Is the cat alive, dead, both or unknown

[Buzz Bloom]

Hi Derek:

That is an assumption which is only true if the question "is this cat alive?" has to have a yes/no answer.

I disagree that it is an assumption. I see it as a philosophical world view. (Whether it is an assumption or a world view, I think we agree that the question is irrelevant to QM.) I do not believe that a person who is trying to understand the way the world works just makes up assumptions. All their life experiences, e.g., upbringing, education, and hard knocks, creates a framework for them that allows some interpretations about experience to be OK, and others not OK. Whether they would call this collection of interrelated beliefs a philosophy is a matter of the way they have learned to use vocabulary.

"No! No! No!" I hear you cry, "A cat has to be one thing or the other."

I assume we can agree that the question can be focussed on the state of the cat just before the box is opened. For some people, not requiring a yes/no answer about "Is the cat alive?" is OK, and for others it is not. For the nots, it might be neither or both. It depends on their world view.

I think you misunderstood where I am about this. I am flexible in my world view, depending on when collapse occurs. On Saturday or Sunday (interaction), OR on Monday or Tuesaday (detector), I believe state of the particle, either at the interaction or as measured by the detector, causes the cat to be either alive or dead (focussing for clarity on just before the box is opened). On Wednesday and Thursday (mind), I think neither, because the probabilistic superposition state still exists until the collapse caused by a mind seeing the state of the cat when the box is opened. On Wendesday it could be anything, including both, but knowing my inclinations I think both is unlikely.

Thanks for your discussion,
Buzz

 

[rootone]

Buzz, I am sure this has been said before but consider this:
The state of the cat gets to be 'known' by a simple apparatus, (a camera for example, which plainly does not have a mind),
however whatever the camera recorded is not revealed to any conscious observer, it is stored as a digital file.
Some thousands of years later when nobody connected with experiment is still alive, and nobody cares that much, the file is copied millions of times and then made available to millions of observers simultaneously.
Did one of those observers cause a signal to travel back in time and cause the outcome which the camera recorded?, which one?

 

[Buzz Bloom]

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.

The existence of a state that is subject to a well-defined model means we have an understanding about the world as well as a recipe for calculation.

(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.

It is this implication of some sort of realism which leads to paradoxes.

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.

paradoxes arise when we try to square superposition with common-sense which wants states to be all-or-nothing.

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

 

[Buzz Bloom]

Hi rootone:

Did one of those observers cause a signal to travel back in time and cause the outcome which the camera recorded?, which one?

The short anwser is no. Your modified thought experiment (TE) and question raises one of the trickier issues concerning the "mind" point of view (POV) about when collapse of superposition of states occurs. If you choose this POV you must do so consistantly. I think only a few (philosophers?) believe this POV is the "true" view about the way the world works. However, no reverse time causality paradox is necessary. Since this modifed TE implies the box is never opened, so no one ever knows what happened to the cat until a photograph is viewed by a suitable mind, This mind must (by other knowledge) recognize the implication about how the cat died (by poison or by starvation). (It is surely dead at the time of picture viewing. The POV simply interprets that the superposed state of the cat at the time just before the box is opened as remaining the same, way into the future of that time, and the state only collapses when a picture is viewed and properly interpreted. Using this POV, the superposition of states relates only to the probability that someone at some time will discover the fate of the cat as being by poison or starvation. Until that happens since the knowledge is absent and there is no collapse, the state remains superposed.

Now there is another wrinkle. There was an interaction regarding the cat that changed the superposed state, but it did not collapse. The picture taking modifies the reasonable range of interpretation of the probabilities and also of the two superposed states. A later interaction with the cat makes another change. That is: when the box and the cat are cremated, so that it is then impossible for a mind to know the cause of death, unless and until a picture is viewed by a suitable mind.

Another modification to the TE: No pictures are taken, and the box and cat are cremated soon after the particle is emitted. Then it beomes imposible for any mind to ever know the cause of death: by poison or by burning. Then the burnning of the box and cat also changes the superposed state without collapsing it. It never collapses.

I hope this tale helps to clarify the nature of the implications of this POV: the mind is the collapser of suprposed states.

Thanks for your post,
Buzz

 

[Derek Potter]

How can we define an operator or a POVM that would act on the wavefunction of a live virus and spit out "1", and give us "0" for a dead virus?
Likewise for an amoeba or a cat?

Define "live" classically first. Use any criterion you like. For instance, live cats run warm, dead cats go cold. Measure the temperature by detecting thermal photons in a million detectors. Cat is alive if N>100,000, dead if not. The criterion should agree with classical intuition: that N will either be <<100,000 or >>100,000.

