Science has often found unique ways to humiliate its devotees. In 1964, two youngish men crawled inside an enormous metal basket carrying brushes and a bucket of soapy water. The 20-foot-long radio receiver looked like the head of a lacrosse stick, but functioned like an ear horn, opening to the heavens and listening to the cosmos. They scrubbed and scrubbed, hoping the caked layer of pigeon poop might (gloved fingers crossed) be the cause of the mysterious, frustrating, and unwanted signal. Maybe taking a manual Q-tip to the horn antenna’s ear would clear up the one note of noise.
They were an unlikely pair in an unlikely place. Robert Woodrow Wilson was a Houston native, and Arno Penzias was a German immigrant who had escaped one of Hitler’s camps at age six. And this hill overlooking New York City was not a normal place to pursue astronomy. Bell Labs had designed the antenna to communicate with the new Telstar satellite, but with down time from its primary duties, the owners let astronomers give it a whirl. Wilson and Penzias wanted to probe the sparse outer reaches of the Milky Way galaxy.1
They needed the signal to be pristine, and with great effort, they had fine-tuned and calibrated the big basket for their measurements. They found ways to filter out local radio broadcasts, noisy radar echoes, and other extraneous signals arising from their own electronics. After all this, the horn still had some kind of tinnitus—there was a little ringing at the wavelength 7.35 centimeters. No matter where in the cosmos they pointed the antenna, no matter the time of day or night, there was the same ringing, always the same strength. The only thing that all directions and all times of day had in common, they figured, was bird crap. When they ran the big device on chilly nights, pigeons gathered at the warm end and made a mess.
Bird crap removed, they pointed the instrument again away from the thick plane of the Milky Way galaxy and out into the darkest, deepest reaches of space. They wanted to make sure the signal was gone, like listening for an unwanted hum in an excellent audio system. Just sit still in the dark until the speakers emitted only pristine, quiet beauty. But no, the ghastly noise peak was there again, as strong as ever. The universe appeared to be emitting radiation similar to that from the Amana Corporation’s new microwave ovens. With heavy sighs, Wilson and Penzias recorded and annotated the mysterious tone, just in case it wasn’t a fingerprint of their own incompetence.
The two had unwittingly made a critical discovery, one for which they would win the Nobel Prize in Physics: The microwave signal is a dim but very real glow emanating uniformly from the universe itself. In further measurements, the “cosmic microwave background” perfectly fit an equation dating to 1900, when the German physicist Max Planck described the natural radiation emitted by any object at any temperature, be it a bright fiery star, a lukewarm nickel in your pocket, or in the case of the universe’s background signal—a faint afterglow of the Big Bang (Figure P.1 ).2
Figure P.1 Spectrum of the cosmic background radiation, or the residual glow of the universe, when all galaxies, dust, and so on are removed from the signal. When these data from the COBE satellite were presented in 1990, they precipitated a spontaneous standing ovation. Planck’s law (the line labeled Black-Body Spectrum) fits the universe’s signal (crosses) so precisely that the uncertainties in the data points are much smaller than the line thickness used here.
As of this writing, humanity now has a cosmic ear horn in orbit, and it listens with the best clarity yet to these low-frequency signals from the universe. Similar in size and shape to the instrument used by Wilson and Penzias, it rotates its narrow view about once every minute, sweeping out a ring of measurements like a second hand. In the cosmic background’s blemishes and tiny inconsistencies, the Planck satellite can see residual clues describing the universe’s initial fireball—a fingerprint of the first physics, or the very hands of God, depending on whom you ask. The satellite’s namesake, the late German physicist Max Planck, did not think much about astronomy, and when his younger friend Albert Einstein turned his own gaze to the cosmos, Planck told him it was probably a waste of time. Yet, when the European Space Agency decided it needed a catchier project title than the acronym COBRAS/SAMBA, the name “Planck” was an easy sell to all parties.
It had been just as easy to sell his name after World War II, as the Allies looked to rebrand all German research programs. Albert Einstein, estranged from Planck and bitterly divorced from Germany, composed a tribute to the man on behalf of American scientists. “Even in these times of ours,” he wrote in 1948, “when political passion and brute force hang like swords over the anguished heads of men, that even in such times there is being held high and undimmed the standard of our ideal search for truth. This ideal, a bond forever uniting scientists in all times and in all places, was realized with rare completeness in Max Planck.” And according to Einstein, Planck’s 1900 discovery, “became the basis of all 20th century research in physics and has almost entirely conditioned its development ever since. Without this discovery it would not have been possible to establish a workable theory of atoms and molecules and the energetic processes which govern their transformations.”3 This was not a hyperbolic statement then, and it holds today.
