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philippeb8
2018-Jan-17, 03:01 AM
I think I already asked this question but I can't recall the answer.

Can gravitational waves be "absorbed" by the Sun before they hit the Earth (or "absorbed" by the Earth itself during the night)?

Grey
2018-Jan-17, 05:45 PM
In principle, yes (or at least attenuated slightly). Gravitational waves interact with any masses they pass by, which scatter them. But because gravity couples so weakly, the scattering is pretty small, even for something massive like the Earth or the Sun.

So in practice, any gravitational waves strong enough for us to detect would be scarcely affected by passing through the Earth or the Sun; we would need much more sensitive measuring equipment to be able to measure the difference in strength.

philippeb8
2018-Jan-17, 06:02 PM
In principle, yes (or at least attenuated slightly). Gravitational waves interact with any masses they pass by, which scatter them. But because gravity couples so weakly, the scattering is pretty small, even for something massive like the Earth or the Sun.

So in practice, any gravitational waves strong enough for us to detect would be scarcely affected by passing through the Earth or the Sun; we would need much more sensitive measuring equipment to be able to measure the difference in strength.

Interesting... does that mean gravity is a particle after all?

Strange
2018-Jan-17, 06:22 PM
Interesting... does that mean gravity is a particle after all?

Why would that imply it is a particle? We would have to see that the absorption was quantised to conclude that. (And as the interaction is too small to be detected, then that isn't practical.)

An article on gravitational lensing of gravitational waves here: https://stuver.blogspot.it/2012/07/the-journey-of-gravitational-wave-ii-gw.html

Grey
2018-Jan-17, 07:03 PM
Interesting... does that mean gravity is a particle after all?It's as strange says. We'd expect that same result whether gravity were mediated by a particle or not. Indeed, the theory that predicts this should happen, general relativity, does not describe gravity as being mediated by gravitons.

philippeb8
2018-Jan-17, 08:10 PM
Why would that imply it is a particle?

Because it acts like a particle and looks like a particle thus it must be a particle.


We would have to see that the absorption was quantised to conclude that. (And as the interaction is too small to be detected, then that isn't practical.)

An article on gravitational lensing of gravitational waves here: https://stuver.blogspot.it/2012/07/the-journey-of-gravitational-wave-ii-gw.html

Interesting... thanks again but I cannot comment on this because my comment will be too close to the ATM domain.

Strange
2018-Jan-17, 09:06 PM
Because it acts like a particle and looks like a particle thus it must be a particle.

It looks more like a wave. There is nothing observably particle-like about it, is there?

philippeb8
2018-Jan-17, 09:42 PM
It looks more like a wave. There is nothing observably particle-like about it, is there?

Well the "shadow" the planet creates if the gravitational wave is absorbed.

Geo Kaplan
2018-Jan-17, 09:47 PM
Well the "shadow" the planet creates if the gravitational wave is absorbed.

Absorption is not specific to particle interactions. Waves can be absorbed, too.

philippeb8
2018-Jan-17, 09:55 PM
Absorption is not specific to particle interactions. Waves can be absorbed, too.

One way or the other it doesn't look like a space-time curvature anymore.

Strange
2018-Jan-17, 10:56 PM
One way or the other it doesn't look like a space-time curvature anymore.

As that is the only theory we have describing gravitational waves, what is the basis of this statement?

philippeb8
2018-Jan-17, 11:10 PM
As that is the only theory we have describing gravitational waves, what is the basis of this statement?

Itís just an observation but this leads to a more important question Iím currently asking permission to ask.


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Hornblower
2018-Jan-17, 11:36 PM
One way or the other it doesn't look like a space-time curvature anymore.

Can you explain what you mean by that remark, in appropriate mathematical detail?

philippeb8
2018-Jan-17, 11:51 PM
Can you explain what you mean by that remark, in appropriate mathematical detail?

Ok Iíll create graphs later.


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Jeff Root
2018-Jan-18, 03:32 AM
One way or the other it doesn't look like a space-time curvature anymore.
Spacetime curvature is precisely what it looks like. Gravitational
waves were predicted by general relativity. They are disturbances
in spacetime. If those waves are predicted to be shadowed by
massive bodies like Earth and the Sun, it is general relativity which
makes that prediction.

-- Jeff, in Minneapolis

philippeb8
2018-Jan-18, 04:07 AM
Can you explain what you mean by that remark, in appropriate mathematical detail?

Let's simplify the problem with the gravity emitted by the Sun.

You can see here the traditional space-time curvature as proposed by Einstein:
22904

And here's the same space-time curvature but since the Earth absorbs gravity then it'll create a "shadow" behind the Earth:
22905

So it doesn't look like an uniformly "curved" space-time anymore. The same idea with gravitational waves.

Jeff Root
2018-Jan-18, 04:15 AM
You are confusing absorption (or diffusion) of gravity with
absorption (or diffusion) of gravitational waves.

-- Jeff, in Minneapolis

philippeb8
2018-Jan-18, 04:17 AM
You are confusing absorption (or diffusion) of gravity with
absorption (or diffusion) of gravitational waves.

Yes but gravitational waves are composed of gravity, no?

cjameshuff
2018-Jan-18, 04:25 AM
Let's simplify the problem with the gravity emitted by the Sun.

You can see here the traditional space-time curvature as proposed by Einstein:
22904

And here's the same space-time curvature but since the Earth absorbs gravity then it'll create a "shadow" behind the Earth:
22905

So it doesn't look like an uniformly "curved" space-time anymore. The same idea with gravitational waves.

Attenuation/scattering of gravitational radiation is not "absorbing gravity". GR does not predict that Earth would "absorb gravity", and there are no observations that indicate that it would.

philippeb8
2018-Jan-18, 04:29 AM
Attenuation/scattering of gravitational radiation is not "absorbing gravity". GR does not predict that Earth would "absorb gravity", and there are no observations that indicate that it would.

Ok thanks.

Jeff Root
2018-Jan-18, 04:38 AM
Gravitational waves are rapid but very, very, very tiny variations
in gravity. The variations might be slightly attenuated/diffused/
scattered/absorbed, but the gravity itself isn't.

-- Jeff, in Minneapolis