by Michio Kaku
Once we finally open the box, we can make a measurement and see for ourselves if the cat is dead or alive. The measurement process, by an outside observer, allows us to “collapse” the wave function and determine the precise state of the cat. Then we know if the cat is dead or alive. The key is the measurement process by an outside observer; by shining a light inside the box, the wave function has collapsed and the object suddenly assumes a definitive state.
In other words, the process of observation determines the final state of an object. The weakness of Bohr’s Copenhagen interpretation lies in the question, do objects really exist before you make a measurement? To Einstein and Schrödinger, all this seemed preposterous. For the rest of his life, Einstein would grapple with these deep philosophical questions (which even today are still the subject of intense debate).
Several upsetting aspects of this puzzle shook Einstein to the core. First, before a measurement is made, we exist as the sum of all possible universes. We cannot say for certain if we are dead or alive, or whether dinosaurs are still alive, or whether the earth was destroyed billions of years ago. All events, before a measurement is made, are possible. Second, it would seem that the process of observation creates reality! Thus, we have a new twist to the old philosophical puzzle of whether a tree really falls in the forest if no one hears it. A Newtonian would argue that the tree can fall, independent of observation. But someone from the Copenhagen school would say that the tree can exist in all possible states (fallen, upright, sapling, mature, burnt, rotten, etc.) until it is observed, at which point it suddenly springs into existence. Thus the quantum theory adds a totally unexpected interpretation: observing the tree determines the state of the tree, that is, whether it fell or not.
Einstein, from his days at the patent office, always had an uncanny knack for isolating the essence of any problem. He would, therefore, ask visitors to his home the following question: “Does the moon exist because a mouse looks at it?” If the Copenhagen school is correct, then yes, in some sense the moon springs into existence when a mouse observes it, and the moon’s wave function collapses. Over the decades, a number of “solutions” have been offered to the cat problem, none of them totally satisfactory. Although almost no one challenges the validity of quantum mechanics itself, these questions still remain as some of the greatest philosophical challenges in all of physics.
“I have thought a hundred times as much about the quantum problems as I have about general relativity theory,” wrote Einstein about how he endlessly grappled with the foundations of the quantum theory. After much deep thought, Einstein fired back with what he thought was the definitive critique of the quantum theory. In 1933, with his students Boris Podolsky and Nathan Rosen, he proposed a novel experiment that even today is causing headaches to many quantum physicists as well as philosophers. The “EPR experiment” may not have demolished quantum theory, as Einstein had hoped it would, but it succeeded in proving that the quantum theory, which was already pretty bizarre, gets weirder and weirder. Suppose that an atom emits two electrons in opposite directions. Each electron is spinning like a top, pointing either up or down. Suppose further that they are spinning in opposite ways, so the total spin is zero, although you don’t know which way they are spinning. For example, one electron may be spinning up, while the other is spinning down. If you wait long enough, these electrons could be separated by billions of miles. Before any measurement is made, you don’t know the spins of the electrons.
Now suppose that you finally measure the spin of one electron. It is, for example, found to be spinning up. Then instantly, you know the spin of the other electron, although it is many light-years away—since its spin is the opposite of its partner, it must be spinning down. This means that a measurement in one part of the universe instantly determined the state of an electron on the other side of the universe, seemingly in violation of special relativity. Einstein called this “spooky action-at-a-distance.” The philosophical implications of this are rather startling. It means that some atoms in our body may be connected with an invisible web to atoms on the other side of the universe, such that motions in our body can instantly affect the state of atoms billions of light-years away, in seeming violation of special relativity. Einstein disliked this idea, because it meant that the universe was nonlocal; that is, events here on Earth instantly affect events on the other side of the universe, traveling faster than light.
On hearing of this new objection to quantum mechanics, Schrödinger wrote to Einstein, “I was very happy that in that paper…you have evidently caught dogmatic quantum mechanics by the coat-tails.” Hearing of the latest Einstein paper, Bohr’s colleague Leon Rosenfeld wrote, “We dropped everything; we had to clear up such a misunderstanding at once. Bohr, in great excitement, instantly began dictating the draft of a rejoinder.”
