A half century after he died, Albert Einstein still knows how to make an entrance. He drops in unexpectedly when I take out the trash: a momentary glance up at the night sky becomes a vertiginous vision of fusion-powered stars, their bulks held together by the curvature of space-time, their light emitted at a steady 186,282 miles per second. He leaps out from among the sun-bleached rocks when I visit Mount Wilson in California, where Edwin Hubble first saw that the universe is expanding and so transformed the general theory of relativity into a road map of the origin and fate of the cosmos. And he greets me from the faint, Xeroxed papers of the Einstein Archives at the Institute for Advanced Study in Princeton, his words still fresh and vibrant in letters to Franklin Roosevelt, Sigmund Freud, Bertrand Russell, adulatory children, even to cranks wishing to debunk his theories.
Over the years, these visitations have consolidated into a portrait of my Einstein—or, more precisely, my three Einsteins, related but distinct aspects of the man, which I envision nested inside one another like Aristotle's heavenly spheres. The symbolic Einstein touches me through his seismic influence on popular culture; the scientific Einstein reaches me through his serpentine formulas and theories; the philosophical Einstein reaches deepest into my heart, challenging my notions of beauty and spirituality. What ties these together is Einstein's miraculous gift for reckless invention. In his public proclamations, his theorizing, and his religious ruminations, he cast a piercing gaze on existing formulations, rejected existing ideas, and freely redefined terms—space and time, pacifism, God—in search of deeper meanings.
The symbolic Einstein offered me his most pointed lessons while I was growing up, just as he has for millions of other academic-minded kids over the past eight decades. Who doesn't know the stories? Einstein famously (if not actually) started out a "slow" child but grew up to become a gentle genius. Einstein was so far ahead of his time, so out of step with his colleagues, that he had to take a menial job at the Swiss patent office while he hammered away at the mysteries of E = mc^2. Einstein encouraged the development of the atomic bomb, then spent the late years of his life arguing for peace and international cooperation. He was an otherworldly presence, visually signified by his mane of untamable hair, who nevertheless uttered deliberately accessible epigrams: "God is subtle, but He is not malicious," or "To punish me for my contempt for authority, Fate has made me an authority myself."
It hardly matters that many aspects of Einstein's pop biography verge on caricature. The messages they convey are valid all the same. This Einstein taught me that great achievement is inextricably tied to a healthy dose of disrespect for mainstream belief. For me, Einstein was a kind of physics hippie, a man whose creativity was inseparable from his refusal to play by the rules of academia and buy into its comfortable certainties. He reminds me of Bob Dylan kicking out an electrifying "Like a Rolling Stone," or John Lennon embracing guitar feedback and Yoko Ono's abrasive Fluxus art. Einstein could easily have compromised, working more on the applied side of physics and taking on teaching duties. Instead he chose a line of work that allowed his thoughts to hum freely until they spun out the song of special relativity.
I still marvel at the diligent vigor that enabled him to remain true to his freethinker conventions even as his place in the world, and the world around him, changed. His fame built steadily after the publication of special relativity in 1905 and accelerated sharply when he unleashed the general theory of relativity in 1915. Then came the crescendo, when the prominent English physicist Arthur Eddington examined observations collected during a 1919 solar eclipse and declared that the sun's gravity bent the light of nearby stars in exactly the manner Einstein predicted. Suddenly Einstein went from the physics journals to the front pages of the world's newspapers and morphed into science's first modern media star.
The adulation changed him, but not in narcissistic ways. He still followed a resolutely independent path through the landscape of physics, seeking a single theory of all the laws of nature. Few followed his lead, and his many published attempts at a unified field theory proved to be frustrating dead ends. He persevered all the same, reportedly calling for a notebook on his deathbed in the hope that a final flash of inspiration might complete the project of his last thirty years.
