Subluminal

No shame !

That’s what Nature said to those Prometheuses who wanted to steal the neutrinos from the realm of light (via).

No shame, because they put themselves at risk, claiming that the centenary rule that nothing can go faster than light might not be so unbreakable, while keeping their calm at all time.

The best is their allegations re-opened the debate on what the speed of light really is the limit of.

Even though I’m not a specialist in special relativity, I was pleased to hear the crazy theories like this one :

The speed of light is like a barrier. You cannot cross it, but you can be already on the other side, where the neutrinos might be.

Photons are exactly on the wall : they cannot go any slower or faster.

(as heard on the radio).

I liked this picture because it relates to two (mis?)conception that I have.

First, to try to understand why sped of light is unattainable, I imagine myself at a certain speed.

Then I accelerate.

But contrary to acceleration at low speed, accelerating when you are close to the speed of light is different : the space itself distorts, so that you cannot reach what you wanted to reach in a certain amount of time, no matter how “fast” you go.

This old school relativistic simulation illustrates this :

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The second image I want to share is that matter is somewhat made of frozen energy : fast photons, when trapped by atoms get stuck in the form of a change in molecular orbital. When they stop speeding, they fall from the wall. Question : what happen if they fall on the other side of the wall (“dark matter!” – ok, thank you, goodbye).

Well, that’s enough philosophy.

Everyday faster-than-light experiments

There are actually many phenomena that lead to faster-than-light (FTL) speeds.

Like for perpetual motion, there’s always a trick.

The first phenomon involving FTL speeds is the Čerenkov radiation, which is responsible for the blue glow in nuclear reactor pools.

It is very similar to the sonic boom : it is due to the interaction of fast electrons (the plane) that pass through water (air) at speed greater than the speed of light in this medium. The blue glow a result of the “perturbation wake” of the electron.

It is not a real FTL phenomenon in the sense that the speed limit holds for light in vacuum ‘c’: you cannot make an electron go faster than ‘c’.

The second experiment is a bit more “everyday”. Take a laser pointer, point it at the moon and now rotate your arm in circle.

What is the speed of the spot at the surface of the moon?

The moon is approximately 400,000km away, meaning that the arc explored by the spot at is 2 pi x 400,000 ~ 2,500,000 km.

If you rotate your arm at 10rpm, the spot travels at ~410,000km/s, which is greater than the speed of light!

But it is a virtual speed. The photon themselves don’t change their speed : you don’t give them a sort of “lateral” speed. And that’s the trick.

Another apparently FTL phenomenon is total internal reflexion.

At the interface, the apparent speed of the crest of the electromagnetic wave appars to be FTL.

To get a more familiar picture, you can imagine a set of waves that do not travel parallel to the shore. If the speed of waves in water is constant and limited, the speed of the crests due to waves hitting the shore is greater than the actual speed of the wave, since they are related through an inverse cosine. But again, it is an apparent speed.

What is interesting in the latter case is that if you provoke a frustrated internal reflexion, the transit time of tunnelled light is unknown, what leads some to declare that in this case, light can travel faster-than-light.

But to me, there are two argument against the case :

• when you create a total internal reflexion condition, you need a high index-medium, in which the speed of light is (by definition) lower than in vaccum. It is not so hard to believe that you can speed up that c/n speed a little bit
• Frustrated internal reflexion tends to suppress higher frequency components (because the evanescent-wave skin-depth is proportional to the wavelength). And information is carried by these higher frequency components.

The last argument is important… for information is an non-analycity in a signal, which relates to higer frequencies

[To be continued…]