Our understanding of the building blocks and the structure of matter trace directly to Planck’s work. And our understanding of how separate chunks of matter then exchange energy—how they chat and inform one another—also starts with Planck’s primary discovery. He expertly described the radiation that leaks from any and every object in the universe. No matter what object, and no matter its temperature, we need just one equation—Planck’s—to describe every single case. At the time he penned his formula, scientists were years from discovering galaxies beyond our own, never mind looking for remnants of the Big Bang. Planck, just like Wilson and Penzias, had been trying to diagnose one thing when he stubbed his toe on something much different and even more important. In trying to once and for all describe this baffling glow from all things—called “black-body radiation”—Planck found the key that unlocked the modern age of physics. Even though he contemplated the physics governing the light inside of a small, dark cavity within a brick, his satellite now gazes in the opposite direction—the ultimate outward—and finds the same fundamental physical law reigning supreme.
Planck is known as the father of quantum theory, and most textbooks give students little more than that. He was German. He was a theoretical physicist (versus an experimental, or laboratory-based one), with a firm grasp of mathematics. In the typical side-column photo, we see him later in life: bald, and stern. He discovered quantum theory. He had a mustache. And that’s about it (Figure P.2 ).
Figure P.2 Max Planck in 1906, at age 48.
Photograph by Rudolf Dührkoop, courtesy AIP Emilio Segre Visual Archives, W. F. Meggers Gallery of Nobel Laureates.
But there is so much more to Planck the scientist and Planck the person.
Max Planck had elevated and refined the formerly obscure notion of “entropy” in the universe—he made it not only a useful tool, but also a central topic. Relevant for diagnostics ranging from car engines to black holes, entropy has even provided a template for the study of information itself. Planck also made great contributions to chemistry, to the then-infant field of statistical mechanics, and to Albert Einstein’s new ideas of relativity.
His human story is equally rich: musical ability, a cherished family, and a sterling reputation; a devotion to his homeland, come what may; a delicate and poignant relationship with Albert Einstein. Planck was first and last a communicator. He assembled prose in the manner of a master watchmaker, and he launched his mind at much more than physics. Planck was also a person in the right place at all the wrong times, watching ridiculous advances in technology reformat his world and then tear it apart. In 1933, just as little Arno Penzias was born into a nervous German Jewish family, Planck was trying to reason with the new German Chancellor Adolf Hitler.
After Planck’s death, the Royal Society sent Charles Darwin’s grandson, Charles George Darwin, to Berlin. Even though the Britain of 1948 had no love lost for Germany, one name transcended the garish wounds of two wars. “But if Planck the originator in scientific achievement commands the homage of our heads,” Darwin said, “no less does Planck the man deserve the approbation of our hearts. His character was modest, kindly and blameless, and amid the trials of distressful times and through many personal sorrows he preserved his integrity and his quiet courage.”
There are many sensible reasons that Planck’s story is not better known, particularly in the English language. His library, personal journals, notebooks, and letters were destroyed with his home in World War II. What exists of his correspondence with other German scientists is often handwritten in an antiquated form of German shorthand, Sütterlin, understood by ever-fewer scholars. And he was certainly eclipsed by the younger, bolder, and more brilliant Albert Einstein. Whereas Planck was very much a nineteenth-century Prussian gentleman walking into a wholly new twentieth century, Einstein saw himself as a modern man of the world, and he benefited from the dawn of global media. He also enjoyed a long presence in America as it took the mantle of worldwide scientific leadership from Planck’s vanquished Germany.
Humbly, I now try to tell some of Max Planck’s rich story. I admit from the start that I can’t approach his life as a science historian, but I come to Planck as a physicist long fascinated by his breakthrough and haunted by those sad eyes. I have for many years wanted to know who he was, what shaped him, and how we might best understand his circumstances—or, as we might say in physics, his fundamental principles, his initial conditions, and his boundary conditions. What follows are my best attempts to discover this German physicist and share the results—not just with scientists, but with any interested reader, since we are bathed one and all, from every direction, in the glow of his law.
Brandon R. Brown, Summer, 2014.