Albert Einstein—creator of relativity, godfather of quantum physics, bender of space and time—had a little problem that dogged him all his career: lack of vision.

It may seem an unlikely charge to levy against the greatest scientific visionary of modern times, but even Einstein had his limits. Despite the extraordinary intuitive leaps he made, he often found himself unable to see what lay beyond his basic insights. As a result, many of the most stunning ideas associated with the theory of relativity were developed not by Einstein but by other scientists interpreting his work. In quantum physics, too, Einstein set out the fundamental concepts but initially failed to recognize where they would lead. And in his final, grandest search for a theory that unified all of physics, he simply never moved far enough beyond the math and science he had learned during his student years.

Illustration by Guy Crittenden

More surprising, Einstein resisted the full implications of his work even after those implications were pointed out to him. Repeatedly he sought to undercut many of his colleagues’ interpretations or to explain them away because they seemed too absurd to be true. These rejections recall the words of Arthur Eddington, a brilliant British physicist and one of Einstein’s most tireless champions: “Not only is the universe stranger than we imagine, it is stranger than we can imagine.” One of history’s most expansive minds was no match for the boundless oddity of nature.

Almost as soon as Einstein completed his 1905 paper introducing the special theory of relativity, he found his ideas taking on a life of their own. That paper spelled out how an observer’s motion through space affects his motion through time (to someone traveling at nearly the speed of light, time slows to a crawl), but it said nothing about treating time as a fourth dimension in a continuum of space-time. That concept, which today’s students learn as quintessential Einstein, was actually the work of German mathematician Hermann Minkowski. Einstein was at first nonplussed by Minkowski’s elaboration of his theory, shaking it off as “superfluous erudition.” Only years later did he recognize space-time as integral to special relativity and to the grander general theory of relativity that followed.

After Einstein published the definitive version of general relativity in 1916, he again found that his theory was full of oddities that he neither expected nor accepted. Just months later, Karl Schwarz­schild, a 42-year-old physicist serving in the German army during the First World War, successfully applied Einstein’s abstract equations of space and time to a realistic physical problem, modeling the geometry of space surrounding a star. His solution impressed Einstein. Yet Einstein expressed one deep concern: Schwarzschild’s calculations showed that if the mass of a star were compressed into a small enough volume, Einstein’s equations went haywire. Time froze; space became infinite. Physicists call that a singularity, a place where the normal laws of nature break down. Schwarzschild had stumbled onto the first clue that black holes might exist.

For years no one paid much attention to Schwarzschild’s discovery, but in 1939 Einstein attempted to disprove the annoying singularity. He argued that a star could not exist under the conditions described by Schwarzschild because the material within it would have to reach orbital velocities equaling the speed of light. But Einstein assumed that the star had to remain stable, whereas the universe is full of objects that explode or collapse violently. In that same year, J. Robert Oppenheimer—the physicist who would soon direct the Manhattan Project—and one of his students showed that highly massive stars could implode under their own gravity, getting denser and more extreme until their gravity trapped even light. That is exactly how astronomers now believe most black holes form.

Not long after Schwarzschild’s discovery came another, even more troubling prediction from general relativity. Like most scientists of the time, Einstein was convinced that the universe (stars included) was static and eternal. So it came as a shock when, in 1922, an obscure Russian physicist and meteorologist named Alexander Friedmann showed that Einstein’s masterpiece theory described a universe that should either collapse on itself or fly apart. Einstein initially rejected Friedmann’s analysis as “suspicious,” then reconsidered and judged that the results might be mathematically correct but physically irrelevant. To fix what appeared to be a flaw in general relativity, Einstein adjusted his equations, adding a factor he called the cosmological constant—a kind of antigravity force—so that the equations yielded an unchanging cosmos.

Not until nearly a decade later did Einstein acknowledge his error. In 1929 the American astronomer Edwin Hubble discovered that all the galaxies appear to be hurtling away from one another at tremendous speeds. The universe was not static; it was expanding, just as general relativity had suggested. Two years later Einstein publicly denounced his cosmological constant. If he had trusted Fried­mann —if he had trusted his own theory—back in 1922, he might have predicted that the universe was expanding, and he wouldn’t have had to scramble to adjust his theory after Hubble’s discovery.

“Einstein was furious with himself,” says Carlo Rovelli, a physicist at the University of the Mediterranean in Marseille, France. “He could have said, ‘My theory says this, so therefore I predict that the universe is expanding.’ But he didn’t have the courage to say that.”

In an unexpected twist, Einstein also failed to appreciate the significance of the cosmological constant that he discarded. Later researchers saw that it could exist even in a universe that was not static. In 1998 astronomers discovered that the expansion rate of the universe was increasing, driven by an unknown repulsive force. Physicists call this force dark energy, and it seems to behave just like the cosmological constant. Einstein’s cast-off mathematical adjustment may thus be crucial to understanding the fate of the universe.

