[markisus]

Is it even theoretically possible to waveguide gravity? The electric field can be positive and negative, but gravity is unsigned -- there is no anti-gravity. This is probably related to what you're saying about faraday cages.

[whatshisface]

Gravitational waves can either stretch or contract spacetime relative to a baseline. Since the Einstein field equations are nonlinear, I think gravitational waves can be "refracted" when traveling through a region with a high baseline curvature, so maybe waveguides are possible. Gravitational lenses do lens gravitational waves in addition to light.

[Optimal_Persona]

It's not unsigned, if you look on the back it says "Come together, you all. Love, The Universe." ;-)

[robotresearcher]

Gravity is antigravity if you run time backwards.

[palmtree3000]

I realize this is a joke, but it isn't! Play a video of a ball flying up and then back down again and it'll be the same forward or backwards (up to air friction anyway).

[robotresearcher]

It wasn't a joke.

[PeterisP]

If it wasn't a joke, then that was simply a misleading false statement.

Let's take the simple example of earth orbiting around the sun. Playing time backwards gets you a orbit in the opposite direction, while gravity becoming antigravity would mean that earth would get repelled by the sun and thus go off to infinity.

[robotresearcher]

That's interesting. Playing time backwards long enough would see the earth disassembled into rocks, dust and gas, repelling each other and indeed flying off into <far away>. Same with the sun. But the short term orbit example challenges the intuition. Perhaps the answer is that the time-forward orbit is (conventional) downhill in spacetime, and the time-backward orbit is uphill in spacetime, but both trajectories are seen in conventional space as a curved path around the center of gravity.