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A Stitch in Time 67 If we return to the ruler example in the case of relativity, where the ruler of the moving observer is measured to be shorter by the other observer than it would be in the frame in which it is at rest, we should also remember that for this observer the ruler is also `spread out" in time—events at either end that are simultaneous to the observer at rest with respect to the ruler are not simultaneous for the second ob- server. Minkowski recognized that one could accommodate this fact, and all the others, by considering that the different three-dimensional perspectives probed by each observer were in some sense different "rotated" projections of a four-dimensional "space-time," where there exists an invariant four-dimensional space-time length" that would be the same for all observers. The four-dimensional space, which we now call Minkowski space, is a little different from its 3-D counterpart, in that time as a fourth dimension is treated slightly differently from the three dimensions of space, x, y, and z. The four-dimensional `space-time length," which we can label as S, is not written, in analogy to the three- dimensional length, which we denoted by L, above, as S2=X2+y2+22+t2 but rather as S2 = X2 + y2 + 22 - The minus sign that appears in front of t2 in the definition of space- time length, S, gives Minkowski space its special characteristics, and it is the reason our different perspectives of space and time when we are moving relative to one another are not simple rotations, as in the case of Plato's cave, but something a little more complicated. Nevertheless, in one fell swoop, the very nature of our universe had changed. As Minkowski poetically put it in 1908: "Henceforth space by 2P_Glealer-StoryEverTold_Atincld 67 12/16116 3:06 PIA EFTA00285989
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68 THE GREATEST STORY EVER TOLD-SO FAR itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality." Thus, on the surface, Einstein's Special Theory of Relativity appears to make physical reality subjective and observer dependent, but rela- tivity is in this sense a misnomer. The Theory of Relativity is instead a theory of absolutes. Space and time measurements may be subjective, but `space-time" measurements are universal and absolute. The speed of light is universal and absolute. And four-dimensional Minkowski space is the field on which the game of nature is played. The depth of the radical change in perspective brought about by Minkowski's reframing of Einstein's theory can perhaps best be under- stood by considering Einstein's own reactions to Minkowski's picture. Initially Einstein called it `superfluous learnedness," suggesting that it was simply fancy mathematics, devoid of physical significance. Shortly thereafter he emphasized this by saying, "Since the mathematicians have invaded relativity theory, I do not understand it myself anymore." Ultimately, however, as happened several times in his lifetime, Ein- stein came around and recognized that this insight was essential to understand the true nature of space and time, and he later built his General Theory of Relativity on the foundation that Minkowski had laid. It would have been difficult if not impossible to guess that Faraday's spinning wheels and magnets would eventually lead to such a profound revision in our understanding of space and time. With the spectacles of hindsight, however, we could have had at least an inkling that the unifi- cation of electricity and magnetism could have heralded a world where motion would reveal a new underlying reality. Returning to Faraday and Maxwell, one of the important discoveries that started the ball rolling was that a magnet acts on a moving elec- tric charge with an odd force. Instead of pushing the charge forward or backward, the magnet exerts a force always at right angles to the motion of the electric charge. This force, now called the Lorentz force—after 2P_Glealer-StoryEverTold_Atincld 88 12/18/18 3:06 PIA EFTA00285990
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A Stitch in Time 69 Hendrik Lorentz, a physicist who came close to discovering relativity himself—can be pictured as follows: force on particle The charge moving between the poles of the magnet gets pushed upward. But now consider how things would look from the frame of the par- ticle. In its frame, the magnet would be moving past it. force on particle But by convention we think of an electrically charged particle at rest as being affected only by electric forces. Thus, since the particle is at rest in this frame, the force pushing the particle upward in this picture would be interpreted as an electric force. 2P_Gtealer-StoryEverTaid_Atirdd 89 12/16116 3:06 PIA EFTA00285991
