The Amazing Story of Quantum Mechanics

by Kakalios, James

  Of course, knowing the probability that Dr. Manhattan may be in a particular state in the future, such as on Mars having a conversation with his girlfriend, is not a guarantee that he will indeed work out his relationship problems on the red planet. The only time something is absolutely certain to occur is when the probability is 100 percent, just as the only time something will never happen is if the probability is zero.

  In most circumstances the most probable outcome is indeed the one that is observed. But what about the other probabilities that are not realized? What do these wave function solutions to the Schrödinger equation correspond to? One interpretation was provided by Hugh Everett III. Everett suggested that all these probabilities describe actual outcomes on other Earths in an infinite number of parallel universes! If the probability of a certain event occurring is 10 percent, then Everett suggested that on 10 percent of the possible parallel Earths this outcome did indeed occur. The world we live in and experience is one that continually unfolds from this multiverse of possible Earths. For everything we experience, there are alternate Earths where different outcomes are realized.

  Everett’s ideas were considered too unconventional even by the standards of quantum theory, and his proposal, described in his physics dissertation at Princeton in 1957, earned him his Ph.D. but was otherwise completely ignored by the scientific community. Disappointed, Everett eventually turned away from pure scientific research and worked for the military, calculating fallout yields of various nuclear weapons for the Department of Defense. He passed away in 1978, but not before his ideas received some measure of recognition by a small group of theoretical physicists, notably Bryce DeWitt, who actually coined the term “many-worlds interpretation of quantum mechanics” to describe Everett’s thesis. Nowadays the number of physicists who subscribe to the many-worlds picture, while still small, is growing, as those who are struggling to reconcile quantum mechanics and Einstein’s General Theory of Relativity find application for the many-worlds model.

  Parallel universes and alternate Earths are, of course, a common feature in science fiction stories, both prior to Everett’s dissertation and since. Sometimes these alternate worlds are profoundly different from ours, as in Flatland, Edwin Abbott’s tale of a two-dimensional world published in 1884, or the 1931 short story “The Fifth Dimensional Catapult,” by Murray Leinster. In 1896 H. G. Wells told “Plattner’s Story,” wherein Gottfried Plattner, in an accident involving a mysterious green powder in a chemistry lab at a boys’ boarding school, is hurled to a parallel world that orbits a green sun and is inhabited by strange alien creatures with human heads and tadpole-like bodies. It is difficult to imagine the branching of possible wave functions that could have led to such an outcome. In Wells’s short story “The Remarkable Case of Davidson’s Eyes,” Sidney Davidson, through another laboratory accident, gains the ability to see another world, where a ship docks on a South Sea island and stocks up on penguin eggs, despite the fact that all the information from his other senses is consistent with his being in a laboratory in London. Gradually Sidney’s normal vision returns, and in time he discovers that the ship that he had seen in this alternate Earth was a real sea vessel that was in fact gathering penguin eggs on Antipodes Island at the time of Davidson’s strange visions. While a definitive explanation is not presented, it is speculated that when Davidson stooped between the poles of a powerful electromagnet in the lab, his retina gained the ability to see through “a kink in space”—though whether of this world or a parallel one remains open to interpretation.

  A few years after Everett published his novel solution to the “measurement problem” in quantum mechanics, the DC super-speedster the Flash of the 1960s vibrated to a parallel Earth and had an adventure with the Flash of the 1940s (same power, different costume and alter ego). In the television program Star Trek broadcast in 1967, a transporter malfunction during an ion storm leads Captain Kirk, Dr. McCoy, Engineer Scott, and Lieutenant Uhura to an alternate universe starship Enterprise, populated by evil twins of the rest of the crew (distinguished by goatees, naturally). In this mirror universe, the crew of the Enterprise are violent and ruthless, but one feature that remains constant in either universe is Captain Kirk’s roving eye for the ladies.