Even as Einstein's scientific inspiration dimmed, fame exposed another aspect of his greatness: a profound understanding of the responsibility that came with celebrity. He was keenly aware that he had become the public face of science, a role he treated with seriously playful irreverence. The genial "Uncle Albert" persona undercut the stereotype of the scientist as a coldhearted materialist. (Think about how many photographs of Einstein on the bicycle or Einstein sticking out his tongue still stand watch over college dorm rooms.) Those famous quotes citing God did the same, in a more penetrating way. I interpret Einstein's use of that word as a symbolic act as much as a theological one. He evidently understood that a science that ignores or seemingly refutes religion would never be fully satisfying to the public—not even to himself.
In politics, too, Einstein carefully evaluated the interplay between his authority and his contempt for authority. He had always been an ardent antinationalist and pacifist, vehemently opposed to World War I and appalled by his many German colleagues who supported it. Now he clung to these ideals but recognized the danger of blind adherence to ideology, even the idealistic ideology of pacifism. In a 1931 talk at the California Institute of Technology, he explained how he had reinvented the word: "I am not only a pacifist but a militant pacifist. I am willing to fight for peace. . . . Is it not better for a man to die for a cause in which he believes, such as peace, than to suffer for a cause in which he does not believe, such as war?" When the threat of a Nazi atomic bomb seemed real, he signed the letter drafted by physicist Leo Szilard urging President Roosevelt to begin an American atomic bomb project. Yet he stuck to his core beliefs, arguing after the war for disarmament and international government to preserve the peace.
Who in the generations of scientists after Einstein has shown such a clear understanding of what to do with the bully pulpit of public acclaim? Look at the most famous living scientists—Stephen Hawking, for example, or James Watson. They have all contributed wonderful ideas to the world, but few interact meaningfully with today's major political and social issues.
Beneath the symbolic Einstein lies the scientific Einstein—the man whose theoretical breakthroughs justified the fame and all that flowed from it. Here, too, he was more than just a superficial radical. Physicist Banesh Hoffman, Einstein's collaborator and biographer, aptly described him as "creator and rebel." Einstein destroyed classical certainty, but only so he could uncover a deeper kind of certainty. Isaac Newton had envisioned a universe built on absolute space, an invisible metric against which all motion can be measured. Einstein replaced Newton's universe with one built on absolute law, meaning that the speed of light and other fundamentals of physics remain the same from all perspectives. The alternative—that physical laws should vary with the observer's motion relative to some undetectable, unknowable frame of reference—now seems absurd. Yet every natural philosopher before Einstein, going back to Aristotle and beyond, accepted some version of that proposition.
Einstein arrived at special relativity almost purely from an examination of logical flaws in the then current theories of physics, flaws that were evident for all to see. Speaking recently at the Aspen Center for Physics, physicist Murray Gell-Mann marveled at Einstein's ability to take James Clerk Maxwell's equations of electromagnetism more seriously than Maxwell himself did and track the full implications of Galileo's idea of relative motion and Newton's model of gravity. Here was the glorious payoff of Einstein's fierce commitment to freethinking. He insisted on examining the workings of the world at a more rigorous level than even the most illustrious of his predecessors, until he was totally certain that the system made sense. His requirement of total consistency forced him to take seriously the problems that his predecessors and colleagues alike had swept aside as trivialities or unanswerable matters of metaphysics.
Einstein's triumphs were guided not by strange new experiments but by rigorous logic, not by the most esoteric questions of the day but by the most basic ones. He famously argued that "all physical theories, their mathematical expressions notwithstanding, ought to lend themselves to so simple a description that even a child could understand them." Similarly, he described the questions that motivated his theories as fundamentally childlike ones that he had carried with him into adult life.
Often Einstein framed these questions in terms of thought experiments that highlighted the universal nature of his thinking. In one conceptual exercise, he wondered what a person would see if he could catch up with a beam of light. Newton's theory of space says that such a thing should be possible; Maxwell's theory of light says that it should not. Special relativity showed how to explain what we observe (Maxwell's laws) by discarding what we cannot observe (Newton's absolute space). These mental pictures convinced Einstein that the cosmos had to operate on a more consistent and fundamentally simple basis than his colleagues believed. He addressed these shortcomings by inventing his own physics and finding new ways to measure space and time.
