On 3/30/2011 11:50 AM, Jim Lux wrote:
Szczepan Bialek wrote:
"Jim Lux" napisal w wiadomosci
...
Szczepan Bialek wrote:
Speed of waves in a dispersive medium is temperature dependent.
Maybe.. depends on the medium, I should think, and the mechanism of
the dispersion. Some dispersion might be due to ionization (which may
or may not be temperature dependent).

It is known that the speed of light in air is temperature dependent (
mirage and E. Schmidt's method in Fluid dynamics).
in vacuum also. But I culd find the results.
In the Solar System the temperatures are decreasing with the
distance from the Sun.

Temperature in a vacuum and with ionized particles is tricky to define.
It has to do with mean free path and the velocity of the particles.
When the number density gets down in the "few atoms per cubic meter"
and the mean free path gets to be meters or km, I think you need to
start thinking in different ways.


(snip)


Again, I'm not sure "temperature" is the relevant measure for something
like that. You can define temperature for a very low pressure gas like
this, but it's not in the same sort of sense as one would apply to a
bulk tangible medium (like air at the Earth's surface or water)

Isaac Asimov touched on this in his book on physics. He said the
temperature up there is high because of the high molecule velocity, but
that *heat* is another matter. So, you can have a high "temperature"
even if the "heat" is practically nil.

That makes you correct. One must carefully state what is meant by
temperature and what is meant by heat.