ANDREI VASILOV is the cosmology wunderkind who had his PhD at 18 and had his work published in Nature the same year. He became a great embarrassment to the scientific community when he lost his mind and began proclaiming that aliens are eating our universe.

In his defence, I want to tell you that he was a brilliant scientist, and likely remains one. Mad, of course. As his best friend, I have my own theories about why it all happened. Unfortunately, I played a role in his collapse.

I first suspected Andrei was losing his grip on reality the night Alpha Centauri A began to implode. At that point, he still lived with Julie. She was not a problem between us. Yet. No, we were just two postdocs in cosmology. I worked on dark matter theory and black holes, and he worked on dark energy (which he didn't believe in) and the expansion of the universe.

That night, at about 3:30 am, my phone rang. I had only just gone to bed - a typical theorist, I'm not much of a morning person - so I didn't much mind. I traded time off at the observatory with Andrei, and knew he was in the middle of his night shift, so I expected it to be him.

"Yeah?"

"Lew-" His Russian accent was unmistakable. "Alpha Centauri A is dimming."

"What?"

"It's growing dim."

"You woke me for some kind of atmospheric disturbance?"

"No other stars are changing their luminescence. This one
alone."

I thought about it. "This could be big. A cloud of dark matter maybe, near Alpha Centauri A, moving in between us and it? This could be big. You try a spectrograph yet?"

"Just the one we have built into the software. No change yet. Nothing unexpected. I don't think this is occlusion. I think the star itself is growing dim."

"Crap," I said. But added, "I'll come up." I heated some pizza and ate before I dressed, then drove up to the mountaintop.

By the time I got to the observatory Andrei had already woken half the cosmologists in the U.S. and even called the press. Nor was I the first local person he'd phoned: a crowd had formed around him already. He hardly noticed my arrival. I watched for a while, intrigued but tired, then went back home to bed.

That's one source of the problem: Andrei was a brilliant scientist who had very good hunches but he always assumed he was right, even when they were no more than hypotheses. And when he thinks he's right, he wants to tell everyone. That's my take on it, anyway.

Of course, he was vindicated - that one time, I mean. Alpha Centauri A, almost the twin of our own Sun, just four lightyears away, not only grew dimmer, it shrank right down and became a little white dwarf within just a few days. Biggest scientific mystery of all time.

A month later, after Andrei had been on all the science programs and interviewed by the popular press and things started to die down a bit, I got a call one morning at a more reasonable hour.

"Lew, hi, this is Julie. Andrei's girlfriend."

"Yes, of course." I'd immediately recognised that sweet French accent. "I remember you." She was the most beautiful girl on campus. And, did I mention, French? She was a doctoral student in geology, researching volcanoes.

"Hi, well, I wanted to ask of you a favour. Could you talk to Andrei? I am worried, you see. He won't leave the lab. He is very obsessed with this Alpha Centauri thing."

"We all are.It contradicts all of our best astrophysics, a young star only five billion years old going straight to white dwarf like that. No one understands it."

"Yes, yes, but Andrei is very ... he is much obsessed with this. It is like he thinks that our own Sun is going next. If you could see him, perhaps talk your physics talk, you could bring him out a bit. Make him eat something, walk outside, see the Sun."

"Sure, Julie," I told her, eager to please. "I'll go over there right now."

ANDREI SAT IN the lab with his feet on his desk, offprints and photocopies of papers from Physica D and Nature heaped around him. He wore no shoes; toes peeked through his unmatched socks, one black, one grey. A week's worth of beard darkened his face, and his longish hair stuck up and badly needed washing.

Slices of pizza lay on a lab table nearby. In other words, a typical scene at a graduate school lab. But Andrei stared, just stared, at a marker board above his desk. On it a square had been erased out of densely written equations and derivations, and in neat, black block letters were three simple phrases:

(1) MISSING MATTER

(2) UNIVERSE EXPANDING TOWARD HEAT DEATH

(3) ALPHA CENTAURI SNUFFED OUT

"That your shopping list?" I asked.

He started, but only a little. "Lew. Good to see you."

