Saturday, December 18, 2004

Schrödinger's cat

If you studied or know a little about quantum physics, you may have heard about Schrödinger's cat.

In fact, this cat was not a pet of Erwin Schrödinger. In 1935, he proposed this to illustrate the quantum theory of superposition. If you read German, you can read his original article 'Die gegenwartige Situation in der Quantenmechanik', in "Naturwissenschaftern" 23: pp. 807-812; 823-823, 844-849. (1935).

According to the principle of superposition, while we do not know what the state of any object is, it is actually in all possible states simultaneously, as long as we don't look to check. The act of the measurement itself causes the object to be limited to a single possibility.

To illustrate this point, Schrödinger suggested that:
A living cat is placed in a thick lead box - there is no question that the cat is alive.
Then throw in a vial of cyanide and seal the box - we do not know if:
(1) the cat is alive; or
(2) if it has broken the cyanide capsule and died.
As we do not know, then the cat is BOTH dead and alive, according to quantum law - in a superposition of states.
When the box is opened to see what condition the cat is in, then the superposition is lost - and the cat must be either alive or dead (one or the other, but not BOTH).

This superposition occurs at the sub-atomic level. The observable effects of interference show that a single particle can be in multiple locations simultaneously.

Hence, Schrödinger's cat is not about a REAL cat. He was using it as an analogy. A cruel one if you ask me. But hey, cats are now immortalised in the field of quantum physics.

Nina's human, Deborah came over in the afternoon to say hello to me, and her offspring Hugh came to mow the lawn. Nina is a Russian Blue and I understand very pretty, but not charming like MOI! Deborah complimented me on my charming manner (thank you Deborah).

Devi came later for dinner. They had roast rolled turkey thigh with cranberry and chestnut stuffing, roast potatoes, pumpkin and beetroot, with peas.

If you enjoyed reading this, let me know. You can email me at


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