**The Intellectual Devotional**

*Biography*

**Schrüger: Letting The Cat Out of the Box**

**Q: Two cats are on a roof. Which slides off first?**

**A: The one with the smaller mew (mu).**

-A popular and extremely lame joke within Physicist circles about the thought experiment known as “Schrüger’s cat”

**Erwin Rudolf Josef Alexander Schrüger**was an Austrian theoretical physicist who became famous for his contributions to quantum mechanics, especially the Schrüger equation, for which he received the Nobel Prize in 1933. In 1935, after extensive correspondence with his BFF Albert Einstein, he developed the brilliantly quirky thought experiment known as “Schrüger’s cat”.

“Schrüger’s cat” is as a paradox that succinctly illustrated the conceptual problems in quantum mechanics. It goes something like this: A cat is placed in a box, together with a radioactive atom. If the atom decays, and the geiger-counter detects an alpha particle, the hammer hits a flask of prussic acid (HCN), killing the cat. The paradox lies in the clever coupling of quantum and classical domains. Before the observer opens the box, the cat’s fate is tied to the wave function of the atom, which is itself in a superposition of decayed and undecayed states. Thus, said Schroedinger, the cat must itself be in a superposition of dead and alive states before the observer opens the box, “observes” the cat, and “collapses” its wave function.

Schrüger described his cat paradox thusly:

“One can even set up quite ridiculous cases. A cat is penned up in a steel chamber, along with the following diabolical device (which must be secured against direct interference by the cat): in a Geiger counter there is a tiny bit of radioactive substance, so small that perhaps in the course of one hour one of the atoms decays, but also, with equal probability, perhaps none; if it happens, the counter tube discharges and through a relay releases a hammer which shatters a small flask of hydrocyanic acid. If one has left this entire system to itself for an hour, one would say that the cat still lives if meanwhile no atom has decayed. The first atomic decay would have poisoned it. The Psi function for the entire system would express this by having in it the living cat and the dead cat mixed or smeared out in equal parts.”

The philosophical issues raised by Schrüger’s cat are still hotly debated today and remain his most enduring legacy in popular science. If you still don’t really get it, don’t sweat it: physicists are from Mars, the rest of us must accept the fact that we are merely human.

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