lördag 26 oktober 2013

Quantum Contradictions 28: Schrödinger's Cat

Schrödinger presents his Cat Paradox in the article The Present Situation in Quantum Mechanics
published in 1935:
  • One can even set up quite ridiculous cases. 
  • A cat is penned up in a steel chamber, along with the following 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 the 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 psi-function of the entire system would express this by having in it the living and dead cat (pardon the expression) mixed or smeared out in equal parts.
Schrödinger questions the central idea of the Copenhagen Interpretation that reality arises from measurement:
  • The rejection of realism has logical consequences. 
  • In general, a variable has no definite value before I measure it; then measuring it does not mean ascertaining the value that it has. But then what does it mean? 
  • There must still be some criterion as to whether a measurement is true or false, a method is good or bad, accurate, or inaccurate - whether it deserves the name of measurement process at all. 
  • Any old playing around with an indicating instrument in the vicinity of another body, whereby at any old time one then takes a reading, can hardly be called a measurement on this body.
Schrödinger concludes with:
  • The simple procedure provided for this by the non-relativistic theory is perhaps after all only a convenient calculational trick, but one that today, as we have seen, has attained influence of unprecedented scope over our basic attitude toward nature.

2 kommentarer:

  1. As I understand it the probability wave collapses when it is observed. But there are other observers than humans, for example other matter. So in the case of the cat it would transfere more or less immediately to the real world, either dead or alive, by the observing other matter (atoms) in the vicinity.

  2. Good point. But I think an observer is supposed to be human in the standard interpretation, which as you say is contradictory.