What Is the Marseille Interpretation of Quantum Mechanics?

[marcus]

the term "Marseille" is used humorously in part, it could also be called the "Haifa Interpretation" because Asher Peres contributed and he was at the Technion

and also David Mermin at Cornell (Ithaca, NY) has written similar stories about how to interpret QM and has called his stories the "Ithaca Interpretation"

Or it could be called "Princeton" because of B. van Fraasen's contribution, or one could cite Michel Bitbol who is somewhere in France and call it the "French" interpretation. That actually sounds OK and would include the Marseille people.

==================

Anyway we need a thread that focuses just on the Marseille interpretation of QM and does not get sidetracked. I need some peace and absence of distraction in order to unfold whatever it is this has to tell us.

==================

The first thing to say is that INTERPRETATION has to do with the STORIES rather than the mathematical notation or "formalism". Two people can use the same or very similar formulations----the same subscripts and the same equations, or almost the same---and interpret them in radically different ways.

when we are discussing interpretation, similarity at the level of symbolic notation is SUPERFICIAL RESEMBLANCE and what is deep is the stories.
===================

An illustration of this is that the math of Special Rel was developed by a highly respectable Dutchman named Hendrik Lorentz, who unfortunately told the wrong STORIES about it.
One could say Einstein's contribution to Special Rel was an INTERPRETATION of formulas that were already there. He found the right philosophical spin to put on them.

In particular he found that you had to give up the intuitive notion of SIMULTANEITY.

=============
Simultaneity was deeply rooted in the human mind, for a reason I will discuss, and in order to tell the right stories about the Lorentz transformations you had to give it up-----eradicate, meaning tear out by the roots. Not easy to do. A purely philosophical step, and nevertheless necessary to the development of physics at that junction.

=============
So we have to be alert to whatever the Marseille Interpretation is asking us to give up. It will be something that seems obvious to us but for which there is no actual concrete evidence.

 

[f-h]

What do you want to talk about in this thread?

 

[marcus]

What do you want to talk about in this thread?

Smerlak Rovelli, and also
Asher Peres (who, while he may not be saying exactly the same thing, says it very nicely)

Also the Laudisa Rovelli article in the Stanford Encyclopedia sheds some light

First and foremost I want to EXPLICATE----to hear receptively what these voices are saying

In case anyone is new to this, I will get some links

==============

Oh BTW Rovelli Smerlak says repeatedly what it is we have to give up. It is Einstein's super-realism. This is a deeprooted mistake for which there is no actual evidence----the unstated assumption that there is one preferred account of the facts.

The several QM paradoxes, by now banal, show that the super-realism assumption is an UNREALISTIC EXPECTATION to have about nature.

Nothing in our experience supports the notion that there is one official account of the facts. But some people persist in believing that there should be. I want to try to understand their psychology.

Why the notion that there should be one preferred wavefunction, one bookkeeping device, should be psychologically appealing to some. I think it is the superbeing perspective, which it may be emotionally satisfying to adopt and this may explain the deep-rooted appeal of what is AFAICS unsupported by the experience of empirical science

 

[marcus]

What do you want to talk about in this thread?

Here is Rovelli Smerlak
http://arxiv.org/abs/quant-ph/0604064
Relational EPR
Matteo Smerlak, Carlo Rovelli
7 pages
"We argue that EPR-type correlations do not entail any form of "non-locality", when viewed in the context of a relational interpretation of quantum mechanics. The abandonment of strict Einstein realism advocated by this interpretation permits to reconcile quantum mechanics, completeness, (operationally defined) separability, and locality."

Here is Peres
http://arxiv.org/abs/quant-ph/0310010
Einstein, Podolsky, Rosen, and Shannon
Asher Peres
2 pages
"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."

