Everybody sees the same elephant (says Carlo Rovelli)

[Careful]

**
I think this is a quite elegant solution to the measurement problem. **

It is not a solution to the measurement problem (remember the born rule is still in there), neither is MWI from the strict reductionist point of view.


**It does not involve any change in the testable predictions of QM, unlike the models with a physical wavefunction collapse;**

It remains to be seen whether that is a good or a bad thing

**it does not involve extra physical baggage like hidden variables models do, and it does not involve the extra ontological baggage of the many worlds interpretation. (From the point of view of the relational interpretation, the many worlds interpretation would seem to privilege as the only "true" state one which is not relative to any particular observer; God’s point of view, so to say.**

There is no need for God in MWI, and if you do the counting MWI is actually equally economical as the relative state interpretation (remember, any observer needs his own wavefunction).

** I think that the relationist should deny that there is any such state, like a "wavefunction of the universe". This should have implications for quantum cosmology.) Even more attractive, for me at least, is that the interpretation is not instrumentalistic: quantum mechanics is not merely a tool for calculating and predicting but a true description of how the world works; the description must be done from the "point of view" of some physical system, but there is no privileged choice for the reference system (much like the situation with reference frames in special relativity).**

It is still instrumentalistic wrt to the observer though.

Cheers,

Careful

 

[Sauron]

Another comment/remark, since *t* is some unphyiscal parameter, it becomes obscure what happens to your equal time commutators, and more in particular to causality itself. Actually, I see no reason why field operators corresponding to causal separations should commute. Could you elaborate more upon the relationship between the standard Fock QFT quantisation and your framework?

I have my own idea about these (I still haven´t readed all these thrread to see how it applies to these relational viewpoint).

The key is to extend quantum mechanics probability interpretation also to the time parameter.that is, $$\Phi(x,t)$$ gives the probability to find the particle in a given position and in a given time.

The source of these attemp (and how to read it) comes from the following kind of imaginary experiments.

Imagine a particle who can go from point A to point B (maay be they are the same point) by two different classical paths of different length.

Imagine the particle is a "quantum clock". Them when it arrives to point B it is in a superposition state of tow states of internal time. And only when it is measured you select a particular time.

A way to build a "auntum clock" could be modifiying the energy of the particle making, for example, the two diferent paths go throught different intensities of a gravitational field. So the indicative of the "clock time" would be the energy of the particle.

Another interesting thing is that in some enviroments you can make clasical clocks and in others, like for example the very first "time" of universe you can´t.

Of course i still didn´t develope all aspectos of the idea and i am not sure if they wil dive me tosome interesting place. But i see some relations betwen it and the problems that LQG faces about the time.

 

[Thomas Larsson]

I must say however that I find your paper ``manifestly covariant canonical quantization I´´ quite interesting and have spent today something like one hour studying it. Careful

Thank you. Coming from you I take that as a serious compliment.

Before addressing the more technical details below, I should state that there are (at least) two serious flaws in my paper:
1. There is an overcounting of states already for the classical harmonic oscillator, as stated in the introduction. At the time I thought this problem would go away if you add interactions, but I was wrong.
2. No inner product was defined.
It turns out to be possible to resolve both these problems by adding extra antifields to kill the unwanted cohomology. One needs to implement a condition which identifies momenta and velocities. Then the involution defined by making frequencies negative gives the correct inner product. With these modifications my method does work for the harmonic oscillator, and by extension for all free theories. Interacting theories give rise to additional complications, which I do not yet understand.

I have some questions and some silly (technical) remarks - since I looked a bit in the details I shall also give some of the typos.

(a) the first remark concerns the computation of the cohomology on page 10 - there you say that each function which contains pi is not closed, that is not true, a counterexample is pi*e + (psi*)*K*(pi*), however this one is in the image of the KT derivative. Careful

This is true. I had completely missed that one. Thank you.

(b) in general, your idea is to quantize first and then impose the dynamics, but are you not running then in similar problems as canonical quantization in the interaction picture for non linear theories? Careful

I am not sure what these problems are.

(c) in formula 4.8, the second psi* should be \bar{psi} and similarly in 4.10, it is correct again in 4.18 Careful

OK.

(d) On page 17, the purpose of your splitting of the Hamiltonians, that is the constraint H_0 and the ``observer´´ H is to define the time derivative relative to the quantum worldline of ``the observer´´ and associated to this, the definition of the Fock vacuum state relative to the worldline and the parameter time t. However, t by itself is just window dressing and should have not any physical significance, this calls the question for reparametrisation invariance of the measured quantities. Careful

On page 16 I specialize to Minkowski spacetime. By replacing the geodesic equation by d^2 q/dt^2 = 0 I made t physical, defined in terms of the gravitational field. This could have been empasized more, though.

This issue is adressed in section 8 where you mention that extra matter coupling is necessary to make sense of this (did I get that right?). Now here I am confused in the beginning, since at page 28 you mention that every bosonic p-jet bundle contributes 2(N+p,N) to the central charge (and minus for the fermions) while in formula 8.6 I suddenly get entirely different numbers. Careful

Apart from a factor of 2, the numbers (N+p, N-k) should be replaced by (N+p-k, N). The numbers came from Lemma 7.1 at page 15 of http://www.arxiv.org/abs/math-ph/0101007, but somewhere on the way they mysteriously mutated. This is of course the problem with doing something that nobody cares about; there is no careful proof-reader.

(e) Also, in the latter construction , one would expect the relative energy to be a measurable quantity only in case the worldline would interact with the matter fields. How would this reflect upon your relative positive energy condition? (sorry, did not really think about this ) Careful

Why blushing? I had worried about this myself. Maybe the worldline in Minkowski space should satisfy something like M d^2 q/dt^2 = F, where F is a force from the fields at q(t). The straight line condition would then correspond to M = infinity, and the backreaction of this infinite mass would cause trouble in gravity.

Another comment/remark, since *t* is some unphyiscal parameter, it becomes obscure what happens to your equal time commutators, and more in particular to causality itself. Actually, I see no reason why field operators corresponding to causal separations should commute. Careful

You mean non-causal separation, no? Since all points on the observer's trajectory are supposedly causally related, and the Taylor coefficients live on this trajectory, the notion of spacelike separated events disappear from the horizon. This is confusing, and I am not sure that I have digested it yet. However, it is the same miracle that underlies the notion of analyticity.

 

[marcus]

I see some points need amplification in my earlier post which quoted Satz. In particular we need to see what is the measurement problem and how relational QM avoids or addresses it. So I will quote Wiki. Here is my post, some non-essentials eliminated and with points highlighted that need discussion.

continuing what I said in post #30 and 31, Alejandro Satz (in his blog "Reality Conditions") does an outstanding job reviewing Smerlak Rovelli "Relational EPR". Here is a key quote:

-------quote from Satz blog----

I think this is a quite elegant solution to the measurement problem. It does not involve any change in the testable predictions of QM, unlike the models with a physical wavefunction collapse; it does not involve extra physical baggage like hidden variables models do, and it does not involve the extra ontological baggage of the many worlds interpretation. (From the point of view of the relational interpretation, the many worlds interpretation would seem to privilege as the only "true" state one which is not relative to any particular observer; God’s point of view, so to say. I think that the relationist should deny that there is any such state, ...
---endquote---

