Why is Light So Fast?

[n2doc]

Light travels at around 300,000 km per second. Why not faster? Why not slower? A new theory inches us closer to an answer

by Sidney Perkowitz

If you visit the Paris Observatory on the left bank of the Seine, you’ll see a plaque on its wall announcing that the speed of light was first measured there in 1676. The odd thing is, this result came about unintentionally. Ole Rømer, a Dane who was working as an assistant to the Italian astronomer Giovanni Domenico Cassini, was trying to account for certain discrepancies in eclipses of one of the moons of Jupiter. Rømer and Cassini discussed the possibility that light has a finite speed (it had typically been thought to move instantaneously). Eventually, following some rough calculations, Rømer concluded that light rays must take 10 or 11 minutes to cross a distance ‘equal to the half-diameter of the terrestrial orbit’.

Cassini himself had had second thoughts about the whole idea. He argued that if finite speed was the problem, and light really did take time to get around, the same delay ought to be visible in measurements of Jupiter’s other moons – and it wasn’t. The ensuing controversy came to an end only in 1728, when the English astronomer James Bradley found an alternative way to take the measurement. And as many subsequent experiments have confirmed, the estimate that came out of Rømer’s original observations was about 25 per cent off. We have now fixed the speed of light in a vacuum at exactly 299,792.458 kilometres per second.

Why this particular speed and not something else? Or, to put it another way, where does the speed of light come from?

Electromagnetic theory gave a first crucial insight 150 years ago. The Scottish physicist James Clerk Maxwell showed that when electric and magnetic fields change in time, they interact to produce a travelling electromagnetic wave. Maxwell calculated the speed of the wave from his equations and found it to be exactly the known speed of light. This strongly suggested that light was an electromagnetic wave – as was soon definitively confirmed.

more

http://aeon.co/magazine/science/the-universal-constants-that-drive-physicists-mad/

[leveymg]

1. Why does light and electromagnetic waves of all frequencies, short & long, travel at the same rate?

[bananas]

7. Only in a vacuum, where there is no medium.

In air, water, glass, etc, different frequencies have different velocities.

edit to add: only in a vacuum in a flat space-time region:
http://en.wikipedia.org/wiki/Variable_speed_of_light

[xocet]

2. Here are links to the two papers mentioned in the article...

Light Dawns
by Sidney Perkowitz

...

In 2010, the physicist Gerd Leuchs and colleagues at the Max Planck Institute for the Science of Light in Germany did just that. They used virtual pairs in the quantum vacuum to calculate the electric constant Ɛ0. Their greatly simplified approach yielded a value within a factor of 10 of the correct value used by Maxwell – an encouraging sign! This inspired Marcel Urban and colleagues at the University of Paris-Sud to calculate c from the electromagnetic properties of the quantum vacuum. In 2013, they reported that their approach gave the correct numerical value.

...

http://aeon.co/magazine/science/the-universal-constants-that-drive-physicists-mad/

The papers are here:

Leuchs et al:

http://link.springer.com/article/10.1140/epjd/e2013-30577-8

Urban et al:

http://link.springer.com/article/10.1140/epjd/e2013-30578-7
viewable at: http://arxiv.org/abs/1302.6165

[TeddyR]

3. Training?

[BlueJazz]

4. !!

**SNORT**

[Flying Squirrel]

6. And genetics

Or Genesistics?

[gvstn]

5. Fascinating!

Really interesting idea to ponder. And thanks to xocet for the other links which I will read later.