Steven Schroeder | let sleeping dogs lie
Imagine a cat in a box.
Strike that.
The cat imagines itself. It goes without saying, in the box, provided you leave the lid off. And a physicist, who does not, of course, go without saying. Slightly stooped. Tiny, wire-rimmed glasses with thick lenses. Vaguely German accent. Graying hair. He says, “Imagine a cat in a box with the lid on.”
Haven’t we been through this before?
The cat imagines itself, goes without saying—however, the physicist doesn’t—in the box. Provided you leave the lid off, but the physicist says imagine it on with the cat inside.
“Provided you cannot see into the box—” (keep the lid on) “—there are two possible states in which the cat in the box exists simultaneously: dead and alive. But take the lid off, and the wave packet—” (that is to say the cat) “collapses into a single state: alive or dead.”
Well, if you take the lid off the cat goes without saying.
This cat has a sweet smile and a deck of cards. When the physicist imagines the lid off, the cat says, “Cut” and goes.
A cat, a smile, a physicist, a deck of cards, a box imagined. Fifty-two states times five or more. Cut. The wave collapses, the physicist, the box, a house of cards. The cat goes without saying.
A fact, the cat imagines itself.
The first time I heard Schrödinger’s old joke, I thought the cat was an innocent victim whose fate was in the hands of a crazed physicist poised to blow the lid off a box.
“But,” said the physicist, “You have left more out of the box than the cat. You must imagine a weak radioactive source in the box with the cat and a detector, turned on just once for just one minute. You must also imagine that the probability that the radioactive source will emit a detectable particle during the minute you have imagined you have imagined the imagined detector on is one out of two. If a particle is detected, the box is flooded with a poison gas that kills the cat. Imagine that. We don’t know if the cat is alive or dead.”
The cat, probably, does and imagines the physicist outside perplexed.
In Copenhagen, they said we could not speak of the cat in a definite state at the end of the minute without observing it.
“So,” said the physicist, “Assign a probability wave to the physical state of a dead cat and a live cat.”
What could be more simple?
“The cat in the box—”
(purring comfortably and dreaming, in all probability, of mice not physicists)
“—is correctly described not as a simple cat but as a wave state consisting equally of the dead cat wave and the live one. The wave state in the box is composed of probabilities, not actualities.”
And outside.
In Copenhagen, they took the lid off; seeing the cat’s smile, hearing the cat’s purr, they said they had put it in a definite quantum state, alive.
The physicist went on: “The cat in the box is far away in space, and observers have to travel in a space shuttle to take the lid off. When they take the lid off, they confront a definite quantum state; but, because their radio is broken, their colleagues back on earth still confront a wave state in a distant box composed of probabilities.”
A smile without a cat.
In space, not in Copenhagen, they fix the radio, open a line of communication, and report a purring cat in a box with a smile. The report is recorded and stored in the memory of a computer on earth, which becomes part of the wave state composed of probabilities.
“Now,” says the physicist, “scientists on earth confront a definite quantum state—”
(a smile without a cat)
“—only when they read the information stored in the computer’s memory.”
They propagate this wave by telling their friends in the next room—or posting it on the Internet—but it will not sit on their lap and purr.
It might have been Danish. The accent, not the cat.
I don’t know what turned up when the physicist cut (though the probabilities are easily computed). The cards, not the cat.
The cat goes without saying.
A cat imagines in all probability that physicists alive or dead exist in Copenhagen equipped with radioactive sources, detectors, poison gas.
A sleeping dog would have been easier, but the wave would never have gone this far.
Detours 2 (Capital University, Ohio) | 1998