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70 THE GREATEST STORY EVER TOLD-SO FAR One person's magnetism is therefore another person's electricity, and what connects the two is motion. The unification of electricity and mag- netism reflects at its heart that uniform relative motion gives observers different perspectives of reality. Motion, a subject first explored by Galileo, ultimately provided, three centuries later, a key to a new reality—one in which not only electric- ity and magnetism were unified, but also space and time. No one could have anticipated this saga at its beginning. But that is the beauty of the greatest story ever told. 2P_Gtealer-SlowEverTaid_Atindd 10 12/16116 3:06 PIA EFTA00285992
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Chapter 6 THE SHADOWS OF REALITY As they were walking along and talking together, suddenly a chariot of fire and horses of fire appeared and separated the two of them. -2 KINGS 2:11 One might have thought that, in 1908, following the after- shock of the discovery of an unexpected hidden connection between space and time, nature couldn't have gotten much stranger. But the cos- mos doesn't care about our sensibilities. And once again, light provided the key to the door of the rabbit hole to a world that makes Alice's expe- riences seem tame. While they may be strange, the connections unearthed by Einstein and Minkowski can be intuitively understood—given the constancy of the speed of light—as I have tried to demonstrate. Far less intuitive was the next discovery, which was that on very small scales, nature behaves in a way that human intuition cannot ever fully embrace, because we cannot directly experience the behavior itself. As Richard Feynman once argued, no one understands quantum mechanics—if by under- stand one means developing a concrete physical picture that appears fully intuitive. 71 29_Glealer-StoryEverTold_Atincld 71 12/16/16 3:OB PM EFTA00285993
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72 THE GREATEST STORY EVER TOLD-SO FAR Even many years after the rules of quantum mechanics were dis- covered, the discipline would keep yielding surprises. For example, in 19s2 the astrophysicist Hanbury Brown built an apparatus to measure the angular size of large radio sources in the sky. It worked so well that he and a colleague, Richard Twiss, applied the same idea to try to mea- sure the optical light from individual stars and determine their angular size. Many physicists claimed that their instrument, called an intensity interferometer, could not possibly work. Quantum mechanics, they ar- gued, would rule it out. But it worked. It wasn't the first time physicists had been wrong about quantum mechanics, and it wouldn't be the last.... Coming to grips with the strange behavior of quantum mechanics means often accepting the seemingly impossible. As Brown himself amusingly put it when trying to explain the theory of his intensity in- terferometer, he and Twiss were expounding the "paradoxical nature of light, or if you like, explaining the incomprehensible—an activity closely, and interestingly, analogous to preaching the Athanasian Creed." In- deed, like many of the stranger effects in quantum mechanics, the Holy Trinity—Father, Son, and Holy Ghost all embodied at the same time in a single being—is also seemingly impossible. The similarity ends there, however. Common sense also tells us that light cannot be both a wave and a particle at the same time. However, in spite of what common sense suggests, and whether we like it or not, experiments tell us it is so. Un- like the Creed, developed in the fifth century, this fact is not a matter of semantics or choice or belief. So we don't need to recite quantum mechanics creeds every week to make them seem less bizarre or more believable. One hears about the interpretation of quantum mechanic? for good reason, because the "classical" picture of reality—namely the pic- ture given by Newton's laws of classical motion of the world as we ex- 2P_GlealerASIonEverTold_Atincld 72 12/16116 3:06 PIA EFTA00285994
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The Shadows of Reality 73 perience it on human scales—is inadequate to capture the full picture. The surface world we experience hides key aspects of the processes that underlie the phenomena we observe. So too Plato's philosophers could not discover the biological processes that govern humans by observing just the shadows of humans on the wall. No level of analysis would be likely to allow them to intuit the full reality underlying the dark forms. The quantum world defies our notion of what is sensible—or even possible. It implies that at small scales and for short times, the simple classical behavior of macroscopic objects—baseballs thrown from pitcher to catcher, for example—simply breaks down. Instead, on small scales, objects are undergoing many different classical behaviors—as well as classically forbidden behaviors—at the same time. Quantum mechanics, like almost all of physics since Plato, began with scientists thinking about light. So it is appropriate to begin to ex- plore quantum craziness by starting with light, in this case by return- ing to an important experiment first reported by the British polymath Thomas Young around iitoo—the famous "double-slit experiment." Young lived in an era that is hard to appreciate today, when a bril- liant and hardworking individual could make breakthroughs in a host of different fields. But Young was not just any brilliant hardworking in- dividual. He was a prodigy, reading at two, and by the age of thirteen he had read the major Greek and Latin epic poems, had built a micro- scope and a telescope, and was learning four different languages. Later, trained as a medical doctor, Young was the first to propose, in 2806, the modern concept of energy, which now permeates every field of scientific endeavor. That alone would have made him memorable, but in his spare time he also was one of the first to help decipher the hieroglyphics on the Rosetta stone. He developed the physics of elastic materials, associ- ated with what is now called Young's modulus, and helped first elucidate the physiology of color vision. And his brave demonstration of the wave nature of light (which argued against Isaac Newton's powerful claim 2P_Glealer-StoryEverTold_Atirdd 73 12/16116 3:06 PIA EFTA00285995
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74 THE GREATEST STORY EVER TOLD-SO FAR that light was made of particles) was so compelling that it helped lay the basis of Maxwell's discovery of electromagnetic waves. Young's experiment is simple. Let's return to Plato's cave and con- sider a screen placed in front of the back wall of the cave. Place two slits in the screen as shown below (as seen from above): wall screen HITTIMInghtraYs If the light is made of particles, then those light rays that pierce the slits would form two bright lines on the wall behind these two slits: 'I` However, it was well known that waves, unlike particles, diffract around barriers and narrow slits and would produce a very different pattern on the wall. If waves impinge on the barrier, and if each slit is narrow, a circular pattern of waves is generated at each slit, and the patterns from the two slits can "interfere" with each other, sometimes constructively and sometimes destructively. The result is a pattern of bright and dark regions on the back wall, as shown below: 2P_GreafestSioniEverrold_Atincld 74 12/18/18 3:06 PIA EFTA00285996
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The Shadows of 75 light waves barrier a Interference pattern Using just such an apparatus, with narrow slits, Young reported this interference pattern, characteristic of waves, and so definitively dem- onstrated the wave nature of light. In 1804, this was a milestone in the history of physics. One can try the same experiment that Young tried for light on el- ementary particles such as electrons. If we send a beam of electrons toward a phosphorescent screen, like the screen in old-fashioned televi- sion sets, you will see a bright dot where the beam hits the screen. Now imagine that we put two slits in front of the screen, as Young did for light, and aim a wide stream of electrons at the screen: Here, based on the reasoning I gave when I discussed the behavior of light, you would expect to see a bright line behind each of the two slits, where the electrons could pass through to the screen. However, as you have probably already guessed, this is not what you would see, at least if the slits are narrow enough and close enough. Instead, you see an interfer- 2P_Glealer-StoryEverrold_Atirdd 75 12/16116 306 PIA EFTA00285997
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76 THE GREATEST STORY EVER TOLD-SO FAR ence pattern similar to that which Young observed for light waves. Elec- trons, which are particles, seem to behave in this case just like waves of light. In quantum mechanics, particles have wavelike properties. That the electron "waves" emanating from one slit can interfere with electron "waves" emanating from the other slit is unexpected and strange, but not nearly as strange as what happens if we send a stream of electrons toward the screen one at a time. Even in this case, the pat- tern that builds up on the screen is identical to the interference pattern. Somehow, each electron interferes with itself. Electrons are not billiard balls. We can understand this as follows: The probability of an electron's hitting the screen at each point is determined by treating each electron as not taking a single trajectory, but rather following many different tra- jectories at once, some of which go through one slit and some of which go through the other. Those that go through one slit then interfere with those that go through the other slit—producing the observed interfer- ence pattern at the screen. Put more bluntly, one cannot say the electron goes through either one slit or the other, as a billiard ball would. Rather it goes through nei- ther and at the same time it goes through both. Nonsense, you insist. So you propose a variant of the experiment to prove it. Put an electron-measuring device at each slit that clicks when an electron passes through that slit. Sure enough, as each electron makes its way to the screen, only one device clicks each time. So each electron apparently does go through one and only one slit, not both. However, if you now look at the pattern of electrons accumulating at the screen behind the slits, the pattern will have changed from the original interference pattern to the originally expected pattern—with a bright region behind each of the two slits, just as if one were shooting billiard balls or bullets and not waves toward the screen. In other words, in attempting to verify your classical intuition, you 2P_Glealer-StoryEverTold_Atindd 18 12/16116 3:06 PIA EFTA00285998
