Questions re Cramer's Transactional Interpretation?

[rkastner]

Hello Forum Users,

I am currently writing up a general discussion of John Cramer's Transactional
Interpretation (TI) , intended to address questions, confusions, or concerns about TI.

I have noticed occasional comments here and there regarding TI on this forum,
both pro and con. I would be interested in hearing from you (in this thread) if you have
such questions, which will be helpful to me in addressing them and in clearing up any
misconceptions about TI. I can't promise to answer all (or even most) posts but will still
appreciate the input.

Many thanks,
Ruth E. Kastner
UMCP Foundations of Physics Group

 

[Demystifier]

Is the wave function everything that exists?
Does wave function allways obey the Schrodinger equation?
If not, what causes the breakdown of the Schrodinger equation? How this breakdown is described mathematically?
If yes, then why there is an appearance of the wave function collapse?

 

[Dmitry67]

While TI makes understanding of some things (like Bell) easier, TI is one of the collapse interpretations. And I guess collapse is like Luminiferous Ether now.

 

[cesiumfrog]

TI is one of the collapse interpretations.

I never fully understood TI: it seemed to be fixing realism at the beginning and end of the universe/experiment, but still leaving everything between in a giant wave-superposition (as to still want MWI there anyway). Is this mistaken?

Has TI proven a fruitful way of looking at the world, in terms of new research? (The pop' science journalism hasn't picked up on much other than that attempt at superluminal communication..)

 

[rkastner]

(1) Is the wave function everything that exists?
(2) Does wave function allways obey the Schrodinger equation?
If not, what causes the breakdown of the Schrodinger equation? How this breakdown is described mathematically?
(3)If yes, then why there is an appearance of the wave function collapse?

My reply:
(1) Not exactly. In TI, what exists are (i) offer waves (OW) and (ii) confirmation waves (CW). OW are represented mathematically by state vectors in Hilbert Space ('kets'). CW are represented by dual vectors ('bras') in a dual H. S. Under Possibilist TI ('PTI'), these are viewed as physically real possibilities. When a transaction occurs between a particular OW and CW, the result is an actualized outcome. So there are two levels of reality: possible and actual.

(2) Not in the sense that there is nothing going on but unitary evolution. An OW is described by the Sch Eqn until it is absorbed. The absorber(s) emit CW which obey the complex conjugate Sch Eqn. A transaction may then form between the emitter and one of the absorbers. The formation of the transaction is an a-spatiotemporal 'collapse' and is not desribed by the Sch Eqn: it is discontinuous and stochastic. There is no 'breakdown' of the Sch Eqn, it's just that it applies to the propagation of the OW and CW (the latter in c.c. form) and not to the formation of the transaction which, by its nature, is discontinuous. The probabilistic weight of the transaction is described by the Born Rule which describes the amplitude of the CW at the locus of the emitter. I sense in your question a desire to have a complete mathematical description, so if you think this is not complete enough even given the discontinuous nature of the transaction, I'd be interested in knowing what else you're looking for in a mathematical description.

(3) there is a collapse but it does not occur within spacetime. In PTI (my possibilist variant of TI), spacetime is viewed as emergent and not as a substantive 'container' for events. It is an epiphenomenon of dynamical process (OW, CW, and transactions).

 

[rkastner]

While TI makes understanding of some things (like Bell) easier, TI is one of the collapse interpretations. And I guess collapse is like Luminiferous Ether now.

Not at all. The problem with collapse has been that is has traditionally been seen as observer-dependent, which brings in "consciousness" and ill-defined use of the term 'measurement'; at what point is the 'measurement' really finished? etc.etc. TI avoids all of this because the collapses are not observer-dependent, they are only absorber-dependent. You don't need a 'conscious observer' or a 'rational observer' or any of those things. All you need is an emitter and one or more absorbers and stuff can happen.

There is currently an interpretation getting serious consideration in the literature which employs an ad hoc modification of qm, called the 'GRW theory,' which puts in collapse 'by hand' by adding a nonlinear term to the Sch Eq. So collapse is very much with us, and it's important to pick an interpretation that describes collapse in a natural way, not in terms of an ad hoc modification to a perfectly good theory (qm).

 

[rkastner]

I never fully understood TI: it seemed to be fixing realism at the beginning and end of the universe/experiment, but still leaving everything between in a giant wave-superposition (as to still want MWI there anyway). Is this mistaken?

Has TI proven a fruitful way of looking at the world, in terms of new research? (The pop' science journalism hasn't picked up on much other than that attempt at superluminal communication..)

See my other answers; this may address your first question. In particular, it is thoroughly realist but it's realism about possibilities. Also, it greatly differs from MWI in that, as noted above, there are transactions, and therefore determinate states of affairs in a single universe, any time an emitter has one or more absorbers available.

An emphatic YES to your second question, although TI is an interpretation of QM, not a new theory, and as such should not be required to generate novel predictions. However, it can shed light on conceptually confusing experiments. See, e.g. my discussion of the bizarre "quantum liar experiment": http://arxiv.org/abs/0906.1626

Also, to all of you with questions, I have posted some recent papers comparing TI with Many-Worlds (Everettian) interps. and with the GRW ad hoc 'collapse' theory, at
arxiv.org (they appear as items 2 and 3 in this list):
http://arxiv.org/find/quant-ph/1/au:+kastner_R/0/1/0/all/0/1

 

[rkastner]

Thanks, I appreciate your questions! Feel free to follow up if you're still skeptical or confused.

