# Does light speed apply to all waves traveling in vacuum?

1. Apr 23, 2008

### Crazy Tosser

Seriosly, waves have different frequencies, and light is somewhere in the middle of the EM spectrum, then maybe the right or left side could travel faster than c

2. Apr 23, 2008

### lzkelley

Light is generally the term used to refer to electromagnetc waves in the visual spectrum (but its really the same as other E&M waves, just at different energies).
They all behave generally the same, i.e. all E&M waves travel at the speed of light.

3. Apr 23, 2008

### Phlogistonian

All massless waves (and all massless particles) travel at the speed of light.

4. Apr 23, 2008

### Danger

That includes gravity, by the way.
I think that in one regard, you can say that not all waves travel at c in vacuum, but I'm not sure if my reasoning applies. It seems to me that the matter waves associated with a particle can't do so, since the particle itself can't.

5. Apr 24, 2008

### _Mayday_

CT, all EM waves travel at the same speed in a vacuum. As far as I am aware this is not the case when dealing with a medium in which the waves are travelling slower.

If by speed of light you mean around $3\times10^8$ then I can't see how that is correct.

6. Apr 24, 2008

### Lojzek

The phase velocity of a wave is a product of the frequency and wavelength:

L*f=v

The electromagnetic wave equation has solutions with different frequences, but the wavelength must be inversely proportional to the frequency, so the product is always the same:

L*f=c

7. Apr 24, 2008

### bassplayer142

Has it been experimentally proven that gravity waves travel at the speed of light.

8. Apr 24, 2008

### Phlogistonian

The original question was about waves in a vacuum.

9. Apr 24, 2008

### _Mayday_

That doesn't make what you said correct.

10. Apr 24, 2008

### Phlogistonian

You can think what you want. I won't engage in a pointless argument over semantics.

11. Apr 24, 2008

### Crazy Tosser

Well, how about traveling slower than the speed of light? If you are in a car that's goin at 100mph and you light a flashlight backwards, does the light travel at c-(100mph)?

12. Apr 24, 2008

### ZapperZ

Staff Emeritus

http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/einvel.html

The speed of light is constant in all inertial frames, no matter the speed of the source.

Zz.

13. Apr 24, 2008

### rbj

only to within 20%, IIRC.

14. Apr 24, 2008

### Severian596

Excellent question, CT, and the answer is very important (ZapperZ already mentioned it). Make sure to keep reading every text you can get your hands on, because we've all asked this question at one time or another; if you can accept the true answer it will blow your mind.