Schrödinger’s cat
This is usually presented as a gedankenexperiment designed to discredit the Copenhagen School’s explanation of quantum uncertainty by exposing the impossibility of having a cat that is alive and dead until an observer collapses the probability waveform. Actually, it was just a ruse to cover up the fact that he had left the cat locked in the shed while the family went on holiday. Out of this tragedy* came some strange insights into the nature of reality.
Schrödinger’s lottery ticket
You have won £80m — provided the ticket is left in the box in the spare room. As soon as the box is opened the probability wave collapses and it becomes just another piece of waste paper that cost you a tenner. Buying a yacht on the basis of an unseen ticket rates as observing it under the Heisenberg rules, a phenomenon that Einstein derided as “spooky action at a distance” after coming second in the Institute for Advanced Study’s Christmas raffle for a turkey and hamper. He won a tin of ham and a bottle of lager**.
Schrödinger’s wife
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In Everett’s many-worlds explanation of quantum uncertainty, every possibility becomes reality in separate universes. Theoretically, these branching realities cannot reach one another, although husbands know that they are constantly being moved from one universe in which the wife didn’t ask them to pick the girls up from ballet into a different one in which she did.***
Schrödinger’s car keys
They are in the drawer in the kitchen until you open it. The theorem shows that the chances of finding them are in direct ratio to the urgency of the occasion. The Lorentz Transformation of the De Broglie Relation proves that you can know either when you last had your keys or where you were going at the time, but never both.
*If you like cats. It was a cause for celebration among Schrödinger’s neighbours, who were sick of having their petunias dug up and replaced with cat bowel movements.
**Heisenberg, probabilistically the best lager in the world. After one pint, you babble of waves and particles, after two you become completely decoherent.
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***Every wife, though, knows that the smart and attentive man she married has been replaced by a forgetful slob from an alternate reality where her doppelganger has clearly made some very poor life choices.
And the textbook explanation...
Schrödinger’s cat
In the mid-1930s the Austrian physicist Erwin Schrödinger proposed a thought experiment to highlight how crazy quantum mechanics was. He suggested taking a box in which we place a cat, some lethal poison and a radioactive source. According to quantum mechanics we cannot say, unless we are checking, whether a radioactive atom has broken apart, or decayed, within a given time, so we must describe it as having both decayed and not decayed at the same time. Only when we check do we force it to be one or the other.
Inside Schrödinger’s box, the experiment is designed so that any decayed atom will have spat out a particle that triggers the release of the poison, killing the cat. Since the cat, said Schrödinger, is also made up of atoms (albeit trillions of them) then it too is presumably subject to the laws of quantum mechanics. So, until we open the box to look, we must describe the cat as being both dead and alive at the same time. Only when we open the box do we force everything inside into one or other state.
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(Explanation taken from 30-Second Theories: The 50 Most Thought-Provoking Theories in Science, Each Explained in Half a Minute, edited by Paul Parsons. Icon Books, £12.99)