Is the cat alive, dead, both or unknown

[Buzz Bloom]

Hi Derek:

But what is the maths behind the disappearence of "particles"?

I was thinking of an interaction, for example, between an electron and a positron, where both of these particles vanish, and two new particles, photons, are created. I am not sure of how the QM wavefunction math represents this phenomenon, butI don't think that whatever this math representation is will make the CMWI untenable.

Thnaks for your post,
Buzz

 

[Derek Potter]

When I referred to particles, I was picking up on your terminology, which is why I put the word in quotes. I assumed you were referring to interference where a particle, which can reach a location by two different routes, cannot reach it if both routes are available. That means that the two possibilities cancel each other out. However, if you really did mean you want to interpret Schrodinger's Cat in terms of QED, good luck, I cannot imagine how anything like that would work but I know zilch about the subject.

 

[Buzz Bloom]

Hi @Derek Potter :

I assumed you were referring to interference where a particle, which can reach a location by two different routes, cannot reach it if both routes are available.

In my scenario (2) I was thinking of a particle that might be (a) is annihilated with an antiparticle, or (b) is transfomed into a different particle, or (c) just vanishes as other particles are transformed. My scenario (3) includes the phenomenon you mention in the quote above. When a particle interacts with a screen with zero or more splits, it's path probabilities are different than when there is no screen, and also different for different number of splits. That is, the presence of a screen changes the probability state of the particle. But now think about: when does the change happen? In this scenario, naively it seem most logical it happens at the interaction, rather than at the detector or in a mind. However, interpretations are logically possible without paradoxes (although perhaps seen as more awkward) using either of the other two possibilities for when.

Thanks for your post,
Buzz

 

[stevendaryl]

I agree that "collapse of the wavefunction" is not physics -- it is a philosophical interpretation of QM which may or may not be useful.

The "collapse" in the following sense is certainly part of physics, in the sense that it makes testable predictions (and those predictions are verified by experiment):

If a system is described by the state |\psi\rangle, and you measure physical variable A and get the result \alpha, then after the measurement, the system is described by the wave function P_{A, \alpha} |\psi\rangle, where P_{A,\alpha} is the projection onto the subspace of the Hilbert space in which A has eigenvalue \alpha. (There's probably a corresponding statement in terms of density matrices, but I'm not sure what it is). Since measurements are often destructive, this rule really only comes into play with entangled two-component systems such as the EPR experiment. But in those cases, this rule makes testable predictions, and those predictions are verified.

It's a matter of interpretation to say exactly what physically is going on when we apply that rule, but the rule itself seems to be a part of physics.

 

[Buzz Bloom]

Hi stevendaryl:

The "collapse" in the following sense is certainly part of physics, in the sense that it makes testable predictions (and those predictions are verified by experiment):

It's a matter of interpretation to say exactly what physically is going on when we apply that rule, but the rule itself seems to be a part of physics.

Perhaps I miswrote when I agreed with, "collapse of the wavefunction" is not physics" The transtion from a state consisiting of a discrete or continuous probability distibution for a collection of possible future measurements to a singular measured state is certainly an important theorectical/conceptual part of QM physics. The use of the term "collapse" for this transition has had different nuanced meanings/intepretrations since the phrase was originally coined. The choice of a particular meaning/intepretration is philosophical. One dimension of the range of meanings/intepretrations is when the transistion occurs, something I have disccused at length in earlier posts. This choice, an aspect of "collapse" much debated, is also philosophical.

Thanks for your post,
Buzz

 

[Derek Potter]

Hi @Derek Potter :
In my scenario (2) I was thinking of a particle that might be (a) is annihilated with an antiparticle, or (b) is transfomed into a different particle, or (c) just vanishes as other particles are transformed. My scenario (3) includes the phenomenon you mention in the quote above. When a particle interacts with a screen with zero or more splits, it's path probabilities are different than when there is no screen, and also different for different number of splits. That is, the presence of a screen changes the probability state of the particle. But now think about: when does the change happen? In this scenario, naively it seem most logical it happens at the interaction, rather than at the detector or in a mind. However, interpretations are logically possible without paradoxes (although perhaps seen as more awkward) using either of the other two possibilities for when.

Thanks for your post,
Buzz

I don't understand. The change to the probabilities happens when you change the system. That need only be you and me talking about different cases. Why should the fact that different cases have different probabilities be worth mentioning?

