The definition of Antigravity

Before going any further we need to clarify what is generally the perceived meaning of the term 'antigravity'. In a sense a helicopter is an antigravity device but few of us would regard this a 'antigravity'. Also a helium balloon defies gravity but here again not really an antigravity device.
If, on the other hand you placed the helium balloon in a vacuum and it still went up instead of down then that would be antigravity.

Antigravity refers to the action of defying gravity without an associated reactive force

The definition above is probably not the best and if you can come up with a better one let me know.

Action with reaction is pretty fundamental as a physical concept. However, sometimes the reaction part is not initially obvious. For example, the moon circles round the earth. The fact that it is moving in a circle means that a force is being applied to it. With every force there is an opposite reaction. The opposite reaction is there somewhere but the dynamics are not as obvious as, say, rocket propulsion.


Is 'antigravity' possible?

A useful analogy to get an understanding of the magnitude of the problem is that it's like you are given the task of creating a machine made only of ice that can move against the flow of a waterfall without touching the rock face. In this analogy, ice equates to matter and the waterfall equates to gravity or the stuff that causes it.

There is one sure fact that if gravity can effect matter then matter can effect gravity.
It is the same logic as saying that if a bat can have an effect on a ball then the ball can have an effect on the bat.
I'm going to substitute the word 'gravity' for 'motional field'. Matter can influence motional field but, unfortunately, very poorly. Matter is like a sieve, almost transparent, to this mass-less substance.
A fast spinning disc will in fact distort gravity. An exotic sounding term for this is 'frame-dragging'. It's really just making the energy field flow in a slightly different manner. This changes the local gravitational vector compared to when the disk is stationary.
A magnetised disc, provided it is magnetised in a sympathetic plane, will enhance this frame-dragging effect. This is due to the trajectory alignment of subatomic elements contributing to the frame-dragging mechanism.

so far so good ...

With the above in mind, the next task is to manufacture a material that can directly and efficiently influence the aether (gravitational) field.
We need an exotic laminate, a sandwich construction, where basically the outer layers retain each other in a lattice structure and also provide a container for an inner layer. This inner layer is seeded with a particular type of subatomic particle.
These particles can be packed many orders of magnitude closer than found in nature. What we are trying to achieve is a composite material that closes up the sieve like properties of normal matter. So we have a wafer thin incredibly dense inner core.
Gravity shielding is one use of such a material.

and a third possibility ...

Instinctively, it would not seem unreasonable to assume that magnetic field in motion with the right dynamic configuration should be effective in influencing the aether and consequently gravity. Unfortunately, easier said than done.
The idea here is to produce an area of low density motional field above the object to be lifted and an area of high density field below.
The frame-dragging effect of a spinning magnetic disc is more than likely a pointer to this technology.



Addendum

In the not too distant future, the human race will understand all things regarding the physical world in which we find ourselves. We will understand how matter is created, the cycles of the universe, all things both micro and macro.

However, there is one thing that is probably going to stump us and that is understanding the concept of Infinity. It is inconceivable that infinity can actually exist either spatially or in time. We know this to be true otherwise the universe would be crawling with mega advanced aliens spawned from aeons in the past. They are not here.