 

[Demystifier]

Not at all. The problem with collapse has been that is has traditionally been seen as observer-dependent, which brings in "consciousness" and ill-defined use of the term 'measurement'; at what point is the 'measurement' really finished? etc.etc. TI avoids all of this because the collapses are not observer-dependent, they are only absorber-dependent. You don't need a 'conscious observer' or a 'rational observer' or any of those things. All you need is an emitter and one or more absorbers and stuff can happen.

So basically, TI replaces observers by emitters and absorbers. However, the physical nature of emitters and absorbers remains obscure. Is that correct? Or is there a mathematical theory/model/description of emitters and absorbers?

 

[Frame Dragger]

I think Dirac was right, and QM is a provisional theory (as Roger Penrose also believes), useful for (possibly) a very long time, but by no means a correct description of nature. I really believe that trying to find an Interpretation is pointless. We have two partial descriptions of nature (GR/QM), and both are useful. I think that a lot of what is happening now, ESPECIALLY with Renormalization, is just mathematical tinkering with no hope of experimental evidence. That isn't physics, which is an exploration of the physical world. Instrumentalism is the only sane response (as we can hardly discount many of the predictions of QM or GR), and having been on these forums has only hardened my stance.

I think the TI is fascinating, but in the end I think it's an attempt to solve a problem that isn't there. I don't know what the solution to apparent wavefunction collapse will be, but I'd bet it will be with a new theory that is novel in the manner of SR/GR. I don't claim that this is anything but my opinion, for the record.

 

[Dmitry67]

So basically, TI replaces observers by emitters and absorbers. However, the physical nature of emitters and absorbers remains obscure. Is that correct? Or is there a mathematical theory/model/description of emitters and absorbers?

'emitters' and 'absorbers' in TI are equivalent to measurement devices. For example, metal which reflects light (mirror) is NOT an absorber while the same metal in photoelectric effect IS an absorber :) The same scent of 'pure magic' as in CI :)

 

[Fredrik]

An emphatic YES to your second question, although TI is an interpretation of QM, not a new theory, and as such should not be required to generate novel predictions.

Unfortunately different people seem to mean different things when they say "interpretation of QM". I started out assuming that it always refers to an attempt to turn the theory defined by the standard axioms of QM into a "description of what actually happens" to the physical system (instead of just a set of rules that tells us how to calculate probabilities of possible results of experiments). But when I started reading articles about the MWI, I found that those guys have something else in mind. They are actually trying to change the axioms (by removing the Born rule), so they're not trying to interpret QM (as defined by those axioms) at all. They're trying to reinterpret the underlying mathematical structure. (I consider a theory to be defined by its axioms, so I would say that they were trying to find a different but equivalent theory. I would also say that they did it really badly and failed miserably. I believe there is an MWI that makes sense, but it's an interpretation of the first kind I mentioned, an interpretation of the theory rather than a reinterpretation of the mathematics).

I have also found that people who talk about interpretations of QM very often don't bother to make their "interpretations" well-defined. They don't write down a set of axioms that are meant to turn the "set of rules that tells us how to calculate probabilities of possibilities" into a description of the real world. Instead they just make a bunch of loosely stated remarks about what sort of things they think are actually happening.

And occasionally you run into someone who wants to tell you their "interpretation of QM" and then proceeds to tell you their ideas about what sort of theory might describe the reality underlying QM.

Of these four different things that people can mean by "interpretation of QM", I think only the first two deserve to be taken seriously. Of course, an interpretation of the third kind ("a bunch of loosely stated remarks") can sometimes be an intermediate step towards an actual interpretation.

My concern is that the "transactional interpretation" is still just an interpretation in that third sense, i.e. that it's not really an interpretation at all, but just a collection of ideas about how to make an interpretation. Now, I'll be the first to admit that this could be due to my ignorance about the TI. I haven't even read Cramer's original paper. But a quick glance at it reveals that it's really short and contains very little mathematics. So I find it hard to believe that it successfully defines something that I would consider an interpretation.

I'd be interested in hearing your thoughts on this. If I choose to read articles on the TI, will I find a bunch of comments about how there might exist some sort of waves going this way and that way, or will I find precise statements that identify the specific pieces of mathematics in standard QM that represent these waves? Does it include an axiom that tells us how to make that identification in all experiments, or is the identification done for one experiment at a time? Does the TI change any of the standard axioms of QM?

 

[Demystifier]

Of these four different things that people can mean by "interpretation of QM", I think only the first two deserve to be taken seriously.

I agree with that.

My concern is that the "transactional interpretation" is still just an interpretation in that third sense, i.e. that it's not really an interpretation at all, but just a collection of ideas about how to make an interpretation.

Yes, that's my impression too.

 

[Frame Dragger]

If I choose to read articles on the TI, will I find a bunch of comments about how there might exist some sort of waves going this way and that way?...

