A Step Farther Out (18 page)

Not that
all
of these differ from the present. Some of the things we kept the same probably will change in a thousand years. Others. . . well, the customs associated with wines and hard liquors are old and stable. If we'd changed everything, and made an attempt to portray every detail of our thousand-year-advanced future, the story would have gotten bogged down in details.

MOTE is probably the only novel ever to have a planet's orbit changed to save a line.

New Chicago, as it appeared in the opening scenes of the first draft of MOTE, was a cold place, orbiting far from its star. It was never a very important point, and Larry Niven didn't even notice it.

Thus when he introduced Lady Sandra Liddell Leonovna Bright Fowler, he used as viewpoint character a Marine guard sweating in hot sunlight. The Marine thinks, "She doesn't sweat. She was carved from ice by the finest sculptor that ever lived."

Now that's a good line. Unfortunately it implies a hot planet. If the line must be kept, the planet must be moved.

So Jerry Pournelle moved it. New Chicago became a world much closer to a somewhat cooler sun. Its year changed, its climate changed, its whole history had to be changed. . .

Worth it, though. Sometimes it's easier to build new worlds than think up good lines. . .

I was one of the first science fiction writers to use black holes in a story. Not
the
first, I hasten to add; but I did make the first use of gravitation waves, and therein lies a tale.

I had just published my story "He Fell Into a Dark Hole" and was in fact reading it—writers generally do read their own work the first time they see it in print—when the telephone rang. The caller was Dr. Robert Forward of the Hughes Research Laboratories; Forward, I later learned, is one of the foremost authorities on gravitation, and holds patents on gadgetry such as a "mass detector."

He had been preparing a paper on gravitation waves and how they might prove to be dangerous; that was the theme of my story; and I had beaten him into print. So not only did I make first use of them in science fiction, but my story may have the first publication anywhere to draw attention to certain aspects of gravity waves.

The result is that I am, to many fans, a sort of "proprietor" of black holes; a role I'm willing to fill for a while. Which gives me the right to tell you about them, as this section does.

I suppose most readers are at least partly aware of the ongoing research on detection of gravitational waves, but it does no harm to summarize a bit. In the Newtonian universe, gravity is a "force" that acts through a field; that is, although it is 10 times weaker than electromagnetism, it's not fundamentally different.

This holds true in the realm of special relativity also: special relativity is the theory that asserts that no material object, and no signal, can travel faster than light. There's a lot of evidence for special relativity, and no really good counter theory lurks in the wings to take its place.

The general theory of relativity is another breed of cat entirely. There are several contenders in that realm, and experimental evidence offers no clear cut way to choose one or another. General relativity does away with gravity fields altogether: in that theory, gravity results from the geometry of space, and is not a "force" at all.

(That is: mass—or energy for that matter—distorts space, bending it; and it is this curvature of the fabric of space itself that causes the effects we call "gravity.")

Whether gravity fields "exist" or merely result from geometry, nearly all theorists believe gravitational attraction propagates with the speed of light. If matter is created—or destroyed—the rest of the universe won't be instantly affected, but must wait until the gravitational effect, traveling at light speed, reaches it.

Thus "gravitation waves," which will have a frequency and an amplitude much like light, but which may also have some rather strange properties as well.

In theory, if we could detect and examine gravitational waves, we might be able to tell whether they result from a field and are thus similar to magnetism, or if they are merely a property of space and its geometry. Unfortunately, gravity is an incredibly weak force. It requires the mass of the whole earth merely to pull things with a puny 980 cm/sec
²
acceleration—and we can overcome that with rather small magnets, or chemical rockets, or even our own muscles when we jump.

Because gravity is so weak, it's hard to play with. You can't turn on a "gravity wave generator" and fiddle with the resulting forces to see if they refract, or can be tuned, or whatever. You can't wiggle a mass to generate gravity waves, because you can't get a large enough mass held into place to be wiggled. It's not even possible to blow off an atomic weapon, turning some matter into energy, and measure the effect of the matter vanishing; the effect is just too small to be noticed, and it's hidden among the rather drastic side effects.

However, there are a number of theoretical ways that gravity waves might be generated by the universe: stars collapsing into black holes or neutronium would do it, for example. The universe might be riddled with gravitational waves, but they'd be terribly weak, and require delicate and sophisticated apparatus to detect them.

Some years ago, Dr. Joseph Weber of the University of Maryland decided to build a gravity wave antenna. He took a large aluminum cylinder and covered it with strain gauges. The idea was that so long as the cylinder was acted on only by the steady gravity of Earth, it would be in a stable configuration, but if a gravity wave passed through it, the cylinder would be distorted, and the strain gauges would show it.

He had to compensate for temperature, and isolate it from vibration, and worry about a lot of other things, but the technology had been developed: the antenna was built. It was incredibly sensitive, able to detect distortions on the order of an atomic diameter. It was also able to detect student demonstrations outside the library, trucks rumbling along the highway a mile distant, and other unwanted events.

The solution to the latter problem was simple: build another copy of the antenna and place it 1000 kilometers away; now hook the two together, and pay no attention to any event that doesn't affect both. Such "coincidences" should be due to a force affecting both antennae—earthquakes take time to propagate and their effects move much slower than lightspeed—the output should be reliable.

Unfortunately, it isn't as straightforward as that. The instruments must be very sensitive, and thus there's a lot of chatter from them. By the laws of chance, some of this chatter will be simultaneous, or near enough so, and thus you are guaranteed some false positive results. The output of the gravity wave detectors, therefore, needs careful analysis to decide what's real data and what's chance.

