Einstein’s Cosmos

by Michio Kaku

  His travels in America not only introduced millions of Americans to the mystery of space and time, but also reaffirmed Einstein’s deep and heartfelt commitment to the Jewish cause. Growing up in a comfortable, middle-class European family, he had no direct contact with the suffering of poor Jews from around the world. “It was the first time in my life that I saw Jews en masse,” he noted. “Not until I was in America did I discover the Jewish people. I had seen many Jews, but neither in Berlin nor elsewhere in Germany had I encountered the Jewish people. The Jewish people I saw in America came from Russia, from Poland, or generally from eastern Europe.”

  After the United States, Einstein went to England, where he met the Archbishop of Canterbury. To the relief of the clergy, Einstein assured him that relativity theory would not undermine people’s morale and belief in religion. He lunched at the Rothschilds and met the great classical physicist Lord Rayleigh, who said to Einstein, “If your theories are sound, I understand…that events, say, of the Norman Conquest have not yet occurred.” When he was introduced to Lord Haldane and his daughter, she fainted at the sight of him. Later, Einstein paid homage to Isaac Newton by gazing at his tomb in England’s most hallowed ground, Westminster Abbey, and laying a wreath. In March 1922, Einstein received an invitation to speak at the Collège de France, where he was mobbed by the Parisian press and followed by huge crowds. One journalist remarked, “He has become the great fashion. Academics, politicians, artists, policemen, cab drivers, and pickpockets know when Einstein lectures. Tout Paris knows everything and tells more than it knows about Einstein.” Controversy surrounded the trip as some scientists, still nursing the wounds from World War I, boycotted his talk, using the excuse that they could not attend because Germany was not a member of the League of Nations. (In response, a Paris paper gibed, “If a German were to discover a cure for cancer or tuberculosis, would these thirty academics have to wait until Germany became a member of the League of Nations to use it?”)

  Einstein’s return to Germany, however, was marred by the political instability of postwar Berlin. Ominously, it had become the season for political assassinations. In 1919, the socialist leaders Rosa Luxemburg and Karl Liebknecht had been killed. In April 1922, Walther Rathenau, a Jewish physicist and colleague of Einstein who had risen to become the German foreign minister, was assassinated by submachine guns as he rode in his car. A few days later, Maximilian Harden, another prominent Jew, was severely wounded in another assassination attempt.

  A day of national mourning was declared, with theaters, schools, and universities closing to honor Rathenau. A million people stood silently near the Parliament building where the funeral services were being held. However, Philipp Lenard refused to cancel his classes at the Physics Institute in Heidelberg. (Previously, he had even advocated killing Rathenau. On the day of national mourning, a group of workers tried to persuade Lenard to cancel his classes, but were drenched with water thrown from the second floor of his building. The workers then broke into the institute and dragged Lenard out. They were about to throw him into the river when the police intervened.)

  That year, a young German, Rudolph Leibus, was charged in Berlin with offering a reward for the murder of Einstein and other intellectuals, saying that “it was a patriotic duty to shoot these leaders of pacifist sentiment.” He was found guilty by the courts but fined only sixteen dollars. (Einstein took these threats seriously, both from anti-Semites as well as deranged individuals. Once, a mentally unbalanced Russian immigrant, Eugenia Dickson, wrote a series of menacing letters to Einstein, raving that he was an imposter masquerading as the real Einstein, and stormed into Einstein’s house trying to kill him. But before this crazed woman could attack Einstein, Elsa struggled with her at the door, managing to subdue her and call the police.)

  Einstein, facing this dangerous tide of anti-Semitism, took the opportunity to launch another world tour, this time to the Orient. The philosopher and mathematician Bertrand Russell was on a speaking tour in Japan and was asked by his hosts to nominate some of the most illustrious people of the time to speak in Japan. He immediately nominated Lenin and Einstein. Since Lenin, of course, was unavailable, the invitation went to Einstein. He accepted it and began his odyssey in January 1923. “Life is like riding a bicycle. To keep your balance you must keep moving,” he wrote.

