Light so fast it goes backwards?

From the "Not only stranger than we imagine, stranger than we can imagine" file-

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.

No way I can wrap my mind around this one, but I had to share it. Here's the link-

Light's most exotic trick yet

Apparently, this doesn't violate Einstein's "nothing faster than light" rule, but you couldn't prove it by me.

I read the entire article. Thanx for the link yeahright. Freaky. Kinda redefines what's possible huh? Wow. This research is quite remarkable and this story will have "legs" for "light" years (sorry I couldn't resist). I was aware of "the slowing" experiments, but not "the faster than" light work, now to find "backwards" is faster yet again, that is well, stunning. We might just have the nature of photonics all wrong. It defies all the normative rules I was raised to believe as fact. Go figure.

If someone would have said this in one of my 70's university courses - we'd have known they were droppin' window pane. Thanx much! When they get it sorted out I can't wait to see the "killer-app" that the research leads to (hopefully peaceful).

I'd never have known if you didn't post this on ATS. Be prepared, I suspect some folks won't be able to "handle" this research; it might be a bumpy ride for a bit.

Thanx,

Victor K.

[edit on 12-5-2006 by V Kaminski]

It won't be bumpy for me, because I don't understand it well enough to comment on it beyond .

I know there's a lot of work going on with quantum computing. Maybe some application for blazing computing speeds with this? This is in its infancy, along with nanotech, another topic that interests and confuses me. I was familiar with some of the "spooky action at a distance" FTL stuff, but this is definitely new.

Glad you found it interesting. I was in college in the '70s myself. Good times. And maybe if they hadn't been so good, I'd know more about this now.

WOW....I was rather dumb-founded by the earlier experiments that I had read about where scientists were able to "slow" the speed of light. I thought that this concept was revolutionary. Now I read that scientists were able to actually make light go backwards! Frankly, I cannot even begin to comprehend the concept. Of course, I'm someone who often has trouble replacing the batteries in my flashlight.

Fascinating.

Originally posted by benevolent tyrant
WOW....I was rather dumb-founded by the earlier experiments that I had read about where scientists were able to "slow" the speed of light. I thought that this concept was revolutionary. Now I read that scientists were able to actually make light go backwards! Frankly, I cannot even begin to comprehend the concept. Of course, I'm someone who often has trouble replacing the batteries in my flashlight.

Fascinating.

Although light goes backwards in time, i.e. it appears on the exit of a fiber optic before it should, information does not travel faster than light, thus preserving the theory of relativity.

What goes faster in this case is the group velocities of the photon beam. The signal velocity remains C.

Now if you ask me what the above means, the answer is "I do not know". How come light appears to be faster than C, but then it also preserves C? ...

Originally posted by yeahright
Apparently, this doesn't violate Einstein's "nothing faster than light" rule, but you couldn't prove it by me.

It's light, it's not going faster than itself. This is a property of light in this medium. In this medium it travels faster than it normally would, and has properties it otherwise wouldn't, but it's not traveling faster than itself. I wonder if that makes as much sense written down as it does in my head.

Originally posted by Rasobasi420
I wonder if that makes as much sense written down as it does in my head.

ummm....no, but thanks for playing.


(I'm laughing with you not at you).

Originally posted by benevolent tyrant
WOW....I was rather dumb-founded by the earlier experiments that I had read about where scientists were able to "slow" the speed of light. I thought that this concept was revolutionary. Now I read that scientists were able to actually make light go backwards! Frankly, I cannot even begin to comprehend the concept. Of course, I'm someone who often has trouble replacing the batteries in my flashlight.

It's actually not hard to slow the speed of light.

When light passes through a transparent substance, such as air, water or glass, its speed is reduced, and it undergoes refraction. The reduction of the speed of light in a denser material can be indicated by the refractive index, n, which is defined as:

n = \frac[c][v] \;\!

This article is confusing me though. I still don't quite understand exactly how they are getting it to go backwards.

It's actually not hard to slow the speed of light.

