Over the years, Einstein received a lot of letters from children. “I am a little girl of six,” one announced in large letters drawn haphazardly across the full width of the writing paper. “I saw your picture in the paper. I think you ought to have a haircut, so you can look better.” Having given her advice, the girl, with model formality, signed it, “Cordially yours, Ann.”
“I have a problem I would like solved,” wrote Anna Louise of Falls Church, Virginia. “I would like to know how color gets into a bird’s feather.” Dear Mr. Einstein was asked the age of Earth and whether life could exist without the sun (to which he replied that it very much could not). One child asked him whether all geniuses were bound to go insane. Frank, from Bristol, Pennsylvania, asked what was beyond the sky—“My mother said you could tell me.”
Kenneth, from Asheboro, North Carolina, was more philosophical: “We would like to know, if nobody is around and a tree falls, would there be a sound, and why.” Similarly, Peter, from Chelsea, Massachusetts, drove straight to the heart of human inquiry: “I would appreciate it very much if you could tell me what Time is, what the soul is, and what the heavens are.”
Other questions were not quite so fraught. A boy named John informed Einstein that “my father and I are going to build a rocket and go to Mars or Venus. We hope you will go too. We want you to go because we need a good scientist and someone who can guide a rocket good.”
Occasionally, skeptical correspondents emerged, such as June, a twelve-year-old student from Trail Junior High School in British Columbia, Canada. “Dear Mr. Einstein,” she wrote. “I am writing to you to find out if you really exist. You may think this very strange, but some pupils in our class thought that you were a comic strip character.”
In a similar vein, Myfanwy from South Africa had thought Einstein dead:
I probably would have written ages ago, only I was not aware that you were still alive. I am not interested in history, and I thought you had lived in the 18th c., or somewhere around that time. I must have been mixing you up with Sir Isaac Newton or someone. Anyway, I discovered during Math one day that the mistress was talking about the most brilliant scientists. She mentioned that you were in America, and when I asked whether you were buried there, and not in England, she said, Well, you were not dead yet. I was so excited when I heard that, that I all but got a Math detention!
Myfanwy proceeded to tell Einstein how she and her friend Pat Wilson would sneak around the school at night to carry out astronomical observations, and about her love of science. “How can Space go on forever?” she wondered. “I am sorry that you have become an American citizen,” she finished. “I would much prefer you in England.” Einstein was obviously taken with Myfanwy’s exuberance, as he sent her a reply in which he praised her nighttime escapades and apologized for remaining alive. (“There will be a remedy for this, however.”)
On his seventy-sixth birthday, Einstein was sent a pair of cuff links and a tie by the fifth-grade children of Farmingdale Elementary School in Pleasant Plains, Illinois. “Your gift,” he wrote to them, “will be an appropriate suggestion to be a little more elegant in the future than hitherto. Because neckties and cuffs exist for me only as remote memories.”
This was one of Einstein’s last letters. He died around three weeks after writing it.
In December 1925, the young Austrian physicist Erwin Schrödinger was holed up in the village of Arosa, Switzerland, with one of his mistresses. He was there for his health: suspecting a mild case of tuberculosis, his doctors had ordered him to rest at high altitude. There, among the calm of the mountains and deep snow, placing a pearl in each of his ears when he wanted quiet, he developed a theory that became known as “wave mechanics.”
Schrödinger’s theory was inspired by the ideas of Louis de Broglie, a physicist who in his doctoral thesis of 1924 had showed how to calculate the wavelength of a particle based on its momentum. In 1905, Einstein had demonstrated that waves can act like particles. What de Broglie argued was that particles can act like waves.
Wave mechanics provided a set of equations that prescribed how wavelike particles could behave. On first encounter with the theory, Einstein and many others were impressed and pleased with its useful- ness, but it was soon noticed that some implications of Schrödinger’s mechanics were a little problematic. For one thing, the theory stated that the waves it described would, given time, propagate over a very large area, much like a ripple on the surface of a lake spreading out and out, making for the shore. But Schrödinger’s waves were, of course, also particles—they were electrons and other subatomic objects. To Einstein it seemed almost nonsensical to say that an electron would propagate over such enormous distances. It simply didn’t accord with reality.
