Physics of the Impossible Part 6

A more novel approach is the [email protected] project, initiated by astronomers at the University of California at Berkeley in 1999. They hit upon the idea of enlisting millions of PC owners whose computers sit idle most of the time. Those who partic.i.p.ate download a software package that will help to decode some of the radio signals received by a radio telescope while the partic.i.p.ant's screen saver is activated, so there is no inconvenience to the PC user. So far the project has signed up 5 million users in more than two hundred countries, consuming over a billion dollars of electricity, all at little cost. It is the most ambitious collective computer project ever undertaken in history and could serve as a model for other projects that need vast computer resources to carry out computations. So far no signal from an intelligent source has been found by [email protected]

After decades of hard work, the glaring lack of any progress in SETI research has forced its proponents to ask hard questions. One obvious defect might be the exclusive use of radio signals at certain frequency bands. Some have suggested that alien life might use laser signals instead of radio signals. Lasers have several advantages over radio, because a laser's short wavelength means that you can pack more signals into one wave than you can with radio. But because laser light is highly directional and also contains just one frequency, it is exceptionally hard to tune into precisely the right laser frequency.

Another obvious defect might be SETI researchers' reliance on certain radio frequency bands. If there is alien life, it may use compression techniques or might disperse messages via smaller packages, strategies that are used on the modern Internet today. Listening in on compressed messages that have been spread over many frequencies, we might hear only random noise.

But given all the formidable problems facing SETI, it is reasonable to a.s.sume that sometime in this century we should be able to detect some signal from an extraterrestrial civilization, a.s.suming that such civilizations exist. And should that happen, it would represent a milestone in the history of the human race.

WHERE ARE THEY?.

The fact that the SETI project so far has found no indication of signals from intelligent life in the universe has forced scientists to take a cold, hard look at the a.s.sumptions behind Frank Drake's equations for intelligent life on other planets. Recently astronomical discoveries have led us to believe that the chance of finding intelligent life are much different than originally computed by Drake in the 1960s. The chance that intelligent life exists in the universe is both more optimistic and more pessimistic than originally believed.

First, new discoveries have led us to believe that life can flourish in ways not considered by Drake's equations. Before, scientists believed that liquid water can exist only in the "Goldilocks zone" surrounding the sun. (The distance from Earth to the sun is "just right." Not too close to the sun, because the oceans would boil, and not too far away, because the oceans would freeze, but "just right" to make life possible.) So it came as a shock when astronomers found evidence that liquid water may exist beneath the ice cover on Europa, a frozen moon of Jupiter. Europa is well outside the Goldilocks zone, so it would appear not to fit the conditions of Drake's equation. Yet tidal forces might be sufficient to melt the ice cover of Europa and produce a permanent liquid ocean. As Europa spins around Jupiter, the planet's huge gravitational field squeezes the moon like a rubber ball, creating friction deep within its core, which in turn could cause the ice cover to melt. Since there are over one hundred moons in our solar system alone, this means that there could be an abundance of life-supporting moons in our solar system outside the Goldilocks zone. (And the 250 or so giant extrasolar planets so far discovered in s.p.a.ce might also have frozen moons that can support life.) Furthermore, scientists believe the universe could be peppered with wandering planets that no longer circle around any star. Because of tidal forces, any moon orbiting a wandering planet might have liquid oceans under its ice cover and hence life, but such moons would be impossible to see by our instruments, which depend on detecting light from the mother star.

Given that the number of moons probably greatly outnumbers the number of planets in a solar system, and given that there could be millions of wandering planets in the galaxy, the number of astronomical bodies with life-forms in the universe might be much larger than previously believed.

On the other hand, other astronomers have concluded, for a variety of reasons, that the chances for life on planets within the Goldilocks zone are probably much lower than originally estimated by Drake.

First, computer programs show that the presence of a Jupiter-sized planet in a solar system is necessary to fling pa.s.sing comets and meteors into s.p.a.ce, thereby continually cleaning out a solar system and making life possible. If Jupiter did not exist in our solar system, Earth would be pelted with meteors and comets, making life impossible. Dr. George Wetherill, an astronomer at the Carnegie Inst.i.tution in Was.h.i.+ngton, D.C., estimates that without the presence of Jupiter or Saturn in our solar system, the Earth would have suffered a thousand times more asteroid collisions, with a huge life-threatening impact (like the one that destroyed the dinosaurs 65 million years ago) occurring every ten thousand years. "It's hard to imagine how life could survive that extreme onslaught," he says.

Second, our planet is blessed with a large moon, which helps to stabilize the Earth's spin. Extending Newton's laws of gravity over millions of years, scientists can show that without a large moon, our Earth's axis probably would have become unstable and the Earth might have tumbled, making life impossible. French astronomer Dr. Jacques Lasker estimates that without our moon the Earth's axis could oscillate between 0 and 54 degrees, which would precipitate extreme weather conditions incompatible with life. So the presence of a large moon also has to be factored into conditions used for Drake's equations. (The fact that Mars has two tiny moons, too small to stabilize its spin, means that Mars may have tumbled in the distant past, and may tumble again in the future.) Third, recent geological evidence points to the fact that many times in the past, life on Earth was almost extinguished. About 2 billion years ago the Earth was probably completely covered in ice; it was a "s...o...b..ll Earth" that could barely support life. At other times, volcanic eruptions and meteor impacts might have come close to destroying all life on Earth. So the creation and evolution of life is more fragile than we originally thought.

