APS News

February 2007 (Volume 16, Number 2)

Zero Gravity: The Lighter Side of Science

The Uncertainty of Cat Molecules

Physicists keep uncovering evidence that unpredictability rules the universe. Molecules and atoms are not solid bits circling one another systematically but erratic little things with fuzzy edges and minds of their own. Newton’s ordered universe is dead.

This is not news to me. I am self-employed, and I live with cats. But for those who find uncertainty hard to grasp, the theoretical physicist Erwin Schrödinger some years ago illustrated it with a thought experiment, the famous Schrödinger’s Cat:

In a box, place a bit of radioactive material, a Geiger counter, a canister of poison gas, and a charge device. Connect the Geiger counter to the charge device and the device to the canister, so that if a particle emitted from the radioactive source hits the Geiger counter, it triggers the charge, blows the cap on the canister, and releases the poison gas. Into this arrangement, drop a live cat. Close the box, and leave for an hour. When you return, will you have a live cat or a dead one? There is no way to tell in advance, the emission of radioactive particles being random.

What a pathetically limited view of uncertainty! Imagine if Schrödinger had taken into account the documented facts about cat molecules:

  1. Cat molecules have been known for centuries to be fuzzy around the edges and highly unpredictable.
  2. A majority of cat molecules enjoys taking off in the same direction at the same time—enough, at least, to propel the entire cat mass across a room at slightly less than the speed of light.
  3. A significant minority of cat molecules is governed by the scientific principle of contrariness. When the majority of cat molecules starts moving in one direction, the contrarion molecules rush headlong in another.
  4. The motion of a cat mass, then, is the sum of the vectors of warring molecules. Thus the direction in which a cat mass will travel is entirely unpredictable.
  5. All cat molecules become extremely agitated at the prospect of confinement in a box.
Add these facts to Schrödinger’s experiment and you can begin to appreciate uncertainty. For example, most cat molecules know who their friends are, and we can assume that Schrödinger is not among them. How long will it take him to capture the cat molecules and jam them into the box? We cannot predict.

For the sake of argument, however, let’s say it takes four hours–an optimistic estimate, considering that Schrödinger will have to stop for first aid, possibly a transfusion. What if some radioactive particle takes off before the cat molecules can be introduced? Surely Schrödinger has armed the poison gas mechanism in advance, since once any cat mass is dropped into a box, slamming and securing the lid is the only priority. But what if he left the lid open while pursuing the cat molecules? Is the gas poisonous to humans? When Mrs. Schrödinger comes to summon her husband to lunch, will she find a live Schrödinger or a dead one? It is impossible to tell.

But let's assume that Schrödinger survives and gets the cat molecules into the box. Say he goes away to work on his next project (something involving live grenades and golden retriever puppies) and returns in an hour. Say he finds a pile of dead cat molecules. What does that prove? That it all went as planned—the random particle took off, the trigger worked, the cap blew, and the cat molecules gasped and died?

This hypothesis seems to assume that the cat molecules went to sleep the instant the lid snaps shut. How probable is that? Might not the cat molecules have attacked the Geiger counter or tried to snap the gas canister’s neck? Couldn't they have died of fright? And what about the effect of cat urine on the charge device?

Or let’s say the cat molecules survive. Can we predict what will happen when Schrödinger opens the box? The effect of confinement on cat molecules is well known. Odds are that when the box is opened, the cat molecules will instantly launch the cat mass directly at Schrödinger’s eyes. But the cat molecules might target
a more vulnerable part of Schrödinger’s anatomy. It’s
impossible to say.

Schrödinger’s Cat clearly shows that Schrödinger was a pathologically orderly man. The uncertainty principle filled him with fear and loathing–and so, of course, did cats. He did, however, get along reasonably well with Mrs. Schrödinger. Otherwise, we would have Schrödinger’s Wife. And there’s no telling what that thought experiment might have illuminated, no telling at all.

Carole Simon

APS encourages the redistribution of the materials included in this newspaper provided that attribution to the source is noted and the materials are not truncated or changed.

Editor: Alan Chodos
Contributing Editor: Jennifer Ouellette
Staff Writer: Ernie Tretkoff

February 2007 (Volume 16, Number 2)

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Articles in this Issue
APS Commemorates Birth of the Transistor
APS Membership Sets a New Record in 2007
Serious Consequences Loom if FY07 Budget is Frozen
PhysicsQuest Kits are Back by Popular Demand
Thursday Night Football with Tim Gay
Physicist Finds His Fortune in the Cards
Engineering Academy Seeks Grand Challenges
H. Frederick Dylla To Succeed Marc Brodsky as Head of American Institute of Physics
Members in the Media
This Month in Physics History
International News
Zero Gravity: The Lighter Side of Science
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