"Speed of Light"

Bullgrit · Feb 3, 2014

In reading some stuff recently because of ideas from a couple other science threads here, I just learned something that surprises me and explains a lot.

The "speed of light" -- 186,000 miles per second -- is not the physics law I always thought it was. It's not the "speed of light" that is the limit, it is the 186,000 mps that is the limit. That is, the ultimate speed is not limited to the speed of light, but rather the speed of light is limited to the ultimate speed.

I'd always thought it was the properties of light that limited speed, but it's the speed that limits light and everything else. I was always told, "Nothing can travel faster than light." But actually it's, "Nothing can travel faster than 186,000 mps." This limits light, as well as other things. It could be called the "speed of gravity" just as accurately.

This may be an obvious concept to some, but it actually puts things into more clear understanding to me to know that the speed limit is the reverse of what I thought for all these years. Calling it the speed of light put more emphasis on light than the physics speed law should have.

Am I understanding the ~~speed of light~~ ultimate speed correctly, now?

Bullgrit

Morrus · Feb 3, 2014

Yes. Light moves at the speed it does because that's the fastest anything can move. Other things move at that speed, too - radio waves, the whole EM spectrum, lots of stuff.

The speed of light's a bit of a misnomer - light moves at various speeds, up to the universal speed limit. In different mediums, it slows down. In a vacuum, though, light moves at c.

Dioltach · Feb 3, 2014

So perhaps it should be called the "universal speed limit"? That might encourage some people to break it.
(I agree with you, by the way: it's an interesting factoid that completely changes the way I look at the issue.)

Morrus · Feb 3, 2014

Dioltach said:
So perhaps it should be called the "universal speed limit"?

It often is!

Although technically its name is "c".

Dungeoneer · Feb 3, 2014

Dioltach said:
So perhaps it should be called the "universal speed limit"? That might encourage some people to break it.
(I agree with you, by the way: it's an interesting factoid that completely changes the way I look at the issue.)

While that phrase does give a better idea of what 'the speed of light' means then the original phrase, it's not strictly accurate. IANAPhysicst, but my understanding is that there are some known exceptions to the 'speed limit' such as when particles engage in quantum tunneling, and we hope to find more.

'The speed of electromagnetic radiation in a vacuum' is more accurate, although admittedly not as catchy.

Umbran · Feb 3, 2014

Bullgrit said:
In reading some stuff recently because of ideas from a couple other science threads here, I just learned something that surprises me and explains a lot.

The "speed of light" -- 186,000 miles per second -- is not the physics law I always thought it was. It's not the "speed of light" that is the limit, it is the 186,000 mps that is the limit. That is, the ultimate speed is not limited to the speed of light, but rather the speed of light is limited to the ultimate speed.

Technically, it is the speed of any and all massless things in a vacuum - they cannot move more slowly. And all things with mass must move more slowly.

At the time the limit was discovered, the only massless particle known was the photon. We've expanded the known massless particles to be all the gauge bosons (so, the photon and the gluon, the latter of which we cannot observe directly, but whose action we can verify indirectly). The graviton is theoretical, but gravity's action in quantum has not been observed by experiment - so they may not exist.

So, in terms of things humans see, "speed of light" is still pretty accurate.

tomBitonti · Feb 3, 2014

More precisely, "c" is "the speed of light in a vacuum", not "the speed of light".

Thx!

TomB

Morrus · Feb 3, 2014

Morrus said:
In a vacuum, though, light moves at c.

Dungeoneer said:
'The speed of electromagnetic radiation in a vacuum' is more accurate

Umbran said:
Technically, it is the speed of any and all massless things in a vacuum

tomBitonti said:
More precisely, "c" is "the speed of light in a vacuum", not "the speed of light".

Has anybody mentioned that c is the speed of light in a vacuum yet? If not, maybe I should mention it!

Kramodlog · Feb 3, 2014

I'm pretty sure c is a grade some people get in physics class.

tomBitonti · Feb 3, 2014

Morrus said:
Has anybody mentioned that c is the speed of light in a vacuum yet? If not, maybe I should mention it!

Wait, as in, speed, and in, like, a vacuum?

I wrote a little more: The focus is on precision: Writing just "the speed of light" is imprecise, leading to issues such as in the original post. One issue of interest (to me) is the consequence of the lack of precision. Or, when is the extra precision (as seems to be in this case), necessary.

Thx!

TomB