The Speed of Light Equals Zero

I am still trying to wrap my lobes around this one. Apparently some scientists have managed to stop light for a brief moment, and then send it on its way again with all of the photons intact. I understand things like wave lengths being different, but I cant comprehend how something that alweays will measure to have the same velocity, no matter how it is measured, can be stopped.... Did it disappear???

Equally as stunning as this news is, it seems they have been slowing light down for quite awhile now. Could one of the higher lobes here please explain to me this seeming contradiction of the law of physics?

A pulse of light has been stopped in its tracks with all its photons intact, reveal US physicists.

In a vacuum, light travels at the phenomenal speed of 300,000,000 metres per second. Scientists can exploit the way that the electric and magnetic fields in light interact with matter to slow it down.

Over the last few years, scientists have become masters of the light beam. Speeds of a few metres per second are now reached routinely in laboratories around the world. It is rather harder, however, to stop light completely and previous attempts have halted light but lost its photons in the process.

www.newscientist.com...


news.bbc.co.uk...

True, scientists have been slowing down light drastically for a while.

I don't think that this is a contradiction of physics, as there is no law that says light can't be slowed down (I think?). Is is accepted that nothing can travel than the speed of light, but that's assuming that the speed of light is the velocity it has in a vacuum.

I bet there's a whole bunch of quantum mechanics involved here. Beyond my scope of knowledge...

Kinda scary realize that all the Newtonian physics and stuff you learned when you grew up isn't completely true.

the only way that I can visualise light being stopped would be as if it were shining against an invisible wall but not leaving the other side but just getting brighter as the rest of the light travelling from the source catches up with it. until you just have a blindingly bright spot at the point that it had stopped. probably nothing like it in reality it's just how I would imagine it.

Thanks. I am sure there must be some kind of explanation for it. I wonder how it is possible to even slow it down, unless they are just stretching the wave lengths...

Its been known for a long time that it was possible to slow light down. Light travels at a range of speeds lower than its absolute maximum dependant on what medium it is travelling through. As it slows it bends away from its axis, ie refraction. The amount of refraction changes with the lights frequency.

This theory is the basis of most every classical optical theory. Allowing us to make lenses to focus light, prisms to split light, and a myriad of other items. As well as explaining many things we see in the world around us. Sunsets, rainbows, the fact that a straight pole seems to bend as you put it under water. And so on.

The trick these guys are mainly working on to slow light is by finding substances with higher and higher refractive indices.

An interesting method used has been coherent population oscillation, and is explained at the bottom of this page:
www.newscientist.com...

The researchers fired two laser beams tuned to slightly different frequencies at a ruby crystal. The frequency difference produced a rhythmic vibration in atoms in the crystal, which in turn altered the refractive index of the material.

As far as the 'frozen' light. The first NS link sort of covered the lay explanation.

This is then "frozen" with the help of two control beams. The light in the control beams interacts with the rubidium atoms to create layers that alternately transmit and reflect the pulse.

So the light is more trapped than frozen. I suppose an analogy could be to imagine the light trapped between two perfect mirrors extremely close to each other, forever bouncing back and forth until one mirror is removed and it is allowed to escape.

Well, wait a minute. Rainbows - changes in wavelengths. Submerged bent poles - refraction - no change in velocity, really don't go toward what is very hard to understand here.

Is this an issue of semantics? Or are they really slowing the speed of light? That seems to be the very important question here.

we talked about this very briefly in my phsyics class once, the way it was explained to me was that the light was passed through a bunch of materials and measured(?) as it passed through the materials but once it left them it went back to its normal speed. dont no how true or right i am in my memory, just tryin to help a lil.

The media that light passes through can only affect its wavelength...not it's speed, unless everything has changed here lately.

That's what I'm trying to get clarification on.

i thought it was only sound that changed speeds in diff medeims

i wonder what speed travels in space IE:vacume>?

From William's quote:
"A pulse of light has been stopped in its tracks with all its photons intact, reveal US physicists. "
I doubt this was said by physicists. Sounds more like a journalist trying to jot words to what they
were hearing.

In William's two references we see a better description:

"...managed to stop light without this loss by firing a short burst of red laser light into a gas of hot rubidium
atoms. This is then "frozen" with the help of two control beams. The light in the control beams interacts
with the rubidium atoms to create layers that alternately transmit and reflect the pulse. "

Read the articles closer. Nowhere does it say light (photons) stopped. Except for the journalist's
translation.

Same for the reference Kano provided.

It seams to be inferred by the descriptions in the articles ( After removing the Psycho-Babel )
that each of the techniques described are making use of refractive index control to induce
standing waves. A good description is:

www.glenbrook.k12.il.us...

I enjoyed the question by Dmsoldier. Light in its wave form does vary its speed in different
mediums, just like sound waves. You voiced a common misconception. I would think
that someone would ask: If light can be slowed down really a lot in a medium such as
water (1/3 of its velocity in a vacuum) or even a lot more, what happens if something
else in that same medium exceeds that velocity?


math.ucr.edu...



