The Amazing Story of Quantum Mechanics (3 page)

This short fiction certainly could never be mistaken for a typical Verne adventure tale—the protagonist is a young poet who loses his job at his uncle’s bank, fails to find gainful employment, loses contact with his only friends and his young love, and ends the novel wandering aimlessly through the streets of Paris during a bitter winter storm until he passes out in the snow in a cemetery containing many famous French authors of the nineteenth century. And yet there are enough accurate descriptions of life in the next century to clearly place it among Verne’s body of work. The 1863 novel describes automobiles that drive quietly and efficiently using a form of the internal combustion engine (thirteen years before Nikolaus Otto invented the four-stroke engine and more than forty years prior to the mass production of automobiles by Henry Ford), and it is suggested that the energy source involves the burning of hydrogen. Elevated trains are propelled by compressed air (while the London Underground opened the year this novel was written, elevated tracks would not see real construction for another five years); the city is illuminated at night by electric lights (Cleveland, Ohio, rather than Paris, would earn the title of first city of electric lights five years later); and skyscraper apartments are accessible by automatic elevators, again five years before the construction of the elevator in the eight-story Equitable Life Assurance Building in New York City.

Verne posited that by 1960 global communication would be an established fact and a worldwide web of telegraph wires would bring “Paris, London, Frankfurt, Amsterdam, Turin, Berlin, Vienna, Saint Petersburg, Constantinople, New York, Valparaiso, Calcutta, Sydney, Peking, and Nuku Hiva
³
“ together. Furthermore, he described “photographic telegraphy,” to be invented at the end of the nineteenth century, which “permitted transmission of the facsimile of any form of writing or illustration, whether manuscript or print, and letters of credit or contracts could be signed at a distance of five thousand leagues.” This last had to await developments in physics more profound than pneumatic trains—for the modern fax machine is a demonstration of quantum mechanics in action!

Verne also suggested in this novel that mechanical progress would result in a military arms race that would yield such destructive cannons and equally formidable armor shielding that the nations of the world would just throw up their hands and abandon war entirely. Friends of the main character in the novel, bemoaning the loss of the honorable occupation of professional soldier, note “that France, England, Russia and Italy have dismissed their soldiers; during the last century the engines of warfare were perfected to such a degree that the whole thing had become ridiculous.” Verne did accurately predict the “mutually assured destruction” theory of war ushered in by intercontinental ballistic missiles, but he underestimated the capacity of humans to find ways to wage wars nevertheless.

There is a deep similarity between the young physicists who developed quantum theory and the fans of the science fiction pulps of the 1920s and 1930s. Namely, they were both able to make a leap—not of faith but of reason—to accept the impossible as real and to will their disbelief into suspension.

Science fiction fans can entertain the possibility of faster-than-light space travel, of alien races on other planets, of handheld ray guns capable of shooting beams of pure destruction, and of flying cars and humanoid robots. The physicists at the birth of quantum mechanics, trying to make sense of senseless experimental data, had to embrace even more fantastic ideas, such as the fact that light, which since the second half of the nineteenth century had been conclusively demonstrated both theoretically and experimentally to be a wave, could behave like a particle, while all solid matter has a wavelike aspect to its motion.

It is perhaps small wonder that, faced with such bizarre proposals concerning the inner workings of a universe that had heretofore exhibited clockwork predictability, these scientists sought relaxation not in fantastic science fiction adventures but in the conventionality of dime-store detective novels and American cowboy motion pictures. In fact, the predictability of these western films led Niels Bohr, one of the founders of quantum theory, and his colleagues to construct theories regarding plot development in Westerns, when not grappling with the mysteries of atomic physics. In one participant’s recollection, Bohr proposed a theoretical model for why the hero would always win his six-shooter duel with the villain, despite the fact that the villain always drew first. Having to decide the moment to draw his pistol actually impeded the villain, according to Bohr’s theory, while the hero could rely on reflex and simply grab his weapon as soon as he saw the villain move. When some of his students doubted this explanation, they resolved the question as good scientists, via empirical testing using toy pistols on the hallways of the Copenhagen Institute (the experimental data confirmed Bohr’s hypothesis).

In most discussions of quantum mechanics, at both the popular and technical levels, one typically begins with a recitation of the experimental findings that challenged accepted theories and then proceeds to describe how these data motivated physicists to propose new concepts to account for these observations. Let’s not do that. In the spirit of the 1970s television detective show
Columbo,
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I’ll begin with the solution to the mystery of the atom and only then describe its experimental justification.

There are three impossible things that we must accept in order to understand quantum mechanics:

It is reasonable at this stage to ask: Why wasn’t this brought to our attention sooner? How is it possible to live a careful and wellobserved life and yet never notice the particle nature of light, the wave nature of matter, and the constant spinning of both? It turns out that these are all easy to miss in our day-to-day dealings. While the human eye is physically capable of detecting a single light particle, rarely do we come across them in ones or twos. On a sunny day, the light striking one square centimeter (roughly equivalent to the area of your thumbnail) is comprised of more than a million trillion of these packets of energy every second, so their graininess is not readily apparent.