Yes.

or will I find precise statements that identify the specific pieces of mathematics in standard QM that represent these waves? Does it include an axiom that tells us how to make that identification in all experiments, or is the identification done for one experiment at a time? Does the TI change any of the standard axioms of QM?

No.


And that's that!

 

[Dmitry67]

One interesting issue with TI is that you can point light beam into black depth of cosmos, and as our Universe is expanding and is less and less dense, that light would never find an absorber!

 

[rkastner]

So basically, TI replaces observers by emitters and absorbers. However, the physical nature of emitters and absorbers remains obscure. Is that correct? Or is there a mathematical theory/model/description of emitters and absorbers?

An emitter is just another dynamical object, and as such is also described by quantum theory. E.g., you can have an offer wave as an emitter: an OW for an electron can emit an OW for a photon, and another electron OW can act as an absorber for that photon. So it would be incorrect to think that emitters and absorbers are undefined or primitive, as is the case with an "observer".

 

[rkastner]

I think Dirac was right, and QM is a provisional theory (as Roger Penrose also believes), useful for (possibly) a very long time, but by no means a correct description of nature.

What would be the basis for such a belief?

I really believe that trying to find an Interpretation is pointless.

Might this be because the current mainstream interpretations are inadequate?

We have two partial descriptions of nature (GR/QM), and both are useful. I think that a lot of what is happening now, ESPECIALLY with Renormalization, is just mathematical tinkering with no hope of experimental evidence. That isn't physics, which is an exploration of the physical world. Instrumentalism is the only sane response (as we can hardly discount many of the predictions of QM or GR), and having been on these forums has only hardened my stance.

One can agree that there is a lot of suspect ad hoc tinkering without resorting
to instrumentalism, which is an abdication of the motivating spirit of scientific inquiry. One can just as easily try to find a deeper, more valid interpretation that vitiates the need for any ad hoc tinkering.

I think the TI is fascinating, but in the end I think it's an attempt to solve a problem that isn't there.

You have already alluded to a problem in your concern about the tinkering, and there is also the demonstrably unsatisfactory nature of most prevailing interpretations. Why reject
a possible solution?

I don't know what the solution to apparent wavefunction collapse will be, but I'd bet it will be with a new theory that is novel in the manner of SR/GR. I don't claim that this is anything but my opinion, for the record.

TI is a good solution for wf collapse, since it describes all physical processes by qm and provides for collapse without reference to an observer. Until TI has been given fair consideration, there is no reason for us to throw up our hands and give up on understanding what qm might be telling us about reality.

 

[rkastner]

'emitters' and 'absorbers' in TI are equivalent to measurement devices. For example, metal which reflects light (mirror) is NOT an absorber while the same metal in photoelectric effect IS an absorber :) The same scent of 'pure magic' as in CI :)

If you mean to suggest that emitters and absorbers are arbitrary or primitive in TI, this is not the case. The reflecting action of a mirror under TI can be modeled just the same as in standard qm , in which the quantum state (OW under TI) undergoes reflection due to an infinite potential barrier. Alternatively, if you want to take into account the specific interaction with the metal, the mirror is an absorber that generates a new OW identical with the one received by it. Thus there is a fully consistent account of emitters and absorbers as quantum objects, and there is no 'magic' involved. The photoelectric effect is not the same phenomenon as perfect reflection from a mirror even in standard qm, (the metal ejects an electron, not an incoming photon beam), so it wouldn't be appropriate to expect that they should be treated the same by a qm interpretation. But thank you for this example, I may want to include it in my presentation in order to help make the distinction.

 

[rkastner]

Unfortunately different people seem to mean different things when they say "interpretation of QM". I started out assuming that it always refers to an attempt to turn the theory defined by the standard axioms of QM into a "description of what actually happens" to the physical system (instead of just a set of rules that tells us how to calculate probabilities of possible results of experiments). But when I started reading articles about the MWI, I found that those guys have something else in mind. They are actually trying to change the axioms (by removing the Born rule), so they're not trying to interpret QM (as defined by those axioms) at all. They're trying to reinterpret the underlying mathematical structure. (I consider a theory to be defined by its axioms, so I would say that they were trying to find a different but equivalent theory. I would also say that they did it really badly and failed miserably. I believe there is an MWI that makes sense, but it's an interpretation of the first kind I mentioned, an interpretation of the theory rather than a reinterpretation of the mathematics).

I agree that Everettian (MWI) approaches neglect the Born Rule and that it is
a very important component of the theory. That's a major reason for my advocacy of TI.

I have also found that people who talk about interpretations of QM very often don't bother to make their "interpretations" well-defined. They don't write down a set of axioms that are meant to turn the "set of rules that tells us how to calculate probabilities of possibilities" into a description of the real world. Instead they just make a bunch of loosely stated remarks about what sort of things they think are actually happening.

And occasionally you run into someone who wants to tell you their "interpretation of QM" and then proceeds to tell you their ideas about what sort of theory might describe the reality underlying QM.

Of these four different things that people can mean by "interpretation of QM", I think only the first two deserve to be taken seriously. Of course, an interpretation of the third kind ("a bunch of loosely stated remarks") can sometimes be an intermediate step towards an actual interpretation.

