OK, we know the speed of light in a vacuum is a constant. We've measured what it is. We speculate that this value might have changed over the lifetime of the universe. But what is the property of the universe which would cause the speed of light to change and why does it currently have the particular value of 299,792,458 metres per second. Can anyone derive this via some means other than simply working it out from measurement? I am curious.
2006-06-20 10:25:39 · 16 answers · asked by siliconglen 2 in Science & Mathematics ➔ Physics
It is a failing of the current theories of physics that the values of the key fundamental constants - of which c is one - cannot be derived but have to be measured and inserted into the equations. In other words, no-one knows what determines the speed of light.
It is true that the permittivity and permeability of free space are related to the speed of light, but the relationship is the other way around - they are what they are because the speed of light is what it is.
There have been two sources of thoughts that the speed of light may vary over time. One is theoretical, because it may help the sums work better when describing the early universe (i.e. moment after the big bang).
The other is experimental, and is controversial as it has not been independently confirmed (see link). This involves looking at light from galaxies so far away the light took billions of years to reach us - ie we are looking back to the early universe. But the measurements show a change in the fine structure constant, and not c directly, so there could be other sources of the discrepancies if the measurements are correct.
2006-06-20 19:31:09 · answer #1 · answered by Epidavros 4 · 8⤊ 0⤋
it's a fundamental property of the universe. There's no real derivation of it, no more than you can explain why gravity exists or why opposite charges attract. You can DESCRIBE these phenomena in a thousand ways, but they are cuz they are.
As for why the speed of light has changed, I would imagine it's a property relative to the size of the universe. i.e. when the universe was smaller, light travelled slower... or perhaps the speed appears to have been higher simply because space-time was more compact.
But yeah, I believe that's in the realm of science where all we have the power to do is observe, and not explain.
2006-06-20 10:36:20 · answer #2 · answered by Firstd1mension 5 · 0⤊ 0⤋
It's like Absolute Zero temperature. It can be quantified but it remains a constant and nothing can be colder than absolute zero. Likewise, the speed of light can be quantified and is a constant and nothing can exceed the speed of light. Whether the speed of light varies doesn't matter because it is only an approximation or average, anyway. What I do not understand is how Einstein came up with squaring the speed of light? If you're using a constant in an equation, how can it be squared? Or is he stating the product of an atomic mass times the speed of light is squared?
2006-06-20 11:03:17 · answer #3 · answered by wefields@swbell.net 3 · 0⤊ 0⤋
The speed of light changed over the course of history because of the change in temperature. When the Big Bang occured, the universe was very, very hot and dense. The hot temperature allowed particles even photons to travel faster in short period of time. Also, the hot temperature allowed new particles to be born out of MACHO's and SUSY's more frequently. So my conclusion is that the hot temperature and richness of particles in the universe somehow affected the speed of light.
2006-06-20 10:52:54 · answer #4 · answered by Nico 3 · 0⤊ 0⤋
Light is an electromagnetic wave. It is composed of an electric and a magnetic field perpendicular to each other and each one oscillating in a sine wave form. Its speed depends on the characteristics of the medium through which it propagates. You can actually calculate (predict) what its speed is by using a set of equations called Maxwell's Equations. You would have to take a course in Electromagnetic Theory to get to derive and understand these equations.
2006-06-20 14:42:57 · answer #5 · answered by Pavi 2 · 0⤊ 0⤋
The speed of light is an empirical measurement and i am certain that its value cannot be derived theoretically without first assuming some values that we know to be true
2006-06-20 10:39:49 · answer #6 · answered by Aaron G 2 · 0⤊ 0⤋
We are the humans, but sorry, it's God who makes the rules.
See the reference for a fascinating speculation on how the speed of light may have changed around the Planck epoch, and how that variation could explain a lot of nagging problems of cosmology.
2006-06-20 11:20:35 · answer #7 · answered by Frank N 7 · 0⤊ 1⤋
This is one of the problems some scientists find with Alberts theories. As of yet we cannot prove exactly what the speed of light is or if it is constant throughout the whole universe.
2006-06-20 10:30:17 · answer #8 · answered by johngrobmyer 5 · 0⤊ 0⤋
Interesting thought experiment and since the observer and adjacent beam of light are in the same reference frame it would appear the same as as an observer and adjacent beam of light when the observer is walking down a country road.
2016-05-20 06:09:16 · answer #9 · answered by Anonymous · 0⤊ 0⤋
According to Maxwell's theory of electromagnetism, the speed of light in a vaccum comes from c = 1/sqrt(u_o*e_o).
u_o = permeability of free space
e_o = permittivity of free space
When we measure this speed using experiments we verify that this is true.
2006-06-20 11:08:44 · answer #10 · answered by Alfonzo J 1 · 0⤊ 0⤋