  In comic books, characters often travel to alternate Earths in parallel universes, and the implication in the stories is that the world of the comic book reader, the one lacking in actual superheroes, is the “real universe.” However, a photo that I came across in the archives of the American Institute of Physics suggests that the situation may be more complicated than we might think. The photo, shown in Figure 21, documents a visit in 1954 to the Princeton University physics department by Niels Bohr (one of the founders of quantum mechanics we encountered in Section 1) as he meets with several physics graduate students. The student on the immediate right of Bohr is Hugh Everett III. The student on the far left appears to be none other than Jon Osterman! Recall that Osterman received his Ph.D. in physics from Princeton in 1957 and so would have indeed been included in the select group of students honored with an audience with one of the grand old men of phys-ics. As mind-bending as the concepts introduced by quantum mechanics into modern thought have been, the suggestion that comic book characters live among us may be a step too far!32

  Figure 21: Niels Bohr (center) visiting with some physics graduate students at Princeton University in 1954. Second from the right, to Bohr’s immediate left, is Hugh Everett III, who would posit the existence of an infinite number of Earths in parallel universes in order to resolve the “measurement problem” in quantum mechanics. At the far left is Charles Misner, a graduate student with a resemblance to Jon Osterman (inset), who would become Dr. Manhattan in Watchmen.

  SECTION 3

  TALES OF THE ATOMIC KNIGHTS

  CHAPTER NINE

  Our Friend, the Atom

  In the 1949 Warner Bros. musical motion picture My Dream Is Yours, a young Doris Day auditions for a spot as a featured singer on a popular radio show. Her manager, played by Jack Carson, advises her to curry favor with the sponsor by crooning a tender love ballad. She instead decides to belt out a bouncy, up-tempo ode to a “new invention . . . [no] larger than an adding machine . . . [that] few have ever seen.” As the song continues, joined by the refrain of “tic, tic, tic,” it becomes clear that Doris Day is singing the praises of—and comparing her quickly beating heart to—a Geiger counter!

  Five years later, a ticking Geiger counter in another film would lead uranium prospector Mickey Rooney onto an atomic bomb testing site. Not realizing that a nuclear weapon detonation was imminent, he innocently took refuge in a test house populated with mannequins and helped himself to a peanut butter sandwich as the countdown progressed. Rooney survived the nuclear explosion without having to take refuge inside the model refrigerator. The resulting exposure to radioactivity would transform Mickey Rooney into The Atomic Kid, and he would go on to employ his newfound ability to glow in the dark and issue explosive sneezes to help the FBI break up a communist spy ring.

  A few years after Mickey Rooney’s misadventures on a nuclear weapon testing site, a darker though equally inaccurate depiction of the effects of radiation exposure would be presented in The Beast of Yucca Flats (1961). In this cautionary tale, former Swedish wrestler Tor Johnson (of Plan 9 from Outer Space fame), also accidentally wanders into an atomic bomb test run. Johnson plays defecting Russian scientist Joseph Javorsky, who, while fleeing KGB assassins, winds up on the famous desert Yucca Flat testing range right before an atomic bomb detonation. The resulting radiation transforms Johnson in a hulking, mindless homicidal monster (though he looks pretty much the same as before the explosion).

  Certainly the true effects of radiation exposure were publicly known at least by August 1946, with the publication in the New Yorker of John Hersey’s “Hiroshima.” But in the years immediately following the conclusion of World War II, popular forms of entertainment maintained, for the most part, an optimistic view of the benefits
to come in an atomic-powered world of tomorrow. The 1957 television program Disneyland featured Dr. Heinz Haber, a German rocketry expert, in Our Friend, the Atom, which likened atomic power to a genie in a bottle that could grant us three wishes for a brighter future. The first wish would be for power, from the generation of electricity to atomic-powered airplanes. The second wish was for food and health and involved using radiation to sterilize foodstuffs and in the treatment of diseases. The third wish was for wisdom, to use nuclear energy wisely and peacefully.