My concern is that the "transactional interpretation" is still just an interpretation in that third sense, i.e. that it's not really an interpretation at all, but just a collection of ideas about how to make an interpretation. Now, I'll be the first to admit that this could be due to my ignorance about the TI. I haven't even read Cramer's original paper. But a quick glance at it reveals that it's really short and contains very little mathematics. So I find it hard to believe that it successfully defines something that I would consider an interpretation.

I'd be interested in hearing your thoughts on this. If I choose to read articles on the TI, will I find a bunch of comments about how there might exist some sort of waves going this way and that way, or will I find precise statements that identify the specific pieces of mathematics in standard QM that represent these waves? Does it include an axiom that tells us how to make that identification in all experiments, or is the identification done for one experiment at a time? Does the TI change any of the standard axioms of QM?

I'm not sure what paper you read by Cramer, but his main TI paper was in 1986 and
appears here:

http://www.npl.washington.edu/ti/

and this is quite a long, and well-written, paper with mathematical, physical, and philosophical details. I would strongly urge you (or anyone else!) to read this before going with any initial impression that TI is somehow not rigorous. TI's identifications between theoretical terms in qm and the ontological entities (OW and CW) are clearly specified for general cases, not just for individual ones, although some specific examples are given to illustrate the principles. So yes, you will find specifics in that paper and it is a rigorous interpretation, not a hand-waving one as you suggest here. It preserves the basic axioms of qm, giving them a physical interpretation. There are also specifics in my arxiv papers on TI, for which a link was provided above. So again, I would urge Forum participants to read the relevant papers before arriving at opinions about TI--is it really fair to think poorly of any interpretation if one has not read the specifics about what it says and how it is applied?

One caveat--in 1986, Cramer still thought of qm OW as 'physically present in space'
and he no longer holds that view in the sense that multi-particle OW are 'too big'
to fit in ordinary spacetime. We both agree that quantum entities such as OW
and CW represent physically real possibilities which transcend spacetime and should be thought of as existing in a 'larger space' described by Hilbert Space. This variant of TI is called PTI.

Of course, I'm happy to address any criticisms or confusions arising from those papers.

 

[rkastner]

I agree with that.


Yes, that's my impression too.

Have you read

http://www.npl.washington.edu/ti/

before arriving at this impression?

 

[rkastner]

Yes.



No.


And that's that!

These comments are not accurate; see my replies above.

Have any of you making the negative comments actually read Cramer's paper?

http://www.npl.washington.edu/ti/

 

[rkastner]

One interesting issue with TI is that you can point light beam into black depth of cosmos, and as our Universe is expanding and is less and less dense, that light would never find an absorber!

yes, and the same is true of standard qm. An OW finding no absorber would not result in a transaction, just as a 'wave function' not being detected would never give rise to an outcome.

 

[Frame Dragger]

An emitter is just another dynamical object, and as such is also described by quantum theory. E.g., you can have an offer wave as an emitter: an OW for an electron can emit an OW for a photon, and another electron OW can act as an absorber for that photon. So it would be incorrect to think that emitters and absorbers are undefined or primitive, as is the case with an "observer".

Good point. They're modestly well defined and primitive.

 

[rkastner]

Good point. They're modestly well defined and primitive.

Frame Dragger, care to explain what you have in mind by this comment? I don't know what "modestly well defined and primitive" means.

 

[ytuab]

I agree that Everettian (MWI) approaches neglect the Born Rule and that it is
a very important component of the theory. That's a major reason for my advocacy of TI.

I'm not sure what paper you read by Cramer, but his main TI paper was in 1986 and
appears here:

http://www.npl.washington.edu/ti/

and this is quite a long, and well-written, paper with mathematical, physical, and philosophical details. I would strongly urge you (or anyone else!) to read this before going with any initial impression that TI is somehow not rigorous. TI's identifications between theoretical terms in qm and the ontological entities (OW and CW) are clearly specified for general cases, not just for individual ones, although some specific examples are given to illustrate the principles. So yes, you will find specifics in that paper and it is a rigorous interpretation, not a hand-waving one as you suggest here. It preserves the basic axioms of qm, giving them a physical interpretation. There are also specifics in my arxiv papers on TI, for which a link was provided above. So again, I would urge Forum participants to read the relevant papers before arriving at opinions about TI--is it really fair to think poorly of any interpretation if one has not read the specifics about what it says and how it is applied?

One caveat--in 1986, Cramer still thought of qm OW as 'physically present in space'
and he no longer holds that view in the sense that multi-particle OW are 'too big'
to fit in ordinary spacetime. We both agree that quantum entities such as OW
and CW represent physically real possibilities which transcend spacetime and should be thought of as existing in a 'larger space' described by Hilbert Space. This variant of TI is called PTI.

Of course, I'm happy to address any criticisms or confusions arising from those papers.

It's interesting. But the site you state here is explaining what the spin1/2 actually is?

The spinning electrons return by the two rotations (not one rotation.) It cann't be explained by the real wave.

-------------------------
The TI permits quantum mechanical wave functions to be interpreted as real waves physically present in space rather than as "mathematical representations of knowledge" as in the CI.
-----------------------

Is it really so? I wonder why everyone involved in the interpretation avoid the spin 1/2.