Here is an exerpt from Wiki article on MEASUREMENT PROBLEM

---quote Wiki---
The measurement problem is the key set of questions that every interpretation of quantum mechanics must answer. The problem is that the wavefunction in quantum mechanics evolves according to the Schrödinger equation into a linear superposition of different states, but the actual measurements always find the physical system in a definite state, typically a position eigenstate. Any future evolution will be based on the system having the measured value at that point in time, meaning that the measurement "did something" to the process under examination. Whatever that "something" may be does not appear to be explained by the basic theory.
The best known example is the "paradox" of the Schrödinger's cat: a cat is apparently evolving into a linear superposition of basis vectors that can be characterized as an "alive cat" and states that can be described as a "dead cat". Each of these possibilities is associated with a specific nonzero probability amplitude; the cat seems to be in a "mixed" state. However, a single particular observation of the cat does not measure the probabilities: it always finds either an alive cat, or a dead cat. After that measurement the cat stays alive or dead. The measurement problem is the question: how are the probabilities converted to an actual, sharply well-defined outcome?
Different interpretations of quantum mechanics propose different solutions of the measurement problem.
The old Copenhagen interpretation was rooted in the philosophical positivism. It claimed that the probabilities are the only quantities that should be discussed, and all other questions were considered as unscientific ones. One could either imagine that the wavefunction collapses, or one could think of the wavefunction as an auxiliary mathematical tool with no direct physical interpretation whose only role is to calculate the probabilities.
While this viewpoint was sufficient to understand the outcome of all known experiments, it did not explain why it was legitimate to imagine that the cat's wavefunction collapses once the cat is observed, but it is not possible to collapse the wavefunction of the cat or the electron before it is measured. The collapse of the wavefunction used to be linked to one of two different properties of the measurement:
The measurement is done by a conscious being. In this specific interpretation, it was the presence of a conscious being that caused the wavefunction to collapse. However, this interpretation depends on a definition of "consciousness". Because of its spiritual flavor, this interpretation was never fully accepted as a scientific explanation.
The measurement apparatus is a macroscopic object. Perhaps, it is the macroscopic character of the apparata that allows us to replace the logic of quantum mechanics with the classical intuition where the positions are well-defined quantities.
The latter approach was put on firm ground in the 1980s when the phenomenon of quantum decoherence was understood. The calculations of quantum decoherence allow the physicists to identify the fuzzy boundary between the quantum microworld and the world where the classical intuition is applicable. Quantum decoherence was proposed in the context of the many-worlds interpretation, but it has also become an important part of modern update of the Copenhagen interpretation that is based on consistent histories ("Copenhagen done right"). Quantum decoherence does not describe the actual process of the wavefunction collapse, but it explains the conversion of the quantum probabilities (that are able to interfere) to the ordinary classical probabilities.
The Hugh Everett's relative state interpretation, often inaccurately referred to as the many-worlds interpretation, attempts to avoid the problem by suggesting it is an illusion. Under this system there is only one wavefunction, the superposition of the entire universe, and it never collapses -- so there is no measurement problem. Instead the act of measurement is actually an interaction between two quantum entities, which entangle to form a single larger entity, for instance living cat/happy scientist. Unfortunately Everett was never able to "close the loop", and demonstrate the way that this system would result in real-world measurements, ones in which the probabilistic nature of quantum mechanics could appear.
The many-worlds interpretation is a development of Everett's that attempts to provide a model under which the system becomes "obvious". Everett's interpretation posits a single universal wavefunction, but with the added proviso that "reality" is defined as a single path in time through the superpositions. That is, "you" have a history that is made of the outcomes of measurements you made in the past, but there are many other "yous" with slight variations in history. Under this system our reality is one of many similar ones.
---endquote---

It is probably obvious to some readers that the measurement problem (as described here) does not arise in RQM. Indeed relational QM avoids the problem rather gracefully by simply labeling the state.
If someone objects as per Wiki
"... it did not explain why it was legitimate to imagine that the cat's wavefunction collapses once the cat is observed, but it is not possible to collapse the wavefunction of the cat or the electron before it is measured. "

Then the RQM person has a very simple answer. The wavefunction in question, which you call the "cat's wavefunction" is actually a state in a Hilbertspace labeled by the name of the OBSERVER that summarizes the information he has acquired about the world. It does not have an absolute existence apart from that observer and his experience. There is a "before-and-after" operator on the observer's hilbertspace that transforms the state from the way it is BEFORE he opens the door to the way it is AFTER he opens the door of the box and has new information. He then incorporates the new information in the subspace logic latticework of his Hilbertspace that he uses to store the fruits of his experience.

Nothing could be more natural than that the state is modified by the operator of Observing the Cat, at precisely the time that the observer opens the door and observes the cat.

Other readers may not understand and want more discussion of this, so I will make a separate post to discuss further.

BTW notice that one should not confuse RQM with "Relative State Interpretation" which is the technical name for Everett's proposal widely known as MWI ("many worlds interpretation").

"Relative State Interpretation", since it an idea of Everett's associated with MWI, should not be carelessly used as a synonym for Relatonal QM---which, as Satz comment explains, is signficantly different.

 

[marcus]

I think this is a quite elegant solution to the measurement problem.

An indication of the confusion some people are in, and the need for more explanation is post #36 in this thread

It is not a solution to the measurement problem

But indeed RQM avoids the measurement paradox as it does others because these cliché contradictions can only exist in the mind of a Superbeing who can simultaneously see everybody's state of knowledge (the cat inside the box and the scientist outside---the eeper measuring a spin on Jupiter and the other eeper measuring one on Uranus)

...it does not involve extra physical baggage like hidden variables models do, and it does not involve the extra ontological baggage of the many worlds interpretation. (From the point of view of the relational interpretation, the many worlds interpretation would seem to privilege as the only "true" state one which is not relative to any particular observer; God’s point of view, so to say.

To which post #36 replies

There is no need for God in MWI, and if you do the counting MWI is actually equally economical as the relative state interpretation (remember, any observer needs his own wavefunction).

Notice that the RELATIONAL QM of rovelli is being discussed, but the poster SAYS "relative state interpretation" as if he thinks that is the same thing or wants to blur the distinction and have readers get that impression.

Indeed MWI can be regarded as equally economical with Relative State because they are essentially the SAME THING----both products of the fertile mind of Hugh Everett. So this is literally correct.
But saying this gives readers the impression that MWI is equally economical with RELATIONAL QM.

and the detail "remember any observer needs his own..." MAKES IT SEEM as if Relational is being talked about because in RQM each observer has his own hilbertspace and state within that representing his information.

But MWI has a lot of additional ontological baggage (as Satz puts it) like millions of parallel universes or whatever, and branching. It is very Baroque. You have to believe in a lot of stuff you can't see. Plus it has, like Wiki says, A SINGLE MASTER WAVEFUNCTION, implying some kind of Super-observer. Wiki says about MWI:
"Under this system[the many-worlds interpretation] there is only one wavefunction, the superposition of the entire universe, and it never collapses..."

This is preposterous. A wavefunction is the state in some observer's hilberspace logic that represents that particular observer's state of knowledge. If you fantasize a huge omniscient wavefunction that implies a huge omniscient observer with all-embracing knowledge and because the state never collapses THE SUPERBEING NEVER EVEN LEARNS ANYTHING! It is an amusing picture, but it is hard to take seriously.

Alejandro Satz puts it forthrightly enough

I think that the relationist should deny that there is any such state, like a "wavefunction of the universe".

 

[Mike2]

Section 5.2 reads,
"The properties of the system are established by its interaction with other quantum systems, and these properties are represented by the corresponding projection operators on the Hilbert space. These projectors are elements of a Boolean sigma-algebra, determined by the physics of the interaction between the two systems. ... The family of all Boolean sigma-algebras forms a category, with the sets of the projectors of each sigma-algebra as objects."

Does this mean to say that the algebra used in the relational quantum mechanics stems uniquely from category theory? Thanks.

