B What is the reason for Schrodinger's cat experiment?

[steveJOBS]

I'm not sure why schrodinger proposed his cat in a box experiment. Can anyone say why?

 

[AdaggerA]

It illustrates the superposition theorem in quantum mechanics which states that if there are two or more quantum states, then they can be superposed to get a new valid quantum state. So, if a cat can be dead or alive, then the cat being dead and alive is also a possibility.

 

[bhobba]

It was to highlight a problem with quantum theory. The great polymath Von Neumann showed you can place the quantum classical cut pretty much anywhere. Its called the Von Neumann regress and without going into details led him to place it at human consciousness because it was the only place that is different.

Since then we now know a place that is different - just after decoherence so its no longer an issue and Schrodinger's cat is now fully resolved although there are a number of slightly different ways of doing it.

Thanks
Bill

 

[Physics Footnotes]

At the time of its proposal (1935), Bohr was successfully convincing physicists that it was meaningless to dig any deeper into reality than the wave-function allows. Einstein and Schrodinger both thought this to be incorrect, and argued forcefully that there was a true reality under the statistical algorithm of quantum mechanics, even if that algorithm didn't allow us to access to it.

Einstein argued his case publicly using the (also famous) EPR paradox. Einstein's paper motivated Schrodinger to publish his own analysis of the (then) current state of quantum mechanics:

"The appearance of this work [i.e. the EPR paper] motivated the present - shall I say lecture or general confession?"

Whereas Einstein argued that Bohr's view, if correct, would entail 'spooky action at a distance', Schrodinger's paper argued that if the micro-world described by the wave function isn't real and objective, nor is the world of tables, chairs, and .. well.. cats!

"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 naively accepting as valid a 'blurred model' for representing reality."

 

[Nugatory]

It illustrates the superposition theorem in quantum mechanics which states that if there are two or more quantum states, then they can be superposed to get a new valid quantum state. So, if a cat can be dead or alive, then the cat being dead and alive is also a possibility.

Although it does indeed illustrate the superposition principle, Schrodinger's point was that something was wrong with quantum mechanics as it was then (around 1935) understood. The problem is that the dead-alive superposition state in which the cat is neither dead nor alive until we open the box makes no sense and shouldn't be expected to happen - but there was nothing in the current understanding of QM to explain why it didn't. It took another few decades and the discovery of quantum decoherence to resolve this problem.

 

[martinbn]

http://hermes.ffn.ub.es/luisnavarro/nuevo_maletin/Schrodinger_1935_cat.pdf

 

[bluecap]

It was to highlight a problem with quantum theory. The great polymath Von Neumann showed you can place the quantum classical cut pretty much anywhere. Its called the Von Neumann regress and without going into details led him to place it at human consciousness because it was the only place that is different.

Since then we now know a place that is different - just after decoherence so its no longer an issue and Schrodinger's cat is now fully resolved although there are a number of slightly different ways of doing it.

Thanks
Bill

But how come in Many Worlds, the cat can still be both alive and dead at same time?

 

[Nugatory]

But how come in Many Worlds, the cat can still be both alive and dead at same time?

There's still no superposition going on. In some worlds the cat is alive and in other worlds the cat is dead, but no world in which the cat is in the weird "neither alive nor dead until we look" state.

 

[stevendaryl]

There's still no superposition going on. In some worlds the cat is alive and in other worlds the cat is dead, but no world in which the cat is in the weird "neither alive nor dead until we look" state.

This is a distinction that I think a lot of people fail to understand (because it is a little subtle to describe without using math): the distinction between

1. The cat is in a superposition of being alive and being dead.
2. The cat is in a mixture of being alive and being dead.

Using the many-worlds interpretation, this amounts to the distinction between:

1. The cat is in a superposition of being alive and being dead.
2. The world is in a superposition of one with a live cat and one with a dead cat.

There is, basically, no possibility of a superposition of a live cat and a dead cat, because a macroscopic object such as a cat can't be isolated from the rest of the world. So the superposition will rapidly "infect" the rest of the world.

 

[bhobba]

But how come in Many Worlds, the cat can still be both alive and dead at same time?

They are in different worlds.

Thanks
Bill