Fourth, intelligent life was also nearly extinguished in the past. About a hundred thousand years ago there were probably only a few hundred to a few thousand humans, based on the latest DNA evidence. Unlike most animals within a given species, which are separated by large genetic differences, humans are all nearly alike genetically. Compared to the animal kingdom, we are almost like clones of each other. This phenomenon can only be explained if there were "bottlenecks" in our history in which most of the human race was nearly wiped out. For example, a large volcanic eruption might have caused the weather to suddenly get cold, nearly killing off the entire human race.

There are still other fortuitous accidents that were necessary to sp.a.w.n life on Earth, including * A strong magnetic field. This is necessary in order to deflect cosmic rays and radiation that could destroy life on Earth.

* A moderate speed of planetary rotation. If the Earth rotated too slowly, the side facing the sun would be blisteringly hot, while the other side would be freezing cold for long periods of time; if the Earth rotated too quickly, there would be extremely violent weather conditions, such as monster winds and storms.

* A location that is the right distance from the center of the galaxy. If the Earth were too close to the center of the Milky Way galaxy, it would be hit with dangerous radiation; if it were too far from the center, our planet would not have enough higher elements to create DNA molecules and proteins.

For all these reasons astronomers now believe that life might exist outside the Goldilocks zone on moons or wandering planets, but that the chances of the existence of a planet like Earth capable of supporting life within the Goldilocks zone are much lower than previously believed. Overall most estimates of Drake's equations show that the chances of finding civilization in the galaxy are probably smaller than he originally estimated.

As Professors Peter Ward and Donald Brownlee have written, "We believe that life in the form of microbes and their equivalents is very common in the universe, perhaps more common than even Drake and [Carl] Sagan envisioned. However, complex life-animals and higher plants-is likely to be far more rare than is commonly a.s.sumed." In fact, Ward and Brownlee leave open the possibility that the Earth may be unique in the galaxy for harboring animal life. (Although this theory may dampen the search for intelligent life in our galaxy, it still leaves open the possibility of life existing in other distant galaxies.) THE SEARCH FOR EARTH-LIKE PLANETS.

Drake's equation, of course, is purely hypothetical. That is why the search for life in outer s.p.a.ce has gotten a boost from the discovery of extrasolar planets. What has hindered research into extrasolar planets is that they are invisible to any telescope since they give off no light of their own. They are in general a million to a billion times dimmer than the mother star.

To find them astronomers are forced to a.n.a.lyze tiny wobblings in the mother star, a.s.suming that a large Jupiter-sized planet is capable of altering the orbit of the star. (Imagine a dog chasing its tail. In the same way, the mother star and its Jupiter-size planet "chase" each other by revolving around each other. A telescope cannot see the Jupiter-sized planet, which is dark, but the mother star is clearly visible and appears to wobble back and forth.) The first true extrasolar planet was found in 1994 by Dr. Alexandr Wolszczan of Pennsylvania State University, who observed planets revolving around a dead star, a rotating pulsar. Because the mother star had probably exploded as a supernova, it seemed likely that these planets were dead, scorched planets. The following year two Swiss astronomers, Michel Mayor and Didier Queloz of Geneva, announced that they had found a more promising planet with a ma.s.s similar to Jupiter orbiting the star 51 Pegasi. Soon after that the floodgates were opened.

In the last ten years there has been a spectacular acceleration in the number of extrasolar planets being found. Geologist Bruce Jakosky of the University of Colorado at Boulder says, "This is a special time in the history of humanity. We're the first generation that has a realistic chance of discovering life on another planet."

None of the solar systems found so far resemble our own. In fact, they are all quite dissimilar to our solar system. Once, astronomers thought that our solar system was typical of others throughout the universe, with circular orbits and three rings of planets surrounding the mother star: a rocky belt of planets closest to the star, next a belt of gas giants, and finally a comet belt of frozen icebergs.

Much to their surprise, astronomers found that none of the planets in other solar systems followed that simple rule. In particular, Jupiter-sized planets were expected to be found far from the mother star, but instead many of them orbited either extremely close to the mother star (even closer than the orbit of Mercury) or in extremely elliptical orbits. Either way the existence of a small, Earth-like planet orbiting in the Goldilocks zone would be impossible in either condition. If the Jupiter-sized planet orbited too close to the mother star, it meant that the Jupiter-sized planet had migrated from a great distance and gradually spiraled into the center of the solar system (probably due to friction caused by dust). In that case, the Jupiter-size planet would eventually cross the orbit of the smaller, Earth-like planet, flinging it into outer s.p.a.ce. And if the Jupiter-sized planet followed a highly elliptical orbit, it would mean that the Jupiter-sized planet would pa.s.s regularly through the Goldilocks zone, again causing any Earth-like planet to be flung into s.p.a.ce.