 

[hossi]

Yes! that is a key point. There is no absolute overseer who
can instantaneously report all the observers' results. (Not even in a
Gedankenexperiment! )

Thanks, marcus. Excuse me for asking more dumb questions. I know about nothing about the topic, but I am too interested to be embarrased

So, I have spatially separated observers, measuring the outcome of an experiment with an initially entangled state. Each observer measures some 'collapsed' state. Usually, the measurements have to be in some kind of relationship that has to be instantaneous, therefore the problem with locality.

Now I say instead, well, there is no evidence for a non-local collapse as long as the observers haven't actually compared their measurements. So, I bounce back the information from one measurement to the other, to compare both. No non-locality in this, which is good. The comparison requires an interaction. Does this interaction process then make sure that the measurements fit together as parts of the entangled state? And if so, what is the difference to saying, that the 'collapse' propagates locally? I.e. imagine a continuum of observers whose measurements get compared. Or what did I miss with Rovelli's interpretation?

Still hoping for enlightenment

B.

 

[Mike2]

And if so, what is the difference to saying, that the 'collapse' propagates locally? I.e. imagine a continuum of observers whose measurements get compared. Or what did I miss with Rovelli's interpretation?

I take it that the universe is a superposition for each observer until he measures something. Then everything collapses to a eignstate in which everything is consistent with that observation, including the information from other observers.

The question then becomes does the universe go back to a superposition until that observer makes another measurement? Or is all the past and future determined by that one observers measurement (at least for him)?

 

[marcus]

Hossi and the Seven Dwarves

So, I have spatially separated observers, measuring the outcome of an experiment with an initially entangled state. Each observer measures some 'collapsed' state. Usually, the measurements have to be in some kind of relationship that has to be instantaneous, therefore the problem with locality.

Now I say instead, well, there is no evidence for a non-local collapse as long as the observers haven't actually compared their measurements.

Still hoping for enlightenment

B.

One day there was an interplanetary adventuress named Hossi who prepared two particles in aligned spinstates. One she kept, and the other she gave to some Dwarves, who were her good friends. Then the Dwarves went off to the planet Pluto. Their plan was that when it got to be Eastertime Hossi and the Dwarves would each measure their spinstates to see if they are East and West.

Now it is Easter, and Hossi doesn't KNOW that the Dwarves actually REMEMBERED to do it! Or they might have accidentally measured in a different direction besides East/West. Or the Dwarves might have just totally screwed up.

In fact, one of the Dwarves, the one called Careful John, actually LIKES screwing up. He always wants to confuse the others and get things wrong. Nothing in this life is certain, so Careful John may have prevailed or he may not have.

As far as Hossi goes there is only one Hilbertspace, hers, and just this one state of the precious pair of particles which as a token of friendship she has divided with the Dwarves. This state represents her Knowledge...

TO BE CONTINUED

BTW I really liked the hatsnakeelephant pictures you put in. they were a beautiful illustration, thanks

 

[hossi]

I take it that the universe is a superposition for each observer until he measures something. Then everything collapses to a eignstate in which everything is consistent with that observation, including the information from other observers.

The question then becomes does the universe go back to a superposition until that observer makes another measurement? Or is all the past and future determined by that one observers measurement (at least for him)?

Now you have completely confused me.

I thought: everything collapses for each observer, but not neccessarily consistently, as long as they have not observed each other. Otherwise: everything is consistent with which observation? And how would that differ from the usual collapse?

 

[marcus]

I should interrupt the story about the Seven Dwarves to make sure everybody knows what Dirac said about the Heisenberg picture. It is the right one---more fundamental.

this is what Dirac said near the end of his life in the last public seminar he gave. It was on the Island of Sicily and he had only one slide for the the whole lecture. the slide said:

The Heisenberg picture is the right one.

---quote from Smerlak Rovelli----
ψ is the coding of the information that A has about S. Because of this irreducible epistemic character, ψ is a relative state, and cannot be taken to be an objective property of the single system S, independent from A. Every state of quantum theory is a relative state. 5

On the other hand, the state ψ is a tool that can be used by A to predict future outcomes of interactions between S and A. In general these predictions depend on the time t at which the interaction will take place. In the Schrödinger picture this time dependence is coded into a time evolution of the state ψ itself. In this picture, there are therefore two distinct manners in which ψ can evolve: (i) in a discrete way, when S and A interact, in order for the information to be adjusted, and (ii) in a continuous way, to reflect the time dependence of the probabilistic relation between past and future events.

From the relational perspective the Heisenberg picture appears far more natural: ψ codes the information that can be extracted from past interactions and has no explicit dependence on time; it is adjusted only as a result of an interaction, namely as a result of a new quantum event relative to the observer. If physical reality is the set of these bipartite interactions, and nothing else, our description of dynamics by means of relative states should better mirror this fact: discrete changes of the relative state, when information is updated, and nothing else. What evolves with time are the operators, whose expectation values code the time-dependent probabilities that can be computed on the basis of the past quantum events. [Footnote 6]Footnote 6: This was also Dirac’s opinion: in the first edition of his celebrated book on quantum mechanics, Dirac uses Heisenberg states (he calls them relativistic) [29]. In later editions, he switches to Schrödinger states, explaining in the preface that it is easier to calculate with these, but it is “a pity” to give up Heisenberg states, which are more fundamental. In what was perhaps his last public seminar, in Sicily, Dirac used a single transparency, with just one sentence: “The Heisenberg picture is the right one”.
---endquote---

 

[vanesch]

BTW notice that one should not confuse RQM with "Relative State Interpretation" which is the technical name for Everett's proposal widely known as MWI ("many worlds interpretation").

"Relative State Interpretation", since it an idea of Everett's associated with MWI, should not be carelessly used as a synonym for Relatonal QM---which, as Satz comment explains, is signficantly different.

I'm really sorry, but I don't see any difference.

What happens in MWI is the following. Let's say that we have Alice who is going to "measure" using a "measuring device", the spin state of a particle. We say that *before the measurement* (which is nothing but an interaction), the state is:

|alice> (|up> + |down>)

The "measurement interaction" will evolve the state:
|alice>|up> into |alice_who_saw_up> |up>
and
|alice>|down> into |alice_who_saw_down>|down>
(this is how the interactions in her apparatus are constructed, and linked, finally to her body by her senses)

which means that the overall state evolves into:

|alice_who_saw_up>|up> + |alice_who_saw_down> |down>

But, "alice" being a subjectively generated experience by a classically-looking state, we have now that the original experience |alice> will evolve into two of these. As if alice's classical body was copied.
The quantum state of Alice's body is now "generator" of two classically-experiencable states, and can hence generate two associated, different, subjective experiences. So Alice's original subjective experience will not be able to "ride both of them" in the same way as twin brothers do not have a "single conscious experience" but have two of them. We had "one" classically generated state before the interaction (associated with a subjective experience) and now we have two. If we would only have had one, we would have made no objections that there was a "continuity" of the original Alice experience (we wouldn't wonder why qlice wasn't suddenly experiencing the next moment "Mary's body" or something, right ?). But there are now two of them.
Which one will be "the original" and which one will be the "copy" ? Answer: use the Born rule. Now, most MWI variants try to naturally deduce this Born rule from an equal-probability rule and world counting, which is impossible without introducing extra hypotheses, but you can simply STATE so. So we say that the "original" alice experience makes a random choice between the two "new" ones using the Born rule and we mark this with an asterix:

before:
|alice*> (|up> + |down>)

after:
|alice_who_saw_up*>|up> + |alice_who_saw_down> |down>

So alice's "original" experience was first connected (in the same term) with a superposition |up> + |down> and after the interaction, with |up>.