One of Einstein's greatest inspirations, as he later recalled, occurred during a flash of insight in 1907: "For an observer falling freely from the roof of a house there exists—at least in his immediate surroundings—no gravitational field." (A note of caution: This may be the symbolic Einstein at work, retroactively fabricating an event to make his concepts clear. What matters, however, is that his ideas can be expressed in such terms and that he chose to do so.) In other words, the acceleration caused by gravity exactly erases the force exerted by gravity. Einstein cast the situation another way. A man in an enclosed elevator cannot in principle say whether he is motionless on Earth's surface and feeling the pull of gravity or moving through space, being pushed upward at an identical rate of acceleration. This became Einstein's principle of equivalence, which states that a uniform acceleration is equivalent to, or indistinguishable from, a uniform gravitational field.
Einstein developed those ideas into general relativity, a theory of gravity that subsumed and expanded on Newton's. General relativity far surpassed special relativity in redefining space and time—not just how they are measured but how they are linked together—to find a clearer, more comprehensive description of reality. The warping of space-time is an exotic-sounding concept that is actually a part of everyday experience. It is what holds together giant clusters of galaxies, but it is also what I experience every time I sit down in a chair or take a step. The symbolic Einstein showed that physicists need not be remote and detached from the real world; the scientific Einstein showed that their research need not be, either. No wonder he makes so many surprise appearances in my life.
Relativity—general relativity in particular—leads me directly from the scientific Einstein to the philosophical Einstein. With general relativity, Einstein completed a program begun in ancient Greece to determine the scope of natural law and thereby define the relationship between us and the universe. In the Greek conception, the flawed earthly laws and elements are distinct from those of the heavenly spheres, which follow perfectly circular motion and consist of aether—the perfect "fifth element." The perceived split between heaven and earth lived on in diminished form, all the way through Newton's absolute space (which he described as "the sensorium of God") and the nineteenth-century reconception of the aether as an invisible, all-pervasive medium that transmits light through empty space and provides the background reference frame of all motion.
In Einstein's universe there is no fifth element, which means that there is no escaping the authority of science. To me, this is one of the most disruptive aspects of Einstein's entire rebellious vision. Shortly after completing general relativity, he published a paper that expressed these ideas in rigorous terms, essentially inventing the field of cosmology, the study of the cosmos as a whole. He also established the terms for a new relationship between science and religion.
The idea that the universe is a single thing, governed by a single set of rules accessible to mathematics, strikes me as stirring, terrifying, and intensely mystical—a word that undoubtedly would have caused Einstein to wince or laugh, or perhaps both. "Mysticism is in fact the only reproach that people cannot level at my theory," he once retorted when a fan praised him for this aspect of relativity. Yet his snipe against mysticism told only half the story, since the outspokenly atheistic Einstein frequently adopted the language of theology. As in politics, as in science, he reached for a deeper truth by redefining and extending commonly used terms. "What I see in Nature is a grand design that we can understand only imperfectly, one which a responsible person must look at with humility," he said. "This is a genuinely religious feeling and has nothing to do with mysticism."
Once again Einstein plays the role of thoughtful revolutionary, reinventing familiar terms to expose broader truths. He implicitly argued that science (aided in no small part by his theories) had expanded to the point where it redefined not only humanity's relationship to the universe but also humanity's relationship to the divine. Einstein's cosmos leaves no place for a literal heaven, no physical realm where our earthly laws of physics do not apply. But in religion as in science, when Einstein overthrew the old order he exposed a new, deeper order. He found a religious interpretation of this deeper order in the philosophy of Baruch Spinoza and came to regard physical law itself as divine. "I believe in Spinoza's God who reveals himself in the harmony of all that exists, not in a God who concerns himself with the fate and actions of human beings," he said.
