Schrödinger wanted to show that the Copenhagen Interpretation can lead to absurd situations. He came up with a thought experiment to demonstrate this. A thought experiment is used to explore and debate the consequences of a theory, without the intention of actually doing the experiment.
In Schrödinger’s cat, a cat is placed in a sealed box with a vial of poison. The poison is positioned under a hammer and the hammer is attached to a trigger. A Geiger counter (detects radioactivity) is attached to the trigger. Inside the box there is also a radioactive particle, which has a 50% chance of emitting radiation during an hour. If the radioactive particle releasing its radiation this will be detected by the Geiger counter, the hammer will fall, smashing the poison vial and killing the cat. At the end of the hour, the cat can be thought of as both alive and dead simultaneously as there is an equal chance that vial is intact or has smashed, killing the cat. Once we open the box and observe the cat it ceases to be both alive and dead simultaneously and becomes either one or the other. Schrödinger intended to demonstrate that many quantum physics principles do not apply to large objects.