Weber immediately got results. He got a lot of results, far too many for chance. Unfortunately, there were far too many for cosmologists to believe. As a result of Weber's early reports, some cosmologists estimated that as much as 98% of the universe must be inside black holes.

The argument went this way: something is producing gravity waves. We can't see enough matter to account for the events, but normal matter falling into a black hole would produce gravity waves. Therefore—

There were other cosmologists who wanted to believe this for different reasons. Readers familiar with black holes must excuse me: it's now necessary to discuss their basics for a moment.

* * *

A black hole is a theoretical construct that can be derived from both general relativity and the older Newtonian universe; in fact, the first speculations about black holes come from Laplace back in 1798. If you take enough matter and squeeze it small enough, you will eventually get so much gravitational force that nothing can prevent the matter from continuing to collapse.

In Einsteinian terms, the space around the matter becomes curved into a closed figure, but the result is the same: the matter is squeezed to infinite density. Long before it reaches that state, though, there is a region around the matter at which the escape velocity is greater than the speed of light.

The effect of that should be pretty obvious. If light can't escape, you can't see down into the hole. Moreover, anything that goes down in the hole can never come out: that is, if you accept the speed of light as the top limiting velocity of the universe, nothing can come out.

The area at which space is curved into a closed figure—or the region at which the escape velocity is equal to the speed of light—is known as an
event horizon,
and interestingly enough both Newtonian and Einsteinian equations give the same location to it.

It is the region at which

R = 2GM/c
²  
(Equation One)

where R is the radius from the center, G is the universal constant of gravitation, and c is the speed of light For our sun, that radius is on the order of 2 kilometers: if the sun is ever squeezed that small, we'll never be able to see it again.

An observer diving into the black hole would never know when he had crossed the event horizon. He could continue to send signals to his friends outside, and as far as he could tell, they would go right on up and out.

Those outside the hole, though, can never under any circumstances receive information from inside it.

Now, as it happens, if we measure the total amount of matter in the universe, and plug that in for M in equation one; and we take the furthest object we can observe and plug that in for R; then the equation almost balances.

Almost, but not quite. There isn't enough matter in the universe; we're missing from 20 to 90%, depending on whose figures you use for M and R.

If the equation were to balance, space would be curved into a closed figure at the boundaries of the universe, and we'd live in a closed universe.

Eventually, in a closed universe, those galaxies receding from us will stop and come back, and the whole universe will be packed into a big wad at the center. What happens after that is debatable, but a number of cosmologists want badly to believe in a closed universe.

It also means, of course, that we live inside a black hole ourselves: that is, our whole universe is a black hole.

If we don't live in a closed universe, the receding galaxies will go right on receding, and this disturbs some theorists. Thus, Weber's coincidences were welcome in many cosmological circles. Others tried to build gravitational antennae to confirm his results.

* * *

Then a second startling result came out of Weber's shop. It appeared that there was a 12 hour sidereal cycle to the coincidences, and furthermore, that this cycle was related to the galactic plane. In other words, gravitational waves originated in the galactic center.

We have a good estimate of the distance to the galactic center, and thus were able to estimate
how
large an effect at the center of the galaxy would be required to deliver that much force to us out here on our spiral arm. The result was once again dismaying. Far too much energy was apparently being turned into gravitational waves.

Now the energy radiating from the galactic center could be either sprayed out in all directions, obeying the inverse square laws, or it could be "beamed" into the galactic plane. Obviously less total energy is involved if it is "beamed," but what mechanism might account for that?

The speculations were many, imaginative, and varied; they were also rather frightening.

* * *

Let's take a moment to go back to black holes. When matter gets dense enough to satisfy equation one, and the event horizon forms, things don't just stop there. The matter goes on collapsing; we just can't see it any longer.

In fact,
nothing can
stop the collapse. In theory, the matter should quite literally become infinite in density. Infinity is a troublesome concept: how can infinite density be present in a finite universe? The answer is obvious: in some respects, the matter no longer remains in the universe at all.

When gravitational forces have got to this point, we have what is known as a "singularity"; a point at which normal laws simply do not apply.

Actually, things are worse than that. Not only don't normal laws apply, but the relativity equations suggest that
no
laws apply. Strange things happen in the region of a singularity. Time is reversed. Conservation laws don't work. Causality is a joke: if you could get into the region of a singularity, you really could go back in time and assassinate your grandfather.

In fact, anything could happen, and science ceases to exist; and you don't even have to physically go to the singularity for this to take place. All you have to do is be able to observe one directly, and science has just gone down the drain. That bothers a lot of theorists and scientists, and rather disturbs me as well.

If there is a naked singularity—that is, a singularity not covered with an event horizon—then, at least in potential, there is no order to the universe.

Out of that thing might come ghosties and ghoulies and things that go bump in the night.

What, then, may we do to save science? Why, invoke censorship, of course.

The kind of censorship invoked is called rather whimsically the "Law of Cosmic Censorship," which states that "There shall be no such thing as a naked singularity." All singularities must be decently clothed with an event horizon.

Given cosmic censorship, a number of interesting laws about black holes may be proved: that they never get smaller, that if one is rotating it can't be sped up until the escape velocity is smaller than the speed of light, and a number of other rules that are collectively known as the laws of black hole dynamics.

Unfortunately, cosmic censorship deprives science fiction writers of some of their best stories.

It does it this way. If all black holes are covered with event horizons, it follows that you can't plunge into a black hole and come out elsewhere or elsewhen. Actually, if you plunge into a random black hole, all that could ever come out anywhere would be a stream of undifferentiated sub-nuclear particles; for all their fantastic properties, singularities do retain one feature, namely that gravitation in their region is rather high, sufficient to disassociate not only the molecular, but the atomic, structure of anything visiting them.