These findings were disappointing to planet hunters and astronomers hoping to discover other Earth-like planets, but in hindsight these findings were to be expected. Our instruments are so crude that they can detect only the largest, fastest-moving Jupiter-sized planet that can have a measurable effect on the mother star. Hence it is not surprising that today's telescopes can detect only monster planets that are moving rapidly in s.p.a.ce. If an exact twin of our own solar system exists in outer s.p.a.ce, our instruments are probably too crude to find it.

All this may change, with the launching of Corot, Kepler, and the Terrestrial Planet Finder, three satellites that are designed to locate several hundred Earth-like planets in s.p.a.ce. The Corot and Kepler satellites, for example, will examine the faint shadow that would be cast by an Earth-like planet as it crosses the face of the mother star, slightly reducing its sunlight. Although the Earth-like planet would not be visible, the reduction in sunlight from the mother star could be detected by satellite.

The French Corot satellite (which in French stands for Convection, Stellar Rotation, and Planetary Transits) was successfully launched on December 2006 and represents a milestone, the first s.p.a.ce-based probe to search for extrasolar planets. Scientists hope to find between ten and forty Earth-like planets. If they do, the planets will probably be rocky, not gas giants, and will be just a few times bigger than the Earth. Corot will also probably add to the many Jupiter-sized planets already found in s.p.a.ce. "Corot will be able to find extrasolar planets of all sizes and natures, contrary to what we can do from the ground at the moment," says astronomer Claude Catala. Altogether scientists hope the satellite will scan up to 120,000 stars.

Any day, the Corot may find evidence of the first Earth-like planet in s.p.a.ce, which will be a turning point in the history of astronomy. In the future people may have an existential shock gazing at the night sky and realizing that there are planets out there that could harbor intelligent life. When we look into the heavens in the future, we might find ourselves wondering if anyone is looking back.

The Kepler satellite is tentatively scheduled for launch in late 2008 by NASA. It is so sensitive that it may be able to detect up to hundreds of Earth-like planets in outer s.p.a.ce. It will measure the brightness of 100,000 stars to detect the motion of any planet as it crosses the face of the star. During the four years it will be in operation, Kepler will a.n.a.lyze and monitor thousands of distant stars up to 1,950 light-years from Earth. In its first year in orbit, scientists expect the satellite to find roughly * 50 planets about the same size as Earth, * 185 planets about 30 percent larger than the Earth, and * 640 planets about 2.2 times the size of the Earth.

The Terrestrial Planet Finder may have an even better chance of finding Earth-like planets. After several delays, it is tentatively scheduled for launch in 2014; it will a.n.a.lyze as many as one hundred stars up to 45 light-years away with great accuracy. It will be equipped with two separate devices to search for distant planets. The first is a coronagraph, a special telescope that blocks out the sunlight from the mother star, reducing its light by a factor of a billion. The telescope will be three to four times bigger than the Hubble s.p.a.ce Telescope and ten times more precise. The second device on the Finder is an interferometer, which uses the interference of light waves to cancel the light from the mother star by a factor of a million.

Meanwhile the European s.p.a.ce Agency is planning to launch its own planet finder, the Darwin, to be sent into orbit in 2015 or later. It is planned to consist of three s.p.a.ce telescopes, each about 3 meters in diameter, flying in formation, acting as one large interferometer. Its mission, too, will be to identify Earth-like planets in s.p.a.ce.

Identifying hundreds of Earth-like planets in outer s.p.a.ce will help to refocus the SETI effort. Instead of randomly scanning nearby stars, astronomers will be able to pinpoint their efforts on a small collection of stars that may harbor a twin of the Earth.

WHAT DO THEY LOOK LIKE?.

Other scientists have tried to use physics, biology, and chemistry to guess what alien life might look like. Isaac Newton, for example, wondered why all the animals he could see around him possessed the same bilateral symmetry-two eyes, two arms, and two legs arranged symmetrically. Was this a fortuitous accident or an act of G.o.d?

Today biologists believe that during the "Cambrian explosion," about half a billion years ago, nature experimented with a vast array of shapes and forms for tiny, emerging multicellular creatures. Some had spinal cords shaped like an X, Y, or Z. Some had radial symmetry like a starfish. By accident one had a spinal cord shaped like an I, with bilateral symmetry, and it was the ancestor of most mammals on Earth. So in principle the humanoid shape with bilateral symmetry, the same shape that Hollywood uses to depict aliens in s.p.a.ce, does not necessarily have to apply to all intelligent life.

Some biologists believe that the reason that diverse life-forms flourished during the Cambrian explosion is because of an "arms race" between predator and prey. The emergence of the first multicelled organisms that could devour other organisms forced an accelerated evolution of the two, with each one racing to outmaneuver the other. Like the arms race between the former Soviet Union and the United States during the cold war, each side had to hustle to keep ahead of the other.

By examining how life evolved on this planet, one may also make the following speculations about how intelligent life might have evolved on Earth. Scientists have concluded that intelligent life probably requires 1. Some sort of eyesight or sensing mechanism to explore its environment; 2. Some sort of thumb used for grabbing-it could also be a tentacle or claw; 3. Some sort of communication system, such as speech.

