Craig swallowed his bite of pizza. The four boys were in Andrew's kitchen an hour later. Phone calls had been made, negotiations completed, and a sleepover was planned for the four of them at Andrew's place. "Yeah Joel, I missed pizza too, but for me it was bananas. I don't know why, but Wednesday morning I just stared at the bunch of bananas in the fruit bowl and my mouth started watering."
"Naturally. Everybody knows monkeys love bananas," giggled Joel as he stood up and ran from the room, expecting Craig to follow.
Craig just gave him a disgusted look and threw a bunched up napkin at him, then took another bite of pizza.
Andrew slid his arm onto Craig's shoulders and looked at him. "I just happen to think he's an awfully cute monkey." Craig smiled back and their lips touched for a brief tomato sauce flavored kiss.
"Geez you guys are sappy," Jamie said. Despite his words he grinned at Andrew. "So when is your dad home and how exactly are we going to do this?"
"I don't know actually. It's strange that he had to go in on a Saturday, that's not like him. He says weekends are family time, and he usually sticks by it. He's been at work a lot the last few days though, and looking stressed. Well, more stressed than usual." Andrew stood up and began gathering the pizza boxes together.
Craig stood up to help. "Well, maybe now's not a good time to tell him then if things aren't going well at work. Maybe we should wait."
Andrew stopped what he was doing for a moment. "Well, maybe. But this is important too, probably even more important than whatever he's working on. I say we tell him. I know my dad. He'd want me to tell him. He always says real life comes first, and work is just work, no matter how interesting or important it seems."
At that moment Joel and Craig's controlled flinch signaled the garage door opening and the arrival of Andrew's dad.
Dr. Pollack walked into the kitchen, looking far more weary than he had on Wednesday evening. "Hi Andrew," he said as Andrew gave him a quick hug and looked around at the boys. "I know Jamie of course, and Craig. Who's your other friend?"
"This is Joel. He's a friend of Craig's, and, well, of ours too now. Joel, this is my dad, Dr. Pollack."
Dr. Pollack smiled a hello, slipped his shoes off with a grateful sigh and sat a large black case on the kitchen counter. "Any of that pizza left kiddo?"
"Yup. We saved some for you. Umm, we were kinda hoping you'd be home pretty soon. Before it got too late to talk."
Dr. Pollack already had a slice of pizza in his hand and took a bite. He gazed around at the four faces looking at him with anxious expressions. He chewed and swallowed and set the half eaten piece of pizza down on a napkin on the counter. "From the looks in your faces, there's something you need to talk about. Something important. Let me guess. It's either girls or someone is in trouble. I hope it's not that someone is in trouble about a girl."
"No Dad, it's nothing like that. Not girls, or drugs, and nobody did anything illegal or anything. It's actually kind of more related to your work. Well, maybe. We don't know." Andrew looked a bit uncomfortable now.
Dr. Pollack looked at him. "About work?" He paused. "Andrew, you haven't hesitated to ask me a question about anything for years. Even when you wanted to know about...well, that's not important right now. But you're looking uncomfortable. And if I'm judging it right, so do the rest of you. Why would anything about string theory or quantum mechanics make teenage boys uncomfortable?"
"Umm, well, can we go sit down in the living room?" asked Andrew.
Dr. Pollack gave the four boys a long look. "Ok, let's go. But, Andrew, you know most of my current project has been classified by the government. I'm still arguing that, science should be open, but, until then, I can't say anything about it if that's going to be your question."
"No. Well, I don't think so. Look, let's just sit down."
They did so, and Dr. Pollack looked around at them expectantly.
Andrew began, "Um, maybe Craig should start. He probably can explain this the best. Or maybe Joel?" He looked at both of them.
Craig looked at Joel's rapidly shaking head. "I guess I'll tell you." He thought for a second. "Dr. Pollack, I have maybe a couple of questions first, if that's ok. I might be way on the wrong track, but, maybe this will help me figure it out as we go. Is that ok?"
