I Why Don't We Detect Gravitational Shadows?

[Mr J]

If gravity is effected by "wave particles", per Einstein's theory and now confirmed by recent observations, why do we not detect 'interference' - gravitational 'shadows' - or do we?

Consider that with light waves, a photon once it hits a detector, nothing behind the detector registers the photon. This is the very basic idea of a shadow. Also, each time a light source emits a photon, it loses energy.

So - if gravity is also transferred by a wave particle (a graviton), why do we not witness "gravitational shadows"? For example, if I stand on a huge lead block on the planet earth, wouldn't the block absorb all the gravitons/waves from the earth? Why don't I fly into space? Do the waves pass through the lead block, accelerating it to the source, then affect me without losing any energy? Is gravity quantized - Do gravitons/waves drop to a lower energy state when they encounter mass? Where is the actual 'source' for the gravity wave/particles? With a light source, we know where the photons originate. Do fermions emit gravitons/waves randomly all the time? Then why doesn't mass 'shrink' over time as gravity is emitted, just as a light source loses energy?

Perhaps these are basic questions, but it seems to me that just by simple observation it doesn't appear that gravity behaves as either a wave or a particle.

 

[Orodruin]

If gravity is effected by "wave particles", per Einstein's theory and now confirmed by recent observations, why do we not detect 'interference' - gravitational 'shadows' - or do we?

Einstein’s theory predicts gravitational waves. It says nothing about wave particles. GR is a classical theory.

Gravitational waves can interfere just like other types of waves. However, setting up an experiment that could show this would be immensely difficult. Keep in mind that we have only just detected the existence of gravitational waves at all.

So - if gravity is also transferred by a wave particle (a graviton), why do we not witness "gravitational shadows"?

You are confusing the wave part with the potential part. Either way, a gravitational wave interacts way too weakly to be appreciably distorted by encountering matter. It goes right through. A more apt analogy would be shining light through a window. Some of the light may be absorbed or reflected, but most just goes right through.

 

[Ibix]

Also, each time a light source emits a photon, it loses energy.

This effect has been directly observed - Hulse and Taylor measured the orbital decay of a binary pulsar, and showed that the decay rate matched the predicted energy loss from gravitational radiation.

This is not to say that gravitational fields involve a continuous emission of gravitational waves. They don't. It's precisely analogous to electromagnetism - an electron sitting there with an electric field doesn't lose energy and doesn't emit electromagnetic radiation. An accelerating electron, however, does emit electromagnetic radiation, and the energy comes from whatever made it accelerate.

why do we not witness "gravitational shadows"?

We would expect to be able to see gravitational wave shadows, but as far as I'm aware everything is pretty much transparent to gravitational waves, so the effect would be incredibly faint. Again, a static gravitational field is not a gravitational wave, and they do not behave the same way. We don't expect gravity shadows.

Is gravity quantized

We expect so (the simplest argument I've seen is that matter is a source of gravity and matter is described by quantum field theory - so it would be odd if gravity were not quantised given that its source is), but we do not have a working theory yet. Largely, I suspect, because we're shooting blind. We've never spotted gravity acting inconsistent with classical relativity, so we don't know what a quantum theory exactly looks like.

Where is the actual 'source' for the gravity wave/particles?

Gravitational waves (not gravity waves, by the way, which are a kind of surface wave in fluids) comes from stress-energy distributions with a changing quadropole moment. So, for example, two masses on opposite ends of a stick, spinning. Or two planets, orbiting.

Do fermions emit gravitons/waves randomly all the time?

No.