do it than less than a hundredth of a second (and since it's only a 5 degree arc, this is possible, though very difficult), he would correct:

Distance travelled: 3476 km = 3,476,000 m
Time required: lets say 0.01 seconds, for the sake of argument

3,476,000 m / 0.01 s = 3.4678 x10^8
c = ~3.0 x10^8

So, if we assume he can move his pen 5 degrees in 0.01 seconds, he would be correct (unless of course simple math doesn't hold at this level, which I wouldn't be surprised to learn).