Dr. Pollack looked at Craig, his face showing his curiosity, "Of course."
"Ok. Well, can you explain about the many-worlds interpretation of quantum mechanics?"
Dr. Pollacks eyebrows shot up. "That's unexpected." He looked around at the four middle school boys. "Ok. Simple explanation. Many worlds theory was devised initially by Hugh Everett to try and reconcile non-deterministic events with the deterministic results of the equations...."
"Dad! We're in grade 8."
Dr. Pollack chuckled. "Sorry, it's been a while since I lectured anybody except grad students on this stuff. Ok. Who's heard of Schrödinger's cat?"
Craig was smiling, and Andrew was nodding, but Joel and Jamie were looking perplexed. "A cat? Like, a pussycat? What does that have to do with this stuff?" asked Jamie.
Dr. Pollack continued. "It's a thought experiment. An experiment you do in your own head to kind of help to understand or explain something. Usually it's used for things that are a bit odd or hard to explain otherwise. We'll get to that, but there's something you need to know first. Quite a while back a scientist discovered something very, very strange. He was sure he made a mistake, so he repeated it over and over again, and so did lots of other people." He seemed to be thinking hard for a few seconds. "Ok. Middle school version. You guys have learned about electrons, protons, and neutrons, right?"
Joel said, "The particles that make up atoms. Atoms are what everything is made of."
"Right. What about photons?"
Craig said, "The most basic unit of light."
"Right again. Light is made up of photons, which can act like particles. We know this because...well, maybe we don't need to get into that right now. Light is weird though. Sometimes it doesn't act like particles at all. It acts like waves. So do other things like electrons and stuff." He stopped for a second, then continued. "What happens when you throw a rock into a still pond?"
"Um, it makes ripples. Waves, I guess," said Jamie.
"And what happens when you throw in two rocks, a couple of feet from each other but at the same time?"
"Well, I guess the waves hit each other when they get far enough away from the rocks," said Jamie again.
Dr. Pollack smiled. "Yes. Where the tops of the waves hit each, they get twice as big, and where the bottom, or troughs, hit each other they get twice as deep. Where a peak hits a trough they kinda cancel out. That's all called an interference pattern. Make sense so far?"
The three boys nodded.
Dr. Pollack continued, "Well, light waves do the same thing. Take a screen, like a film screen, and shine a light at it. You get a lit up screen. Take a real thin board and put it in the way and it blocks the light. Cut a slit in the board and you get a bit of the light shining through on the screen. Cut two slits beside each other and you gets two bits of light. But anyone want to guess what happens?"
Andrew heard his dad explain this before. He answered, "An interference pattern?"
"Yes son, you get an interference pattern. Strips of lighter and darker areas caused by the peaks and troughs of the waves hitting each other. This is called the double slit experiment, or at least part of it. Everybody with me so far?"
"Cats, double slits, and many worlds. Got it," said Jamie.
Dr. Pollack grinned at him. "No need to get sarcastic Jamie. We'll get there. Hang on a minute, ok?"
Jamie nodded and grinned back.
"Ok, there's a lot more to it than this, but here's where we get to the amazing stuff. What do you think happens if we use a special light and turn it on and off so quick that it fires exactly one photon through the board and onto the screen?"
"Well, it either hits the board, or goes through one of the slits and lights up a spot on the screen behind, right?" asked Joel.
"Nope. Believe it or not, it doesn't. It makes an interference pattern on the screen." said a smug Dr. Pollack.
"But that's impossible! One particle can only go through one slit!" asked Jamie.
Craig, for his part, was just grinning and watching this exchange with amusement. He had read about this stuff a couple of years ago when he first became interested.
"Well, it does. Remember how light can act like particles and waves?" continued Dr. Pollack. "I'll bet you thought I was going to tell you that that was the cool part. Well, it gets way weirder. Ready?"