These three characteristics are required for sensing our environment and eventually manipulating it-both of which are the hallmarks of intelligence. But beyond these three characteristics, anything goes. Contrary to so many of the aliens shown on TV, an extraterrestrial does not have to resemble a human at all. The child-like, bug-eyed aliens we see on TV and in the movies, in fact, look suspiciously like the 1950s aliens from B-grade movies, which are firmly buried in our unconscious.

(Some anthropologists, however, have added a fourth criteria for intelligent life to explain a curious fact: humans are vastly more intelligent than they have to be to survive in the forest. Our brains can master s.p.a.ce travel, the quantum theory, and advanced mathematics-skill sets that are totally unnecessary for hunting and scavenging in the forest. Why this excess brainpower? In nature when we see pairs of animals like the cheetah and the antelope that possess extraordinary skills far beyond those required for survival, we find that there was an arms race between them. Similarly, some scientists believe there is a fourth criteria, a biological "arms race" propelling intelligent humans. Perhaps that arms race was with other members of our own species.) Think of all the remarkably diverse life-forms on the Earth. If one, for example, could selectively breed octopods for several million years, it is conceivable that they might also become intelligent. (We separated from the apes 6 million years ago, probably because we were not well adapted to the changing environment of Africa. By contrast, the octopus is very well adapted to its life beneath a rock and hence has not evolved for millions of years.) Biochemist Clifford Pickover says that when he gazes at all the "crazy-looking crustaceans, squishy-tentacled jellyfish, grotesque, hermaphroditic worms, and slime molds, I know that G.o.d has a sense of humor, and we will see this reflected in other forms in the universe."

Hollywood, however, probably gets it right when it depicts intelligent alien life-forms as carnivores. Not only do meat-eating aliens guarantee bigger box office sales, there is also an element of truth to the depiction. Predators are usually smarter than their prey. Predators have to use cunning to plan, stalk, hide, and ambush prey. Foxes, dogs, tigers, and lions have eyes that are on the front of their face in order to judge distance when they pounce on their prey. With two eyes, they can use 3-D stereo-vision to lock on to their prey. Prey, such as deer and rabbits, on the other hand, just have to know how to run. They have eyes that are on the side of their face in order to scan for predators 360 degrees around them.

In other words, intelligent life in outer s.p.a.ce may very well evolve from predators with eyes, or some sensing organ, on the front of their face. They may possess some of the carnivorous, aggressive, and territorial behavior we find in wolves, lions, and humans on Earth. (But since such life-forms would probably be based on entirely different DNA and protein molecules, they would have no interest in eating, or mating with, us.) We can also use physics to conjecture what their body size might be. a.s.suming they live on Earth-sized planets and have the same rough density as water, like life-forms on Earth, then huge creatures are probably not possible because of the scale law, which states that the laws of physics change drastically as we increase the scale of any object.

MONSTERS AND THE SCALE LAW.

If King Kong really existed, for example, he would not be able to terrorize New York City. On the contrary, his legs would break as soon as he took a single step. This is because if you take an ape and increase his size by 10 times, then his weight would go up by the increased volume, or by 10 10 10 = 1,000 times. So he would be 1,000 times heavier. But his strength increases relative to the thickness of his bones and muscles. The cross-sectional area of his bones and muscles goes up by only a square of the distance, that is, by 10 10 = 100 times. In other words, if King Kong were 10 times bigger, he would be only 100 times stronger, but he would weigh 1,000 times more. Thus the ape's weight increases much more rapidly than its strength as we increase its size. He would be, relatively speaking, 10 times weaker than a normal ape. And that is why his legs would break.

In elementary school I remember my teacher marveling at the strength of an ant, which can lift a leaf many times its weight. My teacher concluded that if an ant were the size of a house, it could pick up that house. But this a.s.sumption is incorrect for the same reason that we just saw with King Kong. If an ant were the size of a house, its legs would also break. If you scale up an ant by a factor of 1,000, then it would be 1,000 times weaker than a normal ant, and hence it would collapse of its own weight. (It would also suffocate. An ant breathes through holes in the sides of its body. The area of these holes grows as per the square of the radius, but the volume of the ant increases as per the cube of the radius. Thus an ant 1,000 times bigger than an ordinary ant would have 1,000 times less air than necessary to supply oxygen for its muscles and body tissue. This is also the reason that champion figure skaters and gymnasts tend to be much shorter than average, although they have the same proportions as anyone else. Pound for pound, they have greater proportionate muscle strength than taller people.) Using the scale law, we can also calculate the rough shape of animals on Earth, and possibly aliens in s.p.a.ce. The heat emitted by an animal increases as its surface area increases. Hence increasing its size by 10 increases its heat loss by 10 10 = 100. But the heat content within its body is proportional to its volume, or 10 10 10 = 1,000. Hence, large animals lose heat more slowly than small animals. (This is the reason that in wintertime our fingers and ears freeze first, since they have the most relative surface area, and why small people get colder faster than large people. It explains why newspapers burn very quickly, because of their large relative surface area, while logs burn very slowly, because of their relatively small surface area.) It also explains why whales in the Arctic are round in shape-because a sphere has the smallest possible surface area per unit ma.s.s. And why insects in a warmer environment can afford to be spindly in shape, with a relatively large surface area per unit ma.s.s.

