The Gestapo had imposed curfews and roadblocks for the first time since the occupation of Denmark. They stopped our train at Helgoland, where the tidy streets of Copenhagen blend into the sparse woods and open gray sky of coastal Zealand. An SS captain and two men with short rifles clambered into our car. They demanded papers from every passenger, and I knew that by nightfall my father and I would be on another train, bound for darkness.

The man who sat across from us was also a Jew, but he would not go to the camps with us. Niels Henrik David Bohr would remain in Denmark, or perhaps he would be sent to Berlin. But he would be no less a prisoner.

The black uniforms and burnished weapons cut into the reality of the railcar like nightmares. You could hear the shared thought of everyone aboard: Not here. Not in Copenhagen. There's some mistake.

The Danes had lived with a monster in their house for two years, and they had learned to ignore it. The monster looked like them. It seemed to be housebroken. It kept out of sight, hiding under the bed while Denmark slept. But finally, inevitably, the monster had emerged, and it was ravenous.

Looking for us.

The SS captain was a handsome young man, square-jawed and blue-eyed, Hitler's Aryan ideal in the flesh. But his pale complexion reminded me of a wax doll. His ink-black uniform, with its red armband and skull insignia—the regalia of death—enhanced his pallor. In his eyes I saw the deep hunger that drives a man to devour his fellows. He evaluated the passengers, his head cranking from side to side with each click of his black leather boots, as if clockwork connected his legs to his neck.

He stopped a few rows away from us, to examine a young couple. Speaking in curt, inflected Danish, he demanded their papers. The man, a swarthy fellow with curly black hair, rummaged nervously in a satchel.

The captain put up his hand. "That's all right," he said. "It won't be necessary."

The man nodded with relief.

"You are Juden, yes?" The captain smiled.

One of the most vivid memories of my life is how the air on the bus changed at that moment, suddenly cloying and and thick. A smell of quiet panic, like sweat and rotten meat.

The young man blanched. "I am a Danish citizen," he said, voice quavering.

The officer's expression was not so much a smile as a gash cut into his face. "You are a subject of the German Reich," he said. He made a command with his fingers: on your feet. The young man stood, and he and his wife were led off the bus. The woman carried an infant bundled in blue wool.

I have often wondered what became of that family. Did they die at Theresienstadt? Dachau? Auschwitz? I still have nightmares about the look in that young woman's eyes.

The captain approached us. His gaze settled on me for a moment, then passed to my father.

The Danish resistance had told us we must pass for everyday people. Papa had retorted that we were people, every day, but he hadn't really argued. He had shaved that majestic, iron-gray beard, trading his broad-brimmed black hat and dark coat for the dress of a goy.

Papa had strange gifts. But I could not imagine he would deceive the pale Hauptsturmführer. My father's essence would shine through the rumpled khaki trousers and thick sweater of green wool, and any fool would see him as a rabbi of the Hassidim.

Who could look at my father and fail to see what he was? Until the day I die, his will be the human face of Yahweh: fierce but serene, severe but kind, deeply etched with sadness and humor, encompassing the mystery of opposites that are one. Brilliant, forceful Chockhmah and dark, gentle Binah united in Tiferet, the living heart of Israel that is the center of the universe. No man who met my father, Jew or Gentile, failed to be awed by him. Least of all me.

When he saw Papa, the Hauptsturmführer frowned.

Papa said, "Good morning."

The captain nodded, his frown slowly unwinding. "Good morning. Heil Hitler."

He quickly looked away from Papa's eyes, and next gave a cursory glance to the brother and sister seated next to us. With their light brown hair and sullen expressions, the two teenagers could not possibly have looked more generically and ethnically Danish. They were, in fact, armed members of the threadbare Danish resistance. They didn't get a second look.

The captain turned to scrutinize the three people in the seat facing ours. A frumpy man with unruly red hair pretended to look out the window. Hans Nielsen was the father of the two young partisans. Next to him sat an elegant woman in her midfifties, with a slender neck and fine Nordic features.

Beside her, directly across from me, sat the father of the modern atom.

