Light travels faster backwards than forwards.

[donniedarko]

Here is the link:

http://www.livescience.com/technology/060518_light_backward.html

I am having trouble comprehending this phenomenon. Can anyone clarify?

Specifically, I do not understand how light can be slowed down and indeed what this concept of information as an observable entity means.

Thanks.

[lazserus]

Here is the link:

http://www.livescience.com/technology/060518_light_backward.html

I am having trouble comprehending this phenomenon. Can anyone clarify?

Specifically, I do not understand how light can be slowed down and indeed what this concept of information as an observable entity means.

Thanks.
These experiments provide nothing. Experiments with photons have been done for decades. Photons are classified as particles and can be "slowed" with interference. The article provided spent more time drooling over the concept as opposed to discussing the science. It was also poorly edited. Unfortunately, what this scientist is proclaiming has been performed in the mid 1990s. He's behind the times. Does this mean anything? Absolutely not. If no information is delivered there's nothing ground breaking. Nothing more than an experiment that resulted in nothing that corporations paid too much for. Burn a 50 dollar bill. Same idea.

[donniedarko]

alright, here is a direct link to the scientific article. once again, as I have limited experience with the physics of light, maybe you could explain it to me in easier terms. if not, oh well.

http://www.sciencemag.org/cgi/content/full/312/5775/895

You say that light can be slowed down with "interference", but how do you generate the interference?

[lazserus]

You say that light can be slowed down with "interference", but how do you generate the interference?
Generally what physicists do is shine light through a gas filled chamber. Filling a vaccuum chamber full of gas at low temperatures makes the gas very dense. When shining a beam of light through that chamber, the photons "slow" to a crawl. Now, this is a little misleading. According to Special Relativity, light travels at a constant represented by c. What's actually happening in these experiments is that due to the dense gas cloud, we're just slowing how long it takes light to travel a distance. Basically, the photon will hit an atom and is absorbed. When an atom absorbs light its energetic state increases for a fraction of time. When that atom loses energy another photon is emitted.

http://www.physlink.com/education/askexperts/ae509.cfm

Read some of the answers to the question here. There are lots of different explanations all based around the same thing. Hope that helps.

[lionheart]

i just read the post and need to ask, causes i carnt comprehend it, how on this earth can light travel backwards

[Cartesiantheater]

The ultimate easy explanation (disclaimer: I may be wrong ;) ): as far as the slowing down part, it really isn't slowing down. It's just being absorbed by the atom.

Light is made of photons. A photon shoots at the speed of light, then is absorbed by an atom (because the gas cloud is dense). This atom, then becomes "filled up" and releases a new photon. This new photon shoots out at the speed of light, until it hits another atom. Then the cycle repeats. This makes it appear that light is slowing down. It really isn't. Its photons are all traveling at C, until they are absorbed. The next photon that kicks out also travels at C, until it is absorbed.

As far as light speeding up, I don't think anything is actually going faster than C. If I understand it, a pulse goes in at C, and then another comes out at C almost instantaneously. But I don't think that the pulse that comes out is the same one that goes in. I couldn't find the actual paper- much less understand it, but I KNOW that nothing can accelerate to a speed faster than C. There's something missing here. Maybe it's similar to the quantum pairs of particles who's spin appear to be instantly affected by measuring its "partner" particle? But rest assured, light is not literally traveling faster than the speed of light.

[lazserus]

i just read the post and need to ask, causes i carnt comprehend it, how on this earth can light travel backwards
It's not that light itself travels backwards in time. It's merely hypothetical that if something was accelerated faster than c then it is assumed that it would travel backwards in time. Superluminal velocities tend to only exist in a reversed time reference. However, this in itself is a wild-eyed suggestion not supported in mainstream science. This is all based around Special and General Relativity, which has been dead on for the past century. It starts to get really confusing when you get into the details of gravity and time.

Cartesiantheater's comment summed it up quite nicely. What's happening is that light is being transmitted through dense gas - gas much more dense than what could occur on Earth naturally - and the denser the gas is, the higher the probability that the photon will be absorbed by an atom. This photon energizes the atom. Once the atom settles down another photon is emitted, just as Cartesiantheater explained. Here is the tricky part. The reason the light appears to be slowing is definitely attributed to the absorbtion factor, but also due to the fact the new photon emitted is carrying the same information. Meaning the travel time appears to be slower. Information is conserved in these processes, even though we're dealing with different photons.