Understanding Gravitational Waves and Their Impact on Entropy

[Denton]

Ok so there are gravitational waves traveling through as constantly, and these waves carry energy. Since they travel through space unabsorbed, does this mean they are undetectable (by direct observation) and that the energy they contain cannot be restored?

Lastly then does this mean gravitational waves contribute to entropy: constantly radiate energy without the possibility to create work from them?

 

[JustinLevy]

Einstein's equations look like they have time reversal symmetry to me. So if something can emit gravitational radiation, then something can indeed absorb it.

There is a lot of indirect evidence for gravitational waves, but they have not yet been directly detected. But if GR is correct, they should be in principle detectable. There are some ground based detectors already built, and a detector (which will split into three parts) will be launched into space soon (hopefully).

If you'd like to read on their detection methods, you can check out wikipedia or the actual project websites. The only acronyms I can think of at the moment are LIGO and LISA.

 

[Naty1]

yes..LIGO and LISA are the current detection efforts..

 

[Vanadium 50]

LISA is a future experiment. VIRGO is probably the one you are thinking of.

 

[Naty1]

I should have mentioned that the difficulty in detecting gravitational waves is that they are very weak; gravity is weak enough; gravity waves weaker still hence very hard to detect. When you read about current experiments you'll note problems isolating detecting masses from vibrations such as passing traffic, Earth tremors,etc.

 

[Denton]

So if something can emit gravitational radiation, then something can indeed absorb it.

Has this been observed? And or how is this possible? Does matter absorb the energy currently or only under certain conditions?

 

[ZikZak]

Has this been observed? And or how is this possible? Does matter absorb the energy currently or only under certain conditions?

No, it has not been observed; that is what LIGO is for. The lack of observation (presumably) has nothing to to with its impossibility, but rather with the fact that gravitational radiation contains undetectably low amounts of energy to begin with.

It is possible because as a gravitational wave passes, the distances between objects change due to the changing curvature of spacetime as the wave passes. As the wave passes a piston, for instance, it compresses the gas inside. As the wave passes the Earth, for instance, it compresses the Earth and generates frictional heat. Voila: work is done. An undetectably teeny amount of work, but work nonetheless.