The Copenhagen school withstood the challenge, but at a price: Bohr had to concede to Einstein that the quantum universe was indeed nonlocal (i.e., events in one part of the universe can instantly affect another part of the universe). Everything in the universe is somehow meshed together in a cosmic “entanglement.” So the EPR experiment did not disprove quantum mechanics; it only revealed how crazy it really is. (Over the years, this experiment has been misunderstood, with scores of speculations that one could build EPR faster-than-light radio, or that we can send signals back in time, or that we can use this effect for telepathy.)
The EPR experiment did not negate relativity, however. In this sense, Einstein had the last laugh. No useful information can be transmitted faster than light via the EPR experiment. For example, you cannot send Morse code faster than light via the EPR apparatus. Physicist John Bell used this example to explain the problem. He described a mathematician called Bertlmann who always wore a pink sock and a green sock. If you knew that one foot had the green sock, you knew immediately that the other sock was pink. Yet no signal went from one foot to the other. In other words, knowing something is entirely different from sending that knowledge. There is a world of difference between the possession of information and its transmission.
By the late 1920s, there were now two towering branches of physics: relativity and the quantum theory. The sum total of all human knowledge about the physical universe could be summarized by these two theories. One theory, relativity, gave us a theory of the very large, a theory of the big bang and black holes. The other theory, the quantum theory, gave us a theory of the very small, the bizarre world of the atom. Although the quantum theory was based on counterintuitive ideas, no one could dispute its stunning experimental successes. Nobel Prizes were practically flying off the wall for young physicists willing to apply the quantum theory. Einstein was too seasoned a physicist to ignore the breakthroughs being made almost daily in the quantum theory. He did not dispute the experimental successes of it. Quantum mechanics was the “most successful physical theory of our period,” he would admit. Neither did Einstein impede the development of quantum mechanics, as a lesser physicist might have. (In 1929, Einstein recommended that Schrödinger and Heisenberg share in the Nobel Prize.) Instead Einstein shifted strategies. He would no longer attack the theory as being incorrect. His new strategy was to absorb the quantum theory into his unified field theory. When the army of critics in Bohr’s camp accused him of ignoring the quantum world, he fired back that his real goal was nothing short of cosmic in scope: to swallow up the quantum theory in its entirety in his new theory. Einstein used an analogy drawn from his own work. Relativity did not prove that Newtonian theory was completely wrong; it only showed that it was incomplete, that it could be subsumed into a larger theory. Thus, Newtonian mechanics is quite valid in its own particular domain: the realm of small velocities and large objects. Similarly, Einstein believed that the quantum theory’s bizarre assumptions about cats being dead and alive simultaneously could be explained in a higher theory. In this respect, legions of Einstein’s biographers have missed the point. Einstein’s goal was not to prove the quantum theory incorrect, as many of
his critics have claimed. He has too often been painted as the last dinosaur of classical physics, the aging rebel who found himself becoming the voice of reaction. Einstein’s true goal was to expose the quantum theory’s incompleteness and to use the unified field theory to complete it. In fact, one of the criteria for the unified field theory was that it reproduce the uncertainty principle in some approximation.
Einstein’s strategy was to use general relativity and his unified field theory to explain the origin of matter itself, to construct matter out of geometry. In 1935, Einstein and Nathan Rosen investigated a novel way in which quantum particles such as the electron would emerge naturally as a consequence of his theory rather than as fundamental objects. In this way, he hoped to derive the quantum theory without ever having to face the problem of probabilities and chance. In most theories, elementary particles emerge as singularities, that is, regions where the equations blow up. Think of Newton’s equations, for example, where the force is given by the inverse square of the distance between two objects. When this distance goes to zero, the force of gravity goes to infinity, giving us a singularity. Because Einstein wanted to derive the quantum theory from a deeper theory, he reasoned that he needed a theory totally free of singularities. (Examples of this exist in simple quantum theories. They are called “solitons” and resemble kinks in space; that is, they are smooth, not singular, and they can bounce off each other and maintain their same shape.)