In the Disney movie Honey, I Shrunk the Kids a family is shrunk down to the size of ants. A rainstorm develops, and in the microworld we see tiny raindrops falling onto puddles. In reality a raindrop as seen by an ant would appear not as a tiny drop but as a huge mound or hemisphere of water. In our world a hemispherical mound of water is unstable and will collapse of its own weight under gravity. But in the microworld, surface tension is relatively large, so a hemispherical mound of water is perfectly stable.

Similarly, in outer s.p.a.ce we can estimate the rough surface-to-volume ratio of animals on distant planets using the laws of physics. Using these laws we can theorize that aliens in outer s.p.a.ce would likely not be the giants often portrayed in science fiction, but would more closely resemble us in size. (Whales, however, can be much larger in size because of the buoyancy of seawater. This also explains why a beached whale dies-because it is crushed by its own weight.) The scale law means that the laws of physics change as we go deeper and deeper into the microworld. This explains why the quantum theory appears so bizarre to us, violating simple commonsense notions about our universe. So the scale law rules out the familiar idea of worlds-within-worlds found in science fiction, that is, the idea that inside the atom there could be an entire universe, or that our galaxy could be an atom in a much larger universe. This idea was explored in the movie Men in Black. In the final scene of the movie the camera pans away from the Earth, to the planets, the stars, the galaxies, until our entire universe becomes just a single ball in a huge extraterrestrial game played by gigantic aliens.

In reality a galaxy of stars bears no resemblance to an atom; inside the atom the electrons inside their sh.e.l.ls are totally different from planets. We know that all the planets are quite different from each other and can orbit at any distance from the mother star. In atoms, however, all the subatomic particles are identical to one another. They cannot orbit at any distance from the nucleus, but only in discrete orbits. (Furthermore, unlike planets, electrons can exhibit bizarre behavior that violates common sense, such as being two places at the same time and having wavelike properties.) THE PHYSICS OF ADVANCED CIVILIZATIONS.

It is also possible to use physics to sketch out the outlines of possible civilizations in s.p.a.ce. If we look at the rise of our own civilization over the past 100,000 years, since modern humans emerged in Africa, it can be seen as the story of rising energy consumption. Russian astrophysicist Nikolai Kardashev has conjectured that the stages in the development of extraterrestrial civilizations in the universe could also be ranked by energy consumption. Using the laws of physics, he grouped the possible civilizations into three types: 1. Type I civilizations: those that harvest planetary power, utilizing all the sunlight that strikes their planet. They can, perhaps, harness the power of volcanoes, manipulate the weather, control earthquakes, and build cities on the ocean. All planetary power is within their control.

2. Type II civilizations: those that can utilize the entire power of their sun, making them 10 billion times more powerful than a Type I civilization. The Federation of Planets in Star Trek is a Type II civilization. A Type II civilization, in a sense, is immortal; nothing known to science, such as ice ages, meteor impacts, or even supernovae, can destroy it. (In case their mother star is about to explode, these beings can move to another star system, or perhaps even move their home planet.) 3. Type III civilizations: those that can utilize the power of an entire galaxy. They are 10 billion times more powerful than a Type II civilization. The Borg in Star Trek, the Empire in Star Wars, and the galactic civilization in Asimov's Foundation series correspond to a Type III civilization. They have colonized billions of star systems and can exploit the power of the black hole at the center of their galaxy. They freely roam the s.p.a.ce lanes of the galaxy.

Kardashev estimated that any civilization growing at a modest rate of a few percent per year in energy consumption will progress rapidly from one type to the next, within a matter of a few thousand years to tens of thousands of years.

As I've discussed in my previous books, our own civilization qualifies a Type 0 civilization (i.e., we use dead plants, oil and coal, to fuel our machines). We utilize only a tiny fraction of the sun's energy that falls on our planet. But already we can see the beginnings of a Type I civilization emerging on the Earth. The Internet is the beginning of a Type I telephone system connecting the entire planet. The beginning of a Type I economy can be seen in the rise of the European Union, which in turn was created to compete with NAFTA. English is already the number one second language on the Earth and the language of science, finance, and business. I imagine it may become the Type I language spoken by virtually everyone. Local cultures and customs will continue to thrive in thousands of varieties on the Earth, but superimposed on this mosaic of peoples will be a planetary culture, perhaps dominated by youth culture and commercialism.

The transition between one civilization and the next is far from guaranteed. The most dangerous transition, for example, may be between a Type 0 and a Type I civilization. A Type 0 civilization is still wracked with the sectarianism, fundamentalism, and racism that typified its rise, and it is not clear whether or not these tribal and religious pa.s.sions will overwhelm the transition. (Perhaps one reason that we don't see Type I civilizations in the galaxy is because they never made the transition, i.e., they self-destructed. One day, as we visit other star systems, we may find the remains of civilizations that killed themselves in one way or another, e.g., their atmospheres became radioactive or too hot to sustain life.) By the time a civilization has reached Type III status it has the energy and know-how to travel freely throughout the galaxy and even reach the planet Earth. As in the movie 2001, such civilizations may well send self-replicating, robotic probes throughout the galaxy searching for intelligent life.

