Physics of the Impossible by Michio Kaku
Identifying hundreds of Earth-like planets in outer space 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 God?
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 space, 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 space 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 God 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 space 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. Assuming 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 assumption 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 space. 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 mass. And why insects in a warmer environment can afford to be spindly in shape,
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 space 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 space 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 shells 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 space. 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 space 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 passions 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 space with vast mineral wealth they could harvest without the nuisance of coping with a restive native population. Their attitude toward us might resemble our own attitude 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 shield [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, Japan. 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 analyzed a t
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 Space 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 analysis, 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 ships are leaving the “mother ship.”