h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I came across this in a SF book recently. In the story, it is discovered that the speed of light has inexplicably changed by 5%. This, according to the plot characters, fundamentally changes the physical world. For one thing, the Plancke<?> constant is changed.

Can someone explain:

a) The Plancke constant
b) How the speed of light affects this, and
c) What physical changes would we see in our environment after a 5% change to the speed of light.

The Planck (no e) Constant is 6.6exp-34Js. It's derived from quantum mechanics, which states that an electron (or other similar particles) can only exist at fixed energy levels. You would know them as electronic orbits or shells. The Planck constant assists one in calculating the exact energy of the electron as opposed to an arbitrary quantum number.

The speed of light would affect this, because photons also have fixed (quantized) energy levels. Therefore, if light is slower, the photons have less energy and Planck's constant is smaller.

What physical changes would we see? None, because we need the light to see with.

B

Planck's constant also determines (roughly) the size/length scale at which you have to use quantum mechanics. A lower value of Planck's constant means a smaller size scale, meaning that newtonian mechanics would work OK to smaller distances than it currently does. So maybe the whole development of quantum mechanics would have been delayed, because it's effects wouldn't have been observed (historically) when they were.

Traveller in Time not certan about the speed of light
"I think we would not notice any change in the speed of light. It is embedded in the basics of our existance, changing the speed of light will probably affect the length of a meter as well or change our clock speed to get the light to travel the same distance over an equally changed time. "

E = h x f

E = energy
h = Planck's constant
f = frequency of the wave

Ooh, memories of last year's AS-level Physics are coming flooding back .

I would have thought that if the speed of light changes so many things twould be affected it would create a world where every thing is basicly the same just numbers are sligtly different. For example gravitaioal exceleration at the surface of the earth may go from 9.98m/s^2 to 9.95 but would strill dreease with distance proportional to the square of the distance. Our own perseptions would also be altered in a compensatory manor.

Problem is if gravity was changed it would change the way stars are created. We might never have stars being created, and so never any life.
There is some research which indicate the speed of light might not have been constant, but that is rather cutting edge stuff.

I think stars would still form, they'd just need to be more massive for nucear fusion to begin.

Apparently not. The fact that the constant of nature seem to be "just right" is the basis of the anthropoc principle, the idea that the universe must have been designed by an intelligence specifically to support life.

The anthropic principle has nothing to do with intelligent designers, it merely proposes that the universe is the way it is because if it wasn't we wouldn't be around to observe it. There may be many universes, but only this one can contain people.

There is reason to believe that the speed of light may have been different in the past, but this clearly didn't prevent stars from forming.

No, I would say those are just other explanations than the anthropic principle.

Here´s a little article from New Scientist with some examples:

http://www.newscientist.com/article.ns?id=dn6092