Tesla had a theory of electromagnetic gravity that remains classified to this day. It involved rotating magnetic fields.
The MEG for example (see the bottom of the Tesla Power article on the Free Energy / Tesla page), when a load is pulled, it pulls more energy from the active vacuum, until it eventually caps off, and then very unusual things happen.
I've noticed this accidentally with the Tesla Tower and other energy experiments of mine, that a current will flow so as long as there is a load; and a current will flow to ground and continue to flow to ground from the tower, so as long as that circuit is unbroken. That deals with negative energy.
In my original Tesla tower experiments, there was energy being generated that could be tapped as it flows to ground, but once that connection was broken, the energy was gone.
In an electromagnetic generator experiment of mine, I had obtained an old capacitor that had been sitting around outside for many years, and so I hooked it up. The generator produced more energy with less effort, but as soon as I stopped the generator, and went to restart it, all that excess energy was gone.
Imagine what rotating MEG assemblies can do spinning around, and then we've got something similar to the OTC-X1. Superconductors levitate. An effect of negative energy in some situations also will cause the generator to ice up and levitate (as seen in private tests under certain conditions tuned to certain frequencies). So we see some relations, here. Everything has frequency, even magnets. A magnet can be tuned to generate its magnetic field at a certain frequency, for example when a magnet is being made.
Edward Leedskalnin noticed that gravity and electromagnetism were directly related, in that an electromagnetic field could be applied in a wire, and that could magnetize nearby pieces of steel fishing line, and that the steel fishing line would demonstrate a spin reversal when crossing over the plumb and level axis of the wire (crossing on either side of vertical, or above and below the horizontal planes relative with Earth's gravity field).
When the wire was energized, the tips of the steel fishing line would either curl to the left or to the right as it crossed the exact horizontal or vertical planes of the wire. So hold the fishing line to the side of a wire, and drop it below level, or raise it above the level plane; or hold the fishing line to the left, and cross over the plumb axis to the right side of the wire. All this goes to show that electromagnetic fields and currents do respond to gravity, and the reason is because gravity is another dimension of electromagnetism.
There's a lot of research one could look up about electromagnetic gravity, in fact. It can be said that all fundamental forces are electromagnetic in one way or another, and all relates to electromagnetism, in varying dimensions of action.
All of this above has been discussed at some place in this website.
Here are some links to aid one in exploring electromagnetic mass and electromagnetic gravity:
People have accused me of not understanding this technology I rely heavily upon. I'll admit, some of it I do understand, and I understand what must exist, in order for the technology to exist. But all of the proofs and mathematics and such is overshadowed by a far easier and more simplistic way to test these technologies, and that is simply to back-engineer them. John Searle's SEG and the OTC-X1 are two marvels which have sufficient evidence to conclude that they are possible; and some people working with the SEG have seen it work. The Russians have done work with the SEG and have seen that it reduces its own weight to zero.
Townsend Brown's work has actually been demonstrated, however, and di-electrostatic gravity does work.
I'm planning on publishing Tesla tower Ley-line negative energy technology in 2 - 5 years here on this website. I'll see what happens afterwards; however afterwards, the OTC-X1 should have achieved sufficient development through other private research and developers, I'm hoping. I may however choose to take an entirely different path toward spirituality and metaphysics.
I've done a lot of work on this website to get this technology up to a point of where we can understand what we're dealing with, to encourage people to build it and test it, instead of theorizing about building and testing it, and battling over their own beliefs of "will it work; am I wasting my time," etc. It's not a waste of time, as long as there is sufficient evidence to show it can work. But you won't see any of this in any mainstream university, because a university setting will not include a back-engineering curriculum to get something to work, without a way to truly understand why it works.
However, if one has experience in these matters, then one's intuition will serve one much more in these capacities as an inventor, rather than as a scholar. An inventor rarely comes up with a proof first, but just has a belief, an idea, and the motivation to try something; because invention is that which can begin to establish an understanding of new technology, because an inventor will try things based on intuition most often in contrary to modern accepted ideology and theory. I think inventing is a far easier way to understand the universe, rather than theory. However at least SOME theory must exist prior, otherwise no invention could be conceived, so in order to try.