Physics of the Impossible

by Michio Kaku

  AI research has been suffering from “physics envy,” according to Marvin Minsky. In physics the holy grail has been to find a simple equation that will unify the physical forces of the universe into a single theory, creating a “theory of everything.” AI researchers, overly influenced by this idea, have tried to find a single paradigm that would explain consciousness. But such a simple paradigm may not exist, according to Minsky.

  (Those in the “constructionist” school, like myself, believe that instead of endlessly debating whether thinking machines can be created or not, one should instead try to build one. Regarding consciousness, there is probably a continuum of consciousness, from a lowly thermostat that monitors the temperature in a room to the self-aware organisms that we are today. Animals may be conscious, but they do not possess the level of consciousness of a human being. One should try, therefore, to categorize all the various types and levels of consciousness rather than debate philosophical questions about the meaning of consciousness. Robots may eventually attain a “silicon consciousness.” Robots, in fact, may one day embody an architecture for thinking and processing information that is different from ours. In the future, advanced robots might blur the difference between syntax and semantics, so that their responses will be indistinguishable from the responses of a human. If so, the question of whether they really “understand” the question will be largely irrelevant. A robot that has perfect mastery of syntax, for all practical purposes, understands what is being said. In other words, a perfect mastery of syntax is understanding.)

  COULD ROBOTS BE DANGEROUS?

  Because of Moore’s law, which states that computer power doubles every eighteen months, it is conceivable that within a few decades robots will be created that have the intelligence, say, of a dog or a cat. But by 2020 Moore’s law may well collapse and the age of silicon could come to an end. For the past fifty years or so the astounding growth in computer power has been fueled by the ability to create tiny silicon transistors, tens of millions of which can easily fit on your fingernail. Beams of ultraviolet radiation are used to etch microscopic transistors onto wafers made of silicon. But this process cannot last forever. Eventually, these transistors could become so small that they reach the size of molecules, and the process will break down. Silicon Valley could become a Rust Belt after 2020, when the age of silicon finally comes to an end.

  The Pentium chip in your laptop computer has a layer about twenty atoms across. By 2020 that Pentium chip might consist of a layer only five atoms across. At that point the Heisenberg uncertainty principle kicks in, and you no longer know where the electron is. Electricity will then leak out of the chip and the computer will short-circuit. At that point, the computer revolution and Moore’s law will hit a dead end because of the laws of the quantum theory. (Some people have claimed that the digital era is the “victory of bits over atoms.” But eventually, when we hit the limit of Moore’s law, atoms may have their revenge.)

  Physicists are now working on the post-silicon technology that will dominate the computer world after 2020, but so far with mixed results. As we have seen, a variety of technologies are being studied that may eventually replace silicon technology, including quantum computers, DNA computers, optical computers, atomic computers, and so forth. But each of them faces huge hurdles before it can take on the mantle of silicon chips. Manipulating individual atoms and molecules is a technology that is still in its infancy, so making billions of transistors that are atomic in size is still beyond our ability.

  But assume, for the moment, that physicists are capable of bridging the gap between silicon chips and, say, quantum computers. And assume that some form of Moore’s law continues into the post-silicon era. Then artificial intelligence might become a true possibility. At that point robots might master human logic and emotions and pass the Turing test every time. Steven Spielberg explored this question in his movie Artificial Intelligence: AI, where the first robot boy was created that could exhibit emotions, and was hence suitable for adoption into a human family.

  This raises the question: could such robots be dangerous? The answer is likely yes. They could become dangerous once they have the intelligence of a monkey, which is self-aware and can create its own agenda. It may take many decades to reach such a point, so scientists will have plenty of time to observe robots before they pose a threat. For example, a special chip could be placed in their processors that could prevent them from going on the rampage. Or they could have a self-destruct or deactivation mechanism that would turn them off in case of an emergency.

  Arthur C. Clarke wrote, “It is possible that we may become pets of the computers, leading pampered existences like lapdogs, but I hope that we will always retain the ability to pull the plug if we feel like it.”

  A more mundane threat is that our infrastructure depends on computers. Our water and electricity grid, not to mention transportation and communications networks, will be increasingly computerized in the future. Our cities have become so complex that only complex and intricate computer networks can regulate and monitor our vast infrastructure. In the future it will become increasingly important to add artificial intelligence to this computer network. A failure or breakdown in this all-pervasive computer infrastructure could paralyze a city, country, or even a civilization.

  Will computers eventually surpass us in intelligence? Certainly, there is nothing in the laws of physics to prevent that. If robots are neural networks capable of learning, and they develop to the point where they can learn faster and more efficiently than we can, then it’s logical that they might eventually surpass us in reasoning. Moravec says, “[The postbiological world] is a world in which the human race has been swept away by the tide of cultural change, usurped by its own artificial progeny…When that happens, our DNA will find itself out of a job, having lost the evolutionary race to a new kind of competition.”

  Some inventors, such as Ray Kurzweil, have even predicted that this time will come soon, earlier rather than later, even within the next few decades. Perhaps we are creating our evolutionary successors. Some computer scientists envision a point they call “singularity,” when robots will be able to process information exponentially fast, creating new robots in the process, until their collective ability to absorb information advances almost without limit.

  So in the long term some have advocated a merging of carbon and silicon technology, rather than waiting for our extinction. We humans are mainly based on carbon, but robots are based on silicon (at least for the moment). Perhaps the solution is to merge with our creations. (If we ever encounter extraterrestrials, we should not be surprised to find that they are part organic, part mechanical to withstand the rigors of space travel and to flourish in hostile environments.)

  In the far future, robots or humanlike cyborgs may even grant us the gift of immortality. Marvin Minsky adds, “What if the sun dies out, or we destroy the planet? Why not make better physicists, engineers, or mathematicians? We may need to be the architects of our own future. If we don’t our culture could disappear.”

  Moravec envisions a time in the distant future when our neural architecture will be transferred, neuron for neuron, directly into a machine, giving us, in a sense, immortality. It’s a wild thought, but not beyond the realm of possibility. So, according to some scientists viewing the far future, immortality (in the form of DNA-enhanced or silicon bodies) may be the ultimate future of humanity.

  The idea of creating thinking machines that are at least as smart as animals and perhaps as smart or smarter than us could become a reality if we can overcome the collapse of Moore’s law and the commonsense problem, perhaps even late in this century. Although the fundamental laws of AI are still being discovered, progress in this area is happening extremely fast and is promising. Given that, I would classify robots and other thinking machines as a Class I impossibility.

  8: EXTRATERRESTRIALS AND UFOS

  Either we are alone in the universe, or we are not.

  Either thought is frightening
.

  —ARTHUR C. CLARKE

  A gargantuan spaceship, stretching miles across, looms directly over Los Angeles, filling up the entire sky and ominously darkening the entire city. All over the world, saucer-shaped fortresses position themselves over the major cities of the world. Hundreds of jubilant spectators, wishing to welcome the beings from another planet to L.A., gather on top of a skyscraper to reach out to their celestial guests.

  After days of hovering silently over L.A., the spaceship’s belly slowly opens up. A searing blast of laser light shoots out, incinerating the skyscraper, unleashing a tidal wave of destruction that rolls across the entire city, reducing it to burned rubble within seconds.

  In the movie Independence Day aliens represent our deepest fears. In the movie E.T. we project onto aliens our own dreams and fantasies. Throughout history people have been fascinated by the thought of alien creatures that inhabit other worlds. As far back as 1611, in his treatise Somnium, the astronomer Johannes Kepler, using the best scientific knowledge of the time, speculated about a trip to the moon during which one might encounter strange aliens, plants, and animals. But science and religion often collide on the subject of life in space, sometimes with tragic results.

  A few years earlier, in 1600, former Dominican monk and philosopher Giordano Bruno was burned alive in the streets of Rome. To humiliate him, the Church hung him upside down and stripped him naked before finally burning him at the stake. What made the teachings of Bruno so dangerous? He had asked a simple question: is there life in outer space? Like Copernicus, he believed that the Earth revolved around the sun, but unlike Copernicus, he believed that there could be countless numbers of creatures like us living in outer space. (Rather than entertain the possibility of billions of saints, popes, churches, and Jesus Christs in outer space, it was more convenient for the Church simply to burn him.)

  For four hundred years the memory of Bruno has haunted the historians of science. But today Bruno has his revenge every few weeks. About twice a month a new extrasolar planet is discovered orbiting a star in space. Over 250 planets have now been documented orbiting other stars in space. Bruno’s prediction of extrasolar planets has been vindicated. But one question still lingers. Although the Milky Way galaxy may be teaming with extrasolar planets, how many of them can support life? And if intelligent life does exist in space, what can science say about it?

  Hypothetical encounters with extraterrestrials, of course, have fascinated society and thrilled readers and movie audiences for generations. The most famous incident occurred on October 30, 1938, when Orson Welles decided to play a Halloween trick on the American public. He took the basic plot of H. G. Wells’s War of the Worlds and made a series of short news announcements on CBS national radio, interrupting dance music to reenact, hour by hour, the invasion of Earth by Martians and the subsequent collapse of civilization. Millions of Americans were panic-stricken over the “news” that machines from Mars had landed in Grover’s Mill, New Jersey, and were unleashing death rays to destroy entire cities and conquer the world. (Newspapers later recorded that spontaneous evacuations took place as people fled the area, with eyewitnesses claiming they could smell poison gas and see flashes of light in the distance.)

  Fascination with Mars peaked again in the 1950s, when astronomers noticed a strange marking on Mars that looked like a gigantic M that was hundreds of miles across. Commentators noted that perhaps the M stood for “Mars,” and Martians were peacefully signaling their presence to earthlings, like cheerleaders spelling out their team’s name in a football stadium. (Others noted darkly that the M marking was actually a W, and W stands for “war.” In other words, the Martians were actually declaring war on the Earth!) The mini-panic eventually subsided when this mysterious M disappeared just as abruptly as it had appeared. In all likelihood this marking was caused by a dust storm that covered the entire planet, except for the tops of four large volcanoes. The tops of these volcanoes roughly took on the shape of an M or a W.

  THE SCIENTIFIC SEARCH FOR LIFE

  Serious scientists studying the possibility of extraterrestrial life state that it is impossible to say anything definitive about such life, assuming that it exists. Nonetheless, we can make some general arguments on the nature of alien life based on what we know of physics, chemistry, and biology.

  First, scientists believe that liquid water will be the key factor in creating life in the universe. “Follow the water” is the mantra recited by astronomers as they search for evidence of life in space. Liquid water, unlike most liquids, is a “universal solvent” that can dissolve an astonishing variety of chemicals. It is an ideal mixing bowl to create increasingly complex molecules. Water is also a simple molecule that is found throughout the universe, while other solvents are quite rare.

  Second, we know that carbon is a likely component in creating life because it has four bonds and hence the ability to bind to four other atoms and create molecules of incredible complexity. In particular, it is easy to form long carbon chains, which become the basis for hydrocarbon and organic chemistry. Other elements with four bonds do not have such a rich chemistry.

  The most vivid illustration of the importance of carbon was the famous experiment conducted by Stanley Miller and Harold Urey in 1953, which showed that the spontaneous formation of life may be a natural by-product of carbon chemistry. They took a solution of ammonia, methane, and other toxic chemicals that they believed were found in the early Earth, put it in a flask, exposed it to a small electrical current, and then simply waited. Within one week they could see evidence of amino acids forming spontaneously in the flask. The electrical current was sufficient to break apart the carbon bonds within ammonia and methane and then rearrange the atoms into amino acids, the precursors of proteins. In some sense, life can form spontaneously. Since then, amino acids have been found inside meteorites and also in gas clouds in deep space.

  Third, the fundamental basis of life is the self-replicating molecule called DNA. In chemistry, self-replicating molecules are extremely rare. It took hundreds of millions of years to form the first DNA molecule on Earth, probably deep in the oceans. Presumably, if one could perform the Miller-Urey experiment for a million years in the oceans, DNA-like molecules would spontaneously form. One likely site where the first DNA molecule on Earth might have occurred early in the Earth’s history is near volcano vents on the ocean bottom, since the activity of the vents would create a convenient supply of energy for the early DNA molecule and cells, before the arrival of photosynthesis and plants. It is not known if other carbon-based molecules besides DNA can also be self-replicating, but it is likely that other self-replicating molecules in the universe will resemble DNA in some way.

  So life probably requires liquid water, hydrocarbon chemicals, and some form of self-replicating molecule like DNA. Using these broad criteria one can derive a rough estimate for the frequency of intelligent life in the universe. In 1961 Cornell University astronomer Frank Drake was one of the first to make a rough estimate. If you start with 100 billion stars in the Milky Way galaxy, you can estimate what fraction of them have stars like our sun. Of these, you can estimate what fraction have solar systems revolving around them.

  More specifically, Drake’s equation calculates the number of civilizations in the galaxy by multiplying several numbers together, including

  • the rate at which stars are born in the galaxy,

  • the fraction of these stars that have planets,

  • the number of planets for each star that have the conditions for life,

  • the fraction of planets that actually develop life,

  • the fraction that develop intelligent life,

  • the fraction that are willing and able to communicate, and

  • the expected lifetime of a civilization.

  By taking reasonable estimates and by multiplying these successive probabilities, one realizes that there could be between 100 and 10,000 planets in the Milky Way galaxy alone that are able to harbor intellige
nt life. If these intelligent life-forms are uniformly scattered across the Milky Way galaxy, then we should expect to find such a planet just a few hundred light-years from Earth. In 1974 Carl Sagan estimated that there might be up to a million such civilizations within our Milky Way galaxy alone.

  This theorizing, in turn, has provided added justification for those looking to find evidence for extraterrestrial civilizations. Given the favorable estimate of planets capable of harboring intelligent life-forms, scientists have begun seriously to look for the radio signals such planets may have emitted, much like the TV and radio signals that our own planet has been emitting for the past fifty years.

  LISTENING TO ET

  The Search for Extraterrestrial Intelligence (SETI) project dates back to an influential paper written in 1959 by physicists Giuseppe Cocconi and Philip Morrison, who suggested that listening to microwave radiation of a frequency between 1 and 10 gigahertz would be the most suitable way to eavesdrop on extraterrestrial communications. (Below 1 gigahertz, signals would be washed out by radiation emitted by fast-moving electrons; beyond 10 gigahertz, noise from oxygen and water molecules in our own atmosphere would interfere with any signals.) They selected 1,420 gigahertz as the most promising frequency in which to listen to signals from outer space, since that was the emission frequency for ordinary hydrogen gas, the most plentiful element in the universe. (Frequencies around that range are nicknamed the “watering hole,” given their convenience for extraterrestrial communication.)

  Searches for evidence of intelligent signals near the watering hole, however, have been disappointing. In 1960 Frank Drake initiated Project Ozma (named after the Queen of Oz) to search for signals using the 25-meter radio telescope in Green Bank, West Virginia. No signals were ever found, either in Project Ozma or in other projects that, in fits and starts, tried to scan the night sky over the years.