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

1. ### Crazy Tosser

175
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. ### lzkelley

277
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. ### Phlogistonian

87
All massless waves (and all massless particles) travel at the speed of light.

4. ### Danger

9,879
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. ### _Mayday_

816
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. ### Lojzek

249
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. ### bassplayer142

422

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

8. ### Phlogistonian

87
The original question was about waves in a vacuum.

9. ### _Mayday_

816
That doesn't make what you said correct.

10. ### Phlogistonian

87
You can think what you want. I won't engage in a pointless argument over semantics.

11. ### Crazy Tosser

175
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. ### ZapperZ

29,757
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. ### rbj

only to within 20%, IIRC.

14. ### Severian596

286
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.