Bohr had a paunch, but he was still a lanky man, with that characteristic Danish angularity and length of bone. His brown suit fit him with a balanced, casual elegance. His features had sagged beneath the weight of the occupation, the constant threat from the Nazis who circled him like hyenas, waiting for him to go too far in his vocal defense of Danish culture against the Reich. Thick-lipped, balding, and aged—he should have been ugly. But the intelligence was there, quiet and profound, like clean water pouring out of a rocky cave. I like to think that, even if I had not known him as the man who had resurrected the corpse of Rutherford's atom and made it dance to the strange music of Planck and Einstein, I would have loved him the moment I saw him.

"Herr Doktor Bohr!" The captain's cruel smile returned. "What a relief. We've been very concerned about you."

Hans, the frumpy man at the window, forced himself to look, a film of defeat in his eyes. The two young partisans next to Papa stared at the floor. I thought of the weapons beneath their coats. In their stillness I could sense a gathering, desperate violence.

Bohr sighed, looked up at the Gestapo captain with calm resignation, and took his wife's hand. He started to get up.

"You are mistaken, sir," Papa said.

I wanted to scream at him: No! This creature has already passed us over and now you beg for his attention!

I was nineteen years old. I had followed Bohr's career for half my life, with something bordering on worship. A terrible miracle of circumstance had finally brought me into his presence. But at that moment his life meant nothing next to my own. Niels Bohr was already a prisoner of the Third Reich—nothing could stop that now, save some desperate stupidity from Hans and his children. Papa's action could only put us on a boxcar to Theresienstadt.

The Gestapo captain gave Papa another nervous glare. "What did you say?"

"I said you are mistaken. This is my brother-in-law, Karl Gervuld. This woman is my sister, Frieda."

The captain's features hardened, but Papa's stare held him prisoner. "This man's face is known throughout the world," he said, uncertainty creeping into his voice. "This man is Niels Bohr and he will be taken into protective custody."

"Take a closer look," Papa said.

The captain obeyed: Bohr was unmistakable. He shook his head, frowning. "I'm . . . quite sure . . ."

It won't work, Papa. You're killing us.

"Look at me."

The captain turned. Confusion and fear grew in his eyes.

"This is my brother-in-law, Karl Gervuld." Papa's belly tensed in and out beneath his sweater. I could almost see the power surging between Papa's Tiferet and the captain's Yesod.

"It would be embarrassing if you presented him to your superiors as somebody he is not. You wouldn't want to be embarrassed!"

"I . . ."

"This is my brother-in-law, Karl Gervuld."

The captain licked his lips. "I should see his papers. Yours too."

The young man next to Papa reached into his coat, tensing for action. I thought of the last time Papa had tried this. My mother had died anyway.

"That won't be necessary," Papa said. "This is my brother-in-law, Karl Gervuld."

By now, everyone was staring at Papa, except for the two SS men checking papers a few rows up. Bohr himself was transfixed by the motion of Papa's belly, pumping in and out like a bellows. The partisans watched like mystified children. And I could see from the young captain's face that Papa's eyes had become the center of his universe.

The German's jaw slackened, then snapped shut. His glassy eyes came back into focus. His hand went to rest on his holster, and I knew that Papa had failed again.

But the captain turned away, and did not look at us again. He swaggered back the way he had come, hand at his holster in a posture of Prussian authority. He ordered his men off the train, and moments later we were clattering up the Zealand coast toward Elsinore.

Nobody spoke for a long time. I stared at my knees, running the episode over and over.

Eight years earlier, Papa's power had failed to save Mama from the brownshirts. But even before that I had begun to doubt whether I could follow his path to knowledge.

I looked over at him. He sat with eyes half-closed, as if he were drunk.

No. I refused to regret my decisions. I refused to feel guilty for taking my own path. But for not having the courage to tell him . . . for that I could feel guilty. And I did.

"Sir?" Bohr reached over to touch Papa's knee. "We're grateful for . . . whatever it was you did. I thought for sure we would  . . ." He shook his head. His wife managed a thin smile. She had not let go of her husband's arm.

Papa put out his hand to shake with Bohr and his wife. "I'm Itzak Goldblum. My son, David."

"My wife, Margrethe. Oh. I'm, uh . . ."

"Yes, I know." Papa shrugged. "But you certainly look like my brother-in-law Karl."

Bohr's eyes twinkled. "Do you have a brother-in-law?"

Papa smiled at Margrethe. "I don't even have a sister."