"How are you, Andrei? I haven't seen you much this last month."

"Lewis, Lewis, this thing is crazy. How can Alpha Centauri go out like that? No bang, no nova, nothing. Just a dimming, and a few days later it's a white dwarf. Where is the matter? No one seems to remember conservation of mass anymore. This rude star doesn't obey even the venerable old laws."

I ventured a guess. "The black hole theory?" The popular hypothesis in the astrophysics chat rooms was that a black hole had smacked into the star, and eaten much of it up.

Andrei snorted. "And now what? The black hole has had enough? It eats up the star but then stops?"

"A grazing collision, or it passed right through."

"Oh, do the maths, Lew! A black hole small enough not to disrupt the star completely has to orbit inside it for centuries before it eats enough to be noticed. And then suddenly 'No more, thank you, I'm full now' and it departs? That theory makes no sense."

"There are subsidiary theories," I reminded him. "A black hole could evaporate, after a while." But he snorted again, and rightly so. That only applied to microscopic holes. All black hole theories failed unless someone could make some sense of how the singularity could stop before consuming the whole star.

It did not help that this remained the best approach we had - it still just didn't work. I think it works now, of course, given the modifications that I've made. But alone with Andrei, I felt a lot of caution about speculating, even if he didn't. His criticisms were always fierce, though his own imagination ran wild.

"Well," I continued, adopting a jovial tone. "You aren't planning on staying here till you solve this mystery, are you?"

"No, of course not." He put his feet down and smiled at me, as if expecting some invitation. I should have taken him outside right then, but I let my curiosity get the better of me. I pointed at the marker board.

"So what's with the list?"

"The three things that just don't make sense in cosmology today. The universe appears to lack enough matter, so idiots invent this so-called dark matter. The expansion of the cosmos is accelerating, when the extra matter it ought to have should slow it down and pull it back, so idiots invent this so-called dark energy. No proof of either. And Alpha Centauri A just skipped over all the stages of stellar evolution, hid its mass somewhere, and became a white dwarf."

"All independent issues."

"Right," he whispered. "Should be."

"You sound unconvinced. But, Andrei, we should not make the mystery inference: X is mysterious, Y is mysterious, Z is mysterious, so X is Y is Z."

Clearly not listening, he muttered, "I've just had an idea."

He turned to his keyboard and started banging away on his
Sun workstation.

"Andrei, what about some lunch?"

Without turning around he mumbled, "Sure, sure."

I hovered about for a bit, checking my email on a nearby machine. After half an hour I asked, "You going to be long at that?" He didn't answer, and I left in frustration.

I rang his apartment doorbell. Julie answered. Her hair was pulled up, and she smiled at me hopefully, showing her small teeth and the charming gap between the front two.

"Sorry," I said. "I talked with him. And he seemed OK. But then like an idiot I asked a few questions, and he got obsessed again and started working."

"Oh," she said. Her smile faded.

"I'm sorry. Hey, looks like this has been hard on you too.

You need to get out as much as he does, I bet. I'm about to get some lunch. Why don't you come along?"

"Oh, no," she said.

"Come on. Rocks can wait."

She hesitated a long while. Then she smiled a marvelous smile and said, "OK". Standing in the doorway, she pulled on a pair of black pumps, elegant but worn, with the brown leather showing through the black in a few places. We walked down the drive to my car, and I took her arm, something I never do.

Andrei almost began to live in the lab, and I stopped going in. It was nearly a month before I saw him again. Late, at almost 2:00 am, someone banged on my door, waking me.

I turned on the light.

"What is it?" Julie whispered, pulling the covers up to her chin.

We heard a shout.

"Lew?" It was Andrei, down below.

"Oh no," Julie said.

We waited a moment in silence, not even breathing.

"Lew?"

"He doesn't sound angry," I said. "Stay here."

But after I pulled on a sweatshirt and got out into the hallway, I hesitated. Julie and I had agreed we needed to tell Andrei, but we rationalised and put it off. If he didn't care enough even to come home to see her, then we did not owe him any expedient explanation. Still, I really didn't want to fight. Perhaps I should just let him go home without answering the door?

