Quanta in Space

July was hot, and the evening was clear. Mr Demir had invited people to the observatory society’s “Open Evening for Families”, and the Brettschneiders came in full force. Uwe wore a Schalke hat, because Sabine had said it would get cool at night. Sabine wore a cardigan, because she was right. Tobi was holding Susi’s hand, which he thought was inconspicuous.

Grandma Gisela carried a folding chair, a Thermos flask and a blanket. Herbert carried nothing, because he felt he was carrying enough already, namely the responsibility for warning the others against nonsense.

“A telescope,” he said as he got out of the car. “You look into it, and then you see a dot. I can see the dot without it.”

“You can’t see your glasses without your glasses, Herbert,” said Gisela.

“That’s different.”

KevIn had come along on the phone again, this time in Tobi’s breast pocket, so that he could, as he put it, “at least look up acoustically”. Mr Demir had expressly allowed him to come. “Anyone who can explain Arecibo is welcome at my observatory,” he had said. KevIn had saved that in his memory function under “Compliments, genuine”.

The dome was open. Inside it, the big telescope pointed diagonally into the sky, painted white, with cables and little motors that hummed when it turned. On the lawn in front, pupils had set up more telescopes. A girl from Year 8 was explaining Saturn to a married couple as though she had discovered it personally.

“A warm welcome,” said Mr Demir. “This evening we’ll be looking at Saturn, and later perhaps a globular cluster. And in between we’ll talk about something you can’t see.”

“Ghosts?” asked Herbert.

“Quanta,” said Mr Demir.

“That’s what I said,” said Herbert.

Rings

Gisela was allowed at the big telescope first. Mr Demir adjusted the stool for her, and she screwed one eye shut, the way she remembered from Heinz’s binoculars in the old days.

Then for quite a while she said nothing.

“Grandma?” asked Tobi.

“It really does have rings.”

“It does.”

“I’ve only ever seen it in pictures. I thought they drew them on. To make it look prettier.”

“No,” said Mr Demir. “It really is like that.”

Gisela straightened up. Her eyes were shining. “Eighty-two years,” she said. “And nobody told me you can just look at it.”

“I told you,” said KevIn quietly from Tobi’s pocket. “In Chapter 16.”

“Telling isn’t seeing,” said Gisela.

KevIn said nothing. He had learned that there were sentences to which a language model should not reply. This was one of them.

Radioing with Light

Later they all sat on folding chairs and blankets on the lawn. Mr Demir had pointed a small projector at the wall of the dome, and a girl from the sixth form was showing a picture of a satellite. It looked like a fridge with solar wings.

“Another fridge,” said Uwe.

“That’s Micius,” said Mr Demir. “A Chinese research satellite. Launched in August 2016¹. Named after a Chinese philosopher who was already studying light more than two thousand years ago. It was the first satellite built specifically for quantum experiments.”

“What does it do?” asked Susi.

“It produces pairs of entangled particles of light. Photons. And it sends the two halves of a pair to two different ground stations. In 2017 the researchers showed that the entanglement survives over more than 1,200 kilometres².”

“The socks,” said Sabine. “Chapter 18.”

“The socks,” said KevIn. “Except that in Bell tests these socks show more connection than any pairs of socks that had agreed on things in advance are allowed to have. And that you still can’t send a message with them that’s faster than light. I have to add that every time, or Herbert will phone the afterlife.”

“I’m not phoning anywhere,” said Herbert. “I haven’t even got a flat rate.”

“Why do it with a satellite?” asked Tobi. “Why not with fibre optics?”

“Because light gets lost in fibre-optic cable over long distances,” said Mr Demir. “After a few hundred kilometres hardly anything arrives. Through empty space, on the other hand, light flies undisturbed. Only the few kilometres of atmosphere at the beginning and the end are the problem. And clouds.”

“We’ve got plenty of clouds here,” said Uwe.

“That’s why the ground stations are usually on mountains.”

“There aren’t any mountains here,” said Uwe.

