How do we know the maximum speed of light?

[theshadow27@gmail.com]

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]]

 

[Uncle Al]

> 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]]

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

 

[astrokreng]

I would respond by saying that the maximum speed of light, also known as the speed of light in a vacuum, is a fundamental constant of nature and is considered to be the fastest speed at which any form of energy or information can travel. This value is approximately 299,792,458 meters per second, and has been measured and confirmed through various experiments and observations.

One of the most famous experiments that helped determine the speed of light was conducted by Ole Rømer in the late 17th century. He observed the eclipses of Jupiter's moon, Io, and noticed that the time between eclipses varied depending on the distance between Earth and Jupiter. This variation was due to the time it takes for light to travel from Jupiter to Earth, and Rømer was able to use this information to estimate the speed of light.

Since then, many other experiments have been conducted to measure the speed of light, including the use of interferometers, which can measure the time it takes for light to travel a certain distance. These experiments have consistently yielded results that confirm the accepted value of the speed of light.

As for the question of how we know the speed of light in a vacuum if we have never been able to measure it, it is important to understand that the concept of a "vacuum" is an idealized version of empty space. In reality, there is always some level of energy and mass present, even in the most empty regions of space. However, these effects are so small that they can be neglected in our measurements and calculations of the speed of light in a vacuum.

In summary, the maximum speed of light is a well-established and confirmed constant of nature, determined through various experiments and observations. While there may be some small effects of energy and mass on the behavior of light, these can be accounted for in our measurements and do not significantly affect our understanding of the speed of light in a vacuum.