by Michio Kaku
Other segments of the Millerite movement, however, continued to make predictions, hence precipitating further splits each time a prediction failed. One small splinter group of Millerites was called the Branch Davidians; they broke off from the Seventh-Day Adventists in the 1930s. They had a small commune in Waco, Texas, which fell under the charismatic influence of a young preacher named David Koresh, who spoke hypnotically of the end of the world. That group met a fiery end in their tragic encounter with the FBI in 1993, when a raging inferno consumed the compound, incinerating 76 members, including 27 children, and also Koresh.
CAN WE SEE THE FUTURE?
Can rigorous scientific tests prove that some individuals can see the future? In Chapter 12 we saw that time travel might be consistent with the laws of physics, but for an advanced, Type III civilization. But is precognition possible on Earth today?
Elaborate tests conducted at the Rhine Center seem to suggest that some people can see the future; that is, they can identify cards before they are unveiled. But repeated experiments have shown that the effect is very small, and often disappears when others try to duplicate the results.
In fact, precognition is difficult to reconcile with modern physics, because it violates causality, the law of cause and effect. Effects occur after the cause, not vice versa. All the laws of physics that have been found so far have causality built into them. A violation of causality would signal a major collapse of the foundations of physics. Newtonian mechanics is firmly based on causality. Newton’s laws are so all-embracing that if you know the location and position of all the molecules in the universe, you can calculate the future motion of these atoms. Thus the future is calculable. In principle, Newtonian mechanics states that if you had a large enough computer, you could compute all future events. According to Newton, the universe is like a gigantic clock, wound up by God at the beginning of time, and ticking ever since according to His laws. There is no room for precognition in Newton’s theory.
BACKWARD IN TIME
When we discuss Maxwell’s theory, however, the scenario becomes much more complicated. When we solve Maxwell’s equations for light, we find not one but two solutions: a “retarded” wave, which represents the standard motion of light from one point to another; but also an “advanced” wave, where the light beam goes backward in time. This advanced solution comes from the future and arrives in the past!
For a hundred years when engineers have encountered this “advanced” solution that goes backward in time they have simply dismissed it as a mathematical curiosity. Since the retarded waves so accurately predicted the behavior of radio, microwaves, TV, radar, and X-rays, they simply threw the advanced solution out the window. The retarded waves were so spectacularly beautiful and successful that engineers simply ignored the ugly twin. Why tamper with success?
But for physicists, the advanced wave has been a nagging problem for the past century. Since Maxwell’s equations are among the pillars of the modern age, any solution of these equations has to be taken very seriously, even if it entails accepting waves from the future. It seemed that it was impossible to totally ignore the advanced waves from the future. Why would nature, at this most fundamental level, give us such a bizarre solution? Was this a cruel joke, or was there a more profound meaning?
Mystics began to take an interest in these advanced waves, speculating that they would appear as messages from the future. Perhaps if we could somehow harness these waves, we might be able to send messages back to the past, and hence alert previous generations of events to come. We could, for example, send a message back to our grandparents in the year 1929, warning them to sell all their stocks before the Great Crash. Such advanced waves would not allow us personally to visit the past, as in time travel, but they would enable us to send letters and messages into the past to alert people of key events that would not yet have occurred.
These advanced waves were a mystery until they were studied by Richard Feynman, who was intrigued by the idea of going backward in time. After working on the Manhattan Project, which built the first atomic bomb, Feynman left Los Alamos and went to Princeton University to work under John Wheeler. Analyzing Dirac’s original work on the electron, Feynman found something very strange. If he simply reversed the direction of time in Dirac’s equation, the equation remained the same if he also reversed the electron charge. In other words, an electron going backward in time was the same as an antielectron going forward in time! Normally, a mature physicist might dismiss this interpretation, calling it just a trick, a mathematical sleight-of-hand with no meaning. Going backward in time did not seem to make any sense, yet Dirac’s equations were clear on this point. In other words, Feynman had found the reason that nature allowed these backward-in-time solutions: they represented the motion of antimatter. If he had been an older physicist, Feynman might have thrown this solution out the window. But being a lowly graduate student, he decided to pursue his curiosity further.
As he continued to delve into this conundrum the young Feynman noticed something even stranger. Normally if an electron and an antielectron collide, they annihilate one another and create a gamma ray. He drew this on a sheet of paper: two objects bumping into each other, turning into a burst of energy.
But then if you reversed the charge of the antielectron, it became an ordinary electron going backward in time. You could then rewrite the same diagram with the arrow of time reversed. It now appeared as if the electron went forward in time, then suddenly decided to reverse direction. The electron did a U-turn in time and was now going backward in time, releasing a burst of energy in the process. In other words, it’s the same electron. The electron-antielectron annihilation process was just the same electron deciding to go backward in time!
So Feynman revealed the true secret of antimatter: it’s just ordinary matter going backward in time. This simple observation immediately explained the puzzle that all particles have antiparticle partners: it’s because all particles can travel backward in time, and hence masquerade as antimatter. (This interpretation is equivalent to the “Dirac sea,” mentioned earlier, but it is simpler, and it is the explanation currently accepted today.)
