Extraterrestrial Civilizations (34 page)

Besides, we have no idea how it would be possible to convert matter into photons and then back into matter in such a way as to reproduce all the characteristics of the original matter to the finest details. (Just imagine reproducing a human brain in all its intricacy after it had been dissolved into photons. Some might consider it conceivable, but even those who do can give no hint of the actual method for doing it.)

Then, too, the conversions in either direction would have to be done with very tight simultaneity, for if some conversions into photons
are made even a second later than others the photons will be spread out over hundreds of thousands of kilometers, and it might well then be impossible to reconvert them into compact objects.

How might the photons, even if produced in tight simultaneity, be directed in the proper direction, kept from losing order in the long voyage, and then reconverted with equally tight simultaneity?

Granted that 200 years ago the feats of modern-day television might have seemed just as impossible and out of the question, we cannot safely argue that because
some
things that were thought fantastically impossible have proved possible after all,
all
things that seem fantastically impossible
will
be proved possible.

In this book, I have taken the conservative route at all times and accepted nothing without at least some evidence, however slight and tenuous. At the present moment, there is no reason to suspect that a photonic drive can be made practical, and until some evidence to the contrary arrives (and that could be tomorrow, of course) I must say that while I cannot positively rule out a photonic drive, I consider its chances so close to zero that we may reasonably call it that.

Could we avoid the difficulty of conversion and reconversion, and of directing the light beam, by leaving all the particles as particles but somehow removing their mass? A massless ship-and-contents would instantly accelerate to the speed of light and remain at that speed. Once the mass was restored, it would instantly change to its original speed. That seems a much more comfortable situation than conversion into a beam of photons.

Unfortunately, we know of no way of removing mass from any particle, nor is there any indication anywhere that we will ever find a way. And if we did, we would still be traveling only at the speed of light.

So far, all I have suggested brings us to the speed of light, but doesn’t pass us beyond it.

In 1962, however, the physicists O. M. P. Bilaniuk, V. K. Deshpande, and E. C. G. Sudershan pointed out that Einstein’s equations would allow the existence of objects with mass that is expressed by what mathematicians call an imaginary quantity.

Such objects with “imaginary mass” must always go at speeds faster than that of light if Einstein’s equations are to remain valid. For that reason, the American physicist Gerald Feinberg (1933–) named them
tachyons
from a Greek word meaning fast.

An object with imaginary mass would have properties quite different from ordinary mass. For one thing, tachyons have more energy the
slower
they are. If you push a tachyon and thus add energy to it, it goes more and more slowly, until with an infinitely strong push you can make it go as slowly as the speed of light, but never slower than that speed.
^*

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 do not, strictly speaking, have the time characteristics of our familiar Universe. Indeed, the passageway is sometimes called an Einstein-Rosen bridge because Albert Einstein himself and a coworker named Rosen suggested a theoretical basis for this in the 1930s.

Could black holes someday make interstellar travel or even intergalactic travel possible? By making proper use of black holes, and assuming them to exist in great numbers, one might enter a black hole at point A, emerge at point B (a long distance away) almost at once, and travel through ordinary space to point C, where one enters another black hole and emerges almost at once at point D, and so on. In this way, any point in the Universe might be reached from any other point in a reasonably short time.

Naturally, one would have to work out a very thorough map of the Universe, with black-hole entrances and exits carefully plotted.

We might speculate that once interstellar travel starts in this fashion, those worlds which happen to be near a black-hole entrance would prosper and grow, and space stations would be established still nearer the entrance.

Those space stations can serve as power stations as well, since the energy radiated by matter falling into a black hole can clearly be enormous. We might even visualize space projects that consist of the moving of dead and useless matter into a black hole to increase the energy output (like fueling a furnace).

In fact, this offers still another explanation for the Universe being full of extraterrestrial civilizations that nevertheless do not visit the Earth. It could be that Earth happens to be in a distant backwater
as far as the black-hole networks are concerned. The extraterrestrial civilizations might know all about us, but find us not worth the time and expense of visiting.

Yet the exciting picture of a black-hole-riddled Universe converted into a kind of super-subway-system for interstellar flight has its drawbacks.