So Schrödinger’s mathematical description of waves raised a question. If it didn’t represent literal waves, waves in the real world, what did it represent? Einstein’s good friend Max Born, a professor at the University of Göttingen, devised an answer: it represented the probability of a particle’s location. Which is to say that each particle has what’s called a “wave function,” and one can use this to predict the likelihood of finding a particular particle in a particular place.
Put an electron in a box. According to this idea, the electron has a number of potential locations spread throughout the box, and it exists in a kind of muddled-up mixture of all these possible positions. This mixture is mathematically represented by the electron’s wave function, which gives us the various different probabilities of detecting the electron at the various different locations within the box.
“Einstein, stop telling God what to do.”
Einstein, consistently throughout his career, was unhappy with quantum mechanics’ reliance on probability. In fact, he did not like it at all. He strongly believed, even though evidence suggested otherwise, that at a deep level the universe was not run on chance and that the order apparent in the observable universe was built on order in the subatomic realm.
When debating with the theory’s various advocates, he would often tell them, “God does not play dice.” To which Niels Bohr had a rejoinder: “It cannot be for us to tell God how he is to run the world”—or in other words, “Einstein, stop telling God what to do.”
In the summer of 1925, when he was twenty-three years old, Werner Heisenberg traveled to the tiny island of Heligoland in the North Sea, hoping that its beaches and sheer cliffs would allay his bad hay fever. There, in one intense night, he finalized his interpretation of the difficulties of the quantum realm. Heisenberg worked from the premise that he could completely ignore what could not be observed, measured, or proved to be true. This sounds quite reasonable, but in this instance it meant that, in order to develop his theory of the laws that govern the behavior of electrons, he made no effort to describe, or really even to think about, the motions or orbits of electrons, as they could not be observed. Instead, he looked at the light emitted by electrons under different circumstances. If you bombard an atom with light or disturb it in other ways, an electron will produce light. Heisenberg looked at what went in and what came out, and didn’t concern himself about what happened in between. The result was a paper so mathematically complicated that he couldn’t fully understand it himself. He gave the paper to his supervisor, Max Born, and then went camping, hoping that Born might be able to figure it out for him. Born did just that, and had the paper published.
Einstein didn’t like Heisenberg’s approach any more than he liked Schrödinger’s wave mechanics. He called it “a big quantum egg” and declared outright to one of his friends that he didn’t believe in it. The problem, as far as Einstein was concerned, was that Heisenberg had skipped over the need to actually understand what was happening. The mathematics didn’t really require you to “know” anything about what the electrons were up to between the input and output—they could be doing anything, and it wouldn’t affect Heisenberg’s theory. To Einstein that wasn’t a good enough description of reality.
In 1926, Heisenberg came to Berlin to give a lecture. Einstein, who had already exchanged a few letters with the radical young man, invited him to visit his house, where they soon fell to arguing, as was only to be expected. Heisenberg thought that he would be able to win his host around to his way of thinking, precisely because it had once been Einstein’s way of thinking. With relativity, Einstein had done away with seemingly logical but—crucially—unobservable concepts, such as the ether or Newton’s absolute space and time, and produced a sweeping, progressive theory. Heisenberg felt he was up to much the same thing.
“We cannot observe electron orbits inside the atom. A good theory must be based on directly observable magnitudes,” Heisenberg insisted. “But you don’t seriously believe that none but observable magnitudes must go into a physical theory?”
“Isn’t that precisely what you have done with relativity?”
“Possibly I did use this kind of reasoning, but it is nonsense all the same.”
Einstein was at least consistent in his contrariness to his old beliefs.
To his friend Philipp Frank he made a similar complaint.
“A new fashion has arisen in physics,” he rumbled, “which declares that certain things cannot be observed and therefore should not be ascribed reality.”
“But the fashion you speak of was invented by you in 1905!” Frank reminded him with amused disbelief.
“A good joke should not be repeated too often.”
Excerpted from Einstein in Time and Space: A Life in 99 Particlesby Samuel Graydon. Copyright © 2023 by Samuel Graydon. Excerpted with permission by Scribner, a division of Simon & Schuster, Inc.