 

[Derek Potter]

Hi Derek:
I disagree that it is an assumption. I see it as a philosophical world view. (Whether it is an assumption or a world view, I think we agree that the question is irrelevant to QM.) I do not believe that a person who is trying to understand the way the world works just makes up assumptions. All their life experiences, e.g., upbringing, education, and hard knocks, creates a framework for them that allows some interpretations about experience to be OK, and others not OK. Whether they would call this collection of interrelated beliefs a philosophy is a matter of the way they have learned to use vocabulary.
I assume we can agree that the question can be focussed on the state of the cat just before the box is opened. For some people, not requiring a yes/no answer about "Is the cat alive?" is OK, and for others it is not. For the nots, it might be neither or both. It depends on their world view.

Well it shouldn't do. QM is perfectly clear about the state. Last time I looked, everyday experience did not equip us to deal with superpositions.

I think you misunderstood where I am about this. I am flexible in my world view, depending on when collapse occurs. On Saturday or Sunday (interaction), OR on Monday or Tuesaday (detector), I believe state of the particle, either at the interaction or as measured by the detector, causes the cat to be either alive or dead (focussing for clarity on just before the box is opened). On Wednesday and Thursday (mind), I think neither, because the probabilistic superposition state still exists until the collapse caused by a mind seeing the state of the cat when the box is opened. On Wendesday it could be anything, including both, but knowing my inclinations I think both is unlikely.
Thanks for your discussion,
Buzz

QM does not need collapse of the wavefunction. Talking about the collapse of the wavefunction as if it were a physical process is doubly pernicious - it is not needed and it gets in the way.

I agree with Zeh, who is associated with "Many Minds". In Zeh's interpretation, the wavefunction does not collapse so the observer's brain ends up in a superposition of states. In one state the brain has the sensory data of seeing a dead cat, in the other a live one. Obviously, though perhaps disconcertingly to some, the observer's brain experiences both.

"I never see both!" replies life experience.

"Oh yes you do, but here I am talking to, and you are recalling from, the dead-cat state, not both states. There is, no doubt, another state in which I am talking to, and you are recalling from, the alive-cat state, not both states. As both states exist in the wavefunction I'm afraid it's an inescapable fact unless the Lizard People are messing with our minds again."

 

[Derek Potter]

Buzz, I am sure this has been said before but consider this:
The state of the cat gets to be 'known' by a simple apparatus, (a camera for example, which plainly does not have a mind),
however whatever the camera recorded is not revealed to any conscious observer, it is stored as a digital file.
Some thousands of years later when nobody connected with experiment is still alive, and nobody cares that much, the file is copied millions of times and then made available to millions of observers simultaneously.
Did one of those observers cause a signal to travel back in time and cause the outcome which the camera recorded?, which one?

No. They all did. Only the collapse didn't occur either "back in time" nor when the observers found out. There is one hyper-observer, the composite of a million separate observers. There are 2^1000000 possible outcomes. Various of them were collapsed out of existence at precise intervals according to the digits of pi - in gazillionths of a second - until there was just one left which was actualized on the 19th February 3056, some 1865 years before the observation but 2309 years after the cat died. Nobody knows why nature chose to do it this way.

By the way [hint] people do not always realize when I am being sarcastic. Or that there is (usually) a constructive point behind it.

 

[Buzz Bloom]

Hi Derek:

The discussion seems to me to becoming more and more philosophical. I enjoy it, but it might be more appropriate to move it to a philosophy forum, such as:
http://onlinephilosophyclub.com/forums/ .

QM does not need collapse of the wavefunction. Talking about the collapse of the wavefunction as if it were a physical process is doubly pernicious - it is not needed and it gets in the way.

I agree that "collapse of the wavefunction" is not physics -- it is a philosophical interpretation of QM which may or may not be useful. In this discussion I found it to be useful as a framework for talking about scenarios of a TE.

I agree with Zeh, who is associated with "Many Minds".

As haven't read Zeh, but here is a quote from https://en.wikipedia.org/wiki/Many-minds_interpretation .

The many-minds interpretation of quantum mechanics extends the many-worlds interpretation by proposing that the distinction between worlds should be made at the level of the mind of an individual observer.​

As I interpert this, it seems to require a POV that a conscious mind is necesssary for a transition to occur from a superposed state to a one specifc choice among the possible states. The underlined text is a long-winded way of avoiding saying "collapse". Is that more useful for you?

I do not think Zeh's view is any more useful to me than Everett's many worlds interpretation (MWI). I would prefer not to go into philosophical reasons for my preference, but I prefer a variation of MWI in which the "many worlds" are not "real" but contingent -- a CMWI (contingent many worlds interpretation).

This means that the total instantaneous state of a single real world at any time has a combination of "real" particles with "real" properties which are "real" measurements, together with "real" particles with contingent possible future measurements with specific probabilities that are related to both the present and future times when these measurements might take place. (Whether these contingent possible future states are "real" before they are measured, or not "real", is not relevant to the CMWI.) Each possible combination of future measurements defines a contingent future world. So at any specific time there is one "real" world and (infinitely?) many contingent worlds. When a measurement is made, (infinitely?) many contingent worlds cease to have their contingent existence, since they are no longer compatible with the measurement. When there are interactions among the particles, there are several possible scenarios in which:

(1) new "real" particles are created with possibly some specific properties and some contingent properties
(2) existing "real" particles can cease to exist
(3) the values of both "real" and contingent properties of "real" particles (including their probabilities) are changed.
​

I appologize for the long explanation, but it is the best I can do to make the CMWI POV reasonably clear with relatively few words.