"Lew," he called. "Lew, I'm sorry, but I think I've solved it!"

So he didn't know Julie was there. He probably came straight to my place from the lab. I hurried down the steps, found her coat and put it into a closet, and then opened the door.

"Andrei." I intended to send him home, but he pushed right in, and marched to my kitchen.

"I've got it," he said, turning in place. "You're going to say that it's mad, but I've got it. Listen: remember we used to talk about steady state theory?"

"No," I said. I couldn't help it: I glanced upstairs. But Andrei didn't notice. He started to pace.

"If the dark energy exists, forcing the universe to expand, then to keep it from dying, you'll need to add new mass." He added in a mumbling rush, "Not to mention that if the dark energy doesn't exist then you have to explain why gravitation is not doing its job, and maybe it's not doing the job because some mass is missing - but set that aside for a moment. Back to expansion and matter."

"Right," I said. The universe appeared to be expanding ever faster. In a hundred billion years, the visible universe would be a cold emptiness, all the galaxies flung apart from one another.But you could figure out how many hydrogen atoms per cubic light-year of space you'd need to add every year to keep the universe from being spread so thin it just died and then persisted forever as nothing more than a lifeless near-vacuum.

If you could magically add that extra mass, the universe would expand at a more relaxed rate, and remain lively. Andrei's passion for this extremely remote problem was palpable. He took to it as an engineering challenge, and not a mathematical exercise. I feared he'd rant on till sunrise, and I wanted to get back to bed and Julie. I pointedly looked at the clock.

"But where to get the extra matter?" he continued, unconcerned by my lack of response. "That is the question. And more of it all the time. The need grows exponentially as the volume of the universe grows and it thins out."
"But the conservation laws prove you can't make extra mass or energy, so it's a moot point."

"Exactly!" he shouted. "Exactly, you can't make it. But you could steal it!"

"What?"

He bit his lip in frustration, clearly thinking me a very dull student.

"Look, Lew - the universe, our universe, has less mass than it should."

"Well, it has less observed matter than the old theories predicted. But dark matter-"

"A fiction! Dark matter is not an observed fact. No, that bright matter has gone somewhere. And now we know why. We have caught them in the act. Alpha Centauri is the scene of the crime. We just saw it being taken away, being burgled!"

HE'D FLIPPED HIS LID. I stared at him. "What the hell?"

"Can't you see? There is another universe on another brane."

"The standard string theory models don't have other hypermembranes." Those would be other spaces like ours, but isolated from us except perhaps for gravity.

"But they don't rule it out, either! There is another universe on another brane, facing the same dilemma as ours. Their dark energy, or maybe just the curvature of spacetime, is pushing their universe apart, too, and if they don't feed it more mass the whole thing will die an inevitable cold death. But they've taken action. They're stealing our matter."

I sighed. "Andrei, this is nuts."

"But Lew, it cannot be a natural phenomenon. The matter disappeared, it had to go somewhere, and there is nothing that says our mass could leak naturally into another brane universe. Quite the reverse. Branes should be hermetically isolated. No - they've engineered it."

"Who are they?"

"The beings in the other universe. Engineers. Cosmological tinkerers."

I shook my head in disbelief. "Andrei, listen to yourself. You have nothing but three disconnected mysteries. You're making up conspiracy theories. Unfalsifiable, unscientific speculation."

"Not unfalsifiable." He was dancing on the spot with excitement, face flushed. "I have a prediction. We can confirm that in the past matter has disappeared by finding other premature white dwarfs. We might be able to confirm the rate by looking at disproportionate numbers of white dwarfs. And we don't just have to look at the past results. We know what to look for. It has to accelerate, you see. We can watch for it to speed up. I predict Alpha Centauri B will go next." That was the other Sun-like star in the Centauri triplet; Proxima was small, dull red and uninteresting. "More and more stars," he cried, "more and more often, collapsing into dim husks. We have to learn how they do it, Lew. We have to see if we can stop them. It might take a thousand or a million years to figure that out, but we have to get cracking! No time to lose!"

