Light so fast it goes backwards

[Truronian]

http://www.newscientist.com/article.ns?id=dn6092

My apologies, I've just seen so many creationalist claims that the speed of light has decreased over time to accomodate their beliefs. Interesting that it may actually be doing the opposite!

 

[cgannon64]

This is one of those rare instances when a high school physics course is actually relevent to real-life super-physics...

The phase velocity of light also increases in certain plasmas, where the refractive index is less than 1.

The refractive index can be less than 1? How?

 

[Bluemofia]

Hmm, this might answer some crazy questions on faster than light light.

Researchers in Switzerland have succeeded in breaking the cosmic speed limit by getting light to go faster than, well, light.



Or is it all an illusion?



Scientists have recently succeeded in doing all sorts of fancy things with light, including slowing it down and even stopping it all together. Now a team at the Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland is controlling the speed of light using simple off-the-shelf optical fibers, without the aid of special media such as cold gases or crystalline solids like in other experiments.



“This has the enormous advantage of being a simple, inexpensive procedure that works at any wavelength,” said Luc Thévenaz, lead author of the study detailing the research.



Using a technique called Stimulated Brillouin Scattering, the researchers were able to slow down or ratchet up the speed of light like the gas pedal on a car. They succeeded in reducing the speed of light by almost a factor of 4 (although that’s still plenty fast at 46,500 miles per second), but even more dramatically, the team was also able to speed up the speed of light.



Light in a vacuum travels at approximately 186,000 miles per second, but a popular misconception is that, according to Einstein’s special theory of relativity, nothing in the universe can travel faster than this speed.



This seeming paradox can be resolved because a pulse of light is actually made up of many separate frequency components, each of which moves at their own velocities. This is known as the pulse’s phase velocity. If all the frequency components have the same phase velocity, then the overall pulse will also appear to move at that velocity.



However, if the components have different phase velocities, then the pulse’s overall velocity will depend on the relationships between the velocities of the separate components. If the velocities differ, the pulse is said to be moving at the group velocity.

By tweaking the relationship between phase velocities, it’s possible to adjust the group velocity and create the illusion that parts of the pulse are traveling faster than the speed of light.

One area where such an advance could be enormously beneficial is in the telecommunications industry.



Although information can be channeled through fiber optics at the speed of light, it can’t be processed at this speed because with current technologies, light signals must be transformed into much slower electrical signals before they are useful.



Thevenaz’s technique would essentially allow light to be processed with light without a costly electrical conversion.



The group’s research will be published in an August 22nd issue of the journal Applied Physics Letters.

Source.

What I'm getting here, is that they change the medium at which light goes through using Brillouin scattering... But reading the article on Brillouin scattering (at Wikipedia), makes me doubt the accuracy of what has happened.

How can light be made to go faster? It is slowed down by interacting with matter, by entering the medium at c, being held for a while, then released to travel to the next atom in the medium at c. The temperaral hold it expierences when it impacts the atom in the medium slows it down.

I don't get how they manage to speed up the light wave. The only ways they can do it, is for the medium to release the light wave before it absorbs it, which would be violating the laws of the physics, or the light would be going faster in the medium itself, and not impacting any atoms to slow it down, which makes no sense at all.

 

[malclave]

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

I vaguely remember reading an article in a scientific magazine in the early 80s saying that it was impossible for anything to travel at the speed of light (c), but it was theoretically possible to travel faster than c... you just needed to come up with a way to burrow around (as it were) c.

 

[Bluemofia]

I vaguely remember reading an article in a scientific magazine in the early 80s saying that it was impossible for anything to travel at the speed of light (c), but it was theoretically possible to travel faster than c... you just needed to come up with a way to burrow around (as it were) c.

How can this be? To go faster, you must have gone at c at some point, right? You can't go from less than c to greater than c, skipping all the other speeds in between...

 

[malclave]

How can this be? To go faster, you must have gone at c at some point, right? You can't go from less than c to greater than c, skipping all the other speeds in between...

To quote Hamlet, "aye, there's the rub".

 

[Bluemofia]

What's that supposed to mean?

 

[malclave]

It means that it's a difficult, possibly impossible, question to answer.

The article was over 20 years ago... I remember I was in high school at the time. It was one of the "pop science" magazines, and I only remember it because of my interest in science fiction and a misguided notion that I might make a capable sci fi author.

I don't remember enough of the article (or of physics) to give a decent account... but I think it theorized that if you could somehow convert a mass to an imaginary value (mathematically speaking), the velocity could be changed instantaneously from below to above the speed of light... I guess in sci fi terms, "hyperspace" might be the best description.

 

[Mr. Dictator]

wow, thats confusing.

but what does this mean in practical terms? how will this help people?
unless i can make toast before i ever get it out of the bag i dont care.

 

[Goa]

The refractive index can be less than 1? How?

I don't remember the details how it can get lower than 1, but I remember that when it gets lower than 1, the imaginary part of n gets quite big, and thus you got inevitably big absorption. That's why you need these special active mediums to observe the effect.

 

[ironduck]

How can this be? To go faster, you must have gone at c at some point, right? You can't go from less than c to greater than c, skipping all the other speeds in between...

Light does skip all the steps in between though. From nothing to c.

 

[Pasi Nurminen]

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

Which would eliminate the need for you to have left in the first place, thus creating some kind of tear in the space-time continuum?

I've watched too much Star Trek over the course of my life. Either that or too little...

 

[El_Machinae]

I vaguely remember reading an article in a scientific magazine in the early 80s saying that it was impossible for anything to travel at the speed of light (c), but it was theoretically possible to travel faster than c... you just needed to come up with a way to burrow around (as it were) c.

I remember that this posits that there are particley-ish things that travel faster than the speed of light, but don't really interact with the universe as we know it.

Remember that c is measuring travel in 3 dimensions. So, if learning to travel via other dimensions is possible, then we can travel through those dimensions (likely, with their own version of c) and seem to violate c in our 3 dimensions.

Of course, figuring out how to travel at 90 degress from our reality kinda stumps me.

 

[ironduck]

Tachyons

tententen

 

[Bluemofia]

Light does skip all the steps in between though. From nothing to c.

Because light can only move at c... By definition of c. (it goes from nonexistant to existant at c)

And Tachyons (from what I've read), lose energy when they go faster than the speed of light... And when they lose energy, they go faster, until they reach infinite speed (rather quickly), and are destroyed. Plus they travel backwards in time.

 

[El_Machinae]

So - to our time frame, they slow from infinity to c, and gain energy?

Sound like vacuum photons to me.

 

[blackheart]

Which would eliminate the need for you to have left in the first place, thus creating some kind of tear in the space-time continuum?

Pretty much the common consensus, but then again the speed of light is under debate here so that may not hold true.

 

[Sidhe]

As far as I understand it light as it propogates is always equal to c, its only absorption and reemission that "slows" it, and light is never travelling at less than c when it's actually re-emitted or in motion, as to how this experimental evidence indicates travel faster than light I have no idea, suffice to say as far as I know it, it is as stated by others an illusion probably brought about by a misunderstanding of super position. I'll do what all laymen do in this situation go ask someone more educated than me. I'll get back to you.

Invoking other dimensions is fraught with experimental peril, KISS or at the very least keep it real and not imaginary.

 

[El_Machinae]

Meh, worked for Faust!

 

[Sidhe]

good point he was dragged into the underworld for doing that IIRC, not big on Faustian temporal geometry, I suspect Satan dragged him there faster than the speed of light, but again the Devil was probably a master of illusion.