Einstein and Rosen proposed a novel way to achieve such a solution. They started with two Schwarzschild black holes, defined on two parallel sheets of paper. By using scissors, one could cut out each black hole singularity and glue the two sheets back together. Thus, one obtains a smooth, singularity-free solution, which Einstein thought might represent a subatomic particle. Thus, quantum particles can be viewed as tiny black holes. (This idea was actually revived in string theory sixty years later, where there are mathematical relations that can turn subatomic particles into black holes and vice versa.)
This “Einstein-Rosen bridge,” however, can be viewed in another way. It represents the first mention in the scientific literature of a “wormhole” that connects two universes. Wormholes are shortcuts through space and time, like a gateway or portal that connects two parallel sheets of paper. The concept of wormholes was introduced to the public by Charles Dodgson (otherwise known as Lewis Carroll), the Oxford mathematician and, most famously, the author of Alice in Wonderland and Through the Looking Glass. When Alice puts her hand through the Looking Glass, she is in effect entering a kind of Einstein-Rosen bridge connecting two universes—the strange world of Wonderland and the countryside of Oxford. It was realized, of course, that anyone who fell through an Einstein-Rosen bridge would be crushed to death by the intense gravitational force, enough to rip their atoms apart. Passage through the wormhole to a parallel universe was impossible if the black hole was stationary. (It would take another sixty years before the concept of wormholes would occupy a key role in physics.)
Eventually, Einstein gave up this idea, in part because he could not explain the richness of the subatomic world. He could not entirely explain all the curious properties of “wood” in terms of “marble.” There were simply too many features of subatomic particles (e.g., mass, spin, charge, quantum numbers, etc.) that failed to emerge from his equations. His goal was to find the picture that would reveal the unified field theory in all its splendor, but one crucial problem was that not enough was known at that time about the properties of the nuclear force. Einstein was working decades before data from powerful atom smashers would clarify the nature of subatomic matter. As a result, the picture never came.
CHAPTER 8
War, Peace, and E = mc2
In the 1930s, with the world caught in the vicelike grip of the Great Depression, chaos was once again stalking the streets of Germany. With the collapse of the currency, hard-working, middle-class citizens suddenly found their life savings wiped out almost overnight. The rising Nazi Party fed upon the misery and grievances of the German people, focusing their anger at the most convenient scapegoat, the Jews. Soon, with the backing of powerful industrialists, they became the strongest force in the Reichstag. Einstein, who had resisted the anti-Semites for years, realized that this time the situation was life-threatening. Although a pacifist, he was also realistic, adjusting his views in light of the meteoric rise of the Nazi Party. “This means that I am opposed to the use of force under any circumstances except when confronted by an enemy who pursues the destruction of life as an end in itself,” he wrote. This flexibility would be put to the test.
In 1931, a book called One Hundred Authorities against Einstein was published, containing all kinds of anti-Semitic slander directed against the famous physicist. “The purpose of this publication is to oppose the terror of the Einsteinians with an account of the strength of their opposition,” the document fumed. Einstein later quipped that they did not really need one hundred authorities to destroy relativity. If it were incorrect, one small fact would have been sufficient. In December 1932, Einstein, unable to resist the rising tide of Nazism, left Germany for good. He told Elsa to look at their country house in Caputh and said sadly, “Turn around, you will never see it again.” The situation deteriorated dramatically on January 30, 1933, when the Nazis, already the largest block in the Parliament, finally seized power, and Adolf Hitler was appointed as chancellor of Germany. The Nazis confiscated Einstein’s property and his bank account, leaving him officially penniless, and took over his cherished Caputh vacation house, claiming to have found a dangerous weapon there. (It was later found to be a bread knife. The Caputh house was used during the Third Reich by the Nazi Bund Deutsches Mädel, the “League of German Girls”). On May 10, the Nazis held a public burning of banned books, Einstein’s works among them. That year, Einstein wrote to the Belgian people, who were under the shadow of Germany: “Under today’s conditions, if I were a Belgian, I would not refuse military service.” His remarks were carried by the international media and earned him immediate scorn from both Nazis and fellow pacifists, many of whom believed that the only way to confront Hitler was with peaceful means. Einstein, realizing the true depths of the brutality of the Nazi regime, was unmoved: “The antimilitarists are falling on me as on a wicked renegade…. those fellows simply wear blinders.”
