What makes the speed of light exactly 299,792,458 metres per second?

Question

This may be more of a philosophical question, but I was wondering why the speed of light is what it is. What is it in our universe that makes light travel at this exact speed? Instead of 299,792,458 metres per second, why isn't it 300,000,000 metres per second, or 300,000,001 metres per second?

Is it strange that I find it a bit absurd that there's this mysterious number that defines the maximum speed a massless particle can attain in this universe?

Keep in mind I'm not referring to the number in and of itself (ie unit of measurement). I'm more referring to the reason why light is restricted to this speed rather than being faster or slower than what it currently is.

Answer 1

I guess you are asking why certain fundamental constants in the universe are what they are and nothing else, right? Like 10% larger (independent of units) or a million times smaller?

That is a very good question. And it probably starts with an even more fundamental one: are they really constant?

The answer to the last question is: we don't know and it would be scientifically wrong to assume that they are. The speed of light, Planck's constant etc. are probably just fairly constant in our neck of the woods. We have not much data about what happens to them inside a neutron star or ten nanometers from the event horizon of a black hole. We do not know if they were really the same 10^-13s after the Big Bang.

But we need to find out!

Many physical theories can be reduced pretty much to what they assume axiomatically about the world. Newtonian mechanics, for instance, assumed that there was an absolute time valid in all reference frames. This is more or less equivalent to there being no speed limit in the universe. We now know that neither is true. Special relativity follows in a fairly straight forward way by letting go of that assumption and replacing it with c being the speed limit.

Now imagine that c is not a hard limit. It just happens to be a very flat region of some function that depends on energy or mass or something else. Then what? Obviously the special theory of relativity would be just another approximation to reality, just like Newtonian mechanics.

What does that mean? It means we need to be very careful with counting fundamental constants. Their number totally depends on whether we have the fundamental theory (or a good approximation at it) or not!

There is a famous paper by N. Cahn published in Rev. Mod. Phys.:

The eighteen arbitrary parameters of the standard model in your everyday life, Robert N. Cahn, Vol 68, p. 951

He discusses what would happen to our universe if one changed any one of the eighteen "fundamental" parameters of the standard model of particle physics just a tad (sometimes no more than a percent) and comes to amazing conclusions: the world would look VERY different. Sometimes there would hardly be a world! (If you can, get a copy and try reading it. Much of it is rather straight forward physics and very enjoyable even to the beginner.)

What this kind of intellectual speculation tells us is that we have to be careful with calling things fundamental that in reality might not be. If one applies a better theory to the problem than we have, it might turn out that there are no 18 fundamental parameters but only three. Every other of these parameters would then have a fixed functional dependency of the other ones or they would be nothing but scale dependent coincidences.

Modern physics has a holy grail: it is on the search for the one theory that reproduces the world as we see it and nothing else. The TOE (Theory of Everything) is supposed to have no free parameters at all, or at most one (even that would be too many, actually). Free means that one can't chose units of measurement in such a way that all remaining parameters become unity.

As always with holy grails, they are hard to find but they do attract an awful lot of attention. This one might actually exist, albeit in a form very different from what the current seekers are expecting.

Answer 2

The speed of light is EXACTLY 299,792,458 meters per second because we have used a specific kind of light to define the meter. From a historical perspective, a meter used to be a specific fraction of the distance from the equator to the North Pole, but the intrinsic imprecision of this distance made it impractical for this to remain a standard of length. If you like, you could define a system in which the speed of light is 1.

Answer 3

Everything in our universe is relative.

It seems to me that if you try and investigate the mathematics for this number, you obtain equations that rely on the speed of light! It all ends up being rather circular.

I think the definition involves a certain fraction of red wavelengths emitted by a very stable element...

Why is it that particular number? Well our universe is dictated by a set of physical constants.

http://en.wikipedia.org/wiki/Physical_constant

If any of these numbers were even slightly altered, the universe would be a completely different place and we wouldn't likely exist.

Scary thing is that we aren't so sure if the constants are constant anymore. So speed of light may end up being a wacky random number one day...

Answer 4

Nobody knows why the maximum speed of a photon is what it is. It just IS.

It could be 1.8 Kwarkwurts, if that was a unit that existed. Keep in mind that the units used affect the numbers. If a meter was slightly shorter, then the speed would be exactly 300 million meters per second. But it isn't, so the number we have is what we get.

Answer 5

That is a very interesting question. Of course the speed of light is a constant, c, by observation and is what it is. Common sense tells us that if we install a more powerful engine in a race car it will go faster due to increased energy. However, for light the amount of energy carried by a photon changes its wavelength (and not its speed). For example, UV light has a shorter wavelength than infrared and UV is far more energetic and penetrating and can pass right through a cloud causing a sunburn. X-rays and gamma rays are even shorter and more penetrating passing through bone and lead, respectively. And they all travel at the speed of light. Perhaps you would have to hold the wavelength of a photon constant while increasing its energy level to make it go faster, but no can do.

Answer 6

The speed of light is a phenomenological parameter. That means that, although it is a constant in present physical theory, theories to date do not set its actual value. It must simply be measured. There are many such parameters in the standard particle model. In unitless form, the count is presently 29. If you want to be philosophical about it, this is indicative of present theories being incomplete. The fact that it is incomplete is well known and best demonstrated by the fact that general relativity and quantum mechanics are inconsistent with each other.

Answer 7

It just is. Not a very satisfying answer, I know.

The one that I find more satisfying is this:

c = 1 / square root (permittivity x permeability )

both permittivity and permeability are of 'free space'.

In other words the speed of light - which is an electromagnetic wave - is determined from the basic physical constants that define how electric and magnetic fields work.

I like this - that the speed of electromagnetic waves is just a property determined from the constants that control how its component fields operate.

Of course, this moves the problem from one place to another, but it explains where a *speed* comes from.

Answer 8

As an electromagnetic wave, light is propagated by energy transforming between electric and magnetic fields. It's speed is determined by how quickly these waves are able to propagate. This is why the speed of light is different in a vacuum, and say, water.

Answer 9

well its not very ez to calulate but thats just how long it takes the waves to bounce off of particles in the atmosphere
it is very hard to understand tho

Answer 10

We made it that much when we defined our units of time and distance.