  In 1952 Collier’s Magazine commissioned a series of articles by science writers from Wernher von Braun and Heinz Haber to Willy Ley to envision the future of space travel. With illustrations by Chesley Bonestell, who did the background artwork for Destination: Moon, and Rolf Klep, these articles were published as three issues of the magazine and later compiled into book form under the title Across the Space Frontier. Here again, the “genie” of atomic energy would provide the power to run space stations and enable manned missions to Mars. Before the grim realities of mutated Swedish former wrestlers set in, there was a real sense of optimism—that the taming of the atom and our understanding of nuclear physics would make the promised utopias of science fiction a reality.

  What went wrong? While we fortunately avoided glow-in-the-dark Mickey Rooneys, we never got the atomic planes either. Well, the atomic planes were a bad idea from the start. Haber’s Dell paperback companion to the Disneyland television program argued, “In aviation, the weight of the fuel has always been a discouraging limitation.” (Now it’s the cost of the jet fuel. But back in 1956, no one envisioned the end of cheap oil.) While a smaller nuclear reactor can replace a large quantity of fuel, the shielding necessary to prevent killing or sterilizing the passengers and crew would more than compensate for the missing fuel weight. Haber suggested using water as shielding, but the now heavier plane would require a runway miles long—all of which hardly seems worth the trouble simply to be able to avoid refueling on long flights.

  Similarly stillborn were plans for atomic automobiles. In 1957 Ford proposed a car called the Nucleon,33 in which the internal combustion engine would be replaced by a small nuclear reactor located in the back trunk. The heat from a nuclear fission reaction would boil water, and the steam would turn turbines, providing torque for the wheels and electrical power, as in a nuclear electrical power plant. The hazard to the driver from exposure to nuclear radiation, and to other motorists from a traffic accident, was to be offset by the improved mileage—it was anticipated that the Nucleon could travel five thousand miles before the atomic core needed replacement. Though never built, the three-eighths-scale model unveiled by Ford is notable for a mini-cooling tower behind the passenger section for the nuclear reactor and tail fins nearly as tall as the car itself.

  Certainly the benefits of atomic-powered travel outweigh the costs when considering underwater transportation. The first U.S. Navy nuclear-powered submarine, the Nautilus, was launched in 1954, and since then a considerable fraction of the global fleet of submarines is powered by small nuclear reactors. The Nautilus in Jules Verne’s Twenty Thousand Leagues Under the Sea was powered by electricity drawn from the ocean, via a mechanism not clearly described (“Professor,” said Captain Nemo, “my electricity is not everybody’s and that is all I wish to say about it. . . . “), and consequently was also able to travel great distances without refueling (twenty thousand leagues refers to the distance the Nautilus travels, not its depth beneath the water’s surface, and is equivalent to sixty thousand miles). As the sole market for submarines is the military,34 profitability constraints do not apply.

  It is true that nuclear power is extremely efficient compared to other methods of generating heat, at least when compared to the equivalent mass of fossil fuel needed to produce the same energy. The devil is in the details—particularly in the waste products. While there is danger in the waste exhaust of fossil fuels, there the hazard is long-term, while radioactivity is of immediate concern to all it strikes. To see why we must be concerned when a nucleus decays, we first need to understand why any nucleus sticks together in the first place.

  When Ernest Rutherford’s lab conducted experiments involving high-speed alpha particles (consisting of two protons and two neutrons, essentially a helium nucleus) scattering from thin metal foils, they observed that occasionally, say one time in ten thousand, the alpha particles were reflected backward from the metal foil. These data led them to conclude that the atom was mostly empty space (which we now understand to be occupied by the “probability clouds” for the electrons) and a small inner core in which the positive charges reside. The positive charges have to be in the center, for only a concentrated volume of positive charge could generate a repulsive force sufficient to deflect the high-velocity alpha particles (which themselves contain two positive charges) backward from their initial trajectory. This nucleus had to be small, in fact, roughly one ten-thousandth the diameter of the atom itself, in order to account for the fact that only one in ten thousand alpha particles experiences a significant deflection (as a direct hit is necessary to send the alpha reeling backward).35

  Knowing that the positive charges in the atom were in the nucleus answered the question of the structure of the atom but raised several more. It was known from chemistry that the number of positive charges in an atom (balanced by an equal number of negatively charged electrons) determined its chemical nature. Hydro gen has one proton in its nucleus, helium has two, carbon has six protons, while gold has seventy-nine. The electron’s mass is nearly two thousand times smaller than a proton’s, so nearly all of the mass of the atom derives from its nucleus. But the weight of an atom does not correspond to the number of net positive charges it has. Hydrogen has a mass equivalent to a single proton, but helium’s mass is equal to that of four protons, carbon’s is twelve, and gold’s mass would suggest that it has 197 protons in its nucleus.