Now, if I understand well, the relational approach ONLY CONSIDERS the starred states, and then we see that the complete original "alice-experience" evolved from:

|alice>(|up> + |down>)
into
|alice_who_saw_up*> |up>

and things happen as if projection occurred from her point of view.

This is exactly what's claimed in MWI too - except that one considers that the quantum body is carrier of DIFFERENT classical states which can be subjectively experienced.

In a typical EPR setup with an Alice and a Bob, we can do the same, and we can find that from the point of alice's experience, things happen as expected, and from Bob's point of view, too. However, the difference is of course that "the original bob" can be in another branch than the "original alice" (but they won't be able to find out).

I really fail to see the difference with the relational approach *if you limit yourself to one single observer* - and of course ALL you can only find out is what one single observer has ever observed (eventually through the observation of other physical bodies).

 

[marcus]

Hi Vanesch,
I trust you have read the earlier Wikipedia quotes. In this thread I would like to use Wiki articles, which are clickable for everybody, to keep the use of terminology reasonably consistent (democracy of sources + everybody on same page = happy discussion )

What we have about MWI so far is what I quoted in post #39
----Wiki---
The Hugh Everett's relative state interpretation, often inaccurately referred to as the many-worlds interpretation, attempts to avoid the problem by suggesting it is an illusion. Under this system there is only one wavefunction, the superposition of the entire universe, and it never collapses -- so there is no measurement problem. Instead the act of measurement is actually an interaction between two quantum entities, which entangle to form a single larger entity, for instance living cat/happy scientist. Unfortunately Everett was never able to "close the loop", and demonstrate the way that this system would result in real-world measurements, ones in which the probabilistic nature of quantum mechanics could appear.
The many-worlds interpretation is a development of Everett's that attempts to provide a model under which the system becomes "obvious". Everett's interpretation posits a single universal wavefunction, but with the added proviso that "reality" is defined as a single path in time through the superpositions. That is, "you" have a history that is made of the outcomes of measurements you made in the past, but there are many other "yous" with slight variations in history. Under this system our reality is one of many similar ones.
---endquote---

How are you with this description of MWI? Would you like to provide a link to some alternative definition? I can't promise I will accept it for use in the context of this thread, but I am curious what it would be (if you were to propose another link) and would try to accommodate your proposed change.

As for the definition of Relational QM, I think we have to take Rovelli's article called "Relational Quantum Mechanics" as defining it, don't you?

I suppose the safest thing is to read what Rovelli has to say comparing RQM with various QM versions and interpretations. He goes into the similarities and differences at some length. what is your opinion about that?

Please let me know if you find Rovelli's definition of his own theory acceptable, and whether you believe his account of how it compares to other QM pictures.

If you don't like Rovelli's account of RQM and how it compares, it would be great if you would point to specific paragraphs in the article that you judge questionable.

VANESCH HERE IS THE WIKI LINK that provides the quoted description of MWI:
http://en.wikipedia.org/wiki/Measurement_problem

HERE IS ROVELLI ON RQM:
http://arxiv.org/abs/quant-ph/9609002

FOR MORE ON MWI:
http://en.wikipedia.org/wiki/Many-worlds_interpretation

 

[marcus]

...I really fail to see the difference with the relational approach *if you limit yourself to one single observer* - and of course ALL you can only find out is what one single observer has ever observed (eventually through the observation of other physical bodies).

Perhaps this is not so surprising since RQM is intended to have the look and feel of traditional QM. Especially in the case of *one single observer*
RQM is primarily an adaptation of one's philosophy in such a way that certain paradoxes (associated with two or more observers) fail to materialize, without tampering with the tried and true formalism of standard QM.

This is simply my opinion, as is what follows. To be sure, please don't take my sayso, but instead use authoritative source material, especially Rovelli's writings since it is his version of QM.

One more non-authoritative thing from me. I think that RQM does not involve postulation of additional mechanisms or consciousness or hidden variables or branchings of reality or any of that stuff. It does not give any mechanisms explaining where uncertainty comes from or where probabilities come from. As far as innovation, RQM is minimal and severely economical.

So it is not even in the same ballpark with MRI. In my humble opinion.

However *if you limit yourself to one single observer* then RQM is going to look just like ordinary QM has looked for 75 years.

and so it is going to look pretty much like other Heisenberg picture QMs including what you, Vanesch, might have in mind . I certainly wouldn't argue with that!

 

[vanesch]

What we have about MWI so far is what I quoted in post #39
----Wiki---
The Hugh Everett's relative state interpretation, often inaccurately referred to as the many-worlds interpretation, attempts to avoid the problem by suggesting it is an illusion. Under this system there is only one wavefunction, the superposition of the entire universe, and it never collapses -- so there is no measurement problem. Instead the act of measurement is actually an interaction between two quantum entities, which entangle to form a single larger entity, for instance living cat/happy scientist. Unfortunately Everett was never able to "close the loop", and demonstrate the way that this system would result in real-world measurements, ones in which the probabilistic nature of quantum mechanics could appear.
The many-worlds interpretation is a development of Everett's that attempts to provide a model under which the system becomes "obvious". Everett's interpretation posits a single universal wavefunction, but with the added proviso that "reality" is defined as a single path in time through the superpositions. That is, "you" have a history that is made of the outcomes of measurements you made in the past, but there are many other "yous" with slight variations in history. Under this system our reality is one of many similar ones.
---endquote---

How are you with this description of MWI? Would you like to provide a link to some alternative definition?

Well, in great lines I agree with what's said there, except for one point. I think there are as many flavors of MWI as there are people thinking about it, so I'll give you mine (that I've been telling about since ages on PF), but which is just a mixture of ideas which are since long around. The main idea is that "the wave function" evolves unitarily ; but even for this to make sense, one has to place oneself into a certain reference frame (a Lorentz transformation gives you *another* evolution and *another* wavefunction). And even *within* such a frame, one should consider a coarse-grained Schmidt decomposition into two systems: "observer" x "rest of universe". THESE are the branches in MWI - and clearly they are observer-dependent! They are observer-dependent for the choice of inertial frame (hence how to split up the unitary structure into "state" and "unitary evolution") AND they are observer-dependent in the Schmidt decomposition "observer/rest-of-universe".
The "number of branches" is not equal for all observers, for instance, so there's nothing "objective" about this splitting. It is only in the case when two observer bodies are in contact with the same big thermal bath that there is any hope that they will have decohered in similar branches.

Coarse-grained here means: not making distinction between microscopically different quantum states which would give rise to identical macroscopic observations (while this can include many, many different orthogonal states which may continuously evolve into one another)

As for the definition of Relational QM, I think we have to take Rovelli's article called "Relational Quantum Mechanics" as defining it, don't you?

I suppose the safest thing is to read what Rovelli has to say comparing RQM with various QM versions and interpretations. He goes into the similarities and differences at some length. what is your opinion about that?

Well, almost everything I read in Rovelli's paper made me say "yes, that's also how I see things". For instance, his "Main observation" and his "Hypothesis 1" are in complete sync with how I see things too from an MWI viewpoint.

However, his comments in "objection 7" make me think that Rovelli didn't quite understand (modern views on) MWI, and got stuck with Everett's original idea, while these have been evolving over time. He seems to think that these branches are absolute and objective, and not observer-dependent. That's of course not the case: already the choice of the split between "wavefunction" and "time evolution" (choice of inertial frame) is observer dependent; but also the "split" in branches is observer dependent because depending upon the Schmidt decomposition between "observer body" and "rest of universe".
As far as I understood, MWI starts EXACTLY from the "main observation".

