It’s easy to see why. Solitude in the vast expanse of empty space is unnerving, as the seventeenth-century French mathematician and philosopher Blaise Pascal put it (see the epigraph to this chapter). Infinite quietness is indeed frightening. The human yearning to fill the cosmic darkness with a Divine Presence—or at the very least with kindred forms of life—is as natural as the search for warmth and light in the primeval woods. What could be more exciting, and more comforting, than the discovery of some far-distant cousins in the universe? In the course of writing this book, I asked a number of eminent physicists and cosmologists to give me one question about the universe to which they would like a definitive answer. “Is there intelligent life out there?” was the response of Nobel laureate Sheldon Glashow.
We have all thought about that. In whatever way it happens, first contact would alter our civilization more dramatically than any other single event in human history. At a recent conference in Naples on the possibility of extraterrestrial intelligence, I gave a talk centered on the physics of the subject. At the same conference, George Coyne, who heads the Vatican Observatory, spoke about the challenge to Christian theology presented by the possible existence of extraterrestrial civilizations. His talk reminded me of the remark of the unarguably devout twelfth-century Jewish philosopher Maimonides, in The Guide of the Perplexed, that while the Scriptures were true, if the results of science disagreed with one’s scriptural interpretation then one would have to reexamine that interpretation. After Coyne’s talk, I asked him what seemed the inevitable question: Might theologians who address this issue have to conclude that the existence of extraterrestrial intelligent life is incompatible with the tenets of the Catholic faith? He answered that they very well might. My own feeling is that the discovery of extraterrestrial life would be far more jolting—and not just to orthodox Christians—than was the revelation that the Earth is not the center of the solar system. It is my long-held conviction (and clearly that of the producers of such films as Contact) that the discovery of aliens would surpass the Copernican Revolution in its consequences for our understanding of our own existence and for the persistence of our present belief systems.
So, how would you know a successful interstellar visiting spacecraft if you saw one? How would it behave? Thinking about such questions is a useful precursor to determining how we ourselves might one day carry out the mission of the U.S.S. Enterprise “to explore strange new worlds, to seek out new life and new civilizations, to boldly go where no man has gone before.” The problem of how to recognize a vehicle from another world turns out to be a little more subtle than one might guess.
The traditional notion has been that UFOs don’t behave like rockets or planes (this is, after all, what makes them UFOs). Strange lights that flit unlikely distances back and forth across the sky, like the dazzling display in Steven Spielberg’s Close Encounters of the Third Kind, are typical. More recently, in one of the early episodes of The X-Files, the ardent UFO hunter and FBI agent Fox Mulder finally gets to see some real UFOs in a secret air force installation somewhere in the Southwest (could it be Area 51?), and these vehicles do just what UFOs are supposed to do—namely, everything our own aircraft can’t. Mulder and his colleague Dana Scully are astounded by a series of bright disks moving at incredible speeds through the skies above the remote base, turning at 90-degree angles on a dime. Like many of the action sequences in The X-Files, this one evokes episodes in the canonical UFO literature. Well, Catch-22 comes to mind, too. While a UFO might be defined as something that moves through the air in a manner unlike that of a conventional rocket or plane, I would argue that this is precisely how a genuine UFO would not behave!
Let me offer the following asides: One of the oddly appealing things about The X-Files is that it makes no concessions to reality. And as in all successful dramas, you identify with the characters; that identification is really what compels you to watch. Fox Mulder is the earnest New Age searcher, trained as a psychologist, always willing to be skeptical of the laws of physics and much less willing to be skeptical of his long-held beliefs. Dana Scully, the more rational “skeptic” of the two, was trained as a physicist—no less!—before her stint in medical school, and her gender constitutes a wonderful reversal, as far as the usual run of TV is concerned. I will be forever grateful to the series’ producers for giving us this role model of an intelligent, attractive, and relentlessly pragmatic female physicist. She is the foil to Mulder’s ineffable eagerness. She is always there to ask, Why? And she sometimes does.