/\/ight\/\/ing

I'd just like to comment that C, the constant for the speed of light, is the speed of light in a vaccum. When light travels into a black hole, it stops. The photon may still exist, but the wave aspect was put on hold. Light also slows down when it hits earth's atmosphere, which is what causes our sky to be blue.

I'd be curious to know how they detected the photon in a stasis state, as it wouldn't give off "light", since it can't travel to our eyes.

I'm assuming this detection is possible, though, because a couple years back I read an article about a university which had managed to transport one photon to another location. They didn't actually move the photon, but transfered all of the original photon's properties to another photon. They had to be able to detect it somehow. Just never thought about that until now...

Originally posted by nightwing
what happens if something
else in that same medium exceeds that velocity?

Quite simply, it means nothing. The speed Einstein said couldn't be exceded (or deceded, if that's a word) was C. The constant for the speed of light in a vaccum without gravitational influences.

I'd like to note, though, that a common misperception is that nothing travels faster than the speed of light. That's not what the theory states. Rather it states that nothing can pass the threshhold of C. If you're already going faster than the speed of light, you will continue to do so. If slower, than you will continue to do so.

Things have been shown to be faster than the speed of light in certain media. But like Junglejake says, they are not faster than the speed of light in a vacuum. Look up Cerenkow Radiation. www.physlink.com...

As has been stated on here several times, light slows down in certain media. That is why they always refer to the constant C as the speed of light in a vacuum.

from greenkoolaid:

"Things have been shown to be faster than the speed of light in certain media.
But like Junglejake says, they are not faster than the speed of light in a vacuum. "

From the Univ of California, Riverside Physics FAQ, a few
examples of FTL :

"Think about how fast a shadow can move. If you project a shadow of your finger
using a nearby lamp onto a far away wall and then wag your finger, the shadow
will move much faster than your finger. If your finger moves parallel to
the wall, the speed will be multiplied by a factor D/d where d is the distance from
the lamp to your finger and D is the distance from the lamp to the wall. It can actually
be much faster than this if the wall is at some oblique angle.
If the wall is very far away the movement of the shadow will be delayed because
of the time it takes light to get there but its speed is still amplified by the same ratio.
The speed of a shadow is therefore not restricted to be less than the speed of light.
Others things which can go faster than the speed of light include the spot of a laser
which is pointed at the surface of the moon. Given that the distance to the moon is
385,000 km try working out the speed of the spot if you wave the laser at a
gentle speed. You might also like to think about a wave arriving obliquely at a long
straight beach. How fast can the point at which the wave is breaking travel along the beach?
This sort of thing can turn up in nature. For example the beam of light from a pulsar
can sweep across a dust cloud. A bright explosion emits an expanding spherical shell
of light or other radiation. When it intersects a surface it creates a
circle of light which expands faster than light. A natural example of this has been observed
when an electromagnetic pulse from a lightning flash hits an upper layer of the atmosphere.
These are all examples of things which can go faster than light, but which are not physical objects. "



/\/ight\/\/ing

The frequency remains the same though Valhall.

A few more links (because I'm feeling lazy ):
hyperphysics.phy-astr.gsu.edu...
homepages.tig.com.au...
www.glenbrook.k12.il.us...

Here is my question, the speed of light is greatly increased when in a vacuum, but yet they say that it takes light 8 minutes to get here from the sun. Isn't space a virtual vacuum? So with this being that, wouldn't that actually mean that the light coming from the sun is actually getting here faster than believed. This was just discovered the other year that light travels faster in a Vacuum, have they changed what they are teaching kids about how long it takes for light to travel from the sun to the earth? Also, a rudy can be used to slow down light to 57 metres per sec in room temp.

anyone else here notice that you can do anything with magnets it all comes down to magnetic this magnetic that is there a lab or group that studies magnetics and behavior etc.??? It all comes down to magnetics sooner or later.

Originally posted by Dravenn
Here is my question, the speed of light is greatly increased when in a vacuum, but yet they say that it takes light 8 minutes to get here from the sun. Isn't space a virtual vacuum? So with this being that, wouldn't that actually mean that the light coming from the sun is actually getting here faster than believed. This was just discovered the other year that light travels faster in a Vacuum, have they changed what they are teaching kids about how long it takes for light to travel from the sun to the earth? Also, a rudy can be used to slow down light to 57 metres per sec in room temp.

Einstein stated that light slowed down in a different medium. It wasn't that light speeds up in a vaccum, but light travels at it's natural speed in a vaccum. And yes, space is a vaccum, and that was how the 8 minutes was generated. That's the time to reach earth, not to also penetrate our atmosphere. That's what I was taught in school about 10 years ago...

Looks like my lightsaber isn't that far off!!! Woohoo!!!

Seriously....this kind of makes your brain get fuzzy...don't it??? The implications are pretty profound...unless it ends up being bull-hockey....

Very kool!!!! The speed of light is influenced by gravity as well.