schrodingers cat?

Question

After the box is closed, the cat is said to be in a state of superposition of |dead> and |alive>. Now the person carrying out the experimnt peep into the box and find that the cat is alive. So, it is said that the act of looking causes the wavefunction of the cat to collapse and, in this case, it collapse to the |alive> state. When the box is closed again, the wave function of the cat starts to smear out and after a while one would say the cat is back to the superposition state of |dead> and |alive> again. Intuitively, this cycle can be repeated over and over again as long as the cat is still alive.

Now, if the person peep into the box and saw the cat dead. It is said that the act of looking caused the state of the cat to collapse to the |dead> state. But if the box is closed back, can one say that the cat is back to the state of |dead> and |alive>? If so, could it be possible that the next time someone peep into the box, the cat is back alive? If not, why is the there an asymmetry?

Answer 1

The purpose of "Schrodinger's Cat" thought experiment is to illustrate the strangeness of quantum mechanics and the mathematics necessary to describe quantum states of sub-atomic systems. The idea of a sub-atomic particle existing in a superposition of possible states, while a fact of quantum mechanics, is a concept that does not scale to large systems (like cats), which are NOT indeterminably probabilistic in nature.

And the reason that large scale systems are not in a superposition of possible states is due to "quantum decoherence", which is the mechanism by which quantum systems interact with their environments to exhibit probabilistically additive behavior - a feature of classical physics - and give the appearance of wavefunction collapse. Decoherence occurs when a system interacts with its environment, or any complex external system, in such a thermodynamically irreversible way that ensures different elements in the quantum superposition of the system+environment's wavefunction can no longer interfere with each other.

This explains why the cat, if having been observed in the |dead> state, would not able to return to a superposition of |alive> and dead> states after closing the box, and certainly could not be obsered in the |alive> state upon re-opening the box.

Answer 2

The issue you have pointed out was later determined to be quantum decoherence. You rightly made the assumption that if we see a dead cat the psi function has collapsed to |dead> and thus the waveform has become localized. We could then argue that when we close the box the waveform will once again delocalize and return to the a linear |A> = a|dead> + b|alive>.

Now, depending on who you argue with, some may say that since the |dead> state was what was initially inquired about, that observing that cat in that state indicates a localization permanently at that state - this is a classical interpretation and we must not fall for it. What has occurred is actually quantum decoherence and it has been experimentally demonstrated that non-isolated system exhibit decoherence (in the case of Schroedinger's Cat, you provide the decoherence). The decoherence occurs due to you entering an isolated system and inquiring about the state of it. See http://prola.aps.org/abstract/prl/v77/i2... for the abstract of the proof of this effect. There is a lot of math for quantum decoherence and it would be difficult to type it out so I encourage you to look for it. The wikipedia article about it is more or less accurate (it misses a few steps).

Answer 3

Putting the alive cat in the box at initial time T is the same as putting in an alive cat at some later time T+k.

The status of the cat is unknown while it is in the box, it could be alive or dead.

If you put a dead cat in the box, you know the cat is still dead at any point afterward.

There is no "smearing out after awhile." The instant the live cat is in the sealed box, it is in the superposition state.

Answer 4

Because until the 'state transition' from |alive> to |dead> occurs, the cat is still in she superposed state since the causative event (forcing the |alive? -> |dead> transition) hasn't happened. However, there is no causative event in the system to force the |dead> -> |alive> transition, hench no probability of it's occurance and no superposition of possible states.

Also.... The 'wave function collapse' model (the Copenhagen interpretation) of QM is rapidly losing ground to the 'Everett Multiple Universe' interpretation.

HTH ☺

Doug

Answer 5

No, because that transition is not allowed. It would require the possibility of time travel into the past, which does not happen (even though some subatomic events are time-reversible).

I hope you're not making the assumption that an observer has to be some conscious entity, like the addled people we call newagers do. An observation is any interaction with the world, mental or mechanical.

Quantum mechanics is weird, but not so weird that it can reverse death - as far as we know.

Answer 6

It's theoretical.
Not to be taken literally.
I'm a dog.
In a suit.

Do you like my suit?