Thanks for your discussion,
Buzz

.

 

[Buzz Bloom]

Hi Derek:

I get from our dialog that in your mind you have a very clear POV about interpreting QM.

I do not have a single clear POV about interpreting QM. I have many. My day-of-the-week style was intented to communicate this concept in a somewhat light-hearted way. I have preferences, but I use different POVs at different times because I find different POVs useful in different contexts. I also believe that it's usefulness is more important that it's truth. I believe this belief is very useful.

I hope you won't interpret what I am about to say as negative -- I don't intend it that way.

I believe that having a single fixed POV about anything, QM, or theology, or anything else, is more harmful than useful. The usefulness of this belief is perhaps more visisble in theology than in choosing a philosophical interpretation about QM, but I believe it applies universally.

Regards,
Buzz

 

[Derek Potter]

Hi Derek:
The discussion seems to me to becoming more and more philosophical. I enjoy it, but it might be more appropriate to move it to a philosophy forum, such as:
http://onlinephilosophyclub.com/forums/

Then I have failed completely. I'm sorry. My intention is to divide up the ideas that attach themselves to interpretation into ideas that are the realm of physics and anything left over for the philosophers to play with.

I agree that "collapse of the wavefunction" is not physics -- it is a philosophical interpretation of QM which may or may not be useful. In this discussion I found it to be useful as a framework for talking about scenarios of a TE.

I don't know who you agree with. The collapse of the wavefunction is pure physics. I do not believe it to be a necessary or useful idea but it is a theory of physics nonetheless.

As haven't read Zeh, but here is a quote from https://en.wikipedia.org/wiki/Many-minds_interpretation .

The many-minds interpretation of quantum mechanics extends the many-worlds interpretation by proposing that the distinction between worlds should be made at the level of the mind of an individual observer.​

As I interpert this, it seems to require a POV that a conscious mind is necesssary for a transition to occur from a superposed state to a one specifc choice among the possible states. The underlined text is a long-winded way of avoiding saying "collapse". Is that more useful for you?

That is almost diametrically opposite to what MW is saying. There is no collapse and there is no "specific choice" in MW. Clue - the word "many"! MM follows from MW by adding the assumption that mind supervenes on the state of the brain. This is in order to get round the Hard Problem. If mind is defined as a "mental state" without implying consciousness (e.g. "the computer thinks you have logged off") then MM is indistinguishable from MW.

I do not think Zeh's view is any more useful to me than Everett's many worlds interpretation (MWI). I would prefer not to go into philosophical reasons for my preference, but I prefer a variation of MWI in which the "many worlds" are not "real" but contingent -- a CMWI (contingent many worlds interpretation).

You can have two levels of reality if you wish but you still have to account for the superselection required to transition from contingent to actual existence.

This means that the total instantaneous state of a single real world at any time has a combination of "real" particles with "real" properties which are "real" measurements, together with "real" particles with contingent possible future measurements with specific probabilities that are related to both the present and future times when these measurements might take place. (Whether these contingent possible future states are "real" before they are measured, or not "real", is not relevant to the CMWI.) Each possible combination of future measurements defines a contingent future world. So at any specific time there is one "real" world and (infinitely?) many contingent worlds. When a measurement is made, (infinitely?) many contingent worlds cease to have their contingent existence, since they are no longer compatible with the measurement. When there are interactions among the particles, there are several possible scenarios in which:

(1) new "real" particles are created with possibly some specific properties and some contingent properties
(2) existing "real" particles can cease to exist
(3) the values of both "real" and contingent properties of "real" particles (including their probabilities) are changed.​

I appologize for the long explanation, but it is the best I can do to make the CMWI POV reasonably clear with relatively few words.

There is a vast amount of physics going on in your scenario with creation and destruction of particles. But what is the maths behind the disappearence of "particles"? QM allows the cancellation of terms in a wavefunction: we call it interference. But how do contingent possibilities interfere? You need negative probabilities! These can be used in QM, but they are a warning flag that you are NOT talking about actual probabilities. Who ever heard of a biased coin coming down heads MINUS 40% or the time and tails 140%? Whoever heard of a negative number of events? Interpreting QM is not just a matter of concocting a picture of branching possibilities and labelling some as real, others as contingent and others as defunct. The picture must be consistent with wave mechanics. Which is why Everretian MW is viable but the branching universe picture is not. It is different physics and wrong. In fact viable MWI doesn't have defined braches: whether a branch subdivides depends entirely on what basis you (the commentator, not the observer) choose. (Basis=set of states that span the state space).

 

[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.