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The Shadows of Reality 77 changed the behavior of the electrons. Or, as more commonly asserted in quantum mechanics, measurement of a system can alter its behavior. One of the many seemingly impossible aspects of quantum mechan- ics is that there is no experiment you can perform that demonstrates that in the absence of measurement the electrons behave in a sensible classical way. This strange wavelike nature of objects that would otherwise be con- sidered to be particles—such as electrons—is mathematically expressed by assigning to each electron a "wave function," which describes the probability of finding that electron at any given point. If the wave func- tion takes on non-zero values at many different points, then the elec- tron's position cannot be isolated in advance of accurately measuring its position. In other words there is a non-zero probability that the electron is not actually localized at just some specific point in space in advance of making a measurement. While you might imagine that this is a simple problem of not hav- ing access to all the information we need to locate the particle until we make a measurement, Young's double-slit experiment, when updated for electrons, demonstrated that this is most certainly not the case. Any "sensible" classical picture of what is happening between measurements is inconsistent with the data. • • • The strange behavior of electrons was not the first evidence that the microscopic world could not be understood by intuitive classical logic. Once again, in keeping with the revolutionary developments in our un- derstanding of nature since Plato, the discovery of quantum mechanics began with a consideration of light. Recall that if we perform Young's double-slit experiment in Plato's cave with light rays, we get the interference pattern on the wall that Young discovered, which demonstrated that light was indeed a wave. So far, so good. However, if the light source is sufficiently weak, then if we 2P_Glealer-StoryEverrold_AC.inid 17 12/16116 3:06 PIA EFTA00285999
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78 THE GREATEST STORY EVER TOLD-SO FAR try to detect the light as it passes through either of the slits, something strange happens. We will measure the light beam as traveling through one slit or the other, not both. And as with electrons, in this case the pattern on the wall will now change, looking as it would if light were particles and not waves. In fact, light also behaves like both a particle and a wave, depending on the circumstances under which you choose to measure it. The indi- vidual particles of light, which we now call photons, were first labeled quanta by the German theoretical physicist Max Planck, who suggested in 1900 that light might be admitted or absorbed in some smallest bun- dle (although the idea that light might come in discrete packets had earlier been floated by the great Ludwig Boltzmann in 1877). I have come to admire Planck even more as I have learned about his life. Like Einstein, he was an unpaid lecturer and was not offered an academic position after completing his thesis. During this time he spent his career trying to understand the nature of heat and developed several important pieces of work in thermodynamics. Five years after defend- ing his thesis, he was finally offered a university position, and he then quickly rose up the ranks and became a full professor at the prestigious University of Berlin in 1892. In 1894 he turned to the question of the nature of light emitted by hot objects, in part driven by commercial considerations (the first example I know of in the story I have been telling where fundamental physics was commercially motivated). He was commissioned to explore how to get the maximum amount of light out of the newly invented lightbulbs while using the minimum amount of energy. We all know that when we heat up an oven element it first glows red, and then, when it gets hotter, it begins to glow blue. But why? Sur- prisingly, the conventional approaches to this problem were unable to reproduce these observations. After struggling with the problem for six years, Planck presented a revolutionary proposal about radiation that agreed with observations. 2P_Glealer-StoryEverTold_Atirdd 78 12/16116 3:06 PIA EFTA00286000