  How can helium have a nucleus with only two positive charges, but a mass four times larger than that of hydrogen? For a while, physicists thought that the nucleus contained both protons and electrons. That is, a helium nucleus would consist of four protons and two electrons. That way, it would have a mass four times larger than hydrogen’s single proton, as observed, but a net charge of +4-2 = +2, which also agreed with the experiments. As the electron has a much smaller mass than the proton, measurements at the time were not precise enough to rule this possibility out.

  Experiments on the nuclear magnetic field (remember that protons have small magnetic fields, as discussed in Chapter 4) and how it influenced the manner by which the electrons in the atom absorbed light (more on this when we discuss magnetic resonance imaging) led scientists to conclude that a helium nucleus, for example, could not have four protons and two electrons. Instead there must be two protons in a helium nucleus, and two other particles that weigh as much as a proton but have no electrical charge. In 1932, James Chadwick bombarded beryllium with alpha particles and detected a new part of the atom: the neutron. Thus one mystery about the nucleus was solved—the atom consisted of electrons orbiting a nucleus that contained protons and neutrons.

  But this left another, more challenging mystery. As it is well known that like positive charges repel one another (this was, after all, the basis by which Rutherford had discovered the nucleus—by observing it repel positively charged alpha particles), then why do the positively charged protons in the nucleus not fly away from one another? The answer is—they do! Protons “feel” electrical forces inside the nucleus just the same as outside the nucleus. The fact that they stay inside the small nuclear volume implies that they feel a second, stronger force that prevents them from leaving the nucleus. A clue about this force is found by considering the heavier siblings of each element, termed “isotopes.” Two atoms are isotopes if their nuclei have the same number of protons (thus making them identical chemically) but differing numbers of neutrons (thus giving them different masses). There are versions of hydrogen that have one proton and zero,
one, or two neutrons,36 but there are no isotopes of helium or any other element that have two or more protons and no neutrons. This indicates that the neutrons in the nucleus play a crucial role in providing the “strong force” that holds the nucleus together (the same strong force we encountered in Chapter 5).

  How much stronger is this force than electromagnetism? If this additional force were ten times greater than the electrical repulsion, then it would be hard to make heavy elements such as silicon, with fourteen protons, or titanium, with twenty-two protons. If the force were a thousand times stronger, then we might expect to see elements with several hundred protons in the nucleus, and we do not. The fact that the heaviest natural element found on Earth is uranium, with ninety-two protons, indicates that this strong attractive force holding the nucleus together is roughly one hundred times greater than the electrical repulsion between the protons.

  But even uranium is not stable, and if you wait long enough, all of your uranium will undergo transmutations to smaller elements by a process known as radioactive decay. Lead, with fifty-six protons and 126 neutrons, is the largest element that does not decay and is therefore stable. You can construct heavier nuclei, but when the “tower of blocks” of protons and neutrons becomes too tall (for each additional proton means more neutrons have to be present to keep it together), eventually the slightest perturbation will cause the tower to collapse. When it does, it loses energy by emitting radiation in the form of high-energy photons (gamma rays) or high-speed subatomic particles, such as electrons, neutrons, or alpha particles.

  In fact, some of the larger nuclei are so unstable that all you have to do is give them a tap, and they fly apart. Uranium, so valuable in the middle of the 1950s that it would tempt Mickey Rooney out into an atomic testing site, is one such element. A dictionary from the end of the nineteenth century described uranium as “a heavy, practically worthless metal.” But this was before Otto Hahn and Fritz Strassmann split a uranium nucleus apart in 1938.