In the first place, we don’t really know how many black holes there are in the Universe. Outside the centers of the Galaxy and of globular clusters, there might be only half a dozen black holes per galaxy for all we know, and these would be of no use except to a few planetary systems near an opening, none of which might contain a habitable planet.

Second, the suggestion that matter entering a black hole will emerge elsewhere is by no means certain. Many astronomers believe there is nothing to this theory.

Third, even if matter entering a black hole does emerge elsewhere, nothing material can enter a black hole without being thoroughly smashed, right down to a powder of subatomic particles or less, by the incredible tidal effects of the unimaginably intense gravitational field of the black hole. It may be that some advanced technology will learn how to fend off all gravitational effects and keep the spaceship from serving as fuel to the black-hole furnace or from being torn apart by the tides—but at the present moment that seems impossible even in theory.

Looked at in the light of the Universe as it appears to us today, there seems no reasonable hope that the speed-of-light limit will be defeated in any practical way.

We must see what can be done at speeds below that of light.

One peculiar phenomenon predicted by Einstein’s equations (and verified by studies of speeding subatomic particles) is that the rate at which time seems to progress slows with speed. This is called time dilatation.

On a rapidly moving spaceship everything would go more slowly; atomic motions, clocks, the metabolism of human tissue.
Because everything on a ship slows down with exact synchronism, people on board such a ship would not be subjectively aware of the change. To them it would simply seem that everything in the outside world had speeded up. (This is analogous to the manner in which one isn’t aware of motion in a train moving smoothly forward at a station; instead the station and the countryside seem to be moving backward.)

The slowing of time becomes more marked as one moves faster relative to the Universe generally, until by the time a speed of 293,800 kilometers (182,550 miles) per second is reached—0.98 the speed of light—the rate of time passage is only 1/5 what it would be if the space vessel were at rest. If the speed of light is approached still more closely, the rate of time’s passage continues to drop until, when you are within a kilometer per second of the speed of light, it is nearly zero.

Suppose, then, we are in a spaceship that is accelerating at 1-g. (That is, at a rate that would make us feel pushed against the rear of the ship with the same force that gravitation now pulls us against Earth’s surface. At this acceleration we would feel perfectly normal. The back of the ship would seem down, the front up.)

After about a year of this, the ship would be moving at nearly the speed of light and by that time, although everything on board would seem normal to us, the outside world would seem very strange. It would become impossible, really, to watch many of the stars, for the light from stars ahead would shift far into the x-ray range and would be invisible. (In fact, the ship would have to be shielded from their radiation.) The light from the stars behind would shift into the radio-wave range and would be invisible, too.

If the people on board ship measured their speed against the distances they were covering, they would seem to be going at many times the speed of light, for it would take them only a week perhaps to cover the distance between two stars known to be ten light-years apart. If we could watch them from Earth, we would see that it actually took a little over ten years for the ship to cover the distance, but to the time-slowed sense of the people on board, those ten years would seem only a week long.

By making use of time dilatation, then, a space vessel would cover enormous distances in times that would seem comparatively
short to the people on board. In a length of time that they would experience as 60 years, they would reach the Andromeda Galaxy, which is 2,300,000 light-years away from us.
^*
Does time dilatation solve the problem?

Perhaps not, for there are difficulties. First, to maintain a 1-g acceleration for an extended period of time (or a 1-g deceleration, for that matter) takes enormous quantities of energy, as I indicated earlier.

Suppose we assume the most efficient way of getting energy, interacting equal quantities of matter and antimatter. Such a mixture undergoes mutual annihilation and the total conversion of matter to energy. For a given mass of fuel such a reaction would yield 35 times as much energy as hydrogen fusion, and if there is any way of getting more energy than that out of anything, we have no hint of what it might be at present.

And yet to accelerate a ton of matter to 0.98 times the speed of light would mean the conversion of about 25 tons of mixed matter and antimatter into energy, or the conversion of 100 tons for any round trip, counting two accelerations and two decelerations. If hydrogen fusion were used as the propulsion medium, something like 3,500 tons of hydrogen would have to undergo fusion. In other words, to carry one ton of matter to Alpha Centauri and back—just one ton-would take 10 times as much energy as the people of Earth consume right now in one year.