Observation Of Gravity Waves

[CraigD]

Consider gravity wells themselves, and do it realizing that they can't be accurately described with simple Euclidean geometry.

Gravity as described by General Relativity can’t be perfectly accurately described with “inflexible”, simple Euclidean geometry, but the classical approximation described by the Newtonian theory, which is accurate enough for everything from rocketry to cosmology, can be. The classical approximation isn’t perfectly accurate, but it’s often accurate enough.

 

My reference to "radiating negative energy" Is referring to how gravity removes (potential) energy from objects by reducing them to gound-state potential of the well.

That’s not how gravity works (classical mechanics pun intended). :)

 

Gravity doesn’t reduce gravitational potential energy, but transforms it from or to kinetic energy.

 

When the apple falls from a tree, its GPE decreases, but the decrease is nearly (or exactly, if, weirdly, the tree and apple are in a perfect vacuum) equal and opposite to its increase in kinetic energy. When the apple reaches its “ground state” – resting on the ground with the same velocity it had hanging on the tree, and thus the same kinetic energy – the kinetic energy has been transformed into other kinds of energy, such as heat (which you could measure with a sufficiently sensitive thermometer). If you toss the apple back into the air, gravity transforms the kinetic energy into GPE until it reaches zero at the top of its flight, then from GPE into kinetic energy at it falls back.

 

... so it [the source of GW151226] radiated negative energy?

No. As others have stated, gravitational radiation caries positive energy – that is, it can do physical work.

 

An interesting bit of science history is that, for several years, the question of whether gravitational waves carried zero energy or not was undecided. Albert Einstein initially wrote that it did, then 20 years later changed his mind, deciding that it gravitational waves deformed space, but not in a way from which work would be extracted, then in a famous “double reversal”, decide and wrote that it did. The conclusion that gravitational waves carried non-zero, positive energy was not well understood or accepted by physicists until Richard Feynman promoted it the “sticky beads” though experiment.

[freeztar]

There are all kinds of rabbit holes to venture through here. My favorite is a link from the wiki sticky beads that Craig posted, Abraham-Lorentz force. 

https://en.wikipedia.org/wiki/Abraham%E2%80%93Lorentz_force

 

"It was thought that the solution of the Abraham–Lorentz force problem predicts that signals from the future affect the present, thus challenging intuition of cause and effect."

 

That is something I will have to try and wrap my brain around. It is only tangentially related to the topic of this thread, but interesting nonetheless.

 

As far as gravity waves are concerned, we are still in the infancy. But I do think we can say that gravity carries positive energy. Otherwise LIGO would not work.

 

That said, I do agree with GAHD that negative and positive in this context is clumsy. If we think of gravity waves as distortions of spacetime, wouldn't they be both positive and negative? Stretching and contracting (a peak and trough like any other wave)? But if I understand the sticky beads thought experiment correctly, then spacetime itself (the rod) is not affected while the "beads" are?

 

Ughh...maybe too early in the morning for this. Need to let it simmer.