  While en route to Japan and China, Einstein received a message from Stockholm that many thought was long overdue. The telegram confirmed that he had won the Nobel Prize in physics. But he won the prize not for the relativity theory, his crowning achievement, but for the photoelectric effect. When Einstein finally delivered his Nobel Prize speech the next year, in typical fashion he shocked the audience by not speaking about the photoelectric effect at all, as everyone expected, but about relativity.

  What took so long for Einstein, by far the most visible and respected figure in physics, to win the Nobel Prize? Ironically, he had been rejected eight times by the Nobel Prize Committee, from 1910 to 1921. During that period, numerous experiments had been conducted to verify the correctness of relativity. Sven Hedin, a member of the Nobel nominating committee, later confessed that the problem was Lenard, who had great influence over other judges, including Hedin. The Nobel Prize–winning physicist Robert Millikan also recalled that the Nobel nominating committee, split on the question of relativity, finally gave a committee member the task of evaluating the theory: “He spent all his time studying Einstein’s theory of relativity. He couldn’t understand it. Didn’t dare to give the prize and run the risk of learning later that the theory of relativity is invalid.”

  As promised, Einstein sent the Nobel Prize money to Mileva as part of their divorce settlement ($32,000 in 1923 dollars). She would eventually use the money to purchase three apartment houses in Zurich.

  By the 1920s and 1930s, Einstein had emerged as a giant on the world stage. Newspapers clamored for interviews, his face smiled from film newsreels, he was flooded with requests beseeching him to speak, and journalists would breathlessly print every trivial tidbit from his life. Einstein quipped that he was like King Midas, except everything he touched turned into a newspaper headline. New York University’s Class of 1930, asked to name the world’s most popular figure, chose Charles Lindbergh first, and Albert Einstein second, outranking all of Hollywood’s movie stars. Everywhere Einstein went, his mere presence would spark huge crowds. For example, four thousand people started a near riot trying to crash a film explaining relativity at the American Museum of Natural History in New York. A group of industrialists even bankrolled the building of the Einstein Tower in Potsdam, Germany, a futuristic-looking solar observatory finished in 1924 that housed a telescope in a tower 54 feet high. Einstein was so much in demand from artists and photographers that wanted to capture the face of genius that he listed his job description as “artists’ model.”

  This time, however, he did not make the mistake he made with Mileva, neglecting her while he was on world tours. To Elsa’s delight, he took her along to greet celebrities, royalty, and the powerful. Elsa, in turn, adored her husband and gloried in his world fame. She was “gentle, warm, motherly, and prototypically bourgeois, [and] loved to take care of her Albertle.”

  In 1930, Einstein made his second triumphant trip to the United States. On his visit to San Diego, the humorist Will Rogers noted about Einstein, “He ate with everybody, talked with everybody, posed for everybody that had any film left, attended every luncheon, every dinner, every movie opening, every marriage and two-thirds of the divorces. In fact, he made himself such a good fellow that nobody had the nerve to ask what his theory was.” He visited the California Institute of Technology and the observatory at Mt. Wilson, meeting astronomer Edwin Hubble, who had verified some of Einstein’s theories about the universe. He also visited Hollywood and received a glittering reception worthy of a superstar. In 1931, he and Elsa attended the world premier of Charlie Chaplin’s film City Lights. The crowds strained to catch a fleeting glimpse of the world-famous scientist
surrounded by Hollywood royalty. At the opening, as the audience wildly cheered Chaplin and Einstein, Chaplin remarked, “The people applaud me because everyone understands me, and they applaud you because no one understands you.” Einstein, bewildered by the frenzy that celebrities can generate, asked what it all meant. Chaplin wisely replied, “Nothing.” (When he visited New York’s famed Riverside Church, he saw his face on a stained-glass window portraying the world’s great philosophers, leaders, and scientists. He quipped, “I could have imagined they would make a Jewish saint out of me, but I never thought I would become a Protestant one!”)

  Einstein was also sought out for his thoughts on philosophy and religion. His meeting with a fellow Nobel laureate, Indian mystic Rabindranath Tagore, in 1930 attracted considerable press attention. They made quite a pair, with Einstein’s flaming white hair and Tagore’s equally imposing long white beard. One journalist remarked, “It was interesting to see them together—Tagore, the poet with the head of a thinker, and Einstein, the thinker with the head of a poet. It seemed to an observer as though two planets were engaged in a chat.”

