Where should we start? The antigravity means the hypothetical repelling side of gravity. The effect should be similar to electromagnetic repel. In the cases that somebody turns the minus or plus poles of the magnet against each other, those poles repel each other. All other fundamental interactions other than gravity are the known repelling effect.
So that effect should be in gravity. But when we talk about the electromagnetic repel we don't talk about anti-electromagnetism. We talk about electromagnetic repel or push effect between the same magnetic poles. There are even metals like titanium that are anti-magnetic. The reason for that is that. The magnets are not affected by that kind of metal.
Virtual antigravity means things like superconducting objects' levitation above the ground. It's possible to create silently levitating aircraft or other things using superconducting objects that have chambers inside that thing. The superconducting particles can make those crafts lighter. But the problem is that those systems require high-power cooling systems. This is the reason why researchers are searching for room-temperature superconductors. The magnetic levitation systems are also virtual antigravity. But real antigravity means the gravity field manipulation that is not yet possible.
The gravitational or "real" antigravity means that the system can cut the gravitational interaction between the object and the ground or gravity center.
Antigravity as we know it is the system that manipulates gravity waves and denies their interactions between objects and gravity centers. The systems that can create those things like coherent gravity waves or standing gravity waves are far away in the future.
Above: Superconducting object levitates. "University of Illinois Chicago scientists are working on materials that could allow superconductors to function at room temperature, eliminating the need for extreme cooling". (ScitechDaily, Superconductors at Room Temperature? UIC’s Groundbreaking Materials Could Make It Possible)
The simplest way to make an antigravity system is to create the gravity "tongue" or horizontal standing gravity wave that denies the gravity waves to reach the hovering object. Another way is to use gravitational counter waves or gravitational polarization that denies the gravity waves reach the craft or object.
As I have many times written before. Albert Einstein introduced that gravity is the feature of the fields like Higgs field. The idea is that. The gravity field forms a low-pressure or low-energy tunnel between gravity centers. Then energy. That comes backward and pushes objects into that tunnel or against each other. The idea is like in a low-pressure tunnel.
"A wormhole is the one way, in the context of general relativity, that immediate transport between two disparate, disconnected events in spacetime can occur. These "bridges" are mathematical curiosities only at this point in time; no physical wormholes have ever been found to exist or have ever been created, and would require some sort of negative energy, or "antigravity" source, in order to be physically real." (Big Think, Ask Ethan: Is antigravity even possible?)
So if we think that antigravity is the thing that denies those objects fall or makes them levitate. We can say that antigravity is the thing that closes this tunnel. If that low-energy tunnel between gravity centers is closed, that thing can turn the effect known as "antigravity" real.
That means the system should only send gravity waves or coherent gravity waves between the ground and the object that should levitate. That can deny the gravitational interaction between object and ground.
Another thing that could make antigravity real is the system that makes holes in the gravity field. In that case, the coherent gravity waves- or gravitational laser can create the energy low-pressure tunnel through the gravity field.
In some other ideas, the system can create a miniature black hole at the top of the structure. If the black hole is more massive than the planet. That thing pulls the structure up from the ground.
But when we think about gravity as wave movement, we can say that it's possible that someday we could polarize those waves. That polarization means that we create a layer, that denies the gravity waves travel through it. But the gravity wave polarization seems not to be possible.
In some versions, the system should create the gravitational version of "altermagnetism". In altermagnetism, there is the magnetism inside the object. But the outsider cannot feel the magnetism. The gravitational waves that travel inside the craft or object can make the gravitational waves from the ground reflect. That thing can form standing gravity waves that prevent the gravity waves from reaching the object. The system could use the opposite directions traveling coherent gravitational waves.
https://bigthink.com/starts-with-a-bang/antigravity-possible/
https://scitechdaily.com/superconductors-at-room-temperature-uics-groundbreaking-materials-could-make-it-possible/
https://en.wikipedia.org/wiki/Wormhole
