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Quantum Mechanical Model of the Atom

More exact than the Bohr Model, this model represents atomic energy levels with complex shapes.

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Dead AND Alive

Dead AND Alive

Credit: Laura Guerin
Source: CK-12 Foundation
License: CC BY-NC 3.0

This cat has the probability of being both dead and live at the same time. It is only upon our observation of the cat's state that we able to determine if it is either alive or dead.

Amazing But True

  • Known as Schrodinger's cat, this thought experiment was used to ask when a quantum system stops behaving as a superposition of states. 
  • Erwin Shrodinger's though experiment is as follows: 
    • 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 that 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.
    • It is typical of these cases that an indeterminacy originally restricted to the atomic domain becomes transformed into macroscopic indeterminacy, which can then be resolved by direct observation. That prevents us from so naively accepting as valid a "blurred model" for representing reality. In itself, it would not embody anything unclear or contradictory. There is a difference between a shaky or out-of-focus photograph and a snapshot of clouds and fog banks.
    • —Erwin Schrödinger, Die gegenwärtige Situation in der Quantenmechanik (The present situation in quantum mechanics), Naturwissenschaften (translated by John D. Trimmer in Proceedings of the American Philosophical Society)
  • Learn more about one of the world's most famous cats: 


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Using the information provided above, answer the following questions.

  1. How does the act of the observer looking in the box with the cat affect the probability wave functions?

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    1. [1]^ Credit: Laura Guerin; Source: CK-12 Foundation; License: CC BY-NC 3.0

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