  Ever since he read Kant as a child, Einstein became suspicious of traditional philosophy, which he often thought degenerated into pompous but ultimately simplistic hocuspocus. He wrote, “Is not all of philosophy as if written in honey? It looks wonderful when one contemplates it, but when one looks again it is all gone. Only mush remains.” Tagore and Einstein clashed over the question of whether the world can exist independently of human existence. While Tagore held the mystical belief that human existence was essential to reality, Einstein replied, “The world, considered from the physical aspect, does exist independently of human consciousness.” Although they disagreed on the question of physical reality, they found a bit more agreement on questions of religion and morality. In the area of ethics, Einstein believed that morality was defined by humanity, not by God. “Morality is of the highest importance—but for us, not God,” Einstein observed. “I do not believe in the immorality of the individual, and I consider ethics to be an exclusively human concern with no superhuman authority behind it.”

  Although skeptical about traditional philosophy, he also had the deepest respect for the mysteries posed by religion, especially the nature of existence. He would write, “Science without religion is lame, religion without science is blind.” He would also attribute this appreciation of mystery as the source of all science: “all the fine speculations in the realm of science spring from a deep religious feeling.” Einstein wrote, “The most beautiful and deepest experience a man can have is the sense of the mysterious. It is the underlying principle of religion as well as of all serious endeavor in art and science.” He concluded, “If something is in me which can be called religious, then it is the unbounded admiration for the structure of the world so far as science can reveal it.” Perhaps his most elegant and explicit statement about religion was written in 1929: “I’m not an atheist and I don’t think I can call myself a pantheist. We are in the position of a little child entering a huge library filled with books in many different languages. The child knows someone must have written those books. It does not know how. It does not understand the languages in which they are written. The child dimly suspects a mysterious order in the arrangement of the books but doesn’t know what it is. That, it seems to me, is the attitude of even the most intelligent human being toward God. We see a universe marvelously arranged and obeying certain laws, but only dimly understand these laws. Our limited minds cannot grasp the mysterious force that moves the constellations. I am fascinated by Spinoza’s pantheism, but admire even more his contributions to modern thought because he is the first philosopher to deal with the soul and body as one, not two separate things.”

  Einstein would often make a distinction between two types of Gods, which are often confused in discussions about religion. First, there is the personal God, the God that answers prayers, parts the waters, and performs miracles. This is the God of the Bible, the God of intervention. Then there is the God that Einstein believed in, the God of Spinoza, the God that created the simple and elegant laws that govern the universe.

  Even in the midst of this media circus, Einstein miraculously never lost his focus and devoted his efforts to probing these laws of the universe. While on transatlantic ships or long train rides, he had the discipline to shut out distractions and concentrate on his work. And what intrigued Einstein during this period was the ability of his equations to solve the structure of the universe itself.

  CHAPTER 6

  The Big Bang and Black Holes

  Did the universe have a beginning? Is the universe finite or infinite? Will it have an end? As he began to ask what his theory might say about the cosmos, Einstein, like Newton before him, encountered the same kinds of questions that had puzzled physicists centuries earlier.

  In 1692, five years after Newton completed his masterpiece, Philosophiae Naturalis Principia Mathematica, he received a letter from a minister, Richard Bentley, that perplexed him. Bentley pointed out that if gravity was strictly attractive, and never repulsive, then any static collection of stars will necessarily collapse in on itself. This simple but potent observation was puzzling, as the universe seemed stable enough, yet his universal gravitation would, given enough time, collapse the entire universe! Bentley was isolating a key problem faced by any cosmology in which gravity was an attractive force: a finite universe must necessarily be unstable and dynamic.

  After pondering this disturbing question, Newton wrote a letter back to Bentley, stating that the universe, to avoid this collapse, must therefore consist of an infinite, uniform collection of stars. If the universe were indeed infinite, then every star would be pulled evenly in all directions, and hence the universe could be stable even if gravity was strictly attractive. Newton wrote, “If the matter was evenly disposed throughout an infinite space, it could never convene into one mass…and thus might the sun and fixed stars be formed.”