The Bohrs laughed. Niels looked over at me and smiled. "Nice to meet you, David."

I shook that noble hand and gawked at him, trying to think of something to say.

"Forgive him," Papa said. "If his brain were working now, he'd tell you that he's a great admirer of yours."

Bohr nodded. "Well . . . I'm honored." A polite dismissal of the schoolboy. He turned back to Papa. "I have to ask you. What did you do to that Gestapo man?"

"Barely a man," Papa said, shrugging. "A real man I could not have managed. He was more of a golem."

Bohr frowned. "I beg your pardon?"

"A golem. A fairy-tale monster, yes? An empty creature of wood or clay that can be filled with the will of another. A strong man cannot be manipulated so easily. But a golem. . ."

Margrethe leaned forward to listen. The two partisans were whispering with their father. Bohr shifted in his seat to retrieve a pipe from his pocket. "A golem."

"A man like that," Papa said, "is empty. You just have to know how to fill him. Dress him up in an imposing uniform, fill his head with grand ideas, and point him at a target. The poor Germans."

Bohr, tamping tobacco into the bowl, shook his head. "The poor Germans?"

Papa shrugged. "They've become a nation of golem. To make a golem of clay is a sin, a mortal sin. To make a golem of a man, is that any better? Perhaps God will punish me, although I didn't create that creature. Hitler has tapped into the unconscious, the world of dreams."

Bohr lit his pipe. "You sound like Herr Doktor Freud."

Papa reached up to stroke his beard, found it missing, scratched his chin. "Yes. Well, there's little that's new in Freud, except for the words."

Bohr took exception, and they got into a friendly argument over whether Freud was a scientist or metaphysician. It was exhilarating to watch the two most important men in my life joust and find each other worthy. And maddening, because I wasn't part of it. I could quote every word Bohr had ever published, almost verbatim. But for now I was just the boy.

By the time we passed the low hills of Klampenborg, halfway to Elsinore, I was seething. Papa was doing it deliberately. Another ploy to keep me in his world. Out of Bohr's. Almost before I could read, Papa had taught me that numbers were God's brick and mortar. To his lasting chagrin, I'd followed that teaching in a different direction than he'd intended. While he sought mystery and beauty in the Torah and Sefir Yetzirah, I had found my own truth in the writings of Bohr and Dirac, Heisenberg and Born.

"Of course," Papa said as the argument wound down, "I'm just an old rabbi. There's nothing I can point to and say: There's my proof. Herr Freud, he's in the same boat. But a man like you, you can put a handle on wisdom, no?"

Bohr shook his head. "I'm not sure what you mean."

Papa looked up, begging the roof for patience. "He's not sure what I mean! You are the man who discovered the atoms, no?"

Bohr shifted uncomfortably.

Hans leaned forward, over Margrethe's lap. "Not everybody on this goddamn train is known to us," he said. "I know the cat's out of the bag, but you could still keep it down to a dull roar."

He sat back and shook his head at his two children.

"He didn't discover the atom," I told Papa in a whisper. "He described the atom, in terms of Planck's quantized energy."

"Ahhh," Papa said. "A description."

"A description," I said, "that predicts atomic spectra, including the Zeeman perturbations, to the nanometer. A description that rescues the Rutherford atom from its own angular momentum. A description that explains the periodic table with a few quantum numbers."

Bohr shrugged. "An imperfect description," he said. But he was smiling at me.

"Ah! Numbers!" Papa shook his finger in affirmation. "Yes, I knew it would come down to numbers."

Bohr's grin widened. "Why is that?"

"Because everthing does! My tradition also describes the universe with numbers."

"I am half-Jewish, you know," Bohr said. "In middle school, I dabbled in the Kabbalah."

"And what did you learn from dabbling in the Kabbalah?" Papa looked at Bohr, but I knew he was speaking to me.

Bohr shrugged. "Not much."

"Not much, because you dabbled! But in science you did not dabble. There you gave your all, and you learned a great deal. Am I wrong?"

"I suppose that's true." Bohr's pipe unfurled an aromatic veil that hid his expression from me.

"My son, he dabbles in everything," Papa said. "He dabbles in physics. He dabbles in the Talmud and the Zohar. Any more dabbling, he ends up a nebbish."

