THE PHYSICS OF INTERSTELLAR TRAVEL

... ike a conveyor belt, similar to those you find at many airports. By expanding space-time behind the starship and contracting it in front, a segment of space-time moves and carries the ship with it. The starship itself still moves slower than light within its space-time, but when you add the "conveyor belt" effect; the apparent motion exceeds the speed of light. There are numerous difficulties with these concepts, however. The idea of expanding spacetime is not new. Using the "Inflationary Universe" perspective, for example, it is thought that spacetime expanded faster than the speed of light during the early moments of the Big Bang. So if spacetime can expand faster than the speed of light during the Big Bang, why not for a warp drive? These theories are too new to have either been discounted or proven viable. Other problems: First, to create this effect, an immense ring of negative energy has to be wrapped around the ship. It is still debated in physics whether negative energy can exist. Classical physics tends toward a "no," while quantum physics leans to a "maybe, yes." Second, you'll need a way to control this effect to turn it on and off at will. This will be especially tricky since this warp effect is a separate effect from the ship. Third, all this assumes that this whole "warp" would indeed move faster than the speed of light. It is still unknown if this could happen. And fourth, if all the previous issues weren't complicated enough, these concepts evoke the same time-travel paradoxes as the wormhole concepts.

Negative mass propulsion

It has been shown that it is theoretically possible to create a continuously propulsive effect by the juxtaposition of negative and positive mass and that such a scheme does not violate conservation of momentum or energy. A crucial assumption to the success of this concept is that negative mass has negative inertia. Their combined interactions result in a sustained acceleration of both masses in the same direction. This concept dates back to at least 1957 with an analysis of the properties of hypothetical negative mass by Bondi, and has been revisited in the context of propulsion by Winterberg and Forward in the 1980's. Regarding the physics of negative mass, it is not known whether negative mass exists or if it is even theoretically allowed, but methods have been suggested to search for evidence of negative mass in the context of searching for astronomical evidence of wormholes.

The radiation differential sail

Analogous to the principles of an ideal radiometer vane, a net difference in radiation pressure exists across the reflecting and absorbing sides. ...