 

[Derek Potter]

Hi stevendaryl:
Perhaps I miswrote when I agreed with, "collapse of the wavefunction" is not physics" The transtion from a state consisiting of a discrete or continuous probability distibution for a collection of possible future measurements to a singular measured state is certainly an important theorectical/conceptual part of QM physics. The use of the term "collapse" for this transition has had different nuanced meanings/intepretrations since the phrase was originally coined. The choice of a particular meaning/intepretration is philosophical. One dimension of the range of meanings/intepretrations is when the transistion occurs, something I have disccused at length in earlier posts. This choice, an aspect of "collapse" much debated, is also philosophical.
Thanks for your post,
Buzz

For all events in a scenario, there are two possibilities. Either collapse has occurred or it has not. In every experiment where collapse would be detectable, it fails to manifest itself. Note that the appearence of a probability distribution is not sufficient to demonstrate collapse, indeed QM predicts such appearences, which are called improper mixed states, without collapse. It therefore follows that collapse must occur after all such events if indeed it occurs at all. It must lie in the sandboxed safe area, when all observations have been taken and recorded and collapse can do no harm to the theory. Only here is one free to add collapse for personal philosophical reasons.

If you wish to play that game then there is a philosophical price - you have added something to the model which is contrary to Occam's razor as it explains nothing. Worse that that, the collapse is caused by [insert name of perpetrator here] with precisely no explanation of why it should happen. And worse still, it occurs instantly through the whole universe and is therefore contrary to Einstein causality - i.e. no physical cause is even possible. You may think that a preference for hypotheses which a) are possible b) have explanatory power c) have at least the gist of an explanation, is philosophy, not physics, but I would say the philosophy begins and ends with the realisation that anything else is just a descent into absurdity.

 

[my2cts]

Collapse of wave function is _not_ predicted by the Schrodinger (or Dirac or KG) equation and these equations give a precise account of the physics.
What is happening is the following. The wave function of the detector has to be included in the total wave function.
Possible outcomes of the measurement, assumed mutually exclusive, are described by an orthogonal detector wavefunctions, multiplied with (entangled with) the corresponding, collapsed, eigenfunction of the system to be measured. If the detector part is not taken into account, the wave function of the system to be measured naturally appears to collapse, yet it was already collapsed from the beginning.
Also no interference can occur if such a detector is part of the system, since the wave functions corresponding to different outcomes are mutually orthogonal because of the detector part.
Please refer to this blog post as mytwocts, https://www.physicsforums.com/threa...d-both-or-unknown.819497/page-13#post-5160238, 2015.

 

[Derek Potter]

it was already collapsed from the beginning

?

 

[my2cts]

?

Was already an eigenstate from the beginning.
The complete wave functions is a sum of products of each eigenstate of the system to be measured, collapsed therefore, with the eigenstate of t e detector describing the corresponding detector result.

 

[Evo]

Hi Derek:

I have enjoyed this dialog with you very much, since exploring the philosophy of science (along with the science), has been one of my life-long hobbies. I have found the dialog helpful to my articulating to myself more clearly what my world view is. I think though we are now reaching the point of repetition.

(underlining is mine)

I almost agree with this. I differ regarding the phrase I underlined. I would replace "an understanding" with "many understandings". There are as many undestandings as their are interpretations based on world views. Some of these "understandings are (much?) better suited than others to revise models and design experiments to test the changes.
I almost agree with this also. I would replace "some sort of realism" with "some of the variety of interpretations about what is implied about the real world". Some interpretations immediately lead to paradoxes. Others take a whille until the interpretation leads to a modified model which makes new predictions, and when they produce unexpected results, new intepretations and paradoxes usually arise.
I almost agree with this also. " I would add the word "sometimes" or even "frequently" before "arise". I have found that some "common-sense" is much more deep and/or complex and/or logical than others. To make the statement more true, I would add "naive" after "some". I think I have some common-sense which is not naive, and I don't necessarily want states to be all-or-nothing, especially on Wednesday.

Thanks for your discussion,
Buzz

We don't do philosophy here.

As has been said repeatedly.

That's a common misunderstanding, and illustrates the pitfalls of discussing the philosophical implications of QM without first understanding QM. Schrodinger proposed the thought experiment not because he or anyone else seriously thought that the cat was both dead and alive, but to point out a flaw in the then-current understanding of QM - it didn't say whether the cat was alive or dead. This flaw has been largely corrected during the 75+ years since then.