The conversation aborted. There was only the clattering of the tracks and the whispers of the partisans. Bohr puffed at his pipe and pretended to look at his feet.

It was Margrethe who saved me. Margrethe Bohr, who challenged me with her steely nordic eyes and a look on her face . . . a look she might have given her own son Kristian, had she not lost him in an accident. A look my mother might have given me, had my father not lost her to the brownshirts. The secret message on her face was one of empathy, but not pity. A tiny nod and a curl of her lips that said: Are you going to let these two old men dismiss you like that? Fight!

"I never dabble," I said. "Not in Kabbalah. Not in physics."

Bohr fidgeted. Papa waved a dismissive hand and snorted.

I reached into my coat for the only scrap of paper I had: the letter from Cambridge. I unfolded it and turned it over quickly, so Papa could not read it. I set it on my knee, blank side up, and began to sketch out the Tree of Life: ten Holy Sefirot connected by twenty-two paths.

"My father," I said, "is an international authority on the Zohar and Sefir Yetzirah. In his last book, The Song of Adam Kadmon, he says, 'The Sefirot are not things.'"

Bohr, whose old friend Heisenberg had once said the same of atoms, sat up and looked at my drawing.

"The Sefirot, the ten nodes of existence, are numbers—like everything else," I said. "As my father writes, they are musical notes sung by God. Thus, vibrations. Vibration implies frequency. Frequency implies energy. The Sefirot are the 'quantum numbers,' if you'll forgive me, that describe all creation."

Bohr smiled. The expression was indulgent, but not patronizing. And I had his attention.

"The right branch of the Tree is creative, impulsive, masculine, positive. The left is receptive, nurturing, feminine, negative. The duality reconciles in the middle trunk, the synthesis of opposites that drives all creation. The Tree is a map of the Universe."

Bohr shook his head, but he kept listening.

I kept scribbling. "For example, in Adam Kadmon my father maps the Tree onto human physiology. Catabolism, motor processes and the sympathetic nervous system appear on the right—all the functions that involve action, the release of energy. Anabolism, sensory processes and parasympathetic activity map to the left side." Then I pointed with my pen at Tiferet, the Sefirot in the center of the Tree, the one that connected to all the others.

"The heart?" Bohr offered.

"Ah, he sees!" Papa said.

I shook my head. "No, I don't think that's right."

"What?" Papa leaned over to look at my drawing. "Mishegos! Of course it's right!"

I hesitated, but then I caught Margrethe out of the corner of my eye again.

"No," I said, and continued scribbling. "The heart is a circulatory organ. It belongs at Nezah, on the lower left trunk. No, Tiferet is Beauty, the thing created. Balance, integration, essence."

"And so," Bohr asked, "what is the Tiferet of human physiology, young David?"

I flushed under Papa's withering glare. "The central nervous system," I said, and wrote it in. "The brain and spinal cord."

Bohr's pipe had gone cold from neglect. Papa chewed on his lower lip and stared at my drawing.

"We can also map the atom," I said. Across the top of the page I wrote n, l, m, s. "These are the four quantum numbers that underlie the structure of matter. Shell, subshell, magnetic, spin. But to describe matter, we also need to describe the electric force that binds electrons to the nucleus, and the force that holds the nucleus together. We need mass and charge . . ."

I kept talking, kept scribbling, my hands and brain working together in a storm of delight.

When I finished, Papa shook his head. "Huh. My son a knaker. Mr. Big Shot."

A smile grew on Bohr's thick lips, and he took the paper from my hand, so he didn't have to look at it upside-down. I was afraid Papa would read the other side.

"This is really quite beautiful," Bohr said.

Papa stared at me, and my delight intertwined with my dread. I had not told him of the scholarship I had won to study physics at Cambridge, recently announced in the Letters. I had avoided confronting him by telling myself it didn't matter. We had lost everything in Germany. Everything. Now Denmark was a mess, and if the resistance couldn't get us across the Elsinore Sound and into Sweden I might never go to university at all. So I willed myself to stop worrying about it, to bask in that perfect moment when the two men I loved and admired most looked at me with new eyes and nodded their heads with wonder and respect.

Bohr studied my drawing for a long time. I don't think he wanted to give it back.

Read Part 2 here!