Physicists can now Slow and Stop the speed of LIGHT!

Originally posted by Freelancer
induced transparency in [...] sodium

Transparent Sodium!

While reading the word "transparency" I somehow hoped to read "Aluminium" next.

"Computer"
"..."
"Computer!"
"..."

The speed of light is not only 299,792,458 m/s in a vacuum, it is that speed everywhere. The only thing that causes light to appear to travel slower through different mediums is the rate of absorption and re-emission of photons in that medium. As photons travel through, say, glass, they don't really pass through... they are absorbed by electrons along the way, and those electrons then re-emit photons. All of those photons have the same velocity - 299,792,458 m/s - but the time it takes for the absorption/re-emission process to occur determines what the measured speed of light through the glass is going to be.

In the case of the Bose-Einstein condensate, the absorption and re-emission occurs as such low temperatures (that is, low energy levels) that the rate of this process if reduced considerably. Again, the photons, themselves, still travel at 299,792,458 m/s, but they are absorbed and re-emitted at a MUCH slower rate, thereby reducing the measured speed of light considerably.

As for being able to reach out and touch light... I think I would call that a very generous case of hyperbole.

Now, the effect of this on time: nonexistent. The photons are still travelling at the speed of light, so there are no abnormal relativistic effects to anticipate. Again, they're not actually slowing the photons, themselves. And even if they were, we wouldn't be able to notice it... the time dilation caused by such a slowing of light would apply to their reference frame, counteracting any perceived change in the speed of light by the observing reference frame. Remember, the speed of light is constant in all reference frames... that's what relativity is all about.

And, finally, anytime you read about scientists slowing the speed of light, always keep in mind that that's a bit of a terminological stretch. If the speed of light really was altered, the electromagnetic wave would collapse. For an EM wave to exist, the Ampere-Maxwell Law says it MUST be travelling at 299,792,458 m/s no matter what the conditions. Any speed other than that and the wave would be unable to self-propagate.

reply to post by CLPrime

Great to see you posting here CLPrime, I'm glad to see that at least one other person in this thread sees through the headlines to what is really going on!

It would be nice if more people could see through the misleading and somewhat sensationalistic headlines, but hopefully they will learn something from you about the speed of light being constant despite the headlines.

Originally posted by CLPrime
As photons travel through, say, glass, they don't really pass through... they are absorbed by electrons along the way, and those electrons then re-emit photons.

Regarding the absorption and re-emission of photons, that's a commonly used over-simplification for a layperson which I've used before myself, though I wouldn't say it happens with electrons per se, it's actually very technical. If you or anyone is interested to get really technical about what actually happens, there's a pretty good explanation here, though I fear it will be over most people's heads, though probably not yours:

Do Photons Move Slower in a Solid Medium?

The process of describing light transport via the quantum mechanical description isn't trivial. The use of photons to explain such process involves the understanding of not just the properties of photons, but also the quantum mechanical properties of the material itself (something one learns in Solid State Physics). So this explanation will attempt to only provide a very general and rough idea of the process.

A common explanation that has been provided is that a photon moving through the material still moves at the speed of c, but when it encounters the atom of the material, it is absorbed by the atom via an atomic transition. After a very slight delay, a photon is then re-emitted. This explanation is incorrect and inconsistent with empirical observations. If this is what actually occurs, then the absorption spectrum will be discrete because atoms have only discrete energy states. Yet, in glass for example, we see almost the whole visible spectrum being transmitted with no discrete disruption in the measured speed. In fact, the index of refraction (which reflects the speed of light through that medium) varies continuously, rather than abruptly, with the frequency of light....

A solid has a network of ions and electrons fixed in a "lattice". Think of this as a network of balls connected to each other by springs. Because of this, they have what is known as "collective vibrational modes", often called phonons. These are quanta of lattice vibrations, similar to photons being the quanta of EM radiation. It is these vibrational modes that can absorb a photon....

So rather than the photons being absorbed or delayed by electrons, it's actually phonons the electrons commonly interact with, but since most people have no idea what a phonon is, when you use that explanation of "absorbed by electrons", just leave out the "by electrons" and leave it a little ambiguous by just saying they are absorbed and re-emitted, you don't have to be specific about what is doing the absorbing and re-emitting. At least that's my intent when I use that explanation, rather than trying to expect people to understand a phonon.

Of course the photons can certainly be absorbed and re-emitted by electrons too, but that doesn't really explain the optical properties of materials that appear to slow down the speed of light like glass in the lens of a camera or a pair of glasses.