Now let’s say we have a lump of antimatter and it collides with ordinary matter, creating a huge explosion. There are now trillions of electrons and trillions of antielectrons being annihilated. But if we reversed the direction of the arrow for the antielectron, turning it into an electron going backward in time, this would mean that the same electron went zigzagging backward and forward trillions of times.
There was a further curious result: there must be just one electron in the lump of matter. The same electron went whizzing back and forth, zigzagging in time. Each time it did a U-turn in time it became antimatter. But if it did another U-turn in time then it turned into another electron.
(With his thesis adviser, John Wheeler, Feynman then speculated that perhaps the entire universe consisted of just one electron, zigzagging back and forth in time. Imagine that out of the chaos of the original big bang only a single electron was created. Trillions of years later, this single electron would eventually encounter the cataclysm of Doomsday, where it would make a U-turn and go backward in time, releasing a gamma ray in the process. Then it would go back to the original big bang, and then perform another U-turn. The electron would then make repeated zigzag journeys back and forth, from the big bang to Doomsday. Our universe in the twenty-first century is just a time slice of this electron’s journey, in which we see trillions of electrons and antielectrons, that is, the visible universe. As strange as this theory may appear, it would explain a curious fact from the quantum theory: why all electrons are the same. In physics you cannot label electrons. There are no green electrons or Johnny electrons. Electrons have no individuality. You cannot “tag” an electron, like scientists sometimes tag animals in the wild to study them. Maybe the reason is that the entire universe consists of the same electron, just bouncing back and forth in time.)
But if antimatter is ordina
ry matter going back in time, then is it possible to send a message into the past? Is it possible to send today’s Wall Street Journal back to yourself in the past, so you can make a killing on the stock market?
The answer is no.
If we treat antimatter as just another exotic form of matter and then perform an experiment with antimatter, there are no violations of causality. Cause and effect remain the same. If we now reverse the arrow of time for the antielectron, sending it backward in time, then we have only performed a mathematical operation. The physics remains the same. Nothing has changed physically. All experimental results remain the same. So it is absolutely valid to view the electron as going backward and forward in time. But each time the electron goes backward in time, it simply fulfills the past. So it appears as if the advanced solutions from the future are indeed necessary to have a consistent quantum theory, but they ultimately do not violate causality. (In fact, without these bizarre advanced waves, causality would be violated in the quantum theory. Feynman showed that if we add the contribution of the advanced and retarded waves, we find that the terms that might violate causality cancel precisely. Thus antimatter is essential to preserving causality. Without antimatter, causality might collapse.)
Feynman continued to pursue the germ of this crazy idea until it eventually blossomed into a complete quantum theory of the electron. His creation, quantum electrodynamics (QED), has been experimentally verified to one part in 10 billion, making it one of the most accurate theories of all time. It won him and his colleagues Julian Schwinger and Sin-Itiro Tomonaga the Nobel Prize in 1965.
(In Feynman’s Nobel Prize acceptance speech, he said that as a youth he impulsively fell in love with these advanced waves from the future, like falling in love with a beautiful girl. Today that beautiful girl has matured into a grown woman and is the mother of many children. One of those children is his theory of quantum electrodynamics.)
TACHYONS FROM THE FUTURE
In addition to advanced waves from the future (which have proven their utility over and over again in the quantum theory) there is yet another bizarre concept from the quantum theory that seems just as crazy, but perhaps not as useful. This is the idea of “tachyons,” which appear regularly on Star Trek. Anytime the writers of Star Trek need some kind of new energy to perform some magical operation, they invoke tachyons.
Tachyons live in a strange world where everything travels faster than light. As tachyons lose energy, they travel faster, which violates common sense. In fact, if they lose all energy, they travel at infinite velocity. As tachyons gain energy, however, they slow down until they reach the speed of light.
What makes tachyons so strange is that they come with imaginary mass. (By “imaginary,” we mean that their mass has been multiplied by the square root of minus one, or “i.”) If we simply take Einstein’s famous equations and replace “m” with “im,” then something marvelous happens. All of a sudden particles travel faster than light.
This result gives rise to strange situations. If a tachyon travels through matter, it loses energy because it collides with atoms. But as it loses energy, it speeds up, which further increases its collisions with atoms. These collisions should cause it to lose more energy and hence accelerate even faster. As this creates a vicious cycle, the tachyon naturally attains infinite velocity all by itself!
(Tachyons are different from antimatter and negative matter. Antimatter has positive energy, travels at less than the speed of light, and can be created in our particle accelerators. It falls down under gravity, according to theory. Antimatter corresponds to ordinary matter going backward in time. Negative matter has negative energy and also travels less than the speed of light, but falls up under gravity. Negative matter has never been found in the laboratory. In large quantities, it can in theory be used to fuel time machines. Tachyons travel faster than light and have imaginary mass; it’s not clear if they fall up or down under gravity. They, too, have not been found in the laboratory.)
