Wet Ink

Today we make a rare foray into the twentieth century with a bracing tour through the history of modern physics. …Don’t roll your eyes like that, the history of science is history, too. Plus, quantum physics gives us all sorts of cool things like cell phones, and big kid stuff like nuclear deterrence. Both tres courant, it pays to be in the know.

Our informative volume is Einstein and the Quantum by A. Douglas Stone. It takes us through the unlikely discovery of quantum mechanics…which as any schoolboy knows is an impossibly weird and impossibly difficult topic. Our author can’t help us much with weirdness, the field just is weird. But he does manage to make the topic tractably difficult, rather than impossible…in physics, that’s a big deal. Stone also manages to tell his tale without recourse to mathematics. (Read that last sentence again, you’ll feel better.) In doing so he presents actual science and its history, not just a list of quantum oddities. The Curmudgeon studied quantum mechanics in his undergraduate days (the 1970s…dinosaurs roamed the Earth) and can report that Stone’s treatment is as close as one can get to the underlying science without delving into the math. The author limits his scope to Albert Einstein’s contributions to quantum mechanics, the very field Einstein himself had doubts about; and he approaches it through a marvelous combination of historical fact, thought experiments, and narrative description of relevant lab experiments.

All of it rollicking good fun, actually, and a good chance to let your inner science nerd run free without having to drag out your calculus.

Stone opens with big drama on a big stage: Friday, October 19, 1900. Max Planck is presenting a paper to the German Physical Society on the relationship of heat and light. Why the topic mattered we shall explore shortly, but for now, it was Max who was feeling the heat: also presenting that night was one Ferdinand Kurlbaum, whose experimental data was going to disprove the theoretical work that Planck was about to deliver. Yikes. The saving grace was that the two were friends, and Kurlbaum had previewed his results with Planck before the formal meeting. Planck had the added pressure of being an eminent figure, “the world’s expert” on this and several related topics…double yikes, and what’s a grand old man of science to do?

He did what any physics student would have done: he stuck in a mathematical kludge.

In this context it’s worth understanding what science actually does, rather than what we think it does. As kids we’re told “science is real” to distinguish the objective and factual from dogma and fantasy. Completely true in that context. But what science really does (all of it: physics, chemistry, biology, medicine) is to build models of the physical world. Ultimately these are always mathematical models (yeah I know, it blows) and a model may be a mathematical expression of something “real” in our childlike sense, or a mathematical approximation of something real, or any mixture of the two. So when Planck and our physics students insert a kludge, it at least is in a knowing way and in the service of making the model better predict physical outcomes.

If that seems nerdy, how about Planck’s topic that night? Light and heat…any kid knows that: shorter wavelength light is absorbed by an object and emitted as longer wavelength heat. Simple. Except that it isn’t, when you start asking, “how?” In doing so, you are asking — as Planck was that night — very fundamental questions about how invisible electromagnetic waves (quantified by Maxwell in the nineteenth century) transfer energy to very tangible mass (quantified by Newton in the seventeenth century). Making matters more difficult for Planck and his colleagues that night in 1900 was that atomic theory was in its infancy. Atoms as concepts had been around since antiquity, but J.J. Thompson had only discovered the electron in 1897 (Lorenz predicted it theoretically in 1896). Its place in the atom and the rest of the atomic structure was still a mystery…one school had electrons buzzing around a nucleus, as we envision them today (the “solar system”), but a then-equally plausible model had them embedded in the nucleus (the “plum pudding”). The physics of the time worked to understand atoms as spheres, interacting purely through Newton’s mechanics and Maxwell’s electromagnetism.

What Planck did that night, then, was present a revision of the theory he had originally planned. Our author unwinds the details, but in essence Planck had to introduce a “quantity of action,” which he denoted hv, where v is the frequency of the incoming radiation, and h is a constant, scalar value, now universally known as the Planck constant. Critically, Planck could only get the math to work if the value of hv was a whole number, so he presented his work with that constraint. Which he promptly walked back, saying that further work might prove that hv could take fractional values as well.

