OT: Speed of light [was Re: Why not a Python compiler?]

greg greg at cosc.canterbury.ac.nz
Mon Feb 11 07:54:30 CET 2008

Gabriel Genellina wrote:

> Before the famous Michelson-Morley experiment (end of s. XIX), some  
> physicists would have said "light propagates over ether, some kind of  
> matter that fills the whole space but has no measurable mass", but the  
> experiment failed to show any evidence of it existence.

Not just that, but it showed there was something seriously weird
about space and time -- how can light travel at the same speed
relative to *everyone*? Einstein eventually figured it out.

In hindsight, Maxwell's equations had been shouting "Relativity!"
at them all along, but nobody had seen it.

> previous experiments showed 
> that  light was not made of particles either.

Except that the photoelectric effect showed that it *is* made
of particles. Isn't the universe fun?

> Until DeBroglie formulated 
> its  hypothesis of dual nature of matter (and light): wave and particle 
> at the  same time.

Really it's neither waves nor particles, but something else for
which there isn't a good word in everyday English. Physicists
seem to have got around that by redefining the word "particle"
to mean that new thing.

So to get back to the original topic, it doesn't really matter
whether you talk about light travelling or propagating. Take
your pick.


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