As a simple example, imagine an EPR like experiment, in a frame where Alice did already her measurement, but Bob not.
We then have:

|bob-init> ( |alice+>|-> - |alice->|+>)

As long as both didn't decohere together with a common thermal bath (cannot happen if they are still spacelike separated) there is ONE branch for Bob, and there are two branches for Alice.

However, in another frame, bob made maybe already his measurement, and not alice, so there we have the opposite case. This is entirely dependent on how we "slice" the unitary structure in "state" and "unitary evolution" which is nothing else but the choice of reference frame.
And in yet another frame, both made their measurements. If the axes aren't aligned, however, each appears in a superposition to the other (until they MEET and INTERACT - exchange data) in which case they get entangled, decohere and end up in the same number of branches.

Please let me know if you find Rovelli's definition of his own theory acceptable, and whether you believe his account of how it compares to other QM pictures.

Well, I fully accept what Rovelli writes, but it seems to me that that view WAS already present in different MWI flavors.

What is the "difficulty" (which I think, is not a difficulty) in MWI, namely the "derivation" of the probability rule by world counting, is solved by Rovelli in the same way as I think it should be solved in the same way: by POSTULATING it - but I admit here to be dissonant with most MWI views, which still have the hope of _deriving_ it, which I am profoundly convinced is impossible with an extra postulate anyways.
Just say that for a specific mind to have a "bob" experience, is given by the Born rule, applied to the different branches that appear for the body state of Bob.

Further, the "coarse grained" Schmidt decomposition corresponds exactly to Rovelli's "postulate 1" (namely, a finite amount of information can be "extracted" from the universe by an observer, which comes down to saying that the observer is in one of a finite number of distinguishable states at a certain point - this is exactly the *coarse graining* needed.) His postulate 2 comes down to saying that an observer state can always entangle with some extra stuff, and hence split into two or more states. Postulate 3 is unitary quantum theory.

Nevertheless, there's one problem Rovelli runs into, and that is exactly the same problem as any other view, which is the "preferred basis" problem ; except by using the coarse-grained Schmidt decomposition + decoherence approach. Given the physical structure of a measurement apparatus, there's no way for him to find out with what hermitean measurement operator that apparatus (fully described by a unitary evolution operator of the interaction with the system) is going to correspond to, without specifying what are its pointer states. Pointer states which ONLY have a meaning when we take into account the coarse-grained decohered Schmidt decomposition between "observer" and "rest of universe".
But by even *considering* this Schmidt decomposition, one assumes the DIFFERENT TERMS in the wavefunction - which is MWI-like, no ?

I think the final comment by Rovelli on the first part of p19 makes me think that he missed the essence of "many minds": namely he gives me the impression that these minds ARE the brains, and hence are "physical" - in which case the brains would indeed be "special" things which are treated differently than other things. But minds are NOT brains: minds are "emergent states of awareness" *generated* by a physical brain state. Hence a single brain can give rise to several minds, consciousnesses, subjective experiences or whatever. And in MWI (in this = my) flavor, THIS is the ultimate "observation" (the subjective experience of a mind, as one of several, generated by a brain state). As this is not part of the physical system per se, this does NOT violate his hypothesis 1.

Rovelli leaves in the middle what is an observer ; if I fill in this "mind" stuff then I'm in agreement with all he says. However, if he understands by "observer" *any* physical system, then he has the same problem as any other. For instance, let us consider an electron as an "observer", and consider a 2-slit experiment with that "observer" ; he then has the same problems as everybody else. And given his hypothesis 1, an electron IS a valid observer !
According to the electron, which slit did it go through ? The answer is that the electron, if it ever KNEW, FORGOT through which slit it went.
And I'd like to see how Rovelli talks himself out of this "observing and forgetting" electron, without getting into decoherence, generated classically looking states, and all the stuff that finally makes up an MWI view (in which we would take the position that an electron has a mind and that to each different electron state, corresponds also an electron-mind-experience - but in what basis now ??)...

 

[marcus]

thanks for your comments vanesch!
I think we are beginning to arrive at a fair, undismissive understanding of this kind of new Copenhagen or "Marseille Interpretation"

what I like to see emerging, in your (and like) comment is an idea of similarities AND differences and what this may have to offer a.f.a. resolving contradictions.

============
BTW I am finding the Stanford Encyclopedia article on RQM helpful now
(I see it now as very much like usual Copenhagen but with some unnecessary premise discarded. However it fits much better at first sight with Heisenberg picture----schrödinger has to be reconstructed by giving each observer his own realistic, and therefore quantum and fallible, clock so that he can observe correlations with this real physical clock)

I am increasingly enjoying getting to understand the "marseille interpretation" and am glad to have company of the other PFers also engaged in doing this!

 

[Careful]

**thanks for your comments vanesch!
I think we are beginning to arrive at a fair, undismissive understanding of this kind of new Copenhagen or "Marseille Interpretation"

what I like to see emerging, in your (and like) comment is an idea of similarities AND differences and what this may have to offer a.f.a. resolving contradictions.

**

Vanesch is just explaining in full detail here, what I said from the beginning (thanks for taking this job upon you - I can imagine it took quite a while to type that out for the 50'th time on this forum). In case you might have missed it, me nor Josh1 were ever dismissive about RQM, we just do not understand the FUZZ you are making about this (and neither does Vanesch I think - and highly likely the authors themselves find this a miracle too ).

Cheers

Careful

 

[hossi]

still confused

As far as Hossi goes there is only one Hilbertspace, hers, and just this one state of the precious pair of particles which as a token of friendship she has divided with the Dwarves. This state represents her Knowledge...

Hi marcus, thanks for the dwarves, very nice. Let me play this game too, since I still don't get it. I don't have any problem with my Hilbertspace or with the fact that every observers observation is relative until compared, i.e. I know that my knowledge is limited...

I prepare some entangled state of two particles with total spin=0, send one of them in a box to the dwarves at pluto. Then I open my box and find, it's spin 1. From this I conclude nothing since I have read this thread.

Should the dwarves just not have opened their box, there is no problem. I send them a letter, saying: I have spin 1, and when they open their box, they better find -1. No surprise in that, no problem, not even with usual QM.

So, the interesting case is when the dwarves have opened their box before we could have been in causal contact after I opened mine. Have they found spin=-1, fine. Should that always be the case, there is the miracle, alias, non-local collapse of the wave-function. Instead, I thought, it's now possible they also find 1. That however, does not bother me, since I don't know that. Now I send them a letter saying, I have spin=1. What happens when they receive it?

Or are you trying to say, that the very notion of spin = +/- 1 is relative to the measuring apparatus? But then, what happens to conservation laws or, again, how does/can this relativeness change over spacelike seperations.



B (who just found out that her new neighbor has a wireless...)

 

[vanesch]

what I like to see emerging, in your (and like) comment is an idea of similarities AND differences and what this may have to offer a.f.a. resolving contradictions.

Well, my feeling is that philosophical interpretations of quantum theory have the same "function" as theology has wrt to religion: to make you accept the latter within a picture which doesn't run in direct contradictions with what you think are absolute truths. In other words, they help you to picture the thing without running into obvious contradictions.
On one hand, we have a formalism that spits out mountains of useful results which compare with experiment, and which even help in desiging apparatus. On the other hand, it doesn't make much sense. So the need for the "pastor" to come along and help you fit this at first sight totally nonsensical way of reasoning into an acceptable "world picture".
No matter how you turn quantum theory, there's always something crazy about it. For some, we suddenly shouldn't talk about what "is" but just about "observations" or "information". For others, there's a distinction between "normal" objects and "quantum objects". For still others, the mistake was relativity, and if we allow again for a Newtonian picture, we can do so (the Bohmians). Others (like me) prefer to take the formalism (which works well) as litterally as possible, and dig into the philosophy bag to see if nothing can save us there (and we find stuff about minds and so). And finally, there are those that hope secretly (or openly) that this was just the 20th century bad movie, and that we'll soon see the flaws of it.
But all these views have something profoundly disturbing to them ; so you're just supposed to pick that one which fits the best with your temperament and move on.
After all, each of these views have something crazy and something plausible to them. Real breakthroughs do not come from this ; they come from formal breakthroughs, or experiment.