"Andrei," I said, quietly, trying to calm him. "Look. There are alternatives. Many alternatives. All of them better than yours. Without aliens."

"Let's hear it, then," he demanded, sure that I would have no
explanation to offer.

"Well. Well. All the standard models assume that we're not near the centre of the universe. But, just by chance, we could be near the centre of an immense void bubble-"

"Oh, what are the odds?" he said scornfully.

"Better than your theory's odds, don't you think? So, if we're near the centre, then you know how it goes. Our universe might not have an accelerating expansion. No need for dark energy at all."

I paused. Andrei looked at me in silence for a moment. His eyes flickered rapidly, as if his whole head were trembling with thought. Then he exhaled. He'd been holding his breath.

"That's right," he whispered. "There are other possibilities."
"Simpler hypotheses." I pulled out a chair from the kitchen table. He collapsed into it. I wanted to get him out of the apartment, given that Julie was upstairs, but I couldn't send him home like this. "I'll make some tea."

Andrei nodded.

"That wouldn't explain Alpha Centauri A," he said, nearly in a whisper.

"No," I agreed. I filled the teapot with water and set it on the stove. "But what you should do is look at my work on self-extinguishing black holes."

"OK. OK." His voice lightened as he warmed to the prospect of an alternative approach. He pressed his hands together and stared off in the corner, getting his dreamy look of trance-like concentration. "I could do that. Is it here? Do you have your work here? We could get started..."

He fell silent. For a moment, I thought he stared down at nothing, thinking more about my approach, but then I followed his line of sight and saw what he saw: in the corner of the kitchen, discarded there when kicked away in a moment of passion, lay a single worn black pump.

We both stood a long time, gazing at the shoe. Then he looked up at the ceiling, towards my bedroom. My adrenaline began to flow, my hands started to shake. I was expecting a scene, maybe a fight. After what seemed a long while, however, he just looked at me. His bloodshot eyes misted over with the hint of tears. His mouth moved, as if he wanted to say something but couldn't. As if for once words and theories failed him. Then he stood and walked out, leaving the front door ajar.

I resisted the momentary temptation to call out to him. I closed and locked the door, relieved.

That was the last time Andrei Vasilov and I talked. I called him once, but he hung up on me. I feared approaching him at his office, and so we just avoided one another. I learned about his spiral into ignominy from the endless gossip of graduate students. Everyone talked about it with a certain glee: Andrei had been the object of much jealousy, and now he had been brought down with a satisfactory crash.

The gossipers said Andrei had written up his bizarre claims and submitted them to all the scientific journals, but of course none would print them. He submitted to scientific conferences, all of which denied him. He descended on the conferences anyway, and tried to give speeches during question and answer sessions, where other scientists booed him down.

Really, I have to admit we're an intolerant lot. Finally he ended up publishing in some hack paranormal magazine, where his dire predictions titillated an audience grown bored of la chupacabra and cattle mutilations. After that, he disappeared altogether, moved somewhere beyond the reach of graduate school gossip. No one in the scientific community knows his location now.

Julie and I are still an item, I'm glad to say. Julie did go to see Andrei once. To her attempts at an apology he merely said, "It doesn't matter. Not compared to this." So with little guilt and no delay she moved in with me for the rest of the summer.

Now she has a postdoc position just a few hours drive up the coast, and we spend weekends together. Meanwhile, I've become an expert on the Alpha Centauri A and B collapses. My own theory, which is a variation of the self-extinguishing black hole scenario, is acknowledged as one of the two leading contenders.

That explains it, you see. Andrei's best friend bested him in science and love, and so he just cracked. I'm certain that caused his breakdown and his crazy theorising.

Of course, all of us were surprised when Betelgeuse collapsed into a brown dwarf last week, less than a year after the double Alpha Centauri collapse. It seems so unlikely that three self-extinguishing black holes would eat three stars so near to each other in such a short time. But, after all, coincidences do happen. I'm sure mine is the best scientific explanation for these events. And I'm sure we'll see nothing like them ever again. Especially not with our own Sun.

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