How do you compress space?
We have many theories of gravitation. But Einstein may have been more right than we originally thought.
In the 90's and even now, many think of gravity in a quantum sense as being a scalar force that uses gravitons as force carriers; like the other three forces in the universe (em, strong, weak).
However, Einstein stated that gravity was not a force, and general relativity predicts that gravity is merely the deformation of the space-time manifold which is caused by any and all objects based on their mass-energy.
Thus space itself has
some substance, it isn't merely nothing. In fact, nothingness in quantum mechanics simply doesn't exist - there's no such thing.
When we go down this road, we begin to realize that space acts as a sheet under tension, tension caused by mass-energy (mass or energy, which are equivalent forms of the same concept (e=mc^2)). This tension is what we know as gravity.
Now... when you get into the maths of general relativity, you notice that the equations work for both positive mass energy (what we all know and love), as well as negative mass energy (..wtf..). Most scientists at over the past century had completely dismissed negative mass energy as being a very minor flaw in our own understanding of mathematics, not necessarily a flaw in general relativity and simply discarded it from classical physics.
Quantum mechanics however, proved experimentally in the lab that negative energy not only exists (Casimir effect), but is prevalent throughout all existence. It is a fundamental requirement for the existence of the universe (which has a net energy of 0).
So, what does all this mean?
Well, again, think of that spatial manifold as a sheet, stretched out flat and under tension. When we apply positive mass-energy objects (like us, or the Sun or the Earth) this creates a deformation of space-time. Think of it as a dip in the sheet. Objects that come near enough to this dip are accelerated towards each other due to the depression gradient in the sheet. The greater this gradient, the greater the dip, the greater the accelerative force between the two objects.
But what if we apply a negative mass-energy?
Then instead of a dip, we get the reverse; instead, we get a bump. So think about it in the same analogous terms. Now, objects that exert a negative energy against space will be raised on the sheet, creating a gradient but this gradient will cause objects to be repelled (they'd tend to roll down to the flatter parts of the sheet rather than roll
up a hill). Thus, negative energy has a reverse gravitational effect, such that, instead of being universally attractive, it is universally repulsive.
Thus we can both compress space, and contract space, causing both positive and negative gradients in space-time by using both positive and negative energies.
By conforming these negative energies into particular spatial geometries, we can utilize specific solutions to general relativity, such as the Alcubierre solution, to create a warp bubble. This bubble expands space right behind us , and contracts space right in front of us, creating a uniform difference and moving space around us, rather than us through space.
p.s.
You might be wondering, how do we know this works?
In the 90's we conduct experiments that tested a theory regarding the Casimir effect.. This theory suggested, in layman's terms, that if the virtual particles that pop into and out of existence all the time were constrained between two very smooth metal plates placed very close to one another then there would exist a pressure differential between the interior of the plates and the exterior.
This would happen because there was less probability of the existence of virtual particles between the constrained plates (these particles exist in relatively empty space, by constraining the space, you reduce the number of particles in a non-linear fashion).
Therefore, there would be a force exerted on the exterior plates, pushing them together.
When we tested the theory, we found out, not only do virtual particles exist, but the Casimir effect was real - we could measure this force.
However, scientists began to postulate if this "pressure" wasn't actually the virtual particles colliding with the exterior of the plate -which was happening but didn't really explain the force entirely- but instead was due to a negative energy density within the interior of the two plates causing the space between the plates to actually contract, while the space on the exterior of the plates was inversely expanding.
So we've known about this for some time, but we couldn't really think of how to harness this in any useful way, because you cannot really extract any work from the plate configuration.
However, in comes Harold G. White - more of an engineer than a theoretical physicist. He has apparently (or, supposedly) increased the efficiency of the Alcubierre metric by more several orders of magnitude (which is frankly amazing), completely re-configured the geometry of the warp bubble, and now has supposedly determined that by configuring the casimir plates as capacitors (think of the interior of a capacitor) and then aligning many of them in series into a toroidal configuration (like a donut), that one would end up with a negative energy density displaced within the center and exterior of the toroid (the donut hole).
If looking at a cutout of the toroid, the energy density would look something like:
---++++-^-++++--- << +, positive energy; - negative; ^ is your ship.
That's how this works.