 

[rkastner]

It's interesting. But the site you state here is explaining what the spin1/2 actually is?

The spinning electrons return by the two rotations (not one rotation.) It cann't be explained by the real wave.

-------------------------
The TI permits quantum mechanical wave functions to be interpreted as real waves physically present in space rather than as "mathematical representations of knowledge" as in the CI.
-----------------------

Is it really so? I wonder why everyone involved in the interpretation avoid the spin 1/2.

Wonderful question. TI's reply would be that fermions are described by the Dirac wave equation and their spin does not take place in ordinary spacetime. Under PTI, quantum objects are possibilities whose realm of existence is described by Hilbert Space, which includes room for half-integral spin. You are right to point out that spin 1/2 cannot be pictured as happening in ordinary spacetime. That is why we need a 'higher space of possiblities' to describe quantum objects. Let me clarify that Cramer does not think of offer and confirmation waves as propagating in ordinary space, at this time. So his views on that have changed since his 1986 paper.

 

[cesiumfrog]

In particular, it is thoroughly realist but it's realism about possibilities. Also, it greatly differs from MWI in that, as noted above, there are transactions, and therefore determinate states of affairs in a single universe, any time an emitter has one or more absorbers available.

So according to TI, there are never superpositions? For example, in a two-slit interference experiment (or even a DCQE experiment), you're saying every individual photon really did travel through just one in particular of the two slits (even though still it is frequently impossible even in principle to know which), and that the interference pattern occurs because the real trajectory of the photon (from source/collimator to detector/screen) is arbitrated (perhaps one would say "piloted") by the ferment of the transaction waves (although these waves perhaps do not propagate in the same spacetime as the particles all do)? Is that right?

Also, how is QFT understood wrt TI?

 

[rkastner]

So according to TI, there are never superpositions? For example, in a two-slit interference experiment (or even a DCQE experiment), you're saying every individual photon really did travel through just one in particular of the two slits (even though still it is frequently impossible even in principle to know which), and that the interference pattern occurs because the real trajectory of the photon (from source/collimator to detector/screen) is arbitrated (perhaps one would say "piloted") by the ferment of the transaction waves (although these waves perhaps do not propagate in the same spacetime as the particles all do)? Is that right?

Also, how is QFT understood wrt TI?

I'm afraid you've misunderstood. There *are* superpositions in that the OW and CW corresponding to a *single photon* can be, and frequently are, superposed. In a two-slit experiment, the OW for a single photon goes through both slits, and CW from all possible detectors return through both slits. The detection of a photon at a particular location corresponds to a transaction between the absorber at that location and the emitter. I don't know what you mean by "ferment of transaction waves--there are no 'transaction waves' (a transaction is an atemporal 'collapse' of OW and CW overlaps) and there are no pilot waves. I think you're confusing this with the Bohmian theory.

TI has not yet been explicitly extended into QFT, which is not really a 'theory' but a set of techniques for handling relativistic situations. But TI is already intrinsically relativistic, which you will see if you read Cramer's 1986 paper. TI can be straightforwardly applied to relativistic situations through relativistic wave eqns. Also, this is speculative thus far, but since amplitudes must be squared in QFT to achieve empirical probabilities, those can probably be interpreted in terms of OW and CW as well.

 

[rkastner]

Dear thread participants:

Thanks for your questions and comments thus far. I'd like to emphasize the importance of reading (at the very least) Cramer's 1986 before forming an opinion or attitude towards TI. If you have a specific question about, or criticism of, something in that or any other paper on TI, I'll try to address it. I can't address general comments that don't engage with actual published content concerning TI. Thanks for your understanding.Ruth Kastner

 

[cesiumfrog]

I'm afraid you've misunderstood. There *are* superpositions in that the OW and CW corresponding to a *single photon* can be, and frequently are, superposed. In a two-slit experiment, the OW for a single photon goes through both slits, and CW from all possible detectors return through both slits. The detection of a photon at a particular location corresponds to a transaction between the absorber at that location and the emitter. I don't know what you mean by "ferment of transaction waves--there are no 'transaction waves' (a transaction is an atemporal 'collapse' of OW and CW overlaps) and there are no pilot waves. I think you're confusing this with the Bohmian theory.

I understand that there are superpositions of the O&C waves. I'm asking about the trajectory of the particle itself, between emission and detection.

If TI does say that a particle (like a photon, complex atom or buckyball) ultimately was actually super-positioned as it passed the slits, then does TI not also say that an entire lab can be isolated and prepared such that it (and its occupants, particularly any cats) will develop in a superposition (although each different superposed parallel development must not only start identically, when the lab is prepared, but also must later culminate in exactly identical interactions with the environment, when the lab is detected)?

(This is what I meant in post 4: still needing MWI to explain how those parallel cats didn't perceive each other in the interim.)

QFT, which is not really a 'theory'

Oh?

 

[cesiumfrog]

(Continuing above post)

I'd like to emphasize the importance of reading (at the very least) Cramer's 1986 before forming an opinion or attitude towards TI. If you have a specific question about, or criticism of, something in that or any other paper on TI, I'll try to address it.

