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 Posted: Tue Nov 04, 2008 1:51 pm Post subject: How do we know the maximum speed of light? |
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How do we know the speed of light in a vacuum if we>ve never been able
to measure it? Please correct me if I>m mistaken.
1) All observable space is saturated with CMBR, i.e. electromagnetic
radiation, which is a form of energy.
2) As asserted by the Mass-Energy Equivalence and the Strong
Equivalence Principle energy and mass produce a gravitational field in
the same way.
3) Light must obey the laws of space-time like all other things, as
such it is affected by gravity. Light travailing over locally-
irregular gravitational fields is refracted, e.g. a gravitational
lens, etc.
Thus we cannot observe the behavior of light in a "vacuum" devoid of
both mass and energy, as would be the case on the fringe of an
expanding. Or did I miss something?
JSD
[[Mod. note -- If you work out the likely magnitude of these effects,
they>re *very* tiny. Any experiment has some level of experimental
error, and if effects like (1), (2), and (3) above are well below that
level, then it>s ok to neglect them. More generally, the "speed of
light in a vacuum" is an *abstraction*; any actual experimental
realisation is going to have experimental limitations and approximations.
What>s important is that we understand and can quantify these limitations
and approximations.
-- jt]] |
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Uncle Al
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| Posted: Wed Nov 05, 2008 7:11 am Post subject: Re: How do we know the maximum speed of light? |
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[quote]How do we know the speed of light in a vacuum if we>ve never been able
to measure it? Please correct me if I>m mistaken.
1) All observable space is saturated with CMBR, i.e. electromagnetic
radiation, which is a form of energy.
2) As asserted by the Mass-Energy Equivalence and the Strong
Equivalence Principle energy and mass produce a gravitational field in
the same way.
3) Light must obey the laws of space-time like all other things, as
such it is affected by gravity. Light travailing over locally-
irregular gravitational fields is refracted, e.g. a gravitational
lens, etc.
Thus we cannot observe the behavior of light in a "vacuum" devoid of
both mass and energy, as would be the case on the fringe of an
expanding. Or did I miss something?
JSD
[[Mod. note -- If you work out the likely magnitude of these effects,
they>re *very* tiny. Any experiment has some level of experimental
error, and if effects like (1), (2), and (3) above are well below that
level, then it>s ok to neglect them. More generally, the "speed of
light in a vacuum" is an *abstraction*; any actual experimental
realisation is going to have experimental limitations and approximations.
What>s important is that we understand and can quantify these limitations
and approximations.
-- jt]]
[/quote]
1) Lightspeed is finite *precisely* because there is stuff in the
vacuum: non-zero permeablity and permitivity of free space; Maxwell>s
equations, Lorentz invariance. The stuff that isn>t there is
measurable as the Casimir effect, Lamb shift (try U(91+) rather than
H(+)), Rabi vacuum oscillations, electron anomalous g-factor....
1) Do you want a faster lightspeed?
http://www.npl.washington.edu/AV/altvw43.html
Scharnhorst effect
http://arXiv.org/abs/gr-qc/0107091
http://arXiv.org/abs/quant-ph/0010055
Phys. Lett. B236 354 (1990)
Phys. Lett. B250 133 (1990)
J Phys A26 2037 (1993)
2) http://arXiv.org/abs/0706.2031
Pookie pookie.
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/lajos.htm#a2 |
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