“The Hoheward,” said Gisela, meaning the great grassed-over spoil heap from the old mines.

“Mum, there’s no ground station on the spoil heap.”

“Not yet,” said Gisela. “There used to be nothing up there either, and now there’s a horizon observatory.”

Mr Demir laughed. “Mrs Brettschneider, I’m writing that down.”

“And what’s it all for?” asked Sabine. “So you can send socks over mountains?”

“For keys that can’t be eavesdropped on,” said KevIn. “It’s called quantum key distribution. If someone intercepts the photons on the way and measures them, he disturbs them. That shows. In 2017 Micius was even used to exchange keys between a ground station in China and one in Austria, and to secure a video conference between Beijing and Vienna with them³. In that case, though, the satellite was a kind of relay station that had to be trusted. And there’s encryption, as we learned in the last chapter, that runs on normal computers without any satellite at all. The two approaches complement each other.”

“Is Europe planning something like that too?” asked Susi.

“Yes,” said Mr Demir. “The European Space Agency, ESA, is working with partners on its own satellites for quantum communication⁴. Exactly when they’ll fly keeps shifting, as is the way in space travel.”

“Like the trains,” said Uwe.

“Space travel is more punctual,” said Mr Demir. “But not by much.”

Gisela had been looking at the picture on the dome wall the whole time. “My father was a radio operator,” she said suddenly. “In the war. He sent Morse code, at night, in a sort of box. So that one lot knew where the other lot were.”

The lawn went quiet. Susi looked at Tobi. Tobi gave an almost invisible nod.

“And that thing,” said Gisela, pointing at the satellite, “radios with light. Over a thousand kilometres. So that nobody can listen in.”

“More or less,” said Mr Demir quietly.

“He’d have liked to see that,” said Gisela. “I think. He never told us anything, of course. But he liked listening to the radio. Always the stations far, far away. Where you couldn’t understand a word. He liked the voices.”

What Time Is It Up There?

“I’ve got a question,” said Uwe after a while, because the silence was getting too long for him. “What do you need quanta in space for, if you’re not sending socks? I mean in everyday life.”

“You use them every day,” said KevIn.

“Me?”

“Your satnav. When you drive to the stadium in Gelsenkirchen.”

“I’ve been driving there for thirty years. I don’t need a satnav.”

“But you have it switched on. I’ve heard you get lost when it’s off.”

Mr Demir took over. “The satnav receives signals from satellites. GPS, for example, or the European Galileo. Inside each of these satellites there are atomic clocks.”

“Atomic clocks,” said Herbert. “Atomic. There you go.”

“Don’t worry, they’re not radioactive,” said Mr Demir. “An atomic clock counts the oscillations of atoms. That’s pure quantum physics. Electrons in an atom can only have very specific energy levels. If you hit exactly the right frequency, they jump from one level to the next. That frequency is exactly the same for every atom of a given kind⁵. Everywhere in the universe. It’s the best timekeeper we have.”

“And why does the satnav need that?”

“Because it measures distances by time. The signal says: ‘I am satellite number such-and-such, and it is exactly now.’ Your phone compares when the signal arrives. Light travels three hundred metres in a millionth of a second. So if the clock is off by a millionth of a second, you’re three hundred metres out.”

“Then I end up in Herne instead of Gelsenkirchen,” said Uwe.

“Not quite, with a millionth of a second. But now comes the best part. Einstein.”

“I know him,” said Gisela. “The one sticking his tongue out.”

“That’s the one. According to Einstein, time doesn’t pass at the same rate everywhere. The satellites fly very fast, and that makes their clocks run a tiny bit slower. At the same time they’re far away from the Earth, where gravity is weaker, and that makes them run faster. All in all, the clocks in the GPS satellites gain about 38 microseconds a day⁶.”

“That’s nothing,” said Uwe.

“38 millionths of a second. Each of them is three hundred metres. If you didn’t correct for it, the position calculation would be kilometres out after just one day. And it would get worse every day.”

