I Schrodinger's cat, the multiverse and isolated systems

[quantumfunction]

That's impossible.

Cats can not be in a superposition of alive/dead. For example to be alive it must breath air that quickly decoheres it. The differences in the processes going on in a live and dead cat are such that its impossible for them to be in superposition any more than you can be in a superposition with the person next to you in a checkout line. This is the efficiency of a measurement device issue - some macroscopic states due to their nature will give unambiguous results - a live and dead cat is one of those - like a 1 or 0 appearing on a computer screen.

Thanks

It's not impossible if the system is isolated. You're looking at it as if the Cat has an object classical existence separate from the isolated system. The observable states of the isolated system just have a wave function that's essentially zero. There isn't any evidence that these observable states of an isolated system just vanish and that's why you have these debates between people like Tegmark, Penrose and Deutsch.

 

[bhobba]

All isolated systems evolve according to the Schrodinger's equation.

Yes - but that does not stop mixed states appearing. The interpretation is the mixed state is a proper mixed state. That's the interpretive assumption so we actually get outcomes. Without that, or a similar assumption, outcomes are not possible.

Thanks
Bill

 

[bhobba]

It's not impossible if the system is isolated

It doesn't matter how you cut and dry it there is no way for a cat to be in a superposition of alive and dead - its impossible.

Thanks
Bill

 

[quantumfunction]

Yes - but that does not stop mixed states appearing. The interpretation is the mixed state is a proper mixed state. That's the interpretive assumption so we actually get outcomes. Without that, or a similar assumption, outcomes are not possible.

Thanks
Bill

It's an assumption based on the fact that we don't have any evidence of that there's anything external to the universe. If there's some evidence that shows this I would like to see it. So yes, if the hypothetical box is an isolated system then both live cat/dead cat exist in the box. In this case the box is the universe. If the universe can never be observed (externally) then you have a superposition of states including live cat/dead cat.

 

[bhobba]

It's an assumption based on the fact that we don't have any evidence of that there's anything external to the universe.

Its got nothing to do with that. Its got to do with the physical nature of live and dead cats. A live cat wanders around, has a heart pumping etc etc. A dead cat just lies there - dead. They are both decohered by their environment to have those classical properties - they can't be in superposition any more than the two end points on a line can be in superposition - its impossible by the definition of what a line is.

Thanks
Bill

 

[quantumfunction]

Its got nothing to do with that. Its got to do with the physical nature of live and dead cats. A live cat wanders around, has a heart pumping etc etc. A dead cat just lies there - dead. They are both decohered by their environment to have those classical properties - they can't be in superposition any more than the two end points on a line can be in superposition - its impossible by the definition of what a line is.

Thanks
Bill

Again, they both decohered by their environments because they're not isolated from their environment. Their still observable states of an isolated system. The way you described it in an older post is exactly what I'm saying. You said:

In MW an observation does nothing - everything keeps evolving as is but each outcome is considered a world. Its very very neat mathematically and extremely beautiful - but not to everyone's taste so to speak.

Actually the beauty and allure of MW is no collapse occurs. Everything just keeps evolving - but after decoherence occurs the system is in a mixed state that is the sum of the possible outcomes. Noting at all happens - the universe keeps on evolving - but is now able to be conceptually separated into a number of 'parts' where each part is the outcome of the observation and considered a separate world.

Thanks
Bill

This is what I'm saying but maybe you're still doubt these issues. I agree it's extremely beautiful and you don't run into some of the same problems that a lot of other interpretations run into. So again, you can't think of the live cat/dead cat as two separate classical environments but two environments that exist because their observable states of an isolated system.

Here's an older video of Sean Carroll explaining why he favors MWI and he says some of the same things I'm saying here.

 

[bhobba]

The way you described it in an older post is exactly what I'm saying.

You are not understanding what I said which is different to what you said.

In any interpretation the cat is never in a superposition. The system - cat and particle are entangled so by construction the cat not be in superposition.

Here is the math. The cat can be in two states |a> - alive |d> for dead. The particle is in two states |pn> - particle not detected and |pd> - particle detected. Now due to the setup the cat is alive if the particle is not detected and dead if it is. We will for simplicity assume it is 50-50 which happens. The system is in the entangled state 1/√2 |pd>|d> + 1/√2 |pn>|a>. Because of the entanglement the cat can't be in a pure state hence can't be in a superposition. Only pure states can be in a superposition. It turns out the cat is in the mixed state 1/2|pd><pd| + 1/2 |pa><pa|.

The above is independent of interpretation. In MW each part of the mixed state |pd><pd| and |pa><pa| are interpreted as a separate world so the superposition 1/√2 |pd>|d> + 1/√2 |pn>|a> remains intact. In ignorance ensemble it is interpreted as a proper mixed state so the cat is either alive or dead. What happens there to the original superposition is slightly more complicated but can't be distinguished from the MW version.

Sean Carroll beieves in many worlds - I don't - big deal. Neither do a number of people in the following discussion:


As far as interpretations go none is better than the other.

Thanks
Bill

 

[bahamagreen]

Is there a QM interpretation that formally ascribes that the past is strictly counterfactual definite?

 

[bhobba]

Is there a QM interpretation that formally ascribes that the past is strictly counterfactual definite?

It obviously is. In QM we can always speak with definiteness about observations that occurred in the past.

Thanks
Bill

 

[bahamagreen]

What if when you open the box you observe that it is empty with neither mechanism nor cat...?
If what a past record of observation entails about the present is in conflict with a present observation, do we not take the present observation over the past record?
Maybe I'm using the wrong term. QM seems to be classically acausal and nondynamical... if a present observation is a primitive of theory, it seems the present observation of the record of an alleged past observation would be a primitive, but the object of that present observation (the record of the past observation) might not hold the same warrant with respect to the present.

 

[bhobba]

What if when you open the box you observe that it is empty with neither mechanism nor cat...?
.

With the setup that's impossible.

Thanks
Bill

 

[Dale]

Closed pending moderation.

Edit: This thread will remain closed.