 

[Careful]

**
After all, each of these views have something crazy and something plausible to them. Real breakthroughs do not come from this ; they come from formal breakthroughs, or experiment. **

As always, you are to the point in a diplomatic way. To make it entirely clear: I do not think the Schrodinger/Dirac equations and so on BY THEMSELVES were a bad move - of course not, that would be stupid! As you know, it is **very** difficult to do better, what I find a bad movie however is the pertinent reluctance of trying to do better and taking such philosophical issues SERIOUSLY especially by those who are doing fundamental physics (I am not aiming to anyone in particular here). There is nothing wrong with the shut up and calculate mentality, as long as you are working in a part of QM which is undesputably tested and when your work is phemenologically inspired.

Cheers,

Careful

 

[marcus]

Well, my feeling is that philosophical interpretations of quantum theory have the same "function" as theology has wrt to religion: to make you accept the latter within a picture which doesn't run in direct contradictions with what you think are absolute truths. In other words, they help you to picture the thing without running into obvious contradictions.

I agree with the analogy but my attitude is different in the two cases. I do not WANT to be made to believe in religion and so I do not bother to read theology intended to make it palatable to reason.

On the other hand I WANT to understand the messages nature is sending us through these seeming paradoxes. If we can take seriously all the strange-seeming lessons and find what, of our prejudices, we must give up in order to harmonize, then maybe hopefully we can put it together in a new way that makes sense. I want this, and so I am prepared to listen to an occasional voice like Rovelli who offers to try to do it.

Normally I do not bother with philosophical questions of interpretation but in this case yes*.

...
No matter how you turn quantum theory, there's always something crazy about it. For some, we suddenly shouldn't talk about what "is" but just about "observations" or "information".

I hear you! But for me the idea that QM is about information transactions---one system getting information from another---is more and more seeming NOT CRAZY. Rovelli (and also the late Asher Perez a founder of quantum information theory and someone whose wisdom I respect) have just now TURNED IT A NEW WAY for me so that I see it slightly different and not so puzzling.

But I respect your puzzlement, if it looks crazy to you no matter how you have turned it at least you are trying for it to make sense and you are open to new perspectives, which not all people are.

...
But all these views have something profoundly disturbing to them ; so you're just supposed to pick that one which fits the best with your temperament and move on.
After all, each of these views have something crazy and something plausible to them. Real breakthroughs do not come from this ; they come from formal breakthroughs, or experiment

I disagree here. I think major breaks can come from taking seriously something that our human/animal intuition cannot yet assimilate. The example is Einstein 1905. the FORMALISM of lorentz transf already existed, what he had to do was take it seriously and get over the weirdness. Breaks are sometimes achieved at a PHILOSOPH level and they are often profoundly CONSERVATIVE. Like in 1905 he wanted to conserve and take seriously BOTH maxwell and gallileo----and only he saw the universally accepted obvious truth that you had to give up: simultaneity. So a REVOLUTION IN PHILOSOPHY IS NOT JUST A MATTER OF TASTE as you suggest there, sometimes there is a right way to go

Maybe this is not too much of an oversimplification
1905: one world but no absolute clock---each good-faith observer has his own clock
2005: one world but no single official list of facts---each good-faith observer has his own list of facts labeled his.

but that's just a rough paraphrase, everybody should read the RQM articles--------------------------
* I will always remember how the reactions of people at PF helped me to estimate the value and importance of this recent Rovelli EPR paper. One just has to know how to interpret the signals.

 

[Kea]

Thank you, Vanesh, for writing on your MWI interpretation for the umpteenth time! I agree that what Rovelli says does not seem very different from many MWI viewpoints. However, he has a very nice way of phrasing it, which Marcus for one seems to appreciate, and that makes the paper useful. I have to say that, on your point of dispute re minds, I tend to side with Rovelli. For instance, for electrons going through slits - I think you are making a terribly large assumption that the human observer's slit is important in the state space of the electron. Rovelli does not assume this.

 

[Careful]

**
I disagree here. I think major breaks can come from taking seriously something that our human/animal intuition cannot yet assimilate. The example is Einstein 1905. the FORMALISM of lorentz transf already existed, what he had to do was take it seriously and get over the weirdness. Breaks are sometimes achieved at a PHILOSOPH level and they are often profoundly CONSERVATIVE. Like in 1905 he wanted to conserve and take seriously BOTH maxwell and gallileo----and only he saw the universally accepted obvious truth that you had to give up: simultaneity. So a REVOLUTION IN PHILOSOPHY IS NOT JUST A MATTER OF TASTE as you suggest there, sometimes there is a right way to go **


How, how, Einstein gave up Galileo and later also the inertial observer (special relativity); and up to date there is NO UNIFICATION between GR and Maxwell theory, that is to find a *geometrical* unification between both jeopardizes causality. Also quantum gravity theories are effectively expected to break Lorentz invariance at very high energies, so perhaps promoting Lorentz invariance as a fundamental principle of nature was not such a great idea. But Marcus, you seem to forget the lesson that nobody cared about good old Albert at that time, actually he only became truly recognized after Eddington shouted out that relativity might be a good theory after all (14 years later). Moreover, you seem to overlook the obvious fact that Lorentz still believed in an ether theory and as such must have thought that LI is not a fundamental symmetry for ALL laws of nature. Hence, Einstein REFUTED the ether idea, which was a new PHYSICAL statement about the vacuum. Rovelli's QM does no such thing, it gives indeed some more confort to those trying to interpret quantum gravity amplitudes in a MWI or relative state picture. To be honest, I find it extremely grotesque that you speak about the ``Marseille interpretation´´ and ``a new historical landmark´´.


**
--------------------------
* I will always remember how the reactions of people at PF helped me to estimate the value and importance of this recent Rovelli EPR paper. One just has to know how to interpret the signals. **


I actually read Rovelli's RQM one year ago - so against your opinion I am open to new suggestions, since I know we are still looking for answers to some questions (that is why I truly read some papers still). Rovelli's particular suggestion creates comfort for locality (obviously since it sacrifies realism - which actually has nothing to do with a superobserver) something MWI did 50 years before, but it does not adress the question for a unified dynamics (even) at the quantum level (and as such works with distinguished elements - a very anti Einsteinian thought actually).

Cheers,

Careful

 

[marcus]

... However, he has a very nice way of phrasing it, which Marcus for one seems to appreciate, and that makes the paper useful...

A propos style, Kea, I was just reading Asher Peres on this with considerable pleasure. In the exerpt here (which is germane to our topic) the italics are his.

---quote Peres---
In the EPR article, the authors complain that “it is possible to assign two different wave functions to . . . the second system,” and then, in the penultimate paragraph, they use the word simultaneous no less than four times, a surprising expression for people who knew very well that this term was undefined in the theory of relativity. Let us examine this issue with Bohm’s singlet model. One observer, conventionally called Alice, measures the z-component of the spin of her particle and finds +hbar/2. Then she immediately knows that if another distant observer, Bob, measures (or has measured, or will measure) the z-component of the spin of his particle, the result is certainly -hbar/2. One can then ask: when does Bob’s particle acquire the state with s_z = -hbar/2?