The boys nodded again. Craig and Andrew smiling widely. Andrew, being the son of a physicist, had heard this before too.
"Anyone want to take a shot at what happens if we have a detector set up so we know exactly which slit the photon goes through?"
Neither Joel nor Jamie seemed willing to risk an answer, and Craig and Andrew already knew what was coming so they kept silent.
"Well, if we have a detector, so we know for sure which slit the photon goes through, then the interference pattern disappears. As soon as we turn the detectors off, so we don't know which slit the photons go through, the pattern reappears," Dr. Pollack said.
Jamie was shaking his head and Joel looked baffled. Joel said, "C'mon, that's freaky. Are you saying that just because somebody is watching, it somehow changes if the pattern appears or not?"
Craig finally spoke up, not being able to contain himself any longer. "That's exactly what he's saying."
"But, but...but why the hell would the photon care, or know, if somebody was watching?" Joel asked.
"Well, that's just it," said Dr. Pollack. "Like you said so eloquently Joel, it's freaky. Scientists have been trying to figure this out for a while, and have come up with some pretty interesting ideas. You know us scientists though, we like stupid names for stuff, so we named some of what's going on here. When you don't look at which slit it goes through, we say that a superposition exists. It's like the particle goes through both at the same time. As soon as we look, making the interference pattern vanish, we say that the superposition collapses."
"When do we get to the cat?" asked Jamie.
Andrew punched Jamie lightly on the arm and Dr. Pollack smiled again. "Ok. Right now. What I just told you has some pretty weird implications. So this guy, Schrödinger, made up this thought experiment. It goes like this: Pretend you have a cat penned up in a steel box. Attached to the box is a Geiger counter, you know, those things used to measure radiation, and a tiny bit of radioactive material. The cat can't get at either of these. Now radioactive stuff is radioactive because the atoms in it are randomly shooting off some of their particles, losing energy in the process. It's random though, so we don't really know when the next particle is going to shoot off. Only approximately. So the amount of radioactive stuff we put in the box is just enough so that there's about a 50-50 chance of a particle shooting off in the next one hour. Everyone with me so far?"
Jamie said, "What's the cat's name?"
Dr. Pollack looked befuddled a second before grinning. "Nice try Jamie. It won't work this time though, I'm onto you. It doesn't matter. Uh, his name is Fluffy."
"Ok. Fluffy in a steel box with radioactive stuff and a Geiger counter. Sounds awful. Does the SPCA know about this?" Jamie kept smirking.
Dr. Pollack made a point of ignoring him. "We have the Geiger counter set up so that if it detects a particle from the radioactive stuff because it decayed a bit, remember, there's about a 50-50 chance in the hour we're giving it, umm, where was I? Oh yeah, the Geiger counter. It's set up so if it detects that particle then it releases a hammer that shatters a tiny little glass flask of acid, releasing it. The acid will turn to gas and kill the cat."
"You killed Fluffy?!" trolled Jamie.
Joel, Andrew, Craig, and Dr. Pollack didn't rise to the bait. Dr. Pollack continued, "Now, we can't see into this box. So it's like the double slit experiment. We don't know if the acid killed the cat or not in the hour we're giving it, just like we don't know which slit the photon went through. That means, during the hour, it's indeterminate. So, like the single particle going through two slits at the same time, as long as we don't know what's going on in the box then the cat is both alive and dead at the same time. A superposition exists."
"But really it's one or the other right? We just don't know which until we look." said Jamie, giving up the trolling.
"No, that's just it, it's both. At the same time. It has to be. Otherwise, in the double slit experiment, there couldn't be an interference pattern. In a very real sense, it would be both at the same time. Now you're getting why this stuff is so, uh, freaky. As soon as we take a peek in the box though, the superposition collapses, and it's one or the other."
"Ok, that's just nuts," said Joel. "Are you saying someone did this experiment?"
"No, no, no. The cat part is a thought experiment. It's to show you how odd this stuff is when you think about it. The slit stuff is very real though."
