Haruto was running late, a thermos of tea in one hand and a shoe he hadn't gotten on yet in the other as he stepped into the elevator. His phone started buzzing, and he ignored it. It started ringing, which it was only allowed to do for select people, and he wrestled his shoe on and checked who it was. It was his old professor, not someone who would be calling to tell him that his father was in the hospital. Tanaka–sensei hadn't contacted him in years. He only still had the ability to ring the phone because Haruto had never bothered to change it, not since he was waiting for updates about his thesis. He stuffed the phone back in his pocket and speed walked out of his apartment building, making for the subway.

Over the course of the subway ride Haruto noticed that everyone else was looking at their phone, too. This was such a mundane observation that at first he didn't know what he was noticing. Of course everyone was on their phone.

He added it up, between the second and third stops. He didn't hear any of the little mobile games that people refused to mute. People were showing their phones to their neighbours. There were collisions, as people exited and entered without looking where they were going instead of politely cramming themselves in where there least failed to be space.

Haruto pulled out his phone rather than shoulder–surf his neighbour, and had a lot of accumulated messages and news alerts.

The stars are winking! Its aliens! Read a text from his ex–girlfriend.

Mystery in the sky, said a headline brought up by an algorithm's understanding of his list of interest topics.

Tanaka–sensei's text, sent after the call hadn't gone through, just said Check the school's astronomy channel.

Haruto wished the old man had been more explanatory – he had to download the app the school used for departmental discussions, since he'd never had it on this phone – but by the time he got off at his stop, he was catching up on the last eight hours of astronomy department chatter.

Apparently, as seen from all around the globe, the stars were, in fact... winking.

The first several had to be identified in retrospect from telescopic recordings, and many were of stars in the daylight direction of the Earth as it turned and the stars winked irrespectively, but a few were spotted with the naked eye. Someone had gone to their amateur astronomy forum about two conveniently in the same constellation only thirty seconds apart, and someone else had confirmed that those stars had respectively brightened and dimmed at about those times, and two independent reports was enough to get a few other people poking around. The news had gained speed until it was confirmed by astronomers with serious telescopes, redundant recordings checked against each other. Here someone's aesthetic time–lapse, there someone's staging of UFO footage.

One star per second had been winking; bright or dim, star after star, for hours now, and Haruto couldn't shake the sense he was being pranked, even after source upon source made it clear that none of the people actually sending him messages were the pranksters. These people didn't know each other. The people he was passing on the street, looking at videos of flashing stars on their phones, were not in on a conspiracy. But the alternative was so preposterous.

He reached his sister's apartment ten minutes late, didn't bring up the stars with anyone else there – if they'd heard about it, they were choosing to set it aside to greet his newborn niece instead. He held the baby for an appropriate amount of time, handed her off when she fussed. Hugged his sister. Accepted a snack, since he hadn't had much breakfast.

And went back out onto the street to look at his phone a bit more, for more clues.

Haruto could guess why his ex–girlfriend had thought to text him. And he knew what he'd been reading that gave the news algorithms the idea that he'd like to hear about the stars (if they weren't just telling literally everyone). What he wasn't sure of was Tanaka–sensei's intent. He looked for a quiet place, but there was nowhere he'd be able to hear a phone call clearly enough. He texted back, grumbling his way to the subway station again.

Sensei, why are you telling me?

The reply didn't come until Haruto was back home, debating taking a shower to get the entire subway residue off of him. The phone chirped.

A funder wants to get the drop on founding an organisation dedicated to figuring it all out, in case it's strange enough that it's not in any existing wheelhouse. He doesn't think NASA or whoever is going to figure this out in the next week and wants to look cool if his people get it instead, but he doesn't have people on tap for this. Asked me for suggestions. I don't know what you're doing these days but I didn't find you on any university's faculty list, Kobayashi. Busy?

Haruto ground his teeth. Decided in favour of a shower. Popped out five minutes later and, still towelling water out of his hair with one hand, replied with the other,

How much funding?

"Hajimemashite," said Shelley. "Namae wa, um, Sheri. Douzo yor…"

"I speak English, Ms Katz," said Haruto. "Everyone here does. We start it in elementary school." His accent was substantial, but she could understand him with a little extra effort, and didn't have to pause to fumble for particles and wait until the end of every sentence for a verb, this way.

"Oh, thank God," she said. "They said Japanese was a nice to have and not a requirement, but…"

"You're in math, you peak in five years. We'd like to use this time on the real problem. I am confident the messengers do not speak Japanese. I hope you did not waste too much of your time on it."

"Not... too much time," said Shelley sheepishly.

