Extraterrestrial Civilizations - Isaac Asimov [116]
On the other hand, if you subtract energy by pushing on a tachyon against the direction of its motion or by having it pass through a resisting medium, it goes faster and faster until, when it is at zero energy, it moves with infinite speed relative to the Universe in general.
Suppose, then, we imagine a “tachyonic drive.” Suppose every subatomic particle making up a ship and its contents is converted into the corresponding tachyons. The ship would take off at once, without acceleration, at many times the speed of light, and reach a distant galaxy in perhaps no more than a few days, at which time everything would be reconverted to the original particles and at once, without deceleration, the ship and its contents would be moving at normal velocities.†
Here at last is a way of beating the speed-of-light limit were it not that—
First, we don’t really know that tachyons exist. To be sure, they don’t violate Einstein’s equations, but is that all that is needed for existence? There may be other considerations, outside the equations, that preclude their existence. Some scientists, for instance, hold that tachyons, if they exist, would permit the violation of the law of causality (that cause must precede effect in time) and that this insures their nonexistence. Certainly, no one has detected tachyons so far, and until they are detected, it is going to be hard to argue their real existence, since no aspect of their properties seems to affect our Universe and therefore compel our belief even in the absence of physical detection.* Secondly, even if tachyons exist, we have no idea at all of how to turn ordinary particles into tachyons or how to reverse that process. All the difficulties of the photonic drive would be multiplied in the case of the tachyonic drive, for a mistake in simultaneity of conversion would scatter everything not merely over hundreds of thousands of kilometers but perhaps over hundreds of thousands of light-years.
Finally, even if it could all be handled, I still suspect we can’t beat the energy requirement; that it would take as much energy to shift matter from one end of the Galaxy to the other by tachyonic drive, as it would by acceleration and deceleration. In fact, the tachyonic drive might take far more energy, since time as well as distance must be defeated.
But we have another possible means of escape. If the qualification “the matter we know” fails us, what about the “Universe we know”? As long as the Universe we worked with was that which Newton knew—the Universe of slow movement and small distances-Newton’s laws seemed unassailable.
And as long as the Universe we work with is the one Einstein knew—the Universe of low densities and weak gravitations—Einstein’s laws seem unassailable. We might, however, go beyond Einstein’s Universe as we have gone beyond Newton’s. Consider—
When a large star explodes and collapses, the force of the collapse and the mass of the remnant that is collapsing may combine to drive the subatomic particles together into contact—then smash them and collapse indefinitely toward zero volume and infinite density.
The surface gravity of such a collapsing star builds up to the pitch where anything may fall in but nothing may escape again, so that it is like an endlessly deep “hole” in space. Since not even light can escape, it is the “black hole” I mentioned earlier in the book.
Usually one thinks of matter falling into a black hole as being endlessly compressed. There are theories, however, to the effect that if a black hole is rotating (and it is likely that all black holes do), the matter that falls in can squeeze out again somewhere else, like toothpaste blasting out of a fine hole in a stiff tube that is brought under the slow pressure of a steamroller.
The transfer of matter could apparently take place over enormous distances, even millions or billions of light-years, in a trifling period of time. Such transfers can evade the speed-of-light limit because the transfer goes through tunnels or across bridges that