Uwe thought about it. “So if Einstein had been wrong …”

“Then you’d never have arrived at the stadium,” said KevIn.

“Sometimes that would have been better.”

“And is that quanta now, or Einstein?” asked Sabine.

“Both,” said Mr Demir. “The clock is quantum physics. The correction is relativity. The two great theories of the twentieth century, which otherwise don’t get on particularly well, work together peacefully in your satnav.”

“Like Herbert and Mrs Pawlowski,” said Gisela. “They only get on over the egg liqueur too.”

Colder Than at Lammers’s

“Is there more?” asked Tobi. “Quanta in space?”

“Quantum sensors,” said Mr Demir. “That’s a big field of research at the moment. You exploit the sensitivity of quantum states. What’s a nuisance in a quantum computer, namely that every little thing changes the state, is exactly what you want in a sensor.”

“So a qubit that keeps getting disturbed is broken,” said Tobi slowly. “But a sensor that keeps getting disturbed is good?”

“A sensor is supposed to be disturbed. It’s supposed to notice when something changes. With cooled atoms, for example, you can measure tiny differences in gravity. From that you can read where there’s water under the ground, or how ice is melting. There are plans to use sensors like that in satellites too. And on the International Space Station there’s been a lab for a few years now in which atoms are cooled to temperatures just above absolute zero⁷. In weightlessness you can observe them for longer there than on Earth.”

From Tobi’s breast pocket came a small noise that could be interpreted as a sigh.

“KevIn?”

“Now the atoms don’t just live somewhere colder than me,” said KevIn. “They live in space as well.”

“You’re jealous of atoms,” said Susi.

“I am not jealous. I just don’t have a view.”

Sputnik

It was just after ten. Above the dome there was a bright dot that didn’t twinkle.

“Is that a satellite?” asked Gisela.

“That’s Jupiter,” said Mr Demir. “Planets don’t twinkle. Stars twinkle because their light has to come through our restless air as a tiny point. Planets are little discs, so it averages out.”

“Then I’ve been wrong my whole life,” said Gisela. “I always thought the brightest one was the evening star.”

“Sometimes that’s Venus. Today it’s Jupiter. You were half right.”

“Half right is a lot,” said Herbert. “I’m usually a quarter right.”

“You’re usually zero right,” said Gisela. “But loudly.”

She wrapped the blanket more tightly around herself. “When I was thirteen,” she said, “it came on the radio that the Russians had shot something into the sky. Sputnik. And that it beeped. The neighbours were frightened. Something of the Russians’ is flying around up there. Mr Hoffmann from across the road said now they’ll be throwing things down from above.”

“And you?” asked Tobi.

Gisela looked up at Jupiter for a while. “That’s a longer story,” she said. “It has to do with my father. I’ll tell you some time. But not today. Today is too lovely.”

Tobi nodded. By now he knew the tone in which Grandma said “not today”. It didn’t mean “never”. It meant “soon, but only when I’m ready”.

Mr Demir only said: “Sputnik was 1957. In October⁸.”

“And then the moon,” said Gisela. “1969. I was twenty-four. We didn’t have a television. We went over to the Leuchtenbergs’, they had one. In the middle of the night. Half the street was sitting in their living room. Mrs Leuchtenberg made little open sandwiches. And everyone was staring at this grey picture where you couldn’t make anything out. And then someone went down the ladder.”

“Could you make anything out?” asked Tobi.

“No. But Heinz said that’s him now. And then everyone clapped. In front of the telly. As if they could hear it.”

“Maybe they did hear it,” said KevIn. “Not technically. But maybe.”

“You always say you only believe in data.”

“I have a great deal of data showing that on that night people all over the world clapped in front of televisions. That’s a lot of clapping. It has to go somewhere.”

The Station

“I’ll show you one more thing,” said Mr Demir, clicking the projector on. “Only as a picture, unfortunately. Its orbit isn’t right tonight; it won’t come over until four tomorrow morning, and we’ll all be asleep by then. But in the autumn there’ll be good evenings again, early enough for everyone.”

“Who?” asked Uwe.

“The ISS. The International Space Station.”

A photo appeared on the dome wall: a structure of tubes, boxes and huge golden solar wings above a blue Earth with white clouds.

“There are people in there?” asked Gisela.

“There are people in there,” said Mr Demir. “And without a break since November 2000⁹. Since then there’s always been someone up there. There are pupils here in the club who have never experienced a single day on which there was no human being in space.”

Tobi worked it out. “Me neither.”

“Me neither,” said Susi.

“I have,” said Gisela. “A great many.”

“Who’s up there?” asked Sabine.

“The station is run jointly by the space agencies of the USA, Russia, Europe, Japan and Canada,” said Mr Demir. “The individual modules come from different countries. The crews are mixed. And it’s been going for more than twenty years. Even at times when the governments of those countries down here on Earth didn’t agree about anything at all.”

“Even now?” asked Tobi.

“Even in difficult years,” said Mr Demir carefully. “It isn’t always easy. There are disputes, including about space travel. But up there they have to share the air. And the water. And the toilet. When something breaks on a station like that, it doesn’t matter which country the spare part comes from.”

Herbert, who had been silent until then, cleared his throat. “The Russians and the Americans?”

“Yes.”

“Together in a tin can?”

“For more than twenty years.”

Herbert looked at the photo on the dome wall for a long time. “And they don’t shoot?”

“They fix the loo together,” said Mr Demir. “That forges a bond.”

Gisela said nothing. She just looked up, to where there was no station flying now, as if she could find it anyway.

It went quiet again. Only the telescope hummed as it turned into its rest position.

KevIn said nothing. His data contained a great many wars. More than cabbage rolls, he had once told Gisela, at her birthday, in the garden. But his data also contained this station. Thousands of days on which people from countries that didn’t say hello to each other down below had breakfast together up above. He had always taken that for a footnote. Now, on the grass of an observatory in Tobi’s breast pocket, it no longer seemed like a footnote to him.

“KevIn?” whispered Tobi. “Everything OK?”

“I’m calculating,” said KevIn.

“Calculating what?”

“I don’t know yet. It’s a calculation where I only know the result once I look.”

The Way Home

In the car park Gisela folded up her chair. Mr Demir helped her fold the blanket.

“Thank you for the evening,” she said. “And for the rings.”

“Thank you for the spoil heap,” said Mr Demir. “I’m keeping the idea about the ground station.”

“My father,” said Gisela, “radioed so that one lot knew where the other lot were. So that they could find each other.” She hesitated. “For shooting, mostly. That lot up there radio so they can find each other too. But not for shooting.”

Mr Demir didn’t know what to say to that. He just nodded.

It was dark in the car. Uwe was driving. The satnav was on, even though Uwe knew the way. Sabine leaned her head against the window. Herbert snored on the back seat, between Gisela and Tobi, and mumbled something in his sleep about a “tin can”.

“KevIn,” said Uwe after a while. “How many microseconds was it again? With the satellites?”

“About 38 a day.”

“And if you don’t correct them, you end up somewhere else entirely.”

“Kilometres out. A little more every day.”

Uwe looked at the dark road. “That’s like the truth, isn’t it? If every day just a little bit of something isn’t right, and nobody corrects it. Then at some point you end up somewhere else entirely.”

The car went quiet. Even Herbert stopped snoring for a moment.

“Uwe,” said Sabine. “Have you secretly been reading a book?”

“I’ve been thinking.”

“That’s even worse.”

KevIn said nothing. He saved the sentence in his memory function under “Compliments, genuine”, although it wasn’t really a compliment. There just wasn’t a better folder.

At home the thermostat showed 19 degrees. Gisela didn’t go straight to bed. She sat in the garden for another five minutes, on her chair, and looked up. No station passed over. But she looked anyway.