"Well, stop. If you're good at languages, then you can pick it up by exposure in your spare time. If you don't, you don't. Have you seen the sequence?"

"Uh…"

"A lot of people have. It is not very hard to find if you look for it. Is that an 'um, yes, even though I wasn't supposed to' or an 'um, no, I followed the rules and now I'm wondering if that was a test of my initiative'?"

"The second one," said Shelley. "All I've seen was one actual star–wink during the second message. It was Ashlesha. Epsilon Hydrae."

"I'll stick you in group 2 of your cohort, then, though being in a group doesn't affect much of your preliminary work since the idea for signal–naive cryptographers is that you're to look at it with fresh eyes. You are not to contaminate each other with any observations until we've wrung all the freshness out of those eyes, do you understand? Don't even tell them about Epsilon Hydrae."

"Yes, Mr Kobayashi."

"Welcome to Starwink. Come with me."

She followed him through the corridor to the elevator; it brought them up to his office. The place wasn't much to look at. Rented office space, boring plants no one would be allergic to, tasteful neutral carpet and wallpaper. They spent money on personnel, not on frontage and architecture. Shelley's HR on boarding meeting, before she'd even been sent to meet Mr Kobayashi, had included strict instructions that if she found herself fretting about any financial, bureaucratic, or logistical problem, she was to immediately take it to the Starwink concierge department, explain in full, and expect it to be resolved satisfactorily on her behalf without any further drain on her mental resources. Her take–home pay was substantial, but the real perk was how badly they wanted her brain freed up to work on the most important problem in the world.

Haruto sat down behind his desk. Shelley sat opposite him. "Describe to me the Starwink project as you understand it, as though I am a bright high schooler," he said. "No need to get very detailed; I'm looking for what angle you use to approach the problem, not how many Wikipedia articles you've memorised."

Shelley had been expecting this question. "Eleven years ago, stars started winking. It went on for about a month and a half, and then stopped. The winking stars were all over the galaxy but everyone was visible before brightening or dimming to the naked eye under ideal light and weather conditions from the surface of the Earth. The light conditions weren't ideal and actually about half the stars winked from the daylight direction of Earth as it was at the time they did so, but there aren't any gaps that might belong to stars we don't have a clear line of sight to because of the moon or anything – gaps in the pattern of one star winking per second, I mean. Slightly more than a second."

"Does it matter that it's not exactly a second?" asked Haruto innocently.

"It might," said Shelley. "The message – it has to be a message – was sent by someone or something and whether that someone or something knows what a second is could matter. So it matters that it's not exact – because that's evidence that they don't – but it also matters that it's really close, because that could mean that it does know. Which could mean lots of things, like that it's using an old – or even future – reckoning of a second that's slightly longer, or that there's some technical reason why this was as fast as they could go but they didn't choose longer intervals because this interval was so close to one of our measurements."

"Why does it have to be a message?"

"Light travels at a speed and the stars all winked at Earth on the same schedule. The timing isn't regular even from elsewhere in the Solar system, let alone from another star. To get to us on such strict intervals, the light from those stars has to have been altered with us in mind from the beginning. It's still a very weird way to send a message – those stars are incredibly far apart from each other, affecting them like that would be really difficult, and if they can get to all those stars there's no obvious reason they couldn't get to us here and like... hand us a roll of ticker tape, or a DVD, or something. But it's clearly under control, it's clearly about us, it hasn't... affected our weather patterns or anything... so it's almost certainly communicative. I want to decode it."

"Tell me about that."

"Well, I haven't looked at it yet," she cast him a slightly annoyed look, "since you guys and all the others all have a conspiracy going where you say there's too much value in looking at it without preconceptions to have it flying around..."

"Mm–hm," Haruto said, unruffled.

"...so I don't have an angle specific to the starwink message's content, but I'm interested in coming up with creative ways to present the data, with various factors highlighted or smoothed out – for example, we don't yet know for sure if it matters which stars, is my understanding, so in the case that it doesn't you'll be able to get more flexible visualisations or audialisations by treating it just as a string of bits, but I've come up with a few things for also displaying star–specific facts so something could pop out if there's anything there. I've worked with toy datasets that are actually encodings of episodes of My Little Pony and stuff like that."

"You do this yourself?"

"My brother helps me with some of the coding. He's a programmer, works for HMCF. But I generate all the spec myself, I can tell your guys just as easily how I want things to look."

"I don't know the acronym?" said Haruto.

"I bet they have an equivalent organisation in Japan but I don't – uh, it's Halt Melt Catch Fire, they study that thing that happens if you try to run a program that could make itself smarter and the computer slags itself, but so far I think their only public–facing result is the power plant and it's not actually more efficient than nuclear." –Anonymous