Cramer's 1986 paper does address Schroedinger's cat, but his discussion is restricted to (what MWI might term) only the parallel cats that would result in differing detection outcomes, ignoring the issue of cats that can no longer be distinguished at the detection event.

 

[rkastner]

I understand that there are superpositions of the O&C waves. I'm asking about the trajectory of the particle itself, between emission and detection.

If TI does say that a particle (like a photon, complex atom or buckyball) ultimately was actually super-positioned as it passed the slits, then does TI not also say that an entire lab can be isolated and prepared such that it (and its occupants, particularly any cats) will develop in a superposition

No. You seem to have forgotten about absorbers here, and that's the advantage of TI. The radioactive atom sends out a weak OW which is absorbed by the geiger counter detector which generates CW in response. There may or may not be a transaction at this level, so there is no need for endless superpositions of cats, Wigner, Wigner's friend, lab, etc. The 'buck stops' between the emitter and the absorber: a transaction may or may not occur within a given time frame, so the cat may be either alive or dead after that time based on whether or not it has occurred. Superpositions of OW are not maintained beyond the level of their absorption (unless they get identically re-generated, e.g. as at a mirror).

Re why QFT is not a full and complete theory, see, e.g.,
http://plato.stanford.edu/entries/quantum-field-theory/

 

[rkastner]

(Continuing above post)

Cramer's 1986 paper does address Schroedinger's cat, but his discussion is restricted to (what MWI might term) only the parallel cats that would result in differing detection outcomes, ignoring the issue of cats that can no longer be distinguished at the detection event.

Under TI there would be no cats that can't be distinguished. After a given period of time there is either a live cat or a dead cat, based on whether or not there was a transaction in that time. There are no superposed cats in TI.

 

[rkastner]

For those of you who adhere to the MWI picture, TI is a bit of a paradigm switch, because absorbers enter on an equal footing (almost) with emitters, and play a crucial part in the dynamics. This is how TI can account for the determinacy of cats and of the Born Rule for probabilities of outcomes, the latter remaining a deep conundrum in the MWI picture, where advocates are currently attempting to explain it in terms of 'rational observers' and social theory,which seems to me to be getting a bit far afield from what ought to be a physical theory.

 

[Dmitry67]

If you mean to suggest that emitters and absorbers are arbitrary or primitive in TI, this is not the case. The reflecting action of a mirror under TI can be modeled just the same as in standard qm , in which the quantum state (OW under TI) undergoes reflection due to an infinite potential barrier. Alternatively, if you want to take into account the specific interaction with the metal, the mirror is an absorber that generates a new OW identical with the one received by it. Thus there is a fully consistent account of emitters and absorbers as quantum objects, and there is no 'magic' involved. The photoelectric effect is not the same phenomenon as perfect reflection from a mirror even in standard qm, (the metal ejects an electron, not an incoming photon beam), so it wouldn't be appropriate to expect that they should be treated the same by a qm interpretation. But thank you for this example, I may want to include it in my presentation in order to help make the distinction.

The question neither TI nor CI can answer is "what is an absorber" (measurement device - CI). What *some* configuartions of atoms are NOT absorbers (measurement devices) while some other configurations are? Can we look at some configuration of atoms (without knowing what is the purpose of that thing) and calculate the value of the function IsAbsorber(parameter system)?

Of course, neither CI nor TI provide such answer, because there is no one.

The photoelectric effect is not the same phenomenon as perfect reflection from a mirror even in standard qm, (the metal ejects an electron, not an incoming photon beam)

On the high level, it is the same. The evolution from some state into another state, not taking care of what exactly is emitted (photon, electro, or something else).

So again, I provide you a definition of some tiny systems with 1000000 atoms. You don't know in advance if it is mirror or say, photo-sensitive cell in my photo camera. Can you provide a formal procedure to determine if such system is a measurement device (or, in TI, will it send a back wave, or how is it called...)

 

[Dmitry67]

Note that there is an some equivalence between CI and TI: if you can tell absorber from non-absorber, you can tell measurement device from what is not the one, and vice versa.

 

[Demystifier]

An emitter is just another dynamical object, and as such is also described by quantum theory. E.g., you can have an offer wave as an emitter: an OW for an electron can emit an OW for a photon, and another electron OW can act as an absorber for that photon. So it would be incorrect to think that emitters and absorbers are undefined or primitive, as is the case with an "observer".

But the processes of absorption and emition cannot be described by the Schrodinger equation (or a couple of Schrodinger equations). Right?
So either
1) TI replaces Schrodinger equation(s) by a different (set of) equation(s), or
2) TI does not provide a mathematical description of absorption and emition

Now please tell me which is correct: 1) or 2)?

 

[cesiumfrog]

Under TI there would be no cats that can't be distinguished. After a given period of time there is either a live cat or a dead cat, based on whether or not there was a transaction in that time. There are no superposed cats in TI.

I think this confusion is coming from Cramer's contention that MWI http://www.npl.washington.edu/ti/TI_app.html#A.4" time-symmetric.