In the UFO episode just described, it turns out that what Scully and Mulder have seen are alien spacecraft piloted by crack air force test pilots. The pilots can’t handle the strain of racketing around in these unfamiliar ships, and they start disappearing from sight. Well, it’s indeed likely that terrestrial pilots wouldn’t be able to hack it; however, neither would the alien spacecraft—and Scully, a physicist, probably should have known as much.
Let’s go back to Newton and briefly consider the stresses induced when your average UFO—traveling at, say, twice the speed of sound—makes a 90-degree turn. The speed of sound in air is about 750 miles per hour, or about 350 meters per second, so imagine that we are observing an object traveling at 700 meters per second and we see it turn 90 degrees. In other words, it suddenly stops traveling forward and now moves sidewise at a right angle; in effect, it comes to a halt and then resumes travel in another direction. What kind of force would be required to make a craft moving this fast stop on a dime? To be generous, let’s say it takes 1/10 of a second for the vehicle to stop and change direction—a short enough time so that you might perceive it as instantaneous. Well, the deceleration of the spacecraft performing this maneuver would be about 700 times the acceleration that gravity produces in a falling object at the Earth’s surface. In the language of the G-forces, familiar to aircraft pilots, aficionados of space exploration, and readers of my previous book, this means that the occupants will feel a force of 700 Gs. I remind you that the maximum G-force people can experience and survive for short periods is only 8 Gs or so. Experiencing 700 Gs would be the same as having a 70,000-pound, or 35-ton, weight pressing down on your shoulders (more or less the same force you would feel from the increase in atmospheric pressure due to the visiting saucers in Independence Day).
What effect would such a force have on the craft itself? Well, imagine a plane suddenly losing engine power at, say, 1,000 feet and falling to the ground. If it makes a crater a meter deep, I estimate that the G-force experienced by the plane during impact is about 2,800 Gs. Judging from what most plane crashes look like, I would suggest that no craft made out of mere metal would be likely to survive the X-Files-type aerobatics for long.
But you may argue that UFOs are not made of mere metal. The advanced civilizations that create them have made them out of super-strong materials. Well, OK—but what about the aliens themselves? Would they be able to withstand those levels of G-force? I don’t see how, unless they evolved in an environment that produces 40-ton raindrops.
Be that as it may, what is the point of designing a spacecraft to perform right-angle turns and other such exotic aeronautics? As we will discuss, a voyage from another world is a demanding one, and at least 99.999 percent of the time will be spent in space. It’s unlikely that any alien craft will be tailor-made to behave as an acrobatic sports plane in the Earth’s atmosphere. Remember the Apollo missions to the Moon? (If you are over forty you ought to, and if you are under forty you may well have seen the estimable Apollo 13.) The mission’s lander—the LEM, or Lunar Excursion Module—was spectacularly un-aerodynamic. Why? Because its chief job was to descend from the orbiting command module to the lunar surface, where aerodynamics is irrelevant because there is no air. Our present space shuttle is designed more like an airplane, but that’s because it has to spend a substantial and important part of its time reentering the atmosphere.
We tend to anthropomorphize aliens, and this may well have led us to “humanize” their spa
cecraft as well. For most of the past century, we’ve been used to traveling in the air, so it seems natural to imagine that craft from other planets must also be designed for air travel. Planes bank when they turn because they have to: they operate by using air pressure—that is, they fly because the air pressure above the wings is less than that below the wings. So to turn right, they have to bank, by raising their left wing and lowering their right one, which tips them rightward. In space, where wings do not figure in propulsion, the main reason to bank is removed. Yet the Enterprise and Han Solo’s Millennium Falcon nevertheless always bank. Why? Well, the answer is the same as that for another question I’m sometimes asked: “Why does the Voyager lift its warp nacelles just before going into warp drive?” Simple: It looks good.