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The Shadows of Reality 79 Originally there was nothing revolutionary about his derivation, but within two months he had revised his analysis to accommodate ideas about what was happening at a fundamental level. In a quote that has endeared him to me since I first read it, he wrote that his new approach arose as "an act of despair.... I was ready to sacrifice any of my previous convictions about physics." This reflects to me the fundamental quality that makes the scientific process so effective, and which is so clearly represented in the rise of quantum mechanics. "Previous convictions" are just convictions wait- ing to be overturned—by empirical data, if necessary. We throw out cherished old notions like yesterday's newspaper if they don't work. And they didn't work in explaining the nature of radiation emitted by matter. Planck derived his law of radiation from the fundamental assump- tion that light, which was a wave, nevertheless was emitted only in "packets" of some minimum energy—proportional to the frequency of the radiation in question. He labeled the constant that related the energy to the frequency the "action quantum," which is now called Planck's constant. This may not sound so revolutionary, and as Faraday did with elec- tric fields, Planck viewed his assumption as merely a formal mathemati- cal crutch to aid in his analysis. He later stated, "Actually I did not think much about it." Nevertheless, this proposal that light was emitted in particle-like packets is clearly difficult to reconcile with the classical pic- ture of light as a wave. The energy carried by a wave is simply related to the magnitude of its oscillations, which can change continuously from zero. However, according to Planck, the amount of energy that could be emitted in a light wave of a given frequency had an absolute minimum. This minimum was termed an "energy quantum." Planck subsequently tried to develop a classical physical understand- ing of these energy quanta, but failed—causing him, as he put it, "much trouble." Still, unlike a number of his colleagues, he recognized that the 2P_Glealer-StoryEverTold_Atirdd 79 12/16116 3:06 PIA EFTA00286001
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80 THE GREATEST STORY EVER TOLD-SO FAR universe didn't exist to make his life easier. Referring to the physicist and astronomer Sir James Jeans, who was unwilling to give up classical notions in the face of the evidence provided by radiation, Planck stated, 1 am unable to understand Jeans's stubbornness—he is an example of a theoretician as should never be existing, the same as Hegel was for philosophy. So much the worse for the facts if they don't fit" (Just to be clear, in case readers are moved to write me letters, Planck cast this aspersion on Hegel, not me!) Planck later became friends with another physicist who had let the facts drive him toward another revolutionary idea, Albert Einstein. In 1914, when Planck had become dean at Berlin University, he established a new professorship for Einstein there. At first Planck could not accept Einstein's remarkable proposal—made in 19O5, the same year in which he proposed the Special Theory of Relativity—that not only was light emitted by matter in quantum packets, but that light beams themselves existed as bunches of these quanta—that light itself was made up of particle-like objects, which we now call photons. Einstein was driven to this proposal to explain a phenomenon called the photoelectric effect, discovered by Philipp Lenard in 19oz—a physi- cist whose anti-Semitism would later play a key role in delaying Ein- stein's Nobel Prize, and ensuring, curiously, if perhaps poetically, that it would be not for Einstein's work on relativity, but rather on the photo- electric effect. In the photoelectric effect, light shining on a metal sur- face can knock electrons out of atoms and produce a current. However, no matter how intense the light, no electrons would be emitted if the frequency of the light was below some threshold. The moment the fre- quency was raised above that threshold, a photoelectric current would be generated. Einstein realized, correctly, that this could be explained if the light came in minimum packets of energy, with the energy proportional to the frequency of light—as Planck had postulated for light emitted by mat- ter. In this case, only light with frequencies greater than some threshold 2P_GlealerASIonEverTold_Atirdd 80 12/18/18 306 PIA EFTA00286002