After the transaction (between the OW from the apparatus that prepares the cat-box and the CW from in the apparatus opening the box) is formed one might suppose that the experiences of the cat (over the duration of time that this completed-transaction spans) were now determined uniquely by which memories the cat has afterward (and similar identifiers). (Or in MWI one might suppose that the observation result singles out just one cat, for the entirety of the time-period that the box was closed, from a clutter of parallel cats.) But obviously not every difference possible in the cat's experience would result in such distinguishability afterward. MWI's parallel worlds can merge: the process is called interference. To claim otherwise would be to claim that some fundamental difference exists between consciousness (of the cat) and any mechanistic micro-abacus (or C60, to pick something with thousands of parts, where superpositions of the whole have been confirmed). To be explicit, TI implies that the cat will have always been definitely alive (or dead and not both) but that it could nonetheless have been in a superposition of having forgotten dreaming about mice and having forgotten dreaming about fish.

You seem to be claiming to escape super-positioned cats by not treating the cat as one whole, and by instead considering many shorter transactions between each microscopic part separately. Isn't that inconsistent since the same method wouldn't be applied to C60 experiments?

 

[rkastner]

Note that there is an some equivalence between CI and TI: if you can tell absorber from non-absorber, you can tell measurement device from what is not the one, and vice versa.

The 'equivalence' you suggest is illusory, since CI does not admit that absorption has any role in collapse. That's why you get an endless proliferation of branches in CI (I assume you mean here orthodox interpretation), accompanied by hand-waving accounts of "when a measurement is complete" which have no clear answer. In contrast, In TI an absorber is characterized unambiguously in terms of interacting particles. E.g., any time you have states in > different states out, there has been absorption of the incoming particles and emission of new particles. So this is an objective matter describable in terms of particle states and not handwaving as in the usual 'when is a measurement complete'. In cases where one doesn't bother to go into these details, as in a mirror, it is because the outgoing states are essentially indistinguishable from the incoming states or otherwise trivial. Note that for such interactions there is always a probability amplitude which must be squared. Under TI, the squaring is done because a CW is generated during the absorption/interaction process. Under all other version of qm, you just square the amplitude because 'Born said so'. TI physically characterizes the absorption process in terms of the generation of a CW along with any interaction which transforms incoming particle states into outgoing particle states. This is implicit in Cramer's 1986, Fig. 3, which shows an interaction consisting of an excited particle emitting a photon OW, which is received by an unexcited particle, upon which the second particle generates a CW, resulting in a transaction which leaves it with increased energy. Physics is full of examples like this with amplitudes that must be squared. The point is that any time you square the amplitude it is because there has been a CW generated and a transaction with that probability may occur.

 

[JesseM]

rkastner, do you think the criticisms of Cramer's interpretation made by Tim Maudlin on pages 197-200 of Quantum Non-Locality and Relativity, which can be viewed on google books here, are unfair or misguided? In particular note the section on page 200 dealing with the ambiguity in how the interpretation is supposed to work when the position of the absorber in the future depends on which events occur in the past...

 

[rkastner]

But the processes of absorption and emition cannot be described by the Schrodinger equation (or a couple of Schrodinger equations). Right?
So either
1) TI replaces Schrodinger equation(s) by a different (set of) equation(s), or
2) TI does not provide a mathematical description of absorption and emition

Now please tell me which is correct: 1) or 2)?

Why? You have a false choice here, since it implies that all QM is is the Schrodinger Eqn. Non-relativistic QM is the Sch Eq plus the Born Rule which allows us to make empirical contact. Standard QM has no physical referent for the Born Rule; TI does.

Furthermore, as I've noted elsewhere, the process of emission/absorption would need to be treated in detail in terms of qm for interactions, which includes the relativistic domain, while the Sch eqn describes persistent particles in the nonrelativistic domain, so again your question is misleading, presuming that NRQM must be the whole story, which it isn't. (This is made evident in Cramer's 1986; have you read it?) TI is relativistically consistent, and applies anytime we need to square amplitudes to get probabilities. TI is perfectly capable of doing (2) since it is a time-symmetric account of standard qm which treats such cases; see my other replies. It simply interprets Born Rule squaring process as resulting from CW and OW. Anytime you take an amplitude and square it in standard qm, you are doing it because "Born said so"; in TI you do it because there are CW as well as OW.

In doing philosophical inquiry it helps to have an open mind.

 

[rkastner]

rkastner, do you think the criticisms of Cramer's interpretation made by Tim Maudlin on pages 197-200 of Quantum Non-Locality and Relativity, which can be viewed on google books here, are unfair or misguided? In particular note the section on page 200 dealing with the ambiguity in how the interpretation is supposed to work when the position of the absorber in the future depends on which events occur in the past...

Thanks, good question. Three different authors have addressed this argument by Maudlin. He raised an interesting challenge but I think seriously overstated his case. My arxiv paper

http://arxiv.org/ftp/arxiv/papers/1001/1001.2867.pdf

mentions this and provides reference to the 3 replies to this challenge, which is absolutely NOT fatal for TI.

 

[rkastner]

Dear Thread Participants:

In view of the continuing unfriendly tone and lack of preparation of some posters (by no means all!), I will no longer be regularly checking this board as of 2/24/10. If you have read some of the published material on TI and have an open-minded and sincere question, you could send me a private message. I cannot promise to reply but I will do so if possible.

Thanks for the many interesting questions and comments!