This isn't particularly tough. There's an optics formula (see below) where, if you change the frequency of light, you can either increase the index of refraction by a lot, or decrease it by a lot, including decreasing it below 1. If it drops below 1, then light travels faster through the medium than through a vacuum. The energy (and thus any information it carries, like computer bits) doesn't travel faster than "c", though, which can be shown with math. (but not by me, lol)

The formula is the "dispersion equation"
n^2 = 1 + (N * q^2) / [ e0 * m * (w0^2 - w^2) ]
n=index of refraction
N=# of atoms per unit volume
q= electron charge
e0 = permittivity of material
m = mass of electron
w = frequency in radians of the light
w0 = resonant frequency
^2 = 'squared', to the power of 2
(from Hecht "Optics" 4th ed, p.70)

If w is bigger than w0, then all the stuff to the right of the "1" will be negative, and n will be less than 1, and the wave goes faster than light.

This article is confusing me though. I still don't quite understand exactly how they are getting it to go backwards.

I don't get it either. He doesn't really seem to explain, and that weird analogy with the tv camera didn't help me any. It's definitely cool, though. I can't think of any practical use off the top of my head, though.

Remember, One Rock didn't say that nothing can reach light speed, he said that nothing with mass can do so. You may remember a German scientist published results of sending information on photons at somewhere between two and three times 300 km /sec.
Others have said that the medium (not a vacuum) through the bean passed at the NEC lab probably influenced the interpretation of the result.
I can't do the math so, as usual, I am an observer. lol
sayswho (skep by any other name)

Originally posted by masterp


What goes faster in this case is the group velocities of the photon beam. The signal velocity remains C.

Now if you ask me what the above means, the answer is "I do not know". How come light appears to be faster than C, but then it also preserves C? ...

I was thinking the same thing, it just dosnt make sense how this would work. Hopefully we'll here more on this in the near future.

[edit on 13-5-2006 by TravisT]

www.rochester.edu...

Much better.

Originally posted by yeahright
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.

Use mirrors-instant reverse gear for light . Hehe sorry, coiuldn't resist. This is actualy really cool. Not sure how useful it is...But cool.

Apparently, this doesn't violate Einstein's "nothing faster than light" rule, but you couldn't prove it by me.

Never believed that anyway. Photons should have mass, negligible or not.

i couldnt find the article but in my Physics class we saw a film on a Swedish professor who claimed to send a signal faster than the speed of light AND it also transferred information- he sent a classical song over his device ( i forget what he used as the medium and so forth) but it eveidently seemed to work so i dont really know how to explain that one.

Oh I would like to see that if you find it, txdan. If this guy really did transfer information at faster than light, then some part of 'known' physics will have been proven wrong. That would actually be really cool, if a whole bunch of physics was proven wrong, like it was about a hundred years ago. It saw the birth of concepts like relativity, quantum mechanics, radiation, and a bunch of other really fun stuff .

Originally posted by masterp
What goes faster in this case is the group velocities of the photon beam. The signal velocity remains C. Now if you ask me what the above means, the answer is "I do not know". How come light appears to be faster than C, but then it also preserves C? ...

Indeed, as I had to post some times before. For an explanation of what this group velocity thingy means and how the individual photons can still preserve c, go to this thread.

it seems to show that it -the universe- is all about math...

my wonder is: what happens if, when the pulse of light is exiting the light fiber, we put something in the trajectory of the pulse going backward?
- will it go through it as it was not there?
- will the outgoing pulse suddenly desappear, when the reverse pulse incounter the obstacle(as for twin photon)? And, in this case, what if we catch the outgoing pulse on a sensor before it should be anhilated?

Getting more confuse than before? Good, that what I was looking for!

Wouldn't this now make time travel in the PAST theoretically possible, we can always travel into the future but now the past, woah!

Maybe it means that we move in 4D universe where nothing is fixed... neither the past. If the light, with the help of some trick, can move backward (in time)... why shouldn't it be possible for matter?

Originally posted by Lillo
Maybe it means that we move in 4D universe where nothing is fixed... neither the past. If the light, with the help of some trick, can move backward (in time)... why shouldn't it be possible for matter?

Yes it would be for matter, the arrow of time so to speak is ultimately derived through the movement of light.