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The Shadows of Reality 81 frequency could contain quanta energetic enough to kick electrons out of atoms. Planck could accept the quantized emission of radiation as explaining his radiation law, but the assumption that light itself was quantumlike (i.e., particle-like) was so foreign to the common understanding of light as an electromagnetic wave that Planck balked. Only six years later, at a con- ference in Belgium, the Solvay Conference, which later became famous, was Einstein finally able to convince Planck that the classical picture of light had to be abandoned, and that quanta—aka photons—were real. Einstein was also the first to actually use a fact that he later de- nounced in his famous statement deriding the probabilistic essence of quantum mechanics and reality: "God does not play dice with the uni- verse." He showed that if atoms spontaneously (i.e., without direct cause) absorb and emit finite packets of radiation as electrons jump between discrete energy levels in atoms, then he could rederive the Planck radia- tion law. It is ironic that Einstein, who started the quantum revolution but never joined it, was also perhaps the first to use probabilistic arguments to describe the nature of matter—a strategy that the subsequent physi- cists who turned quantum mechanics into a full theory would place front and center. As a result, Einstein was one of the first physicists to demonstrate that God does play dice with the universe. To take the analogy a little further, Einstein was one of the first phys- icists to demonstrate that the classical notion of causation begins to break down in the quantum realm. Many people have taken exception to my proposal that the universe needed no cause but simply popped into existence from nothing. Yet this is precisely what happens with the light you are using to read this page. Electrons in hot atoms emit pho- tons—photons that didn't exist before they were emitted—which are emitted spontaneously and without specific cause. Why is it that we have grown at least somewhat comfortable with the idea that photons can be created from nothing without cause, but not whole universes? 2P_Glealer-StoryEverTold_Atirdd SI 12/16116 3:06 PM EFTA00286003
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82 THE GREATEST STORY EVER TOLD-SO FAR The realization that electromagnetic waves were also particles began a quantum revolution that would change everything about the way we view nature. To be a particle and a wave at the same time is impossible classically—as should be clear from the earlier discussion in this chap- ter—but it is possible in the quantum world. As should also be clear, this was just the beginning. 2P_GlealestStoryEverTold_Atincld B2 12/16116 3:06 PIA EFTA00286004
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Chapter 7 A UNIVERSE STRANGER THAN FICTION Therefore do not throw away your confidence, which has a great reward. -HEBREWS 10:35 Conventional wisdom might suggest that physicists love to invent crazy esoterica to explain the universe around us, either be- cause we have nothing better to do, or because we are particularly per- verse. However, as the unveiling of the quantum world demonstrates, more often than not it is nature that drags us scientists, kicking and screaming, away from the safety of what is familiar. Nevertheless, to say that the pioneers who pushed us forward into the quantum world lacked confidence would be a profound misstatement. The voyage they embarked upon was without precedent and without guides. The world they were entering defied all common sense, and classical logic, and they had to be prepared at every turn for a change in the rules. Imagine taking a road trip to another country, where the inhabitants all speak a foreign language, and the laws are not based on experiences that compare to any you have ever had in your life. Moreover imagine the traffic signals are hidden and can change from place to place. Then 83 2P_Glealer-StoryEverTaid_Atindd 03 12/16116 3:06 PIA EFTA00286005
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84 THE GREATEST STORY EVER TOLD-SO FAR you can get a sense of where the young Turks who overturned our under- standing of nature in the first half of the twentieth century were heading. The analogy between exploring strange new quantum worlds and embarking on a trek through a new landscape may seemed strained, but exactly such a relationship between the two was paralleled in the life of none other than Werner Heisenberg, one of the founders of quantum mechanics, who once reminisced about an evening in the summer of 1926 on the island of Helgoland, a lovely oasis in the North Sea, when he realized he had discovered the theory: It was almost three o'clock in the morning before the final result of my computations lay before me. The energy principle had held for all the terms, and I could no longer doubt the mathematical consistency and coherence of the kind of quantum mechanics to which my calculations pointed. At first, 1 was deeply alarmed. I had the feeling that, through the surface of atomic phenomena, I was looking at a strangely beautiful interior and felt almost giddy at the thought that I now had to probe this wealth of mathematical structures nature had so generously spread out before me. I was far too excited to sleep, and so, as a new day dawned, I made for the southern tip of the island, where I had been longing to climb a rock jutting out into the sea. I now did so without too much trouble and waited for the sun to rise. Heisenberg, fresh from obtaining his PhD, had moved to the distin- guished German university in Gottingen to work with Max Born to try to come up with a consistent theory of quantum mechanics (a term first used in the paper "On Quantum Mechanics" by Born in 1924). However, spring hay fever had laid Heisenberg low, and he escaped the green coun- tryside for the sea. There, he polished off his ideas about the quantum behavior of atoms and sent it off to Born, who submitted it for publication. You may be familiar with Heisenberg's name, not least because of the 2P_Glealer-StoryEverTold_Atirdd B4 12/16116 3:06 PIA EFTA00286006