Einstein's much repeated use of the word "God" was not an indulgence and not a purely symbolic act. It was a well-considered philosophical position. He acknowledged that a truly universal theory of physics has theological implications; at the same time, he worried intensely about the destructive power of religions whose adherents imagine they can pray for their success or for others' failure. Einstein believed, passionately if a bit naively, that his logical approach could help here, too. "After religious teachers accomplish the refining process indicated, they will surely recognize with joy that true religion has been ennobled and made more profound by scientific knowledge," he wrote in 1941.
I admire the dogged conviction Einstein displayed as he parsed the meaning of God and religion again and again to clarify his self-proclaimed "new religion." Just as his belief in beautiful, orderly scientific theories mirrored a child's view of the world, so his belief in God as the ultimate manifestation of that order expressed an idealistic notion that God is so much greater than humankind that He cannot be found in any one faith. Einstein devoted great energy to publicizing this view. He repeatedly described the "cosmic religious feeling" that accompanies great scientific discoveries and declared in The New York Times Magazine that "in this materialistic age of ours the serious scientific workers are the only profoundly religious people." Although there is no deity to communicate with in Einstein's universe, he presented the possibility of a cosmic connection based on an intellectual comprehension of the rules of reality.
So far, this path to spiritual enlightenment is a lonely one. The theoretical legacy of Einstein's foray into cosmology is everywhere. General relativity provided the underpinning of the Big Bang and introduced the concept of a cosmological constant, the model for the "dark energy" thought to be causing the expansion of the universe to accelerate. Modern cosmology depends so thoroughly on Einsteinian notions of curved space-time, the large-scale homogeneity of matter, and the equivalence of all reference frames that many scientists forget that these ideas were radical speculations less than a century ago. Try looking for Einstein's philosophical legacy, however, and the cupboard looks rather bare.
I cannot recall a researcher ever discussing the cosmic religious feeling. Many scientists and historians dismiss Einstein's use of the terms "religious" and "God" as sloppy shorthand for the beauty of science. Cosmologists today rarely talk about God; if they do, it is in the self-conscious manner of Stephen Hawking, who once asked "What place, then, for a creator?" They largely ignore Einstein's philosophical language and the broad, emotive way in which he spoke about his research. In his groundbreaking book The Inflationary Universe, for example, Alan Guth of MIT, who codeveloped the leading model of the Big Bang, speculates provocatively about whether it would be possible to create a new universe in a basement laboratory, but he treats such a Genesis-on-demand merely as a scientific thought problem. As cosmology grows ever larger, its aesthetic grows paradoxically smaller and in many ways more impoverished.
This is the saddest aspect of Einstein's legacy. Politicians and activists have taken up his dream of a peaceful, unified world. Physicists have carried on his program to unify the laws of nature. The search for uniformity and harmony, which Einstein regarded as the core aesthetic of his science, guides almost all advanced ideas in physics today, from the most far-out theories of universal beginnings to string theory. The unification of science and religion, by contrast, has drawn few takers. The uncompromising rigor that Gell-Mann lauded in Einstein's science drew little support when Einstein applied it in a theological direction. The modern resurgence of religious extremism seems only to have driven people farther from Einstein's ideal.
Perhaps it is just a matter of time. Smashing icons is never a popular business. Special and general relativity, among the grandest theories of our time (rivaled only by quantum mechanics and Darwinian evolution), took years to gain wide acceptance and never received a Nobel Prize. Cosmic religion is far more controversial and far less concrete: there is no equivalent of a solar eclipse experiment to show that Einstein was on the right track in pursuing "the secrets of the Old One." Meanwhile, I continue to commune with Einstein and do what little I can to follow his uncompromising creation: a science that rejects patchwork theorizing but also rejects the notion that rational inquiry cannot speak to the hunger for spiritual truth.