Einstein’s problems with relativity were nothing compared with the passionate manner in which he rejected the legacy of his ideas in quantum physics. In the early years of the 20th century, when most physicists still thought of light as a wave, Einstein was one of the few who believed in particles of light, or photons, and he tried to visualize how light could have both wave and particle aspects. During a 1909 lecture in Salzburg, Austria, he said, “I more or less imagine each such singular point [of light] as being surrounded by a field of force which has essentially the character of a plane wave.” In 1921 he won a Nobel Prize—his only one—for explaining the photo­electric effect, in which particles of light eject electrons from the surface of a substance. This is the principle exploited in solar cells today.

Despite his early advocacy of the quantum nature of reality, by the 1920s Einstein had begun voicing serious doubts about the theory. He objected to the seeming randomness of quantum mechanics, famously asserting that God does not play dice with the universe. The statistical nature of reality at the subatomic level is now well established, however. Einstein was wrong.

A fundamental reason for Einstein’s distrust of quantum physics concerned a startling property that he recognized before anyone else: It allows for instantaneous interactions between two objects, no matter how far apart they might be. In this case his insight was correct, but his understanding missed the mark.

In a 1935 paper titled “Can Quantum-Mechanical Description of Physical Reality Be Considered Complete?” Einstein and two colleagues, Nathan Rosen and Boris Podolsky, presented what they considered a fatal blow to the prevailing interpretation of quantum theory. They argued that in principle it would be possible to carefully prepare two quantum particles—say, two electrons—in such a way that the properties of the two electrons were linked together, or “entangled.” According to quantum theory, a particle can simul­taneously occupy many different states at once, settling into a single state only when it is observed. With two entangled particles, Einstein and his colleagues argued, quantum mechanics predicts that observing the properties of one electron would instantaneously determine the properties of the other, even if the two electrons were at opposite ends of the universe. In other words, quantum mechanics allowed for instantaneous interactions, a violation of the laws of special relativity, not to mention common sense.

Einstein was convinced that what he called “spooky action at a distance” was the result of some as yet undiscovered laws of nature, and that a better theory would explain the mystery without resorting to faster-than-light physics. But since Einstein’s death in 1955, the spooky instantaneous interactions he decried have repeatedly been shown to be real. They may even open the door to a form of teleportation (see “Teleportation? Very Possible. Next Up: Time Travel.” by Michio Kaku). Whether a more fundamental theory will ever replace quantum mechanics is still an open question, but the consensus today is that any such theory will retain the weird interconnectedness that Einstein found so objectionable.

In quantum mechanics as in cosmology, Einstein was so confounded by ideas that other researchers derived from his theories that he sought a way out. “The idea that you could have something here that could instantaneously affect something on the other side of the moon or the other side of the galaxy was to him something like telepathy, not physics,” says Antony Valentini, a physicist at Imperial College London. “He saw that if you believed quantum theory was a final theory, that is where it took you. So he thought, ‘Forget quantum theory; let’s try to develop a better theory.’”

Einstein spent much of the last three decades of his life searching for this alternative to quantum mechanics. He never succeeded. “So the story for most of the 20th century was that people thought Einstein’s later efforts were silly—what on earth was he doing, giving up work on quantum theory?” Valentini says. “But they didn’t see what he had seen. It’s not that other people were more brave in accepting quantum mechanics; they just didn’t see what was coming.”

We now know that Einstein’s efforts to find an all-encompassing “unified field” theory were doomed because he knew nothing about two fundamental forces within the nuclei of atoms, forces that came to be understood only after his death. Yet the search for a theory that would unify all of physics continues to occupy thousands of researchers around the world. The spirit, if not the style, of Einstein’s quest for a unified field theory lives on.

Still, Einstein’s missed connections serve as a warning to today’s physicists. Are they, too, oblivious to the limits of their vision, working with an incomplete understanding of some fundamental aspect of nature? “Yes, it’s perfectly possible,” Rovelli says. “If you look at the history of physics, almost every epoch has the feeling that ‘we know everything now.’ I think what we don’t know is probably huge. We are still far away from knowing all the ingredients.”

Perhaps if Einstein had lived longer he might have come to accept quantum mechanics, making peace with his most unwelcome scientific progeny. “It’s difficult to say, because Einstein changed his mind so many times on so many subjects,” Rovelli says. “That’s a sign of a great scientist. A great scientist is not somebody who believes his own ideas; it’s somebody who does not believe his own ideas. He’s ready to change his mind. What Einstein did was bring back science to its true soul, which is to change our view of the world, not just explain things. Einstein reminded us that what we don’t know is much more than what we know.”