A Step Farther Out

by Jerry Pournelle

  But it's what we get for living in interesting times, and it ought to teach my friend Larry not to rush into print ahead of me. . .

  __________

  Figure 11

  ___________

  *My SR-50 has long been shelved, of course. Now I use a full computer, and anyone can afford a better calculator than the SR-50 was. Marvelous times we live in. . .

  Crashing Neutron Stars, Mini Black Holes, and Spacedrives

  The universe is a queer place. I know that doesn't surprise most of the readers of this book, so let's look at some far-out theories before the relentless march of science catches up and converts them into (yawn) just more engineering.

  There's also a point to be made. At least once a week I get a new "theory" from one of my readers. Sometimes it's blueprints for a device that gives out more energy than it takes in, sometimes it's a refutation of Einstein, sometimes something else, but in nearly every case there's a common factor: the cover letter says no one will listen, and I'm the inventor's last resort. Generally, too, I'm asked "Why won't they listen?" but the question is rhetorical; the next paragraph tells me that orthodox scientists do not have open minds, are afraid of new ideas, etc., etc.

  There's a little truth to that, but not so much as is often supposed. Orthodox science can get pretty far out.

  Everyone knows what a neutron star is, right? A sort of intermediary superheavy object: that is, squeeze atoms hard enough but not too hard and they'll form a super-dense goop. Everything has been shoved together, but it's still ordinary matter. That's what dwarf stars are made of.

  Squeeze more and the atoms can't stand it. The electrons are forced out of their orbits and down into the nucleus. When you push an electron hard into a proton you get a neutron, and a sufficiently squeezed object will be nothing but neutrons, i.e., a neutron star.

  Finally we can continue squeezing (the easy way is to pump more and more matter onto a neutron star and let gravitational collapse do the work) and the very neutrons can't stand it: they're squeezed right out of the universe. Well, maybe not: but the result is a black hole, an object whose surface gravity is greater than the speed of light so that it can never be observed, and that's a very queer thing indeed. For further details consult some of my previous chapters, or there are any number of recent books.

  Surely those theories are far out? And for a very long time they were pure theory. Back in the 30's J. Robert Oppenheimer deduced the possibility of neutron stars from an analysis of Einstein's work on gravitation. He also noted (as had others) the possibility of black holes. He published these speculations. No one laughed. He wasn't thrown out of the union. Why? Why did "they" listen to him, but "they" won't pay attention to outsiders?

  Well, of course there is a certain degree of old-boy networking here; obviously you pay more attention to people you know or have heard of than people you don't know and who don't seem to have any qualifications; but that's not the whole of it by a long shot. Neutron stars and black holes were far out and queer indeed—but they did not challenge basic physics. Quite the contrary, they were deduced from accepted ideas.

  Meanwhile, back in the observatories, the radio astronomers came up with a queer result: pulsars. These were very small objects which emitted quite a lot of energy at fantastically regular intervals on the order of a second They were entirely unexpected: no theory predicted them, no theory accounted for them, yet they had to be explained. And of course explained they were, because it's easy to show that neutron stars will rotate very rapidly, they can send out bursts of radio energy, and even better, they'll be slowing down (very slightly) all the time. Back to the observatory to discover that the pulsars were slowing down at just the right rate (micro-seconds a year) and lo, Oppenheimer's far-out theory becomes universally acceptable.

  That took care of neutron stars: and if those probably existed, then why not black holes? Thus the sudden interest in holes.

  Now there are several ways we can create black holes. The simplest is for a properly-sized star to "go out": that is, the star runs out of fuel and begins to collapse from simple gravitational attraction. Of course the collapsing process will itself produce heat for quite a long time, and that brings us to another far-out theory: has the Sun, our Sun, "gone out"?