  But if one made that assumption, then there arose another, deeper problem, known as “Olbers’ paradox.” It asks, quite simply, why the night sky is black. If the universe is indeed infinite, static, and uniform, then everywhere we look, our eyes should see a star in the heavens. Thus, there should be an infinite amount of starlight hitting our eyes from all directions, and the night sky should be white, not black. So if the universe was uniform and finite, it would collapse, but if it were infinite, the sky should be on fire!

  Over two hundred years later, Einstein faced the same problems, but in disguised form. In 1915, the universe was a comfortable place, thought to consist of a static, solitary galaxy, the Milky Way. This bright swath of light cutting across the night sky consisted of billions of stars. But when Einstein began to solve his equations, he found something disturbing and unexpected. He assumed that the universe was filled with a uniform gas, which approximated the stars and dust clouds. Much to his consternation, he found that his universe was dynamic, that it preferred to expand or contract and was never stable. In fact, he soon found himself in the quicksand of cosmological questions that have puzzled philosophers and physicists like Newton for ages. Finite universes are never stable under gravity.

  Einstein, forced to confront a contracting or expanding dynamic universe like Newton, was still not ready to throw out the prevailing picture of a timeless, static universe. Einstein the revolutionary was still not revolutionary enough to accept that the universe was expanding or had a beginning. His solution was a rather feeble one. In 1917, he introduced what might be called a “fudge factor” into his equations, the “cosmological constant.” This factor posited a repulsive antigravity that balanced the attractive force of gravity. The universe was made static by fiat.

  To perform this sleight of hand, Einstein realized that general covariance, the main guiding mathematical principle behind general relativity, allows for two possible general covariant objects: the Ricci curvature (which forms the foundation of general relativity) and the volume of space-time. I
t was therefore possible to add a second term to his equations that was consistent with general covariance and proportional to the volume of the universe. In other words, the cosmological constant assigned an energy to empty space. This antigravity term, now called “dark energy,” is the energy of the pure vacuum. It can push galaxies apart or bring them together. Einstein chose the value of the cosmological constant precisely to counteract the contraction caused by gravity, so the universe became static. He was unhappy with this, as it smacked of a mathematical swindle, but he had no choice if he wanted to preserve a static universe. (It would take another eighty years before astronomers finally found evidence for the cosmological constant, which is now believed to be the dominant source of energy in the universe.)

  The puzzle deepened in the next few years as more solutions to Einstein’s equations were discovered. In 1917, Willem de Sitter, a Dutch physicist, saw that it was possible to find a strange solution to Einstein’s equations: a universe that was empty of all matter yet still expanded! All that was needed was the cosmological constant, the energy of the vacuum, to drive an expanding universe. This was unsettling to Einstein, who still believed, like Mach before him, that the nature of spacetime should be determined by the matter content of the universe. Here was a universe that expanded without any matter whatsoever, needing only dark energy to propel itself forward.

  The final radical steps were taken by Alexander Friedmann in 1922 and by a Belgian priest, Georges Lemaître, in 1927, who showed that an expanding universe emerges naturally from Einstein’s equations. Friedmann obtained a solution of Einstein’s equations beginning with a homogeneous, isotropic universe in which the radius expands or contracts. (Unfortunately, Friedmann died in 1925 of typhoid fever in Leningrad before he could elaborate on his solution.) In the Friedmann-Lemaître picture, there are three possible solutions, depending on the density of the universe. If the density of the universe is larger than a certain critical value, then the expansion of the universe will eventually be reversed by gravity, and the universe will begin to contract. (The critical density is roughly ten hydrogen atoms per cubic yard.) In this universe, the overall curvature is positive (by analogy, a sphere has positive curvature). If the density of the universe is smaller than the critical value, then there is not enough gravity to reverse the expansion of the universe, so it expands indefinitely. (Eventually, the universe approaches near absolute zero in temperature as it expands toward what is called the “big freeze.”) In this universe, the overall curvature is negative (by analogy, a saddle or a trumpet horn has negative curvature). Last, there is the possibility that the universe will be balanced right at the critical value (in which case it will still expand indefinitely). In this universe, the curvature is zero, so the universe is flat. Thus, the fate of the universe could be determined, in principle, by simply measuring its average density.