But a Type III civilization would likely not be inclined to visit us or conquer us, as in the movie Independence Day, where such a civilization spreads like a plague of locusts, swarming around planets to suck their resources dry. In reality, there are countless dead planets in outer s.p.a.ce with vast mineral wealth they could harvest without the nuisance of coping with a restive native population. Their att.i.tude toward us might resemble our own att.i.tude toward an ant hill. Our inclination is not to bend down and offer the ants beads and trinkets, but simply to ignore them.

The main danger ants face is not that humans want to invade them or wipe them out. Instead it is simply that we will pave them over because they are in the way. Remember that the distance between a Type III civilization and our own Type 0 civilization is far more vast than the distance between us and the ants, in terms of energy usage.

UFOS.

Some people claim that extraterrestrials have already visited the Earth in the form of UFOs. Scientists usually roll their eyes when they hear about UFOs and dismiss the possibility because the distances between stars are so vast. But regardless of scientists' reactions, persistent reports of UFOs have not diminished over the years.

UFO sightings actually date back to the beginning of recorded history. In the Bible the prophet Ezekiel mentions enigmatically "wheels within wheels in the sky," which some believe is a reference to a UFO. In 1450 BC, during the reign of Pharaoh Thutmose III in Egypt, the Egyptian scribes recorded an incident involving "circles of fire" brighter than the sun, about 5 meters in size, which appeared on several days and finally ascended into the sky. In 91 BC the Roman author Julius Obsequens wrote about "a round object, like a globe, a round or circular s.h.i.+eld [that] took its path in the sky." In 1235 General Yoritsume and his army saw strange globes of light dancing in the sky near Kyoto, j.a.pan. In 1561 a large number of objects were seen over Nuremberg, Germany, as if engaged in an aerial battle.

More recently, the U.S. Air Force has conducted large-scale studies of UFO sightings. In 1952 the Air Force began Project Blue Book, which a.n.a.lyzed a total of 12,618 sightings. The report concluded that the vast majority of these sightings could be explained by natural phenomena, conventional aircraft, or hoaxes. Yet about 6 percent were cla.s.sified as being of unknown origin. But as a result of the Condon Report, which concluded that there was nothing of value in such studies, Project Blue Book was closed in 1969. It was the last known large-scale UFO research project of the U.S. Air Force.

In 2007 the French government released its voluminous file on UFOs to the general public. The report, made available over the Internet by the French National Center for s.p.a.ce Studies, included 1,600 UFO sightings spanning fifty years, including 100,000 pages of eyewitness accounts, films, and audiotapes. The French government stated that 9 percent of these sightings could be fully explained, and that 33 percent have likely explanations, but that they were unable to follow up on the rest.

It is hard, of course, to independently verify these sightings. In fact, most UFO reports, on careful a.n.a.lysis, can be dismissed as the result of the following: 1. The planet Venus, which is the brightest object in the night sky after the moon. Because of its enormous distance from the Earth, the planet appears to follow you if you are moving in a car, giving the illusion that it is being piloted, the same way that the moon appears to follow you. We judge distance, in part, by comparing moving objects to their surroundings. Since the moon and Venus are so far away, with nothing to compare them to, they do not move with respect to our surroundings, and hence give us the optical illusion that they are following us.

2. Swamp gas. During a temperature inversion over a swampy area, gas will hover over the ground and can become slightly incandescent. Smaller pockets of gas might separate from a larger pocket, giving the impression that scout s.h.i.+ps are leaving the "mother s.h.i.+p."

3. Meteors. Bright streaks of light can travel across the night sky in a matter of seconds, giving the illusion of a piloted s.h.i.+p. They can also break up, again giving the illusion of scout s.h.i.+ps leaving the mother s.h.i.+p.

4. Atmospheric anomalies. There are all sorts of lightning storms and unusual atmospheric events that can illuminate the sky in strange ways, giving the illusion of a UFO.

In the twentieth and twenty-first centuries the following phenomena might also generate UFO sightings: 1. Radar echoes. Radar waves can bounce off mountains and create echoes, which can be picked up by radar monitors. Such waves even appear to zigzag and fly at enormous velocities on a radar screen, because they are just echoes.

2. Weather and research balloons. The military claims, in a controversial report, that the famous rumor of a 1947 alien crash at Roswell, New Mexico, was caused by an errant balloon from Project Mogul, a top-secret project to monitor radiation levels in the atmosphere in case nuclear war broke out.

3. Aircraft. Commercial and military aircraft have been known to set off UFO reports. This is particularly true of test flights by advanced experimental aircraft, such as the stealth bomber. (The U.S. military actually encouraged stories of flying saucers in order to deflect attention away from its top-secret projects.) 4. Deliberate hoaxes. Some of the most famous pictures that claim to capture flying saucers are actually hoaxes. One well-known flying saucer, showing windows and landing pods, was actually a modified chicken feeder.