  It may have. If it had we wouldn't notice, because it would only have to shrink a few kilometers a year to give off the energy it does. (Gravitational potential energy is powerful stuff) Moreover, the continued collapse would eventually cause it to re-ignite, halting the collapse. There are a very few theorists who seriously propose this alternation between collapse and hydrogen burning as an explanation for Earth's Ice Ages. The theory is not widely held, but those who propose it aren't laughed at. Why not?

  Well, first, the Ice Ages are real, and we don't have a convincing mechanism to explain them. Second, out in the old Homestake Mine, deep underground, they're searching for solar neutrinos—and they can't find them. If the Sun is truly burning hydrogen, there ought to be a lot of neutrinos, and there's no good reason to doubt that the Home-stake apparatus would trap them—so where are they? The "Sun's gone out" theory does explain an experimental result.

  Leaving that particular theory let's get back to black holes. There are other ways they might be formed. One would be to focus a laser small enough. After all, E equals mc-squared works both ways: if matter can become energy, energy can become matter, and thus a sufficient energy density would make a black hole. There'd be no way to tell it from other holes, either. This is not a very practical way to get black holes.

  Finally, we can make black holes by having really humongous pressures. Stephen Hawking of Cambridge first postulated the idea of mini-black-holes, little tiny things massing from a few to a few million kilograms; previous to Hawking's work nobody contemplated a black hole smaller than stellar size.

  Hawking thought that mini black holes had been formed during the Big Bang, when there were certainly sufficient pressures for creating them. Since it was then thought that black holes never go away once formed, we could expect in a few decades to go looking for primordial black holes in the asteroid belt.

  Having created mini-holes, Hawking then proceeded to destroy them. He applied quantum mechanics to black holes and demonstrated that the things aren't stable. Black holes evaporate, small ones doing so rather quickly and quite violently. (See the previous chapter. I'm particularly proud of that one because it was the first popular-press publication of Hawking's evaporation-theory; now—his view is universally accepted.)

  The upshot was that holes massing less than 1015 grams when formed during the Big Bang are all gone now, and any larger holes formed then (and now getting down to small size) will vanish spectacularly with much high-temperature radiation. Consequently, we needn't bother looking for small black holes.

  Well, guess what? Mini-holes are back again. Kenneth Jacobs and Patrick Seitzer have just published a prize-winning essay submitted to the Gravity Research Foundation (for a copy of their paper send a couple of dollars to the GRF at 58 Middle St., Gloucester, Mass. 01930) entitled "Mini Black Holes Are Forming Now." According to Jacobs and Seitzer the little holes are generated inside neutron stars.

  It works this way. Take one common or garden variety neutron star. Pile matter on it. You can do that by putting the star in a dusty region of the galaxy, or by giving it a normal-matter companion in close orbit: the companion loses mass to the neutron star.

  As the neutron star grows, a "pressure and density spike" develops in the interior. If you keep piling on enough matter the neutron star will simply collapse into a large black hole, but let's consider a time just prior to that: a time when the interior of the neutron star is far denser than its surface.

  Jacobs and Seitzer offer mathematical proof that it's at least possible that the interior collapses into a mini-hole, leaving the rest of the neutron star intact!

  Once the mini-hole is formed, it begins to evaporate. On the other hand, it's inside a neutron star, surrounded by
all that lovely dense matter, and it can begin to feed. By eating neutrons the hole grows larger. Thus we have two counteracting tendencies: the hole eats the star, growing larger, and also undergoes Hawking "evaporation." Under certain conditions the two may just balance each other. It's even possible that the tiny hole will prevent the formation of a big black hole, thus giving the neutron star a few billion years more of normal life.

  Sigh. It's hard to see how those holes can be useful. There are all kinds of marvelous things you can do with a mini-hole if you can get at one, but the interior of a neutron star is a well-protected place; nature's safe-deposit box.

  Back in the old days before Hawking evaporation, we thought mini-holes might come to rest inside asteroids, and it would be no great trick to go move the asteroid to get at the hole; but doing that to a neutron star would be a bit more difficult.

