# How do we know the speed of light exists ?

1. Aug 7, 2011

### flyingpig

How do we know the speed of light "exists"?

If we "know" that it can't be reached, how do we know it exists? Like I am looking at this from a math view.

So okay, "infinity" is not a number, it is a concept. It took me about a year of convincing to settle it down.

So is the speed of light the same thing? Not a number, but a concept? How do know this certain number 3 * 10^8 is not possible? Because I am just loooking at this as a number and the book tells me this is impossible.

2. Aug 7, 2011

### romsofia

Re: How do we know the speed of light "exists"?

All light is electromagnetic radiation. It is derived by $${1/\sqrt{\beta_0\epsilon_0}}$$ where $${\beta_0}$$ is the magnetic permitivity in a vacuum and $${\epsilon_0}$$ is the electrical permitivity in a vacuum. This is the direct cause of Maxwell's equations.

Is light like infinity? I don't have that much exposure to the concept of infinity, but I would have to say no. Light is more like a number, than a concept in my opinion.

3. Aug 7, 2011

### SteamKing

Staff Emeritus
Re: How do we know the speed of light "exists"?

Unlike infinity, the speed of light is large but finite and can be measured experimentally.

4. Aug 7, 2011

5. Aug 7, 2011

### Pengwuino

Re: How do we know the speed of light "exists"?

What do you mean how do we know the speed of light exists? We measure it. What exactly is the issue?

You're confusing massive and massless particles. Massless particles (photons) always travel at 'c' and we observe them always traveling at that speed. Massive particles never reach 'c' and we've never observed them reaching 'c'.