Speed of light? [was Re: GPL vs BSD Licence]

[Marc Ramirez]

On Tuesday 02 November 2004 01:21 pm, Mark Murray wrote:
> Marc Ramirez writes:
> > > IANAPhysicist but, isn't the speed of light in a vacuum constant? Well,
> > > it may be being actively debated by cosmologists attempting to explain
> > > the origins of the universe; but, VSL aside... the speed of light is
> > > 2.998something x10^8 m/s in vacuum.
> > >
> > > Sorry, but this is chat, and I figured I ask.
> >
> > Yes, it is a fixed speed in a vacuum; it gets redshifted in a
> > graviational field.

Again, I will preface by saying I am a professional doofus and amateur 
windbag.

> Not quite. The Speed Of Light in a Vacuum Constant is constant in all
> inertial frames of reference, and is exactly 299792458 m/s. In other media
> (air, water etc, it may be slower than this. It is never faster.

True.  More precisely, the slowing of light within materials can be derived 
from first principles by assuming a fixed SoL, c, and factoring in the time 
involved in absorption/re-emission of photons by the molecules.

> If the originator of the light is moving away from you, atomic spectra in
> the light are shifted towards the red end of the spectrum ("redshift"). If
> the originator of the light is moving towards you, atomic spectra are
> blueshifted. This is called the Doppler shift.

All true.

> Gravity may bend light beams.

More precisely, gravity is what we call the curvature of spacetime.  Light 
always heads in the straighest possible line, but in a curved spacetime...  
Also, if light is emitted in an area of lower potential and is absorbed in an 
area of higher potential (e.g., from Sun to Earth) it will be redshifted. 
Other way around, it will be blueshifted. If you are using the frequency of 
light as a clock (and you basically have no other choice), you will notice 
this effect as "time moving more slowly around massive bodies."

Marc.

-- 
Marc Ramirez
Blue Circle Software Corporation
513-688-1070 (main)
513-382-1270 (direct)
http://www.bluecirclesoft.com
http://www.mrami.com (personal)
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