This question has two answers. The first answer is that the question is meaningless — this is undoubtedly true. The second answer is that, although the question is meaningless, it has a definite answer: Bob’s particle acquires this state instantaneously.
---endquote---

BTW have you by ANY improbable chance read Asher Peres remembrance of childhood/adolescence in 1930-1950 Europe called I am the cat who walks by himself
title=quote from Kipling, if you'd had a look I don't think you would've forgotten.

Nathan Rosen was Asher Peres PhD thesis advisor----and in an affectionately remembered incident gave Peres (after some hesitation) his last-but-one reprint of the EPR article.

 

[Kea]

BTW have you by ANY improbable chance read Asher Peres remembrance of childhood/adolescence in 1930-1950 Europe called I am the cat who walks by himself
title=quote from Kipling, if you'd had a look I don't think you would've forgotten.

Marcus

No, I can't say I have. Sounds interesting.

 

[marcus]

Marcus

No, I can't say I have. Sounds interesting.

http://arxiv.org/abs/physics/0404085
I am the cat who walks by himself
Asher Peres
Comments: To be published in a special volume of "Foundations of Physics" honoring the 70th birthday of the author

"The city of lions. Beaulieu-sur-Dordogne. The war starts. Drole de guerre. Going to work. Going to school. Fleeing from village to village. Playing cat and mouse. The second landing. Return to Beaulieu. Return to Paris. Joining the boyscouts. Learning languages. Israel becomes independent. Arrival in Haifa. Kalay high school. Military training. The Hebrew Technion in Haifa. Relativity. Asher Peres. Metallurgy. Return to France. Escape from jail. Aviva."

----------------------------------
The one that is (explicitly) GERMANE, since we should always stay focused and on topic is

http://arxiv.org/abs/quant-ph/0310010
Einstein, Podolsky, Rosen, and Shannon
Asher Peres

"The EPR paradox (1935) is reexamined in the light of Shannon's information theory (1948). The EPR argument did not take into account that the observers' information was localized, like any other physical object."

 

[wolram]

I have one thing to say, and that is prismatics and distorting mirrors, if everyone sees the same thing , it is only after these these (distortions)
are negated, muted.

 

[marcus]

I have one thing to say, and that is prismatics and distorting mirrors, if everyone sees the same thing , it is only after these these (distortions)
are negated, muted.

very true. also one assumes the observers must be competent and of good faith.
we don't allow incompetents who wouldn't know @rse from pickax, and we exclude liars---the kind who insist the elephant is a zebra just to make trouble

but if the observers are all right then EVEN THOUGH THEIR ACCOUNTS may differ in detail, we trust it can all be sorted out
thanks, good point

 

[marcus]

Kea, I mentioned this of Peres

http://arxiv.org/abs/quant-ph/0310010
Einstein, Podolsky, Rosen, and Shannon
Asher Peres

"The EPR paradox (1935) is reexamined in the light of Shannon's information theory (1948). The EPR argument did not take into account that the observers' information was localized, like any other physical object."

You may know it, if not I hope you read it---real nice and only two pages! He likes to make his points by stories.

towards the end of the article, on page 2, Peres says:

"...For Bob, the state of his particle suddenly changes, not because anything happens to that particle, but because Bob receives information about a distant event. Quantum states are not physical objects: they exist only in our imagination. ..."

Einstein Podolsky Rosen asked "Can quantum mechanical description be considered a complete description of physical reality?" As I understand Peres conclusion, he says YES IT CAN and different observers will give different descriptions.

My comment: If Peres is right, then like it or not (I like it) that is just how the world is.
People who like it that way should be happen then.
No one official list of facts that we can say about the world. No one official "wave function".
And people who don't like it should just get over it and get on with their lives.

Great guy.

 

[Careful]

Hi Thomas,

Sorry for the delay, but I liked to take a bit of time to make the phrasing accurately.


**Thank you. Coming from you I take that as a serious compliment.**

Come, come, I am not that severe .

**
I am not sure what these problems are.
**

I was alluding to the usual problems interactions bring along, Haag type misery although you do not work in the interaction picture of course.

**
On page 16 I specialize to Minkowski spacetime. By replacing the geodesic equation by d^2 q/dt^2 = 0 I made t physical, defined in terms of the gravitational field. This could have been empasized more, though.**

I did not miss that but it troubles me somehow. To be precise: if *t* is to be interpreted as an *inertial time function* on spacetime then it would set up an identification between a spacetime vectorfield and \partial_t, which would jeopardize the \partial_t \psi(x,t) = 0 constraint. The same can be said by regarding *t* as eigentime on the selected worldline of the observer where the latter constraint would force zero relative energy. Hence, perhaps it is better not to make such identification at all and quantize the ``full´´ geodesic equation written out wrt to a general non-affine parameter. Then, you could truly speak about the eigentime as a quantum operator with respect to a classical ``life-time parameter´´ t (that is: where is the observer ``alive´´ on the worldline - just a small philosophical remark). I guess this is not such a straightforward thing to do, since in the corresponding equation the eigentime operator will be in the denominator and the spectrum contains zero's as well as purely imaginary numbers which make your life miserable even if you start out with an observer state which is sharply peaked (at t = 0) around some localized (in spacetime) timelike vectorfield. At least, I would naively expect this to be the case .


**
This is of course the problem with doing something that nobody cares about; there is no careful proof-reader.
**

I guess you could submit your papers and at least force the referees to read it through carefully no?


**You mean non-causal separation, no? **

sure- sorry for the typo.

**
Since all points on the observer's trajectory are supposedly causally related, and the Taylor coefficients live on this trajectory, the notion of spacelike separated events disappear from the horizon. This is confusing, and I am not sure that I have digested it yet. However, it is the same miracle that underlies the notion of analyticity.**

Well, this won't be true for the quantum worldline I guess anymore (see my comment above) - though this is negligible of course. But I would like to see that miracle to happen *explicitely*. Generally, I think it would be good if you would somehow clean up the paper and focus on providing rigorous results concerning the issues I adressed during our conversations here (and undoubtedly some others I missed in my quick first reading). In case you manage to do that, I am certainly interested in learning more about it.

Cheers,

Careful

 

[vanesch]

I disagree here. I think major breaks can come from taking seriously something that our human/animal intuition cannot yet assimilate.

Yes, that was in fact the point: you first need that "something" before you can take it seriously. You first needed the Lorentz transformations (which were "too crazy to be really true") before you could take them seriously. My point was - probably I was not very clear - it is not by doing the philosophy that you find the "new something", the philosophy is there to help you take it seriously.

This is BTW, why I prefer an MWI style scheme over a Copenhagen like scheme, or a "modification to introduce collapse": the MWI style scheme is the only one who takes the axioms of quantum theory seriously, all the way. Copenhagen-like versions seem to claim that, no matter the superposition principle, you DO have a classical world, with classical "measurement information" and all that, and there is "of course" no superposition principle valid for macroscopic objects. This sounds a bit like the ether interpretation of Lorentz transformations, which was nothing but a "trick" to calculate outcomes of measurements.
I think that _or_ quantum theory is *totally* misguided, in which case fiddling with it doesn't really help, or it is *fundamentally* correct, in which case we have to take it seriously all the way.

So, let us say that, what leads the game is the formalism, and what "delivers the mind" is the philosophy, which avoids you to cling onto the old paradigms in which you try to force the new scheme.
But without formalism in the first place, there's not much hope to get the view right.

