What's the slowest light can go?

Question

If I told you I wanted you to make a beam of light (preferably visible light, but I'll take what I can get) go really slow, how would you do it? What's the slowest you could make it go?

Answer 1

Since photons are particles and waves they react to electromagnetic fields created by electrons and protons in the medium the photon travels through.

The measure of how a photon changes in particular mediums is called the refractive index:
n = c/v
c is the speed of light in vacuum
v is the speed in the medium
n is the refractive index

The highest refractive number I could find (which means v is much smaller than c) was for
Iodine Crystal .............. 3.34
BTW - this is why things like diamonds sparkle

Edit:
Silicon ....................... 4.24

Edit:
Problems with saying that a photon's speed was reduced to zero:
1) Refractive index goes to infinity (not really a problem but still interesting)
2) Usually means the photon was absorbed (it did not come out of the medium)
3) Light is a particle/electromagnetic wave, a v of zero creates a standing wave which I thought was wasn't possible for electromagnetic waves
4) If the photon is merely caught inside the medium bouncing back and forth then v isn't really zero... Just another way of saying that the photon was absorbed.

Answer 2

The speed of light is slowed by going through a medium of high refractive index. In a recent article (see reference below) light has been slowed down to the speed of a good bicyclist, a few meters per second. Theoretically the speed could approach zero.

"Slow-light effects invariably make use of the rapid variation of refractive index that occurs in the vicinity of a material resonance." It is important also to note that there are different kinds of velocities associated with light. Here they are talking about the "group velocity" of light. Phase is not preserved in many of the materials under consideration. The group velocity depends on the large amount of dispersion in the medium. Typically this leads to a large amount of absorption, but recent work using a coherent optical effect among a gas of atoms that have three energy levels has made a breakthrough.

Answer 3

Our laboratory recently invented 'slow glass', a transparant medium in which light is slowed down to a speed of about 15 centimeter per day. It's a meter thick and by looking through it one can see what happened a week ago. Cool, isn't it?

Any way, to make a long story short: four days ago a murder happened in the room where this piece of glass is placed. This means that we will know the murderer in three days from now, when the light emerges from the 'slow glass'.

Answer 4

In 2003, Mikhail Lukin, with scientists at Harvard University and the Lebedev Institute in Moscow, succeeded in completely halting light by directing it into a mass of hot rubidium gas, the atoms of which, in Lukin's words, behaved "like tiny mirrors", due to an interference pattern in two "control" beams

See the light slowing experiments section:

http://en.wikipedia.org/wiki/Speed_of_light

Answer 5

Speed of light is 3.0*10^8 m/s, no matter what reference frame you use. You can use the same technique as laser making to make a beam of light.

Answer 6

because of the unique properties of light, the speed of light is the slowest, as well as fastest, because no matter how dense the material that the light beam goes through, its speed is impeded neglibly (like maybe one trillionth of a second at most or something), whether reflected or absorbed

Answer 7

Conglomeration slows light -- your coffee cup is 'made' of light/energy that energy is slowed compare to "free light" :: Therefore in the "heat" of BlackHole the 'density' is so profuse that light may stop!
If it does it disappears from the Universe -- like death,
That's why Black Holes may disappear,an,
"They" do not know why -- now YOU do!

- Desta

Answer 8

Speed of light is one and only the unique number 3 E8 regardless of the frame of reference, velocity of the object emmiting it, wavelength frequency of the light etc....