Signal and Noise

The first burst arrived at 11.42 on a Thursday morning, and Dr Priya Raman very nearly ignored it.

She was twenty-nine, eighteen months into a postdoctoral position at a radio observatory in the hills of New South Wales, and she spent most of her days writing software to sift through the enormous quantities of data that the telescope produced. The great dish, sixty-four metres across, listened day and night to the faint radio whispers of the universe: dying stars, distant galaxies, clouds of hydrogen gas drifting between them. Almost all of what it heard was noise. The job of people like Priya was to find, buried within that noise, the tiny fraction that might be a signal.

The burst lasted less than a millisecond. It was intensely bright, far brighter than anything she would have expected from a natural source, and its frequencies were smeared in a distinctive pattern that suggested it had travelled an immense distance through space. To an astronomer, that pattern was thrilling. It was the signature of what were then called fast radio bursts: brief, powerful flashes from somewhere far beyond our galaxy, whose origin was one of the great unsolved puzzles of modern astrophysics.

She checked the data again. She checked the software. She went for a walk around the car park, came back, and checked them both a third time. The burst was still there.

Over the following weeks, it happened again. And again. By the end of the second month she had recorded sixteen of them, and they shared a peculiar characteristic that set them apart from every fast radio burst ever reported: they appeared to come in clusters, on weekdays, usually around lunchtime.

Priya was a careful scientist, and she was aware that the regularity was suspicious. The universe does not, as a rule, observe office hours. But the bursts had the right shape. They had the frequency sweep that indicated they had crossed billions of light years. And she wanted, more than she was entirely comfortable admitting, for them to be real.

She began, cautiously, to develop a hypothesis. Perhaps the bursts were produced by some kind of object whose emissions were modulated by a regular cycle: a rotating neutron star, say, whose beam swept past the Earth at intervals that happened, by coincidence, to roughly match the human working week. It was an elegant idea. It was also, she knew, a conjecture of the most fragile kind, resting on almost no evidence.

She presented her preliminary findings at a departmental seminar. The reaction was mixed. Some colleagues were openly excited; one suggested, only half-joking, that she start drafting her Nobel acceptance speech. But the observatory’s senior astronomer, a quiet man in his sixties named Gerald Finch, who had spent forty years at the telescope, listened without comment and then asked a single question.

“Have you looked at what else happens here at lunchtime?”

Priya felt a flash of irritation. It seemed to her a dismissive question, the kind of reflexive scepticism that senior scientists used to protect their own theories from upstarts. She told him, rather sharply, that the bursts had the unmistakable signature of an astronomical origin, and that she saw no reason to suspect a local cause.

Finch nodded, said nothing more, and left.

But the question lodged itself in her mind and refused to leave. That night she couldn’t sleep. At two in the morning, she found herself thinking, against her will, about the observatory’s small staff kitchen, and the elderly microwave oven that the technicians used to heat their lunches.

It took her a week to work up the courage to test it. On a Saturday, when the site was empty, she put a cup of water in the microwave, set it running, and, before the timer reached zero, yanked the door open. In the control room, the telescope’s receivers recorded a brief, bright burst of radio waves, smeared across its frequencies in a pattern that looked, to any automated analysis, exactly like a signal from the far side of the universe.

She did it again, and again. Every time the door was opened before the cycle had finished, the microwave’s magnetron released a brief pulse of radiation as it shut down, and the telescope, pointed at the sky but sensitive enough to catch stray emissions from its own surroundings, mistook it for something cosmic.

Priya sat alone in the control room for a long time afterwards. She felt foolish, and then embarrassed, and then something closer to grief. For two months she had been living alongside a mystery, and it had made her feel that her work mattered in some enormous, almost spiritual way. Now the mystery had dissolved into something utterly mundane: a technician, hungry and impatient, opening a microwave door a few seconds early.

On Monday, she went to see Gerald Finch.

She expected him to be pleased with himself. Instead, he made her a cup of tea, listened to her account, and then told her about the summer of 1979, when he had spent four months convinced he had detected a new type of pulsar. It had turned out to be a faulty air conditioning unit.

“Everyone has one,” he said. “If you’re lucky, you have it early, when it costs you nothing but your pride.”

“I should have seen it,” Priya said.

“You did see it. Eventually.” He looked at her over his glasses. “Most people, you know, don’t test the boring explanation, because they don’t want it to be true. You did. That’s the difference between someone who wants to discover things and someone who wants to be the person who discovered them. One of those is a scientist.”

She wrote up the episode honestly, in a short paper with the deliberately unglamorous title “Terrestrial Interference Mimicking Fast Radio Bursts: A Cautionary Note”. She was worried that it would damage her credibility. In fact, it did the opposite. The paper was widely read, and it led several other observatories to re-examine their own unexplained bursts, some of which, it emerged, had equally domestic origins.

But it did not mean the real puzzle was solved. Over the following years, the genuine fast radio bursts, the ones that came from beyond the galaxy, were detected again and again by telescopes all over the world, and their true sources began, slowly, to be identified. Priya worked on several of those studies. The rigorous habits she had learned from the microwave episode, she said later, were the most valuable thing she had ever been taught.

There is a framed photograph on the wall of the observatory’s kitchen now. It shows the old microwave oven, retired, with a small brass plaque beneath it that reads: “Anomaly, 2014. With thanks for the lesson.”

Gerald Finch, who put it there, never said whether he felt his question had been vindicated. He didn’t need to.