Gravitational waves

1. Dec 23, 2008

tonyb1969

Gravitational "waves"

First, I confess that I am not a physicist by training; I work for an RF engineering firm. However, I study theoretical and astrophysics from those who have the extensive math background, and attempt to conceptualize their theories. I am not a conspiratist, and I certainly hope never to initiate a crackpot subject. My only purpose is to share ideas that wake me up at night with those who may be able to steer me in the proper direction. Okay, enough of the disclaimer.

If we are hurtling through space at high rates of speed, would not each object be moving through the fabric of spacetime constantly? Wouldn't this result in constant wakes of gravity waves? I picture putting a sphere into a large pool of water and moving it quickly from one end to the other--there would be swirls of wake following it until the water settled again. Would not the same apply to massive objects that curve space in all dimensions (like a sphere in water) moving rapidly through spacetime? When I think of some descriptions of Einstein's vision (a ball on a trampoline, for example), it fails to capture this movement through space, which according to expansion theory, we are.

In short, if our currently accepted view of mass curving spacetime in all dimensions (resulting in the effect we call gravity), should we not expect wakes of gravity waves/disturbances in the fabric of spacetime that we could constantly monitor?

2. Dec 24, 2008

A.T.

Re: Gravitational "waves"

Every object advances trough spacetime, even if at rest in space. And inertial movement is equivalent to rest anyway.
No. GR predicts only that accelerated masses produce gravitational waves. Just like accelerated loaded particles produce EM-waves.
This analogies have little to do, with the model of curved space time in GR. And the expansion doesn't imply that we are moving.
If there where big accelerated masses nearby, would expect to measure such waves.

3. Dec 24, 2008

tonyb1969

Re: Gravitational "waves"

Many thanks, A.T. I will read up on the sections of GR implied by your statements.

4. Dec 24, 2008

Naty1

5. Dec 24, 2008

tonyb1969

Re: Gravitational "waves"

Thanks, Naty1. I will read. Also, A.T., it makes perfect conceptual sense that the space fabric would be expanding equivalient to our space in the universe now that I think of it.

6. Dec 25, 2008

Dmitry67

Re: Gravitational "waves"

I have another question about the waves.

Suppose there are 2 neutron star rotating very close to each other emitting huge amounts of GW and spiralling towards each other. They lose energy, hence, they lose mass too, correct? The energy (and mass?) is carried away by the waves

But GW themselves do not gravitate, as far as I know! So before we had gravitation emiting by like 5 solar masses, after the merge there is only 4.9 solar masses left and 0.1 mass in a form of the gravitational waves.

But that 0.1M does not emit the gravitation!

7. Dec 25, 2008

Vanadium 50

Staff Emeritus
Re: Gravitational "waves"

Yes they do.

8. Dec 25, 2008

Dmitry67

Re: Gravitational "waves"

I read it here:
http://math.ucr.edu/home/baez/physics/Relativity/GR/energy_gr.html

Is it wrong?

9. Dec 25, 2008

Vanadium 50

Staff Emeritus
Re: Gravitational "waves"

I think you're misinterpreting that. The first part has to do with the definition of the tensors in the Einstein field equations, and the second part more or less confirms my point.

Look at it this way - gravitational waves travel along null geodesics, right? A gravitational wave and an electromagnetic wave will travel along the same paths. A mass can gravitational deflect a beam of light, and to conserve momentum, it is (ever so slightly) attracted to that beam of light. Since gravitational radiation follows that same path, the same thing happens to it.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook