Physics of the Impossible

by Michio Kaku

  3. Meteors. Bright streaks of light can travel across the night sky in a matter of seconds, giving the illusion of a piloted ship. They can also break up, again giving the illusion of scout ships leaving the mother ship.

  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 passengers of the JAL flight and was also tracked by ground radar. Similarly, there were mass radar sightings of black triangles over Belgium in 1989–90 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 documents.

  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.

  Assuming for the moment that such UFOs might be real spacecraft rather than illusions, we might ask ourselves what kind of spacecraft 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 pass 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 assumed 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 ship 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 compass 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 space-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 space. Once they have gathered enough monopoles, they can coast through space, 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 ship is certainly compatible with current thinking in physics.

  Lastly, any alien civilization advanced enough to send starships throughout the universe has certainly mastered nanotechnology. This would mean that their starships 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 nanoships. 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 nanoships.)

  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 ships that originate from the moon base.

  Given the rapid advances in SETI and discovering extrasolar planets, contact with extraterrestrial life, assuming it exists in our vicinity, may occur within this century, making such contact a Class I impossibility. If alien civilizations do exist in outer space, 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 li
e in the stars?

  9: STARSHIPS

  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 passages in the English language. But Russell wrote this passage in an era when rocket ships 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 Yucatán 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 space. 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 space. 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 space program, barely reach 40,000 miles per hour. At that speed it would take 70,000 years just to visit the nearest star.

  Analyzing the space program today, there is an enormous gap between our pitiful present-day capabilities and the requirements for a true starship that could enable us to begin to explore the universe. Since exploring the moon in the early 1970s, our manned space program has sent astronauts into orbit only about 300 miles above the Earth in the Space Shuttle and International Space Station. By 2010, however, NASA plans to phase out the Space Shuttle to make way for the Orion spacecraft, 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.

  Obviously a new kind of rocket design must be found if we are ever to reach the stars. Either we must radically increase the thrust of our rockets, or we need to increase the time over which our rockets operate. A large chemical rocket, for example, may have the thrust of several million pounds, but it burns for only a few minutes. By contrast, other rocket designs, such as the ion engine (described in the following paragraphs), may have a feeble thrust but can operate for years in outer space. When it comes to rocketry, the tortoise wins over the hare.

  ION AND PLASMA ENGINES

  Unlike chemical rockets, ion engines do not produce the sudden, dramatic blast of superhot gases that propel conventional rockets. In fact, their thrust is often measured in ounces. Placed on a tabletop on Earth, they are too feeble to move. But what they lack in thrust they more than make up for in duration, because they can operate for years in the vacuum of outer space.

  A typical ion engine looks like the inside of a TV tube. A hot filament is heated by an electric current, which creates a beam of ionized atoms, such as xenon, that is shot out the end of the rocket. Instead of riding on a blast of hot, explosive gas, ion engines ride on a thin but steady flow of ions.

  NASA’s NSTAR ion thruster was tested in outer space aboard the successful Deep Space 1 probe, launched in 1998. The ion engine fired for a total of 678 days, setting a new record for ion engines. The European Space Agency has also tested an ion engine on its Smart 1 probe. The Japanese Hayabusa space probe, which flew past an asteroid, was powered by four xenon ion engines. Although unglamorous, the ion engine will be able to make long-haul missions (that are not urgent) between the planets. In fact, ion engines may one day become the workhorse for interplanetary transport.

  A more powerful version of the ion engine is the plasma engine, for example, the VASIMR (variable specific impulse magnetoplasma rocket), which uses a powerful jet of plasma to propel it through space. Designed by astronaut/engineer Franklin Chang-Diaz, it uses radio waves and magnetic fields to heat hydrogen gas to a million degrees centigrade. The superhot plasma is then ejected out the end of the rocket, yielding significant thrust. Prototypes of the engine have already been built on Earth, although none has ever been sent into space. Some engineers hope the plasma engine can be used to power a mission to Mars, significantly reducing the travel time to Mars, down to a few months. Some designs use solar power to energize the plasma in the engine. Other designs use nuclear fission (which raises safety concerns, since it involves putting large amounts of nuclear materials into space on ships that are susceptible to accident).

  Neither the ion nor the plasma/VASIM
R engine, however, has enough power to take us to the stars. For that, we need an entirely new set of propulsion designs. One serious drawback to designing a starship is the staggering amount of fuel necessary to make a trip to even the nearest star, and the long span of time before the ship reaches its distant destination.

  SOLAR SAILS

  One proposal that may solve these problems is the solar sail. It exploits the fact that sunlight exerts a very small but steady pressure that is sufficient to propel a huge sail through space. The idea for a solar sail is an old one, dating back to the great astronomer Johannes Kepler in his 1611 treatise Somnium.

  Although the physics behind a solar sail is simple enough, progress has been spotty in actually creating a solar sail that can be sent into space. In 2004 a Japanese rocket successfully deployed two small prototype solar sails into space. In 2005 the Planetary Society, Cosmos Studios, and the Russian Academy of Sciences launched the Cosmos 1 space sail from a submarine in the Barents Sea, but the Volna rocket it was being carried on failed, and the sail did not reach orbit. (A previous attempt at a suborbital sail also failed back in 2001.) But in February 2006 a 15-meter solar sail was sent successfully into orbit by the Japanese M-V rocket, although the sail opened incompletely.

  Although progress in solar sail technology has been painfully slow, proponents of the solar sail have another idea that might take them to the stars: building a huge battery of lasers on the moon that can fire intense beams of laser light at a solar sail, enabling it to coast to the nearest star. The physics of such an interplanetary solar sail are truly daunting. The sail itself would have to be hundreds of miles across and constructed entirely in outer space. One would have to build thousands of powerful laser beams on the moon, each capable of firing continuously for years to decades. (In one estimate, it would be necessary to fire lasers that have one thousand times the current total power output of the planet Earth.)