Since the summer of 1947—the same summer as the famous sighting at Roswell, New Mexico—when Kenneth Arnold, a commercial pilot, thought he saw a formation of silvery disks above Mt. Rainier and subsequent newspaper stories dubbed his visions “flying saucers,” saucer-shaped vehicles have been the ship of choice for witnesses of alien visitation. Why not? After all, a spinning disk is satisfyingly stable—it can generate lift and it resists tipping over. Moreover, as an astute editor once remarked to me, “Isn’t it uncanny that flying saucers were observed before Frisbees were invented? We now know that Frisbees are great at moving through the air. How could the early UFO observers have guessed this fact?”
Spinning disks are stable indeed, and Frisbees fly well. But both these facts are largely irrelevant where spacecraft are concerned. In the first place, we all know what happens if you are inside an object that’s spinning at any significant rate. You’re thrown against the outer wall. (You also tend to get sick, especially if you look out the window at scenery that isn’t spinning.) While this is precisely the mechanism we will one day use to produce artificial gravity on spaceflights of long duration—as Arthur C. Clarke and Stanley Kubrick wonderfully depicted in the classic 2001—a small craft spinning as rapidly as the saucers on TV would likely immobilize its crew against its perimeter. And simply causing the outside of the hull to spin won’t do, either, since in order to be stabilized by rotation, most of a vehicle’s mass has to be spinning.
Finally, as I’ve noted, interstellar (and even our own interplanetary) spacecraft are designed for traveling in space. A Frisbee flies well because of its aerodynamic properties. The spinning not only gives it stability but makes the air pressure less above the Frisbee’s surface than below it. Where there’s no air, this effect is useless. In the near vacuum of space, a Frisbee or any other saucer shape would perform as well as a flying pretzel. Should we expect an invasion by flying pretzels? Well, the best answer comes from trying to imagine what we ourselves would build. Whether visitors from space want to conquer us or invite us to join their federations, they will need to have solved the same problems we face if we are ever to escape our ties to the Earth.
CHAPTER THREE
TO BOLDLY GO… IF WE CAN AFFORD IT
Space is big. Really big. You just won’t believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it is a long way down the road to the chemist, but that’s just peanuts to space.
—Douglas Adams, The Hitchhiker’s Guide to the Galaxy
I was recently in the city of Geneva, and the words of a famous former resident, Jean-Jacques Rousseau, came to mind: “Man is born free, and he is everywhere in chains.” More than 20 years have passed since humans last set foot on any object other than the Earth, and not even another manned voyage to the Moon is in our near future. Mars beckons us with tantalizing new hints of extraterrestrial life suggested by recent analyses of Martian meteorites, and recent images from NASA’s Galileo spacecraft suggest that buried beneath the frozen surface of the Jovian moon Europa is organic slush and perhaps even an ocean—a primordial breeding ground for life. Yet the possibility of human voyages to the Red Planet or the moons of Jupiter anytime soon seems remote. It is the threshold of the twenty-first century, and as a species we remain as Earthbound as ever. To those who yearn to break free from our terrestrial chains, our circumstances border on the tragic.
Our imprisonment is in stark contrast to the pictures bombarding us on the big and little screens, where beings voyage among the stars with impunity, using fusion, warp drive, hyperdrive, wormholes, antigravity, and whatever else pops into the fertile minds of the scriptwriters. So, what’s our problem? How can we get from here to there? Well, at the heart of it all—even beyond the issue of what is physically plausible and what isn’t—lies the matter of money. As pedestrian as it may seem, the chief factor limiting our ability to get a manned spacecraft even only to Mars and back again, much less to Alpha Centauri (the nearest star system, only some 4 light-years away), is that we cannot finance a mission involving a ship big enough to accommodate the needed fuel and a reasonable number of astronauts on a voyage of long duration.