At least 95 percent of the sightings can be dismissed as one of the above. But this still leaves open the question of the remaining few percent of unexplained cases. The most credible cases of UFOs involve(a) multiple sightings by independent, credible eyewitnesses, and(b) evidence from multiple sources, such as eyesight and radar. Such reports are harder to dismiss, since they involve several independent checks. For example, in 1986 there was a sighting of a UFO by JAL-Flight 1628 over Alaska, which was investigated by the FAA. The UFO was seen by the pa.s.sengers of the JAL flight and was also tracked by ground radar. Similarly, there were ma.s.s radar sightings of black triangles over Belgium in 198990 that were tracked by NATO radar and jet interceptors. In 1976 there was a sighting over Tehran, Iran, that resulted in multiple systems failures in an F-4 jet interceptor, as recorded in CIA doc.u.ments.

What is frustrating to scientists is that, of the thousands of recorded sightings, none has produced hard physical evidence that can lead to reproducible results in the laboratory. No alien DNA, alien computer chip, or physical evidence of an alien landing has ever been retrieved.

a.s.suming for the moment that such UFOs might be real s.p.a.cecraft rather than illusions, we might ask ourselves what kind of s.p.a.cecraft they would be. Here are some of the characteristics that have been recorded by observers.

a. They are known to zigzag in midair.

b. They have been known to stop car ignitions and disrupt electrical power as they pa.s.s by.

c. They hover silently in the air.

None of these characteristics fit the description of the rockets we have developed on Earth. For example, all known rockets depend on Newton's third law of motion (for every action, there is an equal and opposite reaction); yet the UFOs cited do not seem to have any exhaust whatsoever. And the g-forces created by zigzagging flying saucers would exceed one hundred times the gravitational force on Earth-the g-forces would be enough to flatten any creature on Earth.

Can such UFO characteristics be explained using modern science? In the movies, such as Earth vs. the Flying Saucers, it is always a.s.sumed that alien beings pilot these craft. More likely, however, if such craft exist they are unmanned (or are manned by a being that is part organic and part mechanical). This would explain how the craft could execute patterns generating g-forces that would normally crush a living being.

A s.h.i.+p that was able to stop car ignitions and move silently in the air suggests a vehicle propelled by magnetism. The problem with magnetic propulsion is that magnets always come with two poles, a north pole and a south pole. If you place a magnet in the Earth's magnetic field, it will simply spin (like a compa.s.s needle) rather than rise in the air like a UFO; as the south pole of a magnet moves one way, the north pole moves the opposite way, so the magnet spins and goes nowhere.

One possible solution to this problem would be to use "monopoles," that is, magnets with just one pole, either north or south. Normally if you break a magnet in half you do not get two monopoles. Instead each half of the magnet becomes a magnet by itself, with its own north and south pole; that is, it becomes another dipole. So if you continue to shatter a magnet, you will always find pairs of north and south poles. (This process of breaking a dipole magnet to create smaller dipole magnets continues all the way down to the atomic level, where the atoms themselves are dipoles.) The problem for scientists is that monopoles have never been seen in the lab. Physicists have tried to photograph the track of a monopole moving through their equipment and have failed (except for a single, highly controversial picture taken at Stanford University in 1982).

Although monopoles have never been conclusively seen experimentally, physicists widely believe that the universe once had an abundance of monopoles at the instant of the big bang. This idea is built into the latest cosmological theories of the big bang. But because the universe inflated rapidly after the big bang, the density of monopoles throughout the universe has been diluted, so we don't see them in the lab today. (In fact, the lack of monopoles today was the key observation that led physicists to propose the inflationary universe idea. So the concept of relic monopoles is well established in physics.) It is conceivable, therefore, that a s.p.a.ce-faring race might be able to harvest these "primordial monopoles" left over from the big bang by throwing out a large magnetic "net" in outer s.p.a.ce. Once they have gathered enough monopoles, they can coast through s.p.a.ce, using the magnetic field lines found throughout the galaxy or on a planet, without creating exhaust. Because monopoles are the subject of intense interest by many cosmologists, the existence of such a s.h.i.+p is certainly compatible with current thinking in physics.

Lastly, any alien civilization advanced enough to send stars.h.i.+ps throughout the universe has certainly mastered nanotechnology. This would mean that their stars.h.i.+ps do not have to be very large; they could be sent by the millions to explore inhabited planets. Desolate moons would perhaps be the best bases for such nanos.h.i.+ps. If so, then perhaps our own moon has been visited in the past by a Type III civilization, similar to the scenario depicted in the movie 2001, which is perhaps the most realistic depiction of an encounter with an extraterrestrial civilization. More than likely, the craft would be unmanned and robotic and placed on the moon. (It may take another century before our technology is advanced enough to scan the entire moon for anomalies in radiation, and is capable of detecting ancient evidence of a previous visitation by nanos.h.i.+ps.) If indeed our moon has been visited in the past or has been the site of a nanotech base, then this might explain why UFOs are not necessarily very large. Some scientists have scoffed at UFOs because they don't fit any of the gigantic propulsion designs being considered by engineers today, such as ramjet fusion engines, huge laser-powered sails, and nuclear pulsed engines, which might be miles across. UFOs can be as small as a jet airplane. But if there is a permanent moon base left over from a previous visitation, then UFOs do not have to be large; they can refuel from their nearby moon base. So sightings may correspond to unmanned reconnaissance s.h.i.+ps that originate from the moon base.

