What most people know of Erwin Schrödinger is the cat. In correspondence with Albert Einstein, Schrödinger wrote of an experiment with a cat in a box with a complicated device that had a 50% chance of killing the cat within an hour. According to the theory of quantum superposition, the cat is both dead and alive until the experimenter opened the box to see the condition of the cat. Schrödinger knew quantum mechanics -he won a Nobel Prize in physics for the Schrödinger equation. But he had a problem with quantum superposition, a theory that atoms could exist in more than one state at the same time.
You see, the problem the physicist had with quantum mechanics was that no one knew where its probabilistic effects ended. Why would the life or death of the cat be dependent on our observation? Why would the system care if we observe it or not? Isn’t the cat observing the poison? Who is observing the physicist observing the inside the box? How large could these probabilistic effects be? If it has a limit in its scale, how large is it? How could a system be independent and superpositioned before our observation but then its state be defined only once we observe it? This is a mess to explain because in relative macroscopic terms, everyday objects are not in multiple states until an observer interacts with it. It is therefore illogical that before opening the box, the cat is dead and alive at the same time, and only until you open the box the cat is retroactively dead, if that’s the result observed. This was meant as a direct critique of the Copenhagen interpretation.
Schrödinger never entertained the thought of actually carrying out the experiment, because (beside the cruelty and difficulty) what could possibly be learned about the "unobserved" state? His point was like that of a tree falling in the forest, and the hubris of the observer. Read about the underlying meaning of Schrödinger’s Cat at Today I Found Out.
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