  It would also be dangerous. The hole exists in equilibrium, eating the star at a rate to balance its evaporation. Disturb that and the entire neutron star could become a black hole in milliseconds! It would also toss out a bit of energy: 1055 ergs. (For comparison, our Sun puts out 1039 ergs each year, and an ordinary nova gives off 1044 ergs.)

  In fact, Jacobs and Seitzer describe ways these mini-holes might be the driving mechanism for super-novae. They also speculate that this could be a mechanism to explain gamma-ray bursts, and here we leave the realm of theory to return to the real universe. Gamma-ray bursts exist, and their spectra are consistent with events predicted by the Jacobs and Seitzer mini-hole theory.

  Now that gets interesting. As MIT's Phillip Morrison put it recently, x-ray astronomy strives for predictive power, but so far is more like social science than physics: we can find ways to explain observations, but not predict them. Of course Jacobs and Seitzer haven't made a prediction either, since they knew of the x-ray bursts before they devised their mini-hole theory; still in all, they've as good an explanation as anyone.

  Those x-ray events are bothersome. They're also hard to study, because of the atmosphere. Of course that's fortunate: if we could directly observe those x-rays coming from space, we'd none of us be here. Our atmosphere lets ordinary light squeak through with 20% attenuation, but it stops x-rays cold, and that's just as well for us, but bad for astronomers. Thus it's only since we began sending up satellites that we learned of x-ray events, and we still don't know much about them.

  What we do know is driving astrophysicists nuts. Astronomy, after all, is usually concerned with rather slow and stately phenomena, and highly repetitive events, such as orbits. Things aren't supposed to change very fast. Now suddenly we're confronted with rapid x-ray events, and to make it worse we can't focus the x-ray satellite "telescopes" very well, so we can't even be sure of where the x-ray bursts are coming from. However, the Dutch astronomical satellite has a rather small field, and happens to point in a good direction, and it says that a probable source of x-ray bursts is globular clusters. And that's weird.

  Globular clusters: big balls of very old stars. About 200,000 stars to the ball, packed very close with average interstellar distances of light-months. There are a number of such clusters hanging about the galaxy in a kind of halo. Being very old stars they ought to be stable, without too many strange things happening; but here are these x-ray bursts.

  The bursts themselves look like a spike of energy, then a slow decay. Typical: every 4-1/2 hours the x-ray energy goes from essentially none to a lot in about 0.1 second, the event lasts at peak for about 10 seconds, and then decays over a period of hundreds of seconds. That needs explanation.

  Possibly the Jacobs-Seitzer theory will cover the facts. There are other theories, very far-out, weird in fact, probably wrong, but really beautiful. Take, for example, crashing neutron stars.

  Imagine a rather floppy disk of gaseous matter orbiting a star like the rings of Saturn. Put this whole mess into a globular cluster. The disk probably isn't that hard to come by in there: globular clusters act as gravitational traps, and might easily accumulate all kinds of cosmic junk, including the debris of old stars, etc.

  Now image a neutron star in an orbit tilted with respect to the plane of the floppy disk Every half-orbit the neutron star crashes through the disk, producing x-ray bursts. A lovely idea.

  Alas, it's almost certainly wrong: there are many sources of x-ray bursts, and it's just hard to believe that anything as unlikely as crashing neutron stars are common, even in our queer universe.

  Let's try another theory: flash-burning. Take one neutron star. Let hydrogen fall on it. The hydrogen accumulates on the surface, slowly building up until the neutron star has an "atmosphere" a few millimeters thick The density increases sharply until it hits the critical point, and bang! Every few hours there's a hydrogen bomb enveloping the neutron star.

  Far out, right? Yet those theories were described at a meeting of the super-orthodox AAAS. Now let's look at one "neglected" theory.

  * * *

  Dean Drive: science fiction readers must know about that. Norman Dean was a crackpot inventor. Many years ago he built a gadget. (He also took out a patent; on that, more later.) Dean claimed something that sounds very reasonable, hardly far out at all: that his mechanism "converts rotary acceleration into linear acceleration." After all, a rotating object does have acceleration, right? Acceleration is acceleration, right? Thus to convert from one to the other violates no conservation laws.

  Now that's an attractive concept. Take an electric motor (Dean used an ordinary quarter-inch electric drill) as the source of rotary acceleration; hook up to the Dean mechanism; and lo, you have a spacedrive. Very attractive, because by installing a Dean Machine in a nuclear submarine we'd have a spaceship already built!

  Now Dean did build a machine. It did not lift itself off the floor. Observers agree on that much—and that's about all they do agree on. The machine shook and shimmied and jumped up and down, and there was a famous photograph of Dave Garroway shoving a piece of paper under the machine. Also, John W. Campbell Jr. reported that he'd seen the apparent weight of the Dean Machine, as measured on a bathroom scale, appreciably decrease when the gizmo was turned on, to be restored when it was switched off. G. Harry Stine reports that he felt the machine push against his hand; push hard, and when it was turned off the push wasn't there.

  Unfortunately, that's about the sum total of observational evidence. Dean never let his machine be examined by anyone else. However, the story doesn't quite end there.

  Not long ago Harry Stine published an article about the Dean Drive in that other magazine (the one with rivets). Robert Prehoda (DESIGNING THE FUTURE; Chilton, 1967, among other excellent books) and I were discussing Harry's article (Harry is an old friend of Prehoda's) and it came out that Bob Prehoda had tried to buy the Dean Drive back in the early 6O's. At the time Bob was representing the Rockefeller family, so the ability to pay real folding money wasn't in question. I knew of a couple of other aerospace firms who'd also made the effort. The stories were remarkably similar: Dean wouldn't let anyone examine the machine. He wanted a million dollars and a Nobel prize up front: then you could play with the gadget. No one was going to put up that kind of money without seeing the gizmo in operation. There are just too many ways the reported results could be obtained without anything new. For example, if you jump up and down on your bathroom scale at just the right frequencies, you can fool the scale into thinking you're either lighter or heavier than you are; its response time just can't handle that non-steady weight.

  Prehoda had also known Dr. William Davis, USAF colonel and successful inventor, who had worked out a physics theory which, supposedly, allows the Dean Drive and other "reactionless" drives to work. "Spacedrive" Davis spent a lot of time promoting what came to be called "Davis mechanics," and although his practical work made him a good bit of money, he acquired an unenviable reputation among theoreticians. Harry Stine worked for Davis and built several gadgets supposed to test the Davis theories.

  Davis is dead. Norman Dean is dead. John W. Campbell is
dead. And neither Prehoda nor I could get out of the back of our minds a simple fact: Gregor Mendel discovered genetics but the results lay unused from 1868 to 1900 because no one wanted to listen to this crazy abbot Could something similar be happening here?

  We doubted it, but it did seem reasonable to try to get all the data together in one place before everybody who actually saw the Dean Machine, or tested Davis's theories, went off to Murphy's Hall. We decided to invite Harry to Los Angeles to confer with some other people on how best to test this whole concept once and for all. Understand: none of us, not one, really "believes" in spacedrives; but the concept is so blasted important and the consequences are so far-reaching, that surely it's worth a little effort?

  So who do you invite to such a conference? What's needed are people with minds that are "open," but not minds pierced with gaping holes; with enough knowledge of physics and math to follow the arguments; and enough scientific integrity neither to bite on the idea simply because it's unorthodox nor to reject for that reason.

  We ended up with: Robert Prehoda, chemist and propulsion systems expert; Larry Niven; Dan Alderson, astronomer and computer scientist; Robert Forward, physicist and gravitation expert; G. Harry Stine, engineer and gadgeteer extraordinary; and myself. It was an interesting lunch. Something may come of it. And the result illustrates precisely the point of this chapter.