Craig said, "That's where the many-worlds interpretation came from, right?"
"Yes. It's one possible theory for what's going on. A guy named DeWitt came up with this, building on something another fellow, Everett, came up with earlier. He figured that, well, that maybe when you peeked in, to see if the cat is alive or dead, maybe both things happen," said Dr. Pollack.
"Uh..." said Jamie.
"Listen up, cause this is truly bizarre..." said Dr. Pollack.
Craig muttered quietly, "Wait'll you hear what we have to say..." Dr. Pollack must've caught this, because he looked at Craig strangely, but then he continued.
"What's bizarre is that DeWitt thinks that maybe what happens is that in one universe, the cat lives, and in another, the cat dies. When you peek, the universe splits into two."
"So this is all still weird guesses, right?" asked Joel.
"Well, here's the thing. More and more scientists now believe that's exactly what's going on. Every time there's a quantum event, the universe splits. So there's almost an infinite number of universes, where something happened slightly differently than this one. Someone lived, or someone died. Someone tripped or they didn't. Someone won the lottery, or they lost everything. Guys, this is real science. It's weird, but it's real science," said Dr. Pollack.
The boys sat silently for a moment, digesting this. Then Craig spoke up. "So, uh, would it be possible, for one of these universes, would it be possible for it to split off because people, like, disappeared?"
Dr. Pollack looked at Craig very intently. Craig felt like the Doctor's eyes were burning a hole in his head, it was that intense. It took him long seconds before he answered. "What do you know?" is all he said, his tone scary and intense.
Andrew stared at his dad, "Dad! You're scaring him. Stop it!"
Craig felt lost at sea. "Uh, what do you mean?"
"About the project. What do you know?" He must've heard his son's plea, he seemed to make a point to lower the intensity.
The other three boys were staring at Craig and Dr. Pollack alternately. Craig managed to answer, "Uh, what project? I mean, I don't know what you're asking."
Dr. Pollack kept looking but his gaze lessened in intensity. Then he blinked hard. "All right. Let me answer you. But then you need to tell me exactly what it is that's going on, ok?"
Craig answered, "Yes! I mean, that's exactly why we wanted to talk to you. We want to try and find out what happened."
"Ok, let me answer your question first. Subatomic particles can, theoretically, appear and disappear at any random point in time. The chances are tiny though, infinitesimal. Theoretically, for all of the trillions upon trillions upon trillions of particles that make up a person to disappear at the same time, well, that chances are so small they might as well not exist. Never mind more than one person. Or almost every person."
"The chance is finite though?"
"Finite, yes. In the broadest theoretical sense. But you don't understand how small this probability is." His eyes narrowed. "I still need to know. Why do you ask?"
"What if almost everyone on earth disappeared at the same time? Could a universe split off because that happened?" asked Craig.
"Craig, get to the point. I think it's time you told me what's going on here."
"One more question, then I'll tell you my story. Please Dr. Pollack, I promise," Craig said to Dr. Pollack's increasingly impatient look.
"Ok. One question."
"Well, all those universes. They split apart all the time. I get that. But, would it be possible, I mean, could it ever happen, that they could ever come together again? Like, blend?"
Dr. Pollack stood up suddenly. His eyes were intense, burning with something the boys couldn't figure out. "Boys. Get your shoes on. We're going for a drive."
The boys asked questions but they were pointedly ignored by Dr. Pollack, who just insisted they get into the car.
They climbed into the car and Dr. Pollack pulled out of the garage and began to drive. The mood in the car was silent and intense. "Ok Craig," said Dr. Pollack, "we have a twenty minute drive ahead of us. Maybe you have time now to tell me your story?" Dr. Pollack's tone made it obvious he was trying hard to lighten the mood in the car.
"Uh, well, it's Joel's story too. It began like this..."
And Craig told the story. He was getting quite good at it by this time. He finished just as they pulled into the parking lot of Dr. Pollack's research facility.