A Google Doodle today celebrates Erwin Schrödinger, a Nobel Prize winning Austrian quantum physicist, who was born on this date 126 years ago. He is most notably famous for a thought experiment called Schrödinger's cat, depicted in the logo with an alive and dead cat.
The experiment, which is often referred to as a paradox, demonstrates how there was conflict in applying the Copenhagen interpretation of quantum mechanics to every day objects.
Schrödinger explained the experiment:
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.
Schrödinger's cat has been referenced numerous times in pop culture. Below, you can enjoy Sheldon from "The Big Bang Theory" explaining the Schrödinger's cat experiment as a metaphor for Leonard and Penny's relationship: