5 replies to this topic

[rwoodin]

It is accepted that the speed of light in vacuum is 299 792 458 meters / second.

What is the reason for this?

What causes light, or any electromagnetic radiation, to propogate at exactly this speed through a vacuum ?

I know that all observers in all reference frames always measure light propogating at the same speed. That is not what I'm questioning.

Exactly what physical properties constrain electromagnetic radiation in a vacuum to propogate at exactly 299 792 458 meters / second and not any faster or any slower ?

I know that light passing through different media is refracted, or slowed down. That is not my question either.

Why is the speed of light in vacuum precisely the speed that it is ?

Thanks in advance for any information provided.

[chubtoad]

It is accepted that the speed of light in vacuum is 299 792 458 meters / second.

What is the reason for this?

What causes light, or any electromagnetic radiation, to propogate at exactly this speed through a vacuum ?

The reason why it is exactly that number is that the speed of light is used to define the meter. That is a meter is how far light travels in 1/ 2.99...58 seconds. A second in turned is defined in terms of something with cesium atoms (I don't know the details). Now there are these so called fundamental constants which you get from dividing two dimensional quantities like the mass of some type of quark bythe plank mass to get a dimensionless number. And nobody knows why these have the values they do. Perhaps they will fall out of a more universal theory or if you like the anthropic ideas in physics perhaps there are many universes all having different values for the fundamental constants but in the universes where the constant that dictates the strength of gravity is too weak we don't get the attraction needed to develop stars and hence life to observe the physical constants. At least that is what I have gotten out of the popular science books. Hopefully someone else can give you a better answer (alex?).

[JohnDoe1234]

Hey, yeah... it looks like chubtoad explained it pretty well.

Basically, whatever we use to define a basic unit will look (mathematically) very clean-cut since we slapped a nice label on a weird value, and then other things you measure with this nice little label will seem obscure and random... we don't really understand why light travels that fast, but if we were to use another number and unit system we could say that light travels at 1 Wiggle.... [glasses]

But if we go deeper and further past the superficial number/base system.... we really have no clue why light travels at the speed it does.

[rwoodin]

Right. I'm aware that the speed of light is a fundamental constant and that the spatial length of a meter and the temporal length of a second depends upon it and not the other way around. I'm asking why the speed of light has the value it does. Like the speed of a wave in water, the speed of sound (waves) in air, the speed of sesmic waves through the earth, etc. etc. It would seem that there should be a reason for light to have the speed that it does in vacuum. Maybe the amount of force being applied against the resistance that a vacuum presents to that force ? I don't know. That's why I'm asking. It just seems that there should be an underlying, physical cause for the speed to be what it is. I appreciate the answers so far. I guess I enjoy thinking about questions that seem simple that nobody seems to have answers to. Posting the questions is a way for me to think out loud and get some feedback about those thoughts.

[bgwowk]

The speed of light is equal to the inverse square root of the product of the magnetic permeability (mu) and electric permittivity (epsilon) of a medium. This is a consequence of Maxwell's equations. So mu and epsilon (mu0 and epsilon0 in free space), which respectively determine how much magnetic field is generated by a given current and how much electric field is generated by a given charge, can be thought of as the "elasticity" parameters that determine the speed of light.

[rwoodin]

Now that, bgwowk, is an answer. Thank You !