That mathematical term, hv, taken with the constraint that it be a whole number, is a quantum. And it opened a whole can of worms.

The central problem is the constraint that quanta, the packets of hv, correspond to whole numbers. That constraint meant that the world of continuous energy and motion we all experience in daily life falls apart at the atomic level…it becomes, well, weird. Since Newton’s mechanics assumed continuous motion, these new, weird findings were challenging Newton himself. In physics that’s like questioning the Apostle Paul, which is why Planck was waffling.

Having dropped the quantum on us, Planck promptly walked away from it. Backing into a solution is student stuff after all, and theoretical physicists are a notably snobby lot. (Planck later lost out on a Nobel prize because of it: while the nominated work was unrelated, the Nobel committee decided it was Planck who had introduced the disrespectable quantum to classical physics and passed him over.) Stone makes a very convincing case that initially Einstein, and Einstein alone, had the insight to realize that hv might represent something fundamental about atoms and their behavior.

Planck had been analyzing the behavior of gases when heated, and he figured at worst the hv thing was a quirky property of gases. Between 1905 and 1907 Einstein extended Planck’s quantum concept to solids, explaining their so-called specific heat. (Diamonds, it turns out, have interesting thermal properties.) Einstein continued to revisit the quantum model over the next decades of his career, both as researcher and as reviewer and mentor of other scientists in the field. We have seen that Einstein extended the quantum understanding to solids…in doing so he confirmed the Third Law of thermodynamics using quantum principles; he discovered the light/particle duality of light, and in doing so gave us the photon. It was he who gave us the concept of randomness in atomic interactions, and predicted the utterly weird Bose-Einstein condensates, later proven experimentally. And it was Einstein who first noted that quantum theory contained what is now known as quantum entanglement, which Einstein called “spooky action at a distance.”

As the subatomic structure became increasingly understood, difficulties arose in describing the exact behavior of individual particles. Physics turned increasingly to matrix descriptions and probability to estimate subatomic behavior. Einstein’s work on randomness was a precursor to Werner Heisenberg’s proof that it is not possible to know the precise location and behavior of particles at the atomic level, his famous Uncertainty Principle. This result went against the gut for Einstein…scientists like to believe the world is deterministic: if you understand a problem well enough, then given a set of inputs, you can determine the exact outcome. Quantum mechanics doesn’t work that way: the best you can do is choose the most probable outcome. It was this nondeterminism that led Einstein to utter his famous lines, “Quantum mechanics…offers a lot, but it hardly brings us closer to the Old Man’s secret. For my part, at least, I am convinced He doesn’t throw dice.”

That comment, reported as the more thundering, “God does not play dice with the Universe!” was picked up by the press and is the basis for the mistaken idea that Einstein was somehow opposed to quantum mechanics. Instead, he was one of its founders.

In music, we occasionally refer to a new composition as “wet ink,” especially if it is somehow outside the expected norm. Einstein and the Quantum presents us with a great deal of scientific wet ink. In today’s world of packet-switched everything the existence of quanta seems almost intuitive…if porn can arrive in a packet, why not matter and energy? Stone gives us a fascinating and objective story of how man approached a truly new physical phenomenon, and the extent to which even the brilliant and highly trained looked, looked again, and still said, “that can’t be right.” Until, of course, mathematical proof and laboratory experiment both demonstrated that however unintuitive, quantum mechanics was in fact correct.

On his deathbed Einstein is supposed to have said, “Perhaps God throws dice, after all.” That line has always seemed a little too good to me. He was, after all, as famous as anyone on Earth at that point…my hunch is that he had given it some thought and gave himself a great exit line.

But you never know: Einstein was one of the great minds of all time. Maybe — like Planck — he’d come up with a new kludge.