The second principle discusses the wavelike nature of matter. I show in Chapter 3 that a thrown baseball has a wavelength less than a trillionth the size of an atomic nucleus; it is consequently undetectable. The wavelength of an electron within an atom, in contrast, is about as large as the atom itself, and thus this wavelike property cannot be ignored as we seek to understand how the atomic electrons behave.

Atoms interact with light in minute quantities, and the wavelike nature of the motion of electrons in the atom turns out to be crucial to determining how it can absorb or lose the energy contained in light. Thus any model of the atom and of light that relies solely on our day-to-day experiences fails to accurately account for observation. The influence of the third principle, concerning the “intrinsic angular momentum,” also referred to as “spin,” is fairly subtle and comes into play when two different electrons or two atoms are so close to each other that their matter-waves overlap. This effect turns out to be rather important and is the key to understanding solid-state physics, chemistry, and magnetic resonance imaging.

While it is certainly true that these three basic principles of quantum mechanics seem weird, it is important to note that making counterintuitive proposals about nature is
not
a unique aspect of quantum mechanics. In fact, putting forth a seemingly weird idea to describe some aspect of the physical world, developing the logical consequences of this weird idea, experimentally testing these consequences, and then accepting the reality of the weird idea if it conforms to observations is pretty much what we call “physics.”

Weird ideas have been the hallmark of physics for at least the past four hundred years. Sir Isaac Newton argued in the mid-1600s, in his first law of motion, that an object in motion remains in motion unless acted upon by an external force. In my personal experience, when I am driving in a straight line along a highway at a constant speed of 55 miles per hour, I must continue to provide a force in order to maintain this velocity. If I take my foot off the accelerator, I do not remain in uniform straight-line motion (even if my tires are properly aligned) but rather slow down and eventually come to rest. This is, of course, due to the influence of other external forces acting on my automobile, such as air drag and friction between the road and my tires. We do not find the effects of friction strange or mysterious, as we have had a few centuries to accept the concept of dissipative forces. These forces appear “invisible” to us, and it required tremendous insight and abstraction on Newton’s part to imagine what an object’s motion would be like in their absence. This strange idea of drag and frictional forces, no less counterintuitive than anything quantum theorists have suggested, applies to large objects such as people and apples.

The quantum realm is more mysterious, as most of us, aside from superheroes such as the Atom or the Incredible Shrinking Man, do not regularly visit the interior of an atom. Nevertheless, it took roughly sixteen hundred years for Newton’s first law of motion to overturn Aristotle’s proposal that objects slowed down and came to rest not due to friction, but owing to the fact that they longed to return to their “natural state” on the ground.

In the century preceding the development of quantum theory, physicists such as Michael Faraday and James Clerk Maxwell suggested that the forces felt by electric charges and magnets were due to invisible electric and magnetic fields. Faraday was the first to suggest that electric charges and magnetic materials create “zones of force” (referred to as “fields”) that could be observed only indirectly, through their influence on other electrical charges or magnets. Scientists at the time scoffed at such a bizarre idea. To them, even worse than Faraday’s theory was his pedigree: He was a self-taught experimentalist who had not attended a proper university such as Oxford or Cambridge. But Maxwell took Faraday’s suggestion seriously and was able to theoretically demonstrate that visible light consists of an electromagnetic wave of oscillating electric and magnetic fields.

Changing the frequency of oscillation of the varying electric and magnetic fields yields electromagnetic waves that can range from radio waves, with wavelengths of up to several feet, to X-rays, with a wavelength of less than the diameter of an atom. Each of these forms of light are outside our normal limits of detection but can be detected with appropriate devices. The weird ideas of Faraday and Maxwell are the basis of our understanding of all electromagnetic waves, without which we would lack radio, television, cell phone communication, and Wi-Fi.

If the nature of progress in physics involves the introduction and gradual acceptance of weird ideas, then why does quantum mechanics have a particular reputation for bizarreness? It can be argued that, in part, the weirdness of the ideas underlying quantum mechanics is a consequence of their unfamiliarity. It is no less counterintuitive, in my opinion, to state that electric charges generate fields in space, and that we are always moving through a sea of invisible electromagnetic waves, even in a darkened room, than to say that light is composed of discrete packets of energy termed “photons.” Phrases such as “magnetic fields” and “radio waves” are part of the common vernacular, while “wave functions” and “de Broglie waves” are not—at least not yet. By the time we are done here, such terms will also become part of your everyday conversation.
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The cover of the August 1928
issue of
Amazing Stories,
shown in Figure 1, which contained Buck Rogers’s debut, featured a young man flying via a levitation device strapped to his back. While rocket packs would be labeled “Buck Rogers stuff” (and levitating belts would soon be featured in Buck Rogers’s newspaper strip adventures), the cover of this issue of
Amazing Stories
actually illustrated E. E. Smith’s story “The Skylark of Space.” The cover depicts Dick Seaton, a scientist who is testing out a flying device that employs a newly discovered chemical. When an electrical current is passed through this substance, Element X, while it is in contact with copper, the “intra-atomic energy” of the copper is released, providing an energy source for a personal levitation belt, a spaceship (the Skylark of the title), or a handheld weapon firing “X-plosive bullets.”