Shadowprophet
Truthiness
Produce? No. Repel, yes. Robert L. Forward provided a simple schematic for a device that can do that in his 1963 paper "Guidelines to Antigravity."
The demise of a black hole is a lot like that if Hawking was correct about Hawking radiation - in the final moments of black hole evaporation they would erupt in a blast of energy, emitting the last of their mass as high-energy radiation. In fact they looked for that signature in the LHC experiments, in case the higher-dimensional theories were correct, but they never saw it.
No, quantum field theory doesn't explain the existence of spacetime. Not in its current form anyway. General relativity is our model of spacetime, and - oddly, it doesn't speak the same language as quantum field theory (which is still a huge problem in theoretical physics; unifying the two).
No, gravity isn't a wave. In the weak field limit gravitational charge is analogous to electrical charge, with a reverse sign interaction, which is why Coulomb's law has the same structure as Newton's law of gravitation:
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Electromagnetic waves are radiated whenever an electric charge distribution has a changing charge dipole (or higher) moment, and gravitational waves are radiated whenever a mass distribution has a changing mass quadrupole (or higher) moment, but that doesn't mean that the electric and gravitational fields generating those waves, are waves themselves. Electric and gravitational charges have the same radial spherical symmetry.
Surprisingly though, electromagnetic waves can be converted into gravitational waves when they pass through a very intense magnetic field at the proper angle - this is called the Gertsenshtein effect:
"Wave resonance of light and gravitational waves," Mikhail Gertsenshtein, Soviet Physics Journal of Experimental and Theoretical Physics, 1961
http://www.jetp.ac.ru/cgi-bin/dn/e_014_01_0084.pdf
I've got to look up that guidelines to antigravity paper Thank you
That's why I love it when you're around, There's a lot to unpack here and when I do I will probably learn about seven months' worth of GR. How have you been Brother?