Our best theory of gravity no longer belongs to Isaac Newton. It’s Einstein’s General Theory of Relativity. There’s just one problem: it is incompatible with quantum theory. The effort to tie the two together provides the greatest challenge to physics in the 21st century.
Werner had been a happy cat until the day he woke up inside a box. He looked up to see a human in a white coat. “Good luck, Werner,” the man said, replacing the lid to the box. It became quite dark, but being a cat, Werner could still see well enough from the weak light leaking through one corner of the box. He could make out an odd lump next to a small metal box, which appeared to be making a faint clicking sound. Next to that was a hammer, poised and ready to smash a glass jar positioned beneath it. Werner turned around to see another lump, one that he hadn’t noticed when the box was open.
“Hello,” said a voice behind him. Startled, Werner spun around, hackles raised.
“Who’s there?!” he meowed. He saw a ghostly image of a man wearing wire-rimmed spectacles and a bowtie floating in front of him.
“I am the ghost of a scientist,” said the shadow, “the scientist responsible for your current circumstance. My name is Erwin Schrödinger.”
“Can you get me out of here?” Werner replied.
“I’m afraid not. You are part of an important experiment relating to quantum mechanics, a science of the tiny particles that comprise this universe.”
“Am I in any danger, Mr. Show-dinger?”
“Call me Erwin. Werner, you yourself are not in any danger, but your wave-function is. Take a closer look at that other shadow over there,” Erwin commanded, gesturing to the larger unknown shape. Werner did as he was told. He looked carefully and recognized the shape of a cat, but knew at once that it was dead, as well as partially transparent, as if it were a shadow or a ghost.
“What is this dead cat doing here, Mr. Erwin? Is this part of the experiment?” Werner asked.
“I’m sorry to say, Werner, that this cat is not the input of this experiment, but the outcome,” Erwin replied, fearing Werner’s reaction.
“So you mean that something happened to kill this cat already? Did I miss it?”
“Actually, Werner, it hasn’t happened yet. At least not to you. Look one more time at the dead cat. Werner did so, and recognized the cat as—himself.
“You’re saying that I’m going to die in this box, but for that cat, it’s already happened? That’s crazy. I can’t be alive and dead at the same time!” Werner said, uncertain.
“Ah but to the scientists out there, you actually are,” Erwin said, pleased at the poor cat’s naïveté. “You see, the smaller lump over there—the one next to the clicking metal box—it has a near 50 percent chance of emitting a certain radiation at any time, which will trigger the hammer to fall and break the bottle. The bottle contains a poisonous gas, which will kill you. But until the scientists observe you, they have no way of knowing whether you have died yet, so the chance that you are dead is equal to the chance that you are alive. So essentially, you’re both alive and dead at the same time. And as time passes, it is more probable that the poison has been released, and that the dead cat is the reality. Look at your paws, Werner.” Werner looked down at himself and noticed that he was becoming ghostly too. He could see the floor of the box through his paws, but their color was still overlapping the floor.
“My god,” he gasped, “I’m disappearing! How can killing a cat relate to science?!”
Erwin replied, “Dear cat, it’s all about probability and uncertainty. Your fate can be described as a ‘wave-function’, a mathematical function that describes the possible properties that certain particles can acquire, or, in this case, the possible states you as a living entity could be in. This function says right now that you could be alive or dead. When you are observed, your wave will break down into one state, which means that when the observers open the box, they will not see two ghostly images of cats. They will either see you alive or dead, depending on which way the wave breaks down.”
Werner glanced at the hammer, which was still sitting in its original position. “But I haven’t died yet, and aren’t I observing my state? Shouldn’t I be either alive or dead?”
“In theory, yes, but because the scientists don’t know it yet, both states are equally possible to the rest of the universe.”
“This is silly,” said Werner, chuckling in disbelief, “It’s not the observation that determines the outcome, it’s what actually happens. Probability is for math!”
“But science is math, my friend! Science is the art of math. But unfortunately for you, Werner, the numbers fall against you. You just have to wait—and hope.”
“So, you’re saying that, when the scientists open the box, I have to hope that my wave function breaks down in my favor?”
“That’s right, Werner,” Erwin said. “I must leave now, because this experiment is almost at an end. For you at least. Goodbye, Werner. And good luck.”
“Wait, what do you mean, goodbye? What is going to happen to me?” But the shadow of Erwin Schrödinger had departed, leaving the box empty but for the equipment and the two ghostly cats. Werner sighed heavily, uncertain of his fate.
The small metal box began clicking loudly.