As bizarre as tachyons are, they have been seriously studied by physicists, including the late Gerald Feinberg of Columbia University and George Sudarshan of the University of Texas at Austin. The problem is that no one has ever seen a tachyon in the laboratory. The key experimental evidence for tachyons would be a violation of causality. Feinberg even suggested that physicists examine a laser beam before it was switched on. If tachyons exist, then perhaps light from the laser beam could be detected even before the apparatus was turned on.
In science fiction stories tachyons are regularly used to send messages back to the past to seers. But if one examines the physics it is not clear if this is possible. Feinberg, for example, believed that the emission of a tachyon going forward in time was identical to the absorption of a negative-energy tachyon going backward in time (similar to the situation with regard to antimatter) and hence there was no violation of causality.
Science fiction aside, today the modern interpretation of tachyons is that they might have existed at the instant of the big bang, violating causality, but they don’t exist anymore. In fact, they might have played an essential role in getting the universe to “bang” in the first place. In that sense, tachyons are essential for some theories of the big bang.
Tachyons have a peculiar property. When you put them into any theory, they destabilize the “vacuum,” that is, the lowest energy state of a system. If a system has tachyons, it is in a “false vacuum,” so the system is unstable and will decay down to the true vacuum.
Think of a dam that holds back the water in a lake. This represents the “false vacuum.” Although the dam appears perfectly stable, there is an energy state that is lower than the dam. If a crack develops in the dam and the water comes bursting out of the dam break, the system attains the true vacuum as the water flows toward sea level.
In the same way, the universe before the big bang, it is believed, originally started off in the false vacuum, in which there were tachyons. But the presence of tachyons meant that this was not the lowest energy state, and hence the system was unstable. A tiny “rip” appeared in the fabric of space-time, representing the true vacuum. As the rip got larger, a bubble emerged. Outside the bubble the tachyons still exist, but inside the bubble the tachyons have all disappeared. As the bubble expands, we find the universe as we know it, without tachyons. This is the big bang.
One theory taken very seriously by cosmologists is that a tachyon, called the “inflation,” started the original process of inflation. As we mentioned earlier, the inflationary universe theory states that the universe started off as a tiny bubble of space-time that underwent a turbocharged inflationary period. Physicists believe that the universe originally started off in the false vacuum state, where the inflation field was a tachyon. But the presence of a tachyon destabilized the vacuum, and tiny bubbles formed. Inside one of these bubbles the inflation field assumed the true vacuum state. This bubble then began to inflate rapidly, until it became our universe. Inside our bubble-universe the inflation has disappeared, so it can no longer be detected in our universe. So tachyons represent a bizarre quantum state in which objects go faster than light and perhaps even violate causality. But they disappeared a long time ago, and perhaps gave birth to the universe itself.
All this may sound like idle speculation that is not testable. But the theory of the false vacuum will get its first experimental test, starting in 2008, when the Large Hadron Collider is turned on outside Geneva, Switzerland. One of the key purposes of the LHC is to find the “Higgs boson,” the last particle in the Standard Model, the one that has yet to be found. It is the last piece of this jigsaw puzzle. (The Higgs particle is so important but elusive that Nobel laureate Leon Lederman called it “The God Particle.”)
The Higgs boson, physicists believe, originally started out as a tachyon. In the false vacuum, none of the subatomic particles had any mass. But its presence destabilized the vacuum, and the universe made a transition to a new vacuum, in which the Higgs boson turned into an ordinary partic
le. After the transition from a tachyon to an ordinary particle, the subatomic particles begin to have the masses that we measure in the laboratory today. Thus the discovery of the Higgs boson will not only complete the last missing piece of the Standard Model, it will also verify that the tachyon state once existed but has been transformed into an ordinary particle.
In summary, precognition is ruled out by Newtonian physics. The iron rule of cause and effect is never violated. In the quantum theory, new states of matter are possible, such as antimatter, which corresponds to matter going backward in time, but causality is not violated. In fact, in a quantum theory, antimatter is essential to restoring causality. Tachyons at first seem to violate causality, but physicists believe that their true purpose was to set off the big bang and hence they are not observable anymore.
Therefore precognition seems to be ruled out, at least for the foreseeable future, making it a Class III impossibility. It would set off a major shake-up in the very foundations of modern physics if precognition was ever proved in reproducible experiments.
Epilogue
THE FUTURE OF THE IMPOSSIBLE
There is nothing so big nor so crazy that one out of a million technological societies may not feel itself driven to do, provided it is physically possible.
—FREE MAN DYSON
Destiny is not a matter of chance—it is a matter of choice. It is not a thing to be waited for—it is a thing to be achieved.
—WILLIAM JENNINGS BRYAN
Are there truths that will be forever beyond our grasp? Are there realms of knowledge that will be outside the capabilities of even an advanced civilization? Of all the technologies analyzed so far, only perpetual motion machines and precognition fall into the category of Class III impossibilities. Are there other technologies that are similarly impossible?