Given the rapid advances in SETI and discovering extrasolar planets, contact with extraterrestrial life, a.s.suming it exists in our vicinity, may occur within this century, making such contact a Cla.s.s I impossibility. If alien civilizations do exist in outer s.p.a.ce, the next obvious questions are: Will we ever have the means to reach them? And what about our own distant future, when the sun begins to expand and devour the Earth? Does our destiny really lie in the stars?

9: STARs.h.i.+PS.

This foolish idea of shooting at the moon is an example of the absurd length to which vicious specialization will carry scientists...the proposition appears to be basically impossible.

-A. W. BICKERTON, 1926.

The finer part of mankind will, in all likelihood, never perish-they will migrate from sun to sun as they go out.

And so there is no end to life, to intellect and the perfection of humanity. Its progress is everlasting.

-KONSTANTIN E. TSIOLKOVSKY, FATHER OF ROCKETRY.

One day in the distant future we will have our last nice day on Earth. Eventually, billions of years from now, the sky will be on fire. The sun will swell into a raging inferno that will fill up the entire sky, dwarfing everything in the heavens. As temperatures on Earth soar, the oceans will boil and evaporate, leaving a scorched, parched landscape. The mountains will eventually melt and turn liquid, creating lava flows where vibrant cities once stood.

According to the laws of physics, this grim scenario is inevitable. The Earth will eventually die in flames as it is consumed by the sun. This is a law of physics.

This calamity will take place within the next five billion years. On such a cosmic time scale, the rise and fall of human civilizations are but tiny ripples. One day we must leave the Earth or die. So how will humanity, our descendants, cope when conditions on Earth become intolerable?

Mathematician and philosopher Bertrand Russell once lamented "that no fire, no heroism, no intensity of thought or feeling, can preserve a life beyond the grave; that all the labors of the ages, all the devotion, all the inspiration, all the noonday brightness of human genius, are destined to extinction in the vast death of the solar system; and the whole temple of Man's achievement must inevitably be buried beneath the debris of a universe in ruins..."

To me this is one of the most sobering pa.s.sages in the English language. But Russell wrote this pa.s.sage in an era when rocket s.h.i.+ps were considered impossible. Today the prospect of one day leaving the Earth is not so far-fetched. Carl Sagan once said we should become a "two planet species." Life on Earth is so precious, he said, that we should spread to at least one other inhabitable planet in case of a catastrophe. The Earth moves in the middle of a "cosmic shooting gallery" of asteroids, comets, and other debris drifting near the orbit of the Earth, and a collision with any one of them could result in our demise.

CATASTROPHES TO COME.

Poet Robert Frost asked the question whether the Earth will end in fire or ice. Using the laws of physics, we can reasonably predict how the world will end in the event of a natural catastrophe.

On a scale of millennia, one danger to human civilization is the emergence of a new ice age. The last ice age ended 10,000 years ago. When the next one arrives 10,000 to 20,000 years from now most of North America may be covered in half a mile of ice. Human civilization has flourished within the recent tiny interglacial period, when the Earth has been unusually warm, but such a cycle cannot last forever.

Over the course of millions of years, large meteors or comets colliding with Earth could have a devastating impact. The last big celestial impact took place 65 million years ago, when an object about 6 miles across slammed into the Yucatan Peninsula of Mexico, creating a crater about 180 miles in diameter, wiping out the dinosaurs that up until then were the dominant life-form on Earth. Another cosmic collision is likely on that time scale.

Billions of years from now the sun will gradually expand and consume the Earth. In fact, we estimate that the sun will heat up by approximately 10 percent over the next billion years, scorching the Earth. It will completely consume the Earth in 5 billion years, when our sun mutates into a gigantic red star. The Earth will actually be inside the atmosphere of the sun.

Tens of billions of years from now both the sun and the Milky Way galaxy will die. As our sun eventually exhausts its hydrogen/helium fuel, it will shrink into a tiny white dwarf star and gradually cool off until it becomes a hulk of black nuclear waste drifting in the vacuum of s.p.a.ce. The Milky Way galaxy will eventually collide with the neighboring Andromeda galaxy, which is much larger than our galaxy. The Milky Way's spiral arms will be torn apart, and our sun could well be flung into deep s.p.a.ce. The black holes at the center of the two galaxies will perform a death dance before ultimately colliding and merging.

Given that humanity must one day flee the solar system to the nearby stars to survive, or perish, the question is: how will we get there? The nearest star system, Alpha Centauri, is over 4 light-years away. Conventional chemical propulsion rockets, the workhorses of the current s.p.a.ce program, barely reach 40,000 miles per hour. At that speed it would take 70,000 years just to visit the nearest star.

a.n.a.lyzing the s.p.a.ce program today, there is an enormous gap between our pitiful present-day capabilities and the requirements for a true stars.h.i.+p that could enable us to begin to explore the universe. Since exploring the moon in the early 1970s, our manned s.p.a.ce program has sent astronauts into orbit only about 300 miles above the Earth in the s.p.a.ce Shuttle and International s.p.a.ce Station. By 2010, however, NASA plans to phase out the s.p.a.ce Shuttle to make way for the Orion s.p.a.cecraft, which will eventually take astronauts back to the moon by the year 2020, after a fifty-year hiatus. The plan is to establish a permanent, manned moon base. A manned mission may be launched to Mars after that.