Explain the Schrödinger's cat theory in layman's terms?

Question

I'm kinda confused. Exactly how does the whole principle work? How can the cat be both simultaneously alive and dead? And exactly what is the reasoning behind the idea? And why was the theory even thought up in the first place?

Answer 1

1. It's not a theory, it's a thought experiment or a paradox.



2. A cat is in a box with a geiger counter connected to a vat of poison in the presence of a radioactive source. If a decay event occurs, the geiger counter detects it, releases the poison and the cat dies. Otherwise, the cat remains alive.



3. The paradox comes in when considering the mathematical description of the system using the formalism of quantum mechanics, which by definition cannot be described in layman's terms. The point is that due to the inherent randomness of the atomic decay process, the wavefunction describing the system has terms representing the live cat and the dead cat, weighted by some probability. Until the cat is observed, its mathematical description will involve a superposition (linear sum) of terms describing the cat in a living and a dead state. However, once the cat is observed, the system will resolve into one state or the other - you obviously cannot observe a half-dead cat. So the question is: At what point, if any, does a quantum-mechanical system that is initially in a superposition of states collapse into a single observed state?



4. Schrodinger formulated this paradox in order to shake up the Copenhagen interpretation of quantum mechanics, which was the dominant interpretation at the time.



5. This whole scenario is based on a naive understanding of quantum mechanics, so don't lose too much sleep over it.

Answer 2

I agree with final destination, but I'm not quite sure his answer falls into the category of "layman's terms", so let me give it a shot. In quantum physics, you are allowed to have states that are superpositions of other states. A superposition means that it is both states at once. So you can have a particle being spin up and spin down at the same time, or an electron existing and not existing at the same time. Or, Schrodinger's cat can be alive and dead. When a system is in a superposition, it evolves in time differently than it would if it were in just one of the states (which gives rise to interference in the double slit experiment). But when you measure a state in a superposition, the state collapses into just one of the two (or more) possible states in the superposition. From that point on, it evolves as if it were only in the state it collapsed into, instead of in both states. So simply measuring a system causes it to completely change behavior. As long as it remains unmeasured, the system will continue to evolve as a superposition. So the problem is, how could a system know whether or not you measured it. Somehow, the observer, who has no control over the system and isn't even directly touching the system, can completely change the dynamics by simply looking at it. This leads to lots of problems. How can you interpret such an odd behavior? Some people would think that the system was never in a superposition, it was just that you didn't know what state it was in. Others think that the observer really does has some role to play in the dynamics, but there are many ideas as to what exactly the nature of that role is. And a further issue is that this weird behavior is only seen on small scales. Schrodinger's cat is a paradox where an atom, which can easily be in a superposition, is put into a detector, so that if it decays, a cat gets poisoned and if it doesn't decay, the cat is fine. When the atom is in a superposition of 'decaying' and 'not decaying', the cat should be in a superposition of 'dead' and 'not dead'. But we never come across large scale superpositions like live/dead cat, while we come across superpositions of a decayed/not decayed atom all the time. Why the discrepancy in size scales? The answer is not straight forward and this is an open question in physics.

Answer 3

Obviously, a cat can't be alive and dead at the same time.

But do you get that you can't know until you open the box? its kind of like if a tree falls in a forest and there is nobody to hear it, does it make a sound.

Basically, its a bad analogy to describe how we can never know two things about a sub-atomic particle at once, since by observing it we are changing its natural state ect.