In real life, and sometimes in science fiction, money determines the difference between what may happen, even in principle, and what does happen. I remind you that it was money, or rather the lack of it, that led Gene Roddenberry to invent the transporter allowing the Enterprise crew to “beam down” to planets, since he didn’t have the budget to depict the landing of a spacecraft in the course of each episode. Finally, after 30 years, confident of a seventh surefire hit movie and a third spin-off hit television series, Paramount showed us the Enterprise crash-landing on a planet, and Kathryn Janeway’s Voyager has also landed, a bit more smoothly, in a number of episodes. Nothing turns on a screenwriter’s imagination like money—witness the words attributed to Kevin Smith, writer of the new Superman movie, due out in 1998: “The budget is big. God almighty, it is big!” As far as real spaceflight is concerned, money translates not into production values (at least for those of us who believe that NASA really did put men on the Moon and didn’t stage the whole thing on a Hollywood back lot) but into energy. Energy, in turn, means fuel.
This aspect of our problem may seem baffling at first. After all, two decades ago we were able to rocket a manned command module, complete with LEM, to the Moon and back; surely, rocket engines have not become less powerful since that time! Of course, Mars is about 1,000 times farther from the Earth than the Moon is, which appears to suggest that going there at the same speed would take 1,000 times longer, or almost 10 years one way—too long for any manned mission given the present state of our space technology. But the Earth is barreling around the Sun at something like 20 times the speed at which Apollo journeyed to the Moon. Thus, a Mars-bound spacecraft leaving Earth orbit will be launched from a platform already moving at considerable velocity relative to Mars. If one uses Earth’s solar-system velocity as a springboard to propel a rocket to Mars, a one-way trip would take no more than six months to a year, assuming the craft traveled away from the Earth at only 2 or 3 times the speed of Apollo.
So, I repeat, what’s the problem? Well, while the aforementioned increase in speed may not sound like much, it comes at a high cost. To understand this, we have to remember how a rocket works. Rocket propulsion depends on the law of physics called Conservation of Momentum. Put simply, this law states that if I throw something away from me, I will recoil in the opposite direction. Rockets “recoil” forward because they throw mass out their back ends. The speed with which a rocket is propelled forward depends on three factors: the speed at which the propellant leaves the back end, the mass of the expelled propellant, and the mass of the rocket and the fuel remaining on board. Thus, for example, an inflated balloon that is not tied off will fly forward if I let it go, because it expels air quickly out the back. If the balloon were not so light—say, if it were made of concrete—it wouldn’t go anywhere. Similarly, if the balloon is not inflated very much, so that the walls of the balloon are hardly stretched and the air is expelled out the back very slowly, it won’t go anywhere.
Where balloons are concerned, one doesn’t worry about the additional mass represented by the air inside. Not
so for rockets: they require so much fuel that its additional weight cannot be ignored. And there’s the rub: If I want my rocket to move faster, I have to throw more propellant out the back; but if I have to throw more propellant out the back, I must start out with more fuel aboard the ship. But if I start out with more fuel aboard the ship, I must expel a little more propellant than I would have to get the ship (plus fuel) moving in the first place. But that means I have to bring along more propellant… and so on and so forth.
The Greek philosopher Zeno faced a similar problem two millennia ago when he tried to add up an infinite series of numbers. The resolution is still the same: as long as the increment I keep adding gets smaller fast enough, even an infinite series of terms can have a finite sum. In this case, do the fuel increments needed get small enough fast enough? It turns out that the answer is yes—at least as long as one is traveling well below the speed of light; when you approach light speed, the effects of relativity begin to complicate things. Nevertheless, the final total amount of fuel required depends sensitively—in fact, exponentially—on the final speed of the ship relative to the speed at which propellant shoots out the back of the ship.
As this final, cruising velocity begins to exceed the speed of the propellant, things get unwieldy. Increasing the final velocity of a rocket from 1 to 2 times the speed of the propellant out the back requires 4 times as much fuel. But increasing the final speed to 4 times that with which the propellant leaves the ship will increase the required amount of fuel by a factor of more than 30! In this case, the initial mass of the ship plus fuel would be about 55 times the mass of the ship without fuel.
Beyond Star Trek Page 2