R. E. Kastner

 

[rkastner]

Concerning this question: " You seem to be claiming to escape super-positioned cats by not treating the cat as one whole, and by instead considering many shorter transactions between each microscopic part separately. Isn't that inconsistent since the same method wouldn't be applied to C60 experiments?"

I thought I posted an answer but don't see it.
So here is my answer again:

I would put it differently: in MWI one is failing to escape superposed cats by failing to notice that the cat (actually the geiger counter) is a collection of absorbers, anyone of which can give rise to a transaction. In physics there are just collections of interacting particles (quanta). 'Cat-particles' don't care that they happen to be part of a cat; they are capable of emission/absorption and as such can trigger collapses. Of course, before that, the geiger counter detector particle(s) are absorbing the atomic decay product OW and generating a CW, so the collapse takes place on a level before any 'entanglement' with a macroscopic object like a cat. Offer waves and confirmation waves certainly can be superposed; but their sums provide for transactions (collapses) that result in determinate situations, like either an alive or dead cat.

As for superpositions of mesoscopic objects (I don't know about the specific object here but I assume that's what it is); this is all perfectly consistent. Detecting such a superposition would be analogous to detecting a photon landing in an interference pattern in a two-slit experiment (as if it went through both slits). Similarly, with a more complicated object you could get a transaction reflecting some exotic superposed state. TI allows for that. It's just that, the more complicated the object, the less likely such superposed states are; objectively, their squared amplitude gets smaller. This is where decoherence is relevant.

 

[rkastner]

The question neither TI nor CI can answer is "what is an absorber" ...

Of course, neither CI nor TI provide such answer, because there is no one.

Of course it can. A quantum system in its ground state, or in any energy state capable of being excited, is an absorber. Why the alleged big mystery here about absorbers? It's standard physics.

It's trying to decide when a measurement is complete without taking into account absorption that is the problem.

 

[Demystifier]

Why? You have a false choice here, since it implies that all QM is is the Schrodinger Eqn. Non-relativistic QM is the Sch Eq plus the Born Rule which allows us to make empirical contact. Standard QM has no physical referent for the Born Rule; TI does.

None of this answers my questions.

Furthermore, as I've noted elsewhere, the process of emission/absorption would need to be treated in detail in terms of qm for interactions, which includes the relativistic domain, while the Sch eqn describes persistent particles in the nonrelativistic domain, so again your question is misleading, presuming that NRQM must be the whole story, which it isn't.

This has a potential to be the answer, but it is not. So let me rephrase my questions: In my questions, replace the word "Schrodinger" with "Dirac" or "Klein-Gordon" or something of that sort. What would be the answers in that case?

(This is made evident in Cramer's 1986; have you read it?)

No I didn't, that's why I ask you.

In doing philosophical inquiry it helps to have an open mind.

I certainly agree with that. And you should know that I am not a fan of the Copenhagen interpretation. If that helps, I am a fan of the Bohmian interpretation. But I am open minded and before philosophy I want to understand what new TI says on the mathematical level. So let me rephrase my question again: Does TI contains any EQUATION that is not contained in standard QM?

 

[Dmitry67]

...

To get rid of ambiguity, I will try to use only Yes/No questions.

1. A chunk of carbon (monocrystal containing 1'000'000'000'000'000'000 atoms) is an absorber for light in terms of Ti or not?
2. Monocrystal containing 1000'000 atoms is an absorber or not?
3. C60 molecule is an absorber or not?
4. Single C atom is an absorber or not?
5. single electron, u and d quarks are absorbers or not?

To symplify, all monocrystals are cooled to near zero temperature so they have regular structure.
Thank you in advance.

 

[Demystifier]

Good question, Dmitry! I also want to see how will he deal with it.

 

[cesiumfrog]

Ruth, would you clarify, do you agree or disagree that TI allows Schroedinger's cat to have actually been in a superposition of "having forgotten dreaming about mice" and "having forgotten dreaming about fish"? (Presuming we observe it to have survived, I'm sure we both agree TI also says the cat was not ever in a superposition with a dead version of itself, but that is unconnected to my query.)

It seems to me that a slippery slope argument can be demonstrated using double slit interference patterns: I think you agree that TI says a photon really is in a superposition as it travels between the source and detector? So I presume TI also says that a single atom can have been in a superposition (in the same kind of interference experiment). And the same will go for progressively bigger objects, composed even of far more fundamental parts than an atom is. So then the same even for cats (or people), fired by cannon through a partition with two gaps, provided that the room can be made dark and cold enough to avoid decoherence issues etc.

To me, it seems that accepting this conclusion should be anathema to any proponent of TI over MWI, but I also don't see how it can legitimately be avoided. I would elaborate, but after reading your posts I still don't yet understand exactly what your position is regards the above.

 

[rkastner]

Re recent questions/intended challenges: please read the relevant literature before asking questions. No need for me to repeat what is already available out there in print. My purpose was to address questions arising from those papers. But as I said, I cannot promise to check this regularly due to other pressing commitments, and won't feel inspired to do so if there continue to be questions from people who refuse to read the basic literature before presenting alleged challenges. Thanks! :)

And of course, I have already answered in very specific terms what counts as an absorber in TI--the same things that count as absorbers in standard physics.