# Gravity and sound waves

1. Feb 21, 2016

### jerromyjon

I'm curious if there is any relation between sound waves and gravity waves. I don't mean as an analogy. I mean can the speed of sound in matter be derived from the energy of gravity waves.

2. Feb 21, 2016

### Staff: Mentor

No, not at all.

3. Feb 21, 2016

### DaveC426913

Unrelated to the OP's question - one of the pop sound-bites going around is that of the LIGO signal from the merging BHs played as sound.

These particular gravitational waves have a frequency in the audible range of hearing. It's the bloip! at the end of this recording:
https://www.ligo.caltech.edu/video/ligo20160211v2

4. Feb 21, 2016

### jerromyjon

That means technically that the waves create that sound in all matter it passes through. The LIGO equipment is really just amplifying it.

5. Feb 21, 2016

### Staff: Mentor

They do create oscillations, but those are not sound-like.

6. Feb 21, 2016

### jerromyjon

...in magnitude.

7. Feb 21, 2016

### Orodruin

Staff Emeritus
There is a difference between gravity waves and gravitational waves.

8. Feb 21, 2016

### Staff: Mentor

Oh, good point. As this thread is in the relativity forum, I read it as gravitational waves. Gravity waves (e.g. waves on a water surface) do have a lot in common with sound waves.

9. Feb 21, 2016

### jerromyjon

Looking at it from the center out I imagine anywhere near this event we detected the gravitational waves would rip everything to shreds. I figure there is a distance boundary where humans could place themselves away from this event and feel the "bloip" pass through your body like a loudspeaker at a concert... would you also hear it exactly like a sound? The obvious difference being you'd see it the same time you'd hear it, and I'm thinking you'd feel it much more strongly and it would sound soft.

Last edited: Feb 21, 2016
10. Feb 21, 2016

### DaveC426913

OK, it would seem you really did mean gravitational waves.

Last edited: Feb 21, 2016
11. Feb 21, 2016

### DaveC426913

There are quite few discussions going on here, and on other fora, as well as in some news articles about exactly that. I was surprised to learn that you have to be quite close to experience much of an effect. Some estimates are 'closer than 10,000km', whereas others are 'near or within the event horizon itself' where you would feel a spacetime distortion of 'more than a millimetre or two'.

We are talking here only about the impact of gravitational waves - ignoring the apocalyptic-level EM radiation inevitably experienced by proximity to a BH merge.

12. Feb 21, 2016

### jerromyjon

Yeah, I could hear it just before my ears would melt off my head! I guess there are more than just gravitational waves to count for 3 suns worth of mass being lost?

13. Feb 21, 2016

### jerromyjon

But nothing "except" gravitational waves escapes from what I keep reading... even the ringdown is the out of equilibrium mass settling internally.

14. Feb 21, 2016

### jerromyjon

Ah, but perhaps that's the ticket after all. Instead of bead on a string I'm thinking bead on a wire...

15. Feb 21, 2016

### DaveC426913

Well, in an ideal setup, sure - like in a large volume of hard vacuum, with no accretion disc and no infalling dust or gas.

16. Feb 21, 2016

### jerromyjon

But if you were in a field of dust wouldn't it glow as the waves pass?

17. Feb 21, 2016

### DaveC426913

Perhaps I misunderstood what you were asking.

I thought what you were saying was 'in a black hole merge, the only thing that would be emitted is gravitational waves - no EMR'. And I'm saying that would only be the case in an ideal setup, where there is no accreted matter outside the EH. In reality, the merge would presumably result in a large emission of EMR from the matter disc.

18. Feb 21, 2016

### DaveC426913

I don't know what this means.

19. Feb 21, 2016

### jerromyjon

The bead on the string is the thought about how a sticky bead on a string could displace gravitational wave energy in the form of heat energy into matter through friction, confirming the validity of the presumption that 3 suns worth of mass/energy was expelled in a very brief period. Just saying the inverse square law thing still has to get me quite a distance away before a very small fraction of the suns magnitude worth of energy passes through the space I'm taking up as it passes quickly imparting a small amount of energy into everything the waves passes which offers resistance (matter) but travels freely in vacuum.