Forced to flee Germany, Einstein the world traveler was once again a person without a home. On his trip to England in 1933, he stopped by to see Winston Churchill at his estate. Under “address” in Churchill’s guest book, Einstein wrote, “None.” Now near the top of the Nazi’s hate list, he had to be careful of his personal security. A German magazine listing the enemies of the Nazi regime showed Einstein’s picture on the front cover with the caption, “Not yet hanged.” Anti-Semites were proud to say that if they could drive Einstein out of Germany, they could drive all Jewish scientists out. Meanwhile, the Nazis passed a new law requiring the dismissal of all Jewish officials, which was an immediate disaster for German physics. Nine Nobel laureates had to leave Germany because of the new civil service law, and seventeen hundred faculty members were dismissed in the first year, causing a vast hemorrhaging of German science and technology. The mass exodus out of Nazi-controlled Europe was staggering, virtually depleting the cream of the scientific elite.
Max Planck, ever the conciliator, refused all efforts by his colleagues to oppose Hitler publicly. He preferred to use private channels and even met personally with Hitler in May 1933, making one last final plea to prevent the collapse of German science. Planck would write, “I had hoped to convince him that he was doing enormous damage…by expelling our Jewish colleagues; to show how senseless and utterly immoral it was to victimize men who had always thought of themselves as Germans, and who had offered up their lives for Germany like everyone else.” At that meeting, Hitler said that he had nothing against Jews, but they were all Communists. When Planck tried to reply, Hitler shouted back to him, “People say that I get attacks of nervous weakness, but I
have nerves of steel!” He then slapped his knee and continued his tirade against Jews. Planck would regret, “I failed to make myself understood…. There is simply no language in which one can talk to such men.”
Einstein’s Jewish colleagues all fled Germany for their lives. Leo Szilard left with his life savings stuffed in his shoes. Fritz Haber fled Germany in 1933 for Palestine. (Ironically, as a loyal German scientist he had helped to develop poison gas for the German army, producing the notorious Zyklon B gas. Later, his own gas was used to kill many members of his family at the Auschwitz concentration camp.) Erwin Schrödinger, who was not Jewish, was also swept up by the hysteria. On March 31, 1933, when the Nazis declared a national boycott of all Jewish stores, he happened to be in front of Berlin’s large Jewish department store, Wertheim’s, when he suddenly witnessed gangs of storm troopers with Nazi swastikas beating up Jewish shopkeepers as the police and the crowd stood by and laughed. Schrödinger was incensed and went up to one of the storm troopers and berated him. Then the storm troopers turned and began to beat him instead. He could have been seriously hurt by this ferocious beating, but a young physicist wearing a Nazi swastika instantly recognized Schrödinger and was able to get him to safety. Badly shaken, Schrödinger would leave Germany for England and Ireland.
In 1943, the Nazis occupied Denmark, and Bohr, who was part Jewish, was targeted for extinction. He managed to escape just one step ahead of the Gestapo via neutral Sweden and then fly to Britain, although he almost died of suffocation on the plane because of an ill-fitting oxygen mask. Planck, a loyal patriot who never left Germany, also suffered horribly. His son was arrested for trying to assassinate Hitler, for which he was tortured by the Nazis and later executed.