By the way, anybody who has ever used either of those could also claim to have "slowed down light" since the apparent slowing down of light in glass is what gives a glass lens its optical properties. Cameras are pretty cool, but the optical properties of the camera lens aren't exactly a gateway to time travel as CLPrime explained, though some people might like to try to extrapolate that from these somewhat misleading headlines.

Originally posted by Arbitrageur
reply to post by CLPrime

 

Regarding the absorption and re-emission of photons, that's a commonly used over-simplification for a layperson which I've used before myself, though I wouldn't say it happens with electrons per se, it's actually very technical.

Indeed, it's a ridiculously simple oversimplification. But it seems to get the point across without being over people's heads. It would seem to me that, if someone is going to believe that light is actually physically slowed down, then they're probably not going to take very well to the concept of phonons. The best thing to do, in that case, is to appeal to the most basic explanation possible... which just happens to be the absorption and re-emission of photons.

But, certainly, once it's understood that no photon is ever actually slowed down, then people should by all means research the physics of phonons through media. And what you referenced is a great start.

Originally posted by Freelancer

Originally posted by PhoenixOD
The speed of light is only 186282 a second in a VACUME

edit on 17-7-2011 by PhoenixOD because: (no reason given)

Wasnt the experiment done in a Vacuum (Bose-Einstein condensate) and isnt Space a vaccuum? So the two apply when quoting the maximum speed of light in this O.P.

A Bose-Einstein condensate isn't a vacuum. It's a state of matter. Vacuums aren't states of matter; they're states of emptiness.

Light is always slowed when it hits some sort matter -- it travels more slowly in glass and water and air than it does in a pure vacuum.

reply to post by Freelancer

Everyone know's that the speed of light is 186,282 miles a second, but what-if this 'constant' can be shown that its possible to not only slow it down to say 38 miles per HOUR, but to stop it dead in its tracks without breaking Einstein's theory of relativity, which places an upper, but not lower, limit on the speed of light.

Why doesn't the theory of relativity place a lower limit on the speed of light? If you can square the constant by the amount of mass you should then be able to inversely square the constant in the same manner. I see it as a sliding scale that is relative to our frame of reference or we always observe light traveling at the same rate.

Since the universe is one huge vaccuum and is super-cold by many magnitudes to anything here on earth and no doubt does contain super-dense clouds of atoms [of various elemets], could this not ALSO slow down the light we recieve here on earth, their-by making calculations of distances and ages to other galaxies and stars UNCERTAIN?

I think the difference here is in the density of the gas and its low temperature. We can observe low temperatures in space but not much in the way of dense gas.

This idea makes me wonder if holographic images in glass are the product of "frozen" light. Imprinted EM waves into the glass that constantly reproduce the image.

reply to post by jude11

That being if light were indeed slowed down, would it become possible to attain the benchmark of Speed of Light and thus attaining Time Travel?

This benchmark is a relative perspective. Which means that no matter how fast you go light will always be measured going 186,282 miles per second. The problem that you're dealing with has to do with accelerations and not velocity. We could certainly travel at any speed imaginable just not accelerate past the speed of light. This sounds counter-intuitive but it is a problem with acceleration which requires a constant force.

reply to post by loneranger26

So now if we can capture light and slow it down and even bring it a stop, when we release it again does it accelerate back to light speed?

Yes, light resumes its previous speed. Or as CLPrime put it, light does not slow down but rather its absorption rate is slowed. As light comes in contact with transparent glass it does not go through the glass but rather the image is transferred through from one side and out the other. Some energy is lost on both sides of the glass and this is why you can "see" a glass window even though it is transparent.

Would that mean we can slow down the light enough to hitch a ride with it as it accelerates back up?

How would you go about fixing yourself to something that has almost no mass?

reply to post by kwakakev

If there is no lower limit on the speed of light, then could we end up with negative speeds as well, go back in time?

Mathematically the lower limit gets infinitley close to zero. It is a product of inversley squaring the constant by the mass. Put another way, you can take a finite number, 1, and divide it in half an infinite number of times. You never actually get to zero. Of coarse we are talking relative observations here which is different from math. Light will always appear to be traveling at the speed of light no matter how fast you are moving in whichever direction.

reply to post by jude11

How one could 'hitch a ride' is the next question. Using the theory of teleportation and breaking our physical bodies down to the atom, would it then be possible to hitch that ride?

We can do this with our images and voice, TV and radio. You would need to convert your physical body into eletro-magnetic waves and then send it out on a carrier wave to be recieved at a later distance. It might sting a little.

reply to post by miniatus


I made a thread about this about a week ago, I do believe a lot of science we accepttoday will be proven wrong in the future. Its amazing thinking about stoping the speed of light, what I dont get is how do you stop the speed in one area and not the other (i.e. The universe)?