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A Universe Stranger than fiction 85 famous principle associated with it. The Heisenberg uncertainty principle has gained a New Age aura, providing fuel for many a charlatan to take advantage of people for whom quantum mechanics seems to offer hope of a world where any dream, no matter how outlandish, is realizable. Other familiar names, Bohr, Schrodinger, Dirac, and later Feynman and Dyson, each made great leaps into the unknown. But they weren't alone. Physics is a collaborative discipline. Too often science stories are written as if the protagonists had a sudden Aha! experience alone late at night. Heisenberg had been working on quantum mechanics for sev- eral years with his PhD supervisor, the brilliant German scientist Arnold Sommerfeld (whose students would win four Nobel Prizes, and whose postdoctoral research assistants would win three), and later with Born (who was finally recognized with a Nobel almost thirty years later), as well as a young colleague, Pascual Jordan. Every major triumph we cel- ebrate with a name and a prize is accompanied by a legion of hardwork- ing, often less heralded, individuals, each of whom moves forward the line of scrimmage by a little bit. Baby steps are the norm, not the exception. The most remarkable leaps into the unknown are often not fully ap- preciated, even by their developers, until much later. Thus Einstein, for example, never trusted his beautiful General Relativity enough to believe its prediction that the universe cannot be static but must be expanding or contracting—until observations demonstrated the expansion. And the world didn't stand on its head when Heisenberg's paper appeared. Heisenberg's friend and contemporary the brilliant and irascible physi- cist Wolfgang Pauli (another future Nobel laureate assistant to Som- merfeld) thought the work to be essentially mathematical masturbation, leading Heisenberg to respond in jocular form: You have to allow that, in any case, we are not seeking to ruin physics out of malicious intent. When you reproach us that we are such big donkeys that we have never produced anything new in physics, it may well be true. But then, you are also an equally big 2P_Glealer-StoryEverTold_Atirdd BS 12/16116 3:06 PIA EFTA00286007
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86 THE GREATEST STORY EVER TOLD-SO FAR jackass because you have not accomplished it either . . . Do not think badly of me and many greetings. Physics doesn't proceed in the linear fashion that textbooks recount. In real life, as in many good mystery stories, there are false leads, mispercep- tions, and wrong turns at every step. The story of the development of quan- tum mechanics is full of them. But I want to cut to the chase here, and so I will skip over Niels Bohr, whose ideas laid out the first fundamental atomic rules of the quantum world as well as the basis for much of modern chemis- try. We'll also skip Erwin Schrtidinger, who was a remarkably colorful char- acter, fathering at least three children with various mistresses, and whose wave equation is the most famous icon of quantum mechanics. Instead I will focus first on Heisenberg, or rather not Heisenberg himself, but instead the result that made his name famous: the Heisen- berg uncertainty principle. This is often interpreted to mean that the observations of quantum systems affect their properties—which was manifest in our earlier discussions of electrons or photons passing through two slits and impinging on a screen behind them. Unfortunately this leads to the misimpression that somehow observers, in particular human observers, play a key role in quantum mechanics—a confusion that has been exploited by my Twitter combatant Deepak Cho- pra, who, in his various ramblings, somehow seems to think the universe wouldn't exist if our consciousness weren't here to measure and frame its properties. Happily the universe predates Chopra's consciousness and was proceeding pretty nicely before the advent of all life on Earth. However, the Heisenberg uncertainty principle at its heart has noth- ing to do with observers at all, even though it does limit their ability to perform measurements. It is instead a fundamental property of quan- tum systems, and it can be derived relatively straightforwardly and mathematically, based on the wave properties of these systems. Consider for example a simple wavelike disturbance with a single frequency (wavelength) oscillating as it moves along the x direction: 2P_Glealer-StoryEverTold_Atirdd 88 12 /18/18 308 PIA EFTA00286008