Like in 1905 he wanted to conserve and take seriously BOTH maxwell and gallileo----and only he saw the universally accepted obvious truth that you had to give up: simultaneity. So a REVOLUTION IN PHILOSOPHY IS NOT JUST A MATTER OF TASTE as you suggest there, sometimes there is a right way to go

Let's say that the "right" philosophy should follow the formalism, and not have its own prerogatives.
So what I consider an error is to say that quantum theory is "only concerned with certain quantum systems" or "a trick to calculate measurement outcomes". This is forcing it into the classical paradigm somehow.
If, when applying quantum theory strictly, I arrive at describing my body state as a superposition of two totally different states, and as I clearly don't see this, then of two things one:
- or this is in a certain way correct, and I then have to explain WHY I don't see this (MWI style, relative-state approaches in all their variants)
- or this is fundamentally wrong, and what I see is correct. In that case, quantum theory is fundamentally wrong, and all ways to "weasel out" by saying that it is "about information I have, not what's going on" or "there's no such thing as a quantum description of my body" or the like are, exactly, philosophical attempts to remain in the old classical paradigm.

 

[Careful]

**
I think that _or_ quantum theory is *totally* misguided, in which case fiddling with it doesn't really help, or it is *fundamentally* correct, in which case we have to take it seriously all the way. **

This I find a bit simplistic, what is wrong e.g. with the point of view of 't Hooft who takes QM as an operational scheme very seriously? I mean Lord Kelvin did not have to understand the kinetic theory of gasses and solid state physics either in order to find out about the laws of thermodynamics. And as you know, in this context, it is still troublesome to describe something like friction starting from a time reversible microscopic dynamics.

**
So what I consider an error is to say that quantum theory is "only concerned with certain quantum systems" or "a trick to calculate measurement outcomes". This is forcing it into the classical paradigm somehow. **

Well, in any case, it tells us a lot about potential classical alternatives too.

**
If, when applying quantum theory strictly, I arrive at describing my body state as a superposition of two totally different states, and as I clearly don't see this, then of two things one:
- or this is in a certain way correct, and I then have to explain WHY I don't see this (MWI style, relative-state approaches in all their variants)
- or this is fundamentally wrong, and what I see is correct. In that case, quantum theory is fundamentally wrong, and all ways to "weasel out" by saying that it is "about information I have, not what's going on" or "there's no such thing as a quantum description of my body" or the like are, exactly, philosophical attempts to remain in the old classical paradigm.**

Well, the first option leads to a dual world view (whatever you try out) and the second one is not for tomorrow (at least ).

Cheers,

Careful

 

[Thomas Larsson]

**
This is of course the problem with doing something that nobody cares about; there is no careful proof-reader.
**

I guess you could submit your papers and at least force the referees to read it through carefully no? Careful

This paper and its two follow-ups were written as a preparation for an article appearing in a book which will be available very soon: https://www.novapublishers.com/catalog/product_info.php?products_id=3848 . I am sure that submitting it to an independent referee would be useful (although perhaps would lead to copyright violations), but since I am lazy and have no use for an academic CV, it did not happen. However, the two key papers on the representation theory, http://www.arxiv.org/abs/physics/9705040 and http://www.arxiv.org/abs/math-ph/9810003 , did appear in CMP.

At any rate, what you found are nitpicks compared to the flaws I mentioned myself in my previous post (overcounting for the harmonic oscillator and the absense of an inner product). These are the areas that need to be, and are being, addressed first. But I agree that my discussion on reparametrization invariance is confused. I thought it was clear when I wrote it, though.

I am not particularly happy about having to invent a new formulation of QM. However, I see no alternative. The key lesson from the multi-dimensional Virasoro algebra is that all fields have to be expanded in a Taylor series around the observer's trajectory. To profit on this insight, I need a formulation of QM written solely in terms of Taylor expandable objects. Non-local integrals, like the Hamiltonian and the action functional, do not satify this criterion, but the Euler-Lagrange equations do. Therefore, I need a formulation of QM where these encode the dynamics.

Finally, let me comment again on the relation between observer independence and QG infinities. The philosophical kinship between MCCQ and Rovelli's RQM is observer dependence, and that the observer possesses physical properties. AFAIU, the only property that Rovelli attaches to the observer is position, but this is naturally generalized to other physical properties, in particular energy (or mass) and a clock.

In conventional QM, time just marches on independent of what happens. Time must operationally be defined by ticks on the observer's clock, and thus the observer does not accelerate. However, observation means that the observer interacts with the system, experiencing a force F = ma. If F != 0 and a = 0, the observer's mass m is necessarily infinite. This is no problem we observe an electric phenomenon, say. Then F = ma = qE, where q is the observer's charge and E the electric field generated by the system. That q and E are non-zero and a = 0 is OK, since m = infinity is a good approximation to reality.

But when we introduce gravity, the force on the observer is rather F = ma = mg, where g is the gravitational field generated by the system. This leads to the equation a = g, which is clearly incompatible with no observer acceleration (a = 0) and non-zero gravitational field (g != 0). That the inertial and gravitational masses are the same thus immediately implies that ignoring observer acceleration leads to inconsistencies in quantum gravity.

This is a happy thought indeed!

 

[Careful]

**but since I am lazy and have no use for an academic CV, it did not happen.**

I do not see how this fits with your wish to have a careful proofreader.

**
At any rate, what you found are nitpicks compared to the flaws I mentioned myself in my previous post (overcounting for the harmonic oscillator and the absense of an inner product). These are the areas that need to be, and are being, addressed first. But I agree that my discussion on reparametrization invariance is confused. I thought it was clear when I wrote it, though. **

That went without saying no, I felt no need to comment about the latter issues since you were so forthcoming about this yourself.


**
In conventional QM, time just marches on independent of what happens. Time must operationally be defined by ticks on the observer's clock, and thus the observer does not accelerate.**

? There is no problem whatsoever in defining QFT with respect to (non-uniformly) accelerating observers (and bending the foliation according to local eigentime - as long as one does not encounter focal points).


** However, observation means that the observer interacts with the system, experiencing a force F = ma. If F != 0 and a = 0, the observer's mass m is necessarily infinite. **

Obviously a is not zero.

** This is no problem we observe an electric phenomenon, say. Then F = ma = qE, where q is the observer's charge and E the electric field generated by the system. That q and E are non-zero and a = 0 is OK, since m = infinity is a good approximation to reality. **

? The m in the Newton formula is the physical mass and not the bare mass, for an electron that is still the very tiny number of 10^{-30} kilo at least when it moves smaller than c wrt an inertial observer. You can find such information in Eric Poisson, ``An introduction to the Lorentz Dirac equation´´ gr-qc/9912045 where such understanding is offered at a classical level.

The rest of your comments get equally many question marks.

 

[hossi]

still confused

Hey brainy guys,

me and my dwarves, we would really like to play your adult's games. But I still did not get the point.

I have observers A and B, measuring alpha and beta when not in causal contact. That does not neccessarily have to be the same time (which is not well defined anyway), but let's say in whatever slicing its the same time t_0. We know the total spin is zero. Let us say they measure

S_A,alpha = 1
S_B,beta = 1

which is not a problem, because they have not compared their stuff. Now go to time t_1 when they are in causal contact and measure the other part of the previously entangled state. They find

S_A,beta = -1
S_B,alpha = -1

Now, I would have thought S_B,beta is what B has measured for beta at t_0. According to Rovelli, the important thing is now to let A ask at t_1 what B has measured. This is

S_AB = S_A,beta = -1

which is not what B has measured at t_0. Has B changed his mind concerning the measurement of beta from 1 to -1? Or has he not changed his mind but A always hears the answer he wants to hear? If so, does that make sense macroscopically?



B.