# Cycling faster than light

Hi,
so while I was learning some optics, I bumped into this page that talked about refractive index which I was just studying. I wondered what is the highest refractive index ever found and there it was, not in number though I think we can calculate it.

### Refractive index

Since you probably have not read my post about refractive index or you have not heard about it, it is dimensionless value that shows how much is light (electromagnetic radiation) slow in the medium where it travels and also how much it will change its direction when traveling through one medium into the other. You can calculate the index like this:

n=c/v

Where n is the refractive index, c is speed of light in vacuum and v is the velocity in the medium you are talking about. From this, it is easy to see that vacuum and only vacuum has the refractive index exactly 1 because there is nothing that blocks its way and you just divide speed of light in vacuum by speed of light in vacuum.

So as the index of refraction increases the only thing that can change is velocity in the medium and it is decreasing.

I found that scientists were able to create stuff in which the light was traveling in “only” 17 meters per second! This is 61.2 kilometers per hour. From steep hill or if you are really good cyclist you can be faster than that, though I think it is bit more easier and safer to do it in car.

So what is the refractive index of this miraclous stuff? Roughly 17,647,059. While normally n lies somewhere between 1 to 3.

What is this thing made of?

… gas of sodium atoms – a high-tech version of the insides of the bulbs of street lamps – cooled to within a fraction of a degree above absolute zero … the effect of cooling reduces thermal effects, and this in itself contributes to the retardation of light.

There is also special state of matter created that packs those atoms closer together.

Dragallur

## 11 thoughts on “Cycling faster than light”

1. Pretty cool. Never knew n goes up that high.

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• That is a good question. Though I have not find so much more about this particular experiment I would guess no, not yet. First of all it must have been very expensive and it was probably even used only on tiny area.

There is some usage to high index material but here when I am talking about “high” index it is somewhere around 2 though again, it depends on the material, sometimes 2 is very good for something that is normally around 1.2 or so (I am just guessing to give an example, probably you can imagine it).

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• I’ve heard of special glass recipes that get up to n = 4 or 5. The ones in your post in the > 10,000 range are off my mental chart. 🙂

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• It is indead quite insane when you compare it to normal every day refraction.

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2. Several years ago we visited the Corning Museum of Glass … which had a series of wonderful demonstrations.

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