Here is the Stanford Encyclopedia 2005 article of Rovelli Laudisa
http://plato.stanford.edu/entries/qm-relational/
Relational Quantum Mechanics

Miscellaneous additional links or material cited in the above
Here is James Hartle on throwing out excess baggage (as the way to make progress)
http://arxiv.org/abs/gr-qc/0508001

Here is Rovelli 1996 RQM
http://arxiv.org/abs/quant-ph/9609002

 

[f-h]

I see, I'm quite familiar with RQM by now and will just give my own personal perspective here. There are two analogies that drive it, galillean and special relativity, which both say that different observer descriptions on something particular might not agree, that the valid statements are "relational".

What is critically missing from RQM is synchronisation. Due to this RQM is IMO best understood as an account of why the formalism of QM, which escapes any consistent onthological interpretation, even as relational data, is still consistent epistemologicaly for all observers.

 

[marcus]

...formalism of QM which escapes any consistent onthological interpretation... is still consistent epistemologicaly...

Asher Peres put this nicely in "EPR Shannon" he said

Quantum states are not physical objects: they exist only in our imagination. [/color][/size]

====================

But as to what is really missing, or rather what has been EJECTED, Rovelli Smerlak tell us over and over what excess baggage they think we have to throw out: they refer to it as "EINSTEIN'S STRICT REALISM" and words to that effect---some single-minded insistence on one preferred account of the facts.

maybe it comes to the same thing as what you said

 

[Hurkyl]

I'll have to read some more to decide what I think about these...

But, I am quite pleased to see people addressing the EPR paradox from the perspective that EPR is asking some sort of "non-local question".

 

[f-h]

Well, the question is, are we done if we keep saying let's throw away the excess baggage and take quantum states as epistemological.

Imagine we have three systems A, B and C. A and B meassure C. Now if A meassures what B has meassured with respect to C it will find it consistent with it's own meassurement of C. So will B with respect to A. What they will find if the epistemological states are all there is is not related at all.
So B might observe that itself and A have found C to be in state c_1 while A might find that B and itself have found C in state c_2. There is no paradox here of course.
But in this sense this complete "epistemologisation" of physics implies an extreme soliplism.

If we "synchronise" the different experiences we get something equivalent to collapse again.

In this sense it shows first and foremost that physical predictions are insensitive to the interpretation of Quantum Mechanics, but I wouldn't really call RQM an interpretaion of QM.

 

[Hurkyl]

Now if A meassures what B has meassured with respect to C it will find it consistent with it's own meassurement of C. So will B with respect to A. What they will find if the epistemological states are all there is is not related at all.
So B might observe that itself and A have found C to be in state c_1 while A might find that B and itself have found C in state c_2. There is no paradox here of course.

I think you're still thinking externally.


I think you're imagining "Okay, A did his experiment, and saw this". And "B did her experiment, and saw that". And you, from your external viewpoint, are comparing things.


But if you do things internally, it all works out. You perform an experiment in which A and B meet to compare notes.


It's (IMHO) easy to see that the formalism predicts the only possible outcome is that A and B agree on what they saw.

 

[f-h]

Hurkyl, yes, this is correct.

But outlawing all external thinking is precisely the extreme soliplism I was talking about.

 

[Hurkyl]

I meant my post to counter your assertion that we have to add in something called "synchronization", and that it's equivalent to collapse.

I assert it's already in the formalism, and doesn't involve collapse.

 

[f-h]

Hmmm...

What I meant is that if there is a third system D asking A and B what they saw it will find that A and B saw the same thing, but the problem remains that what A saw might be different from what B saw, because what they saw has reality only with respect to themself and not with respect to D.

I don't see a mechanism in the formalism that does what you say. Could you elaborate?

 

[Careful]

I meant my post to counter your assertion that we have to add in something called "synchronization", and that it's equivalent to collapse.

I assert it's already in the formalism, and doesn't involve collapse.

Logically correct (that is basically also Patrick's position), f-h is trying to put in realism again by his synchronisation procedure (which of course I do appreciate ). Ah elaborating upon f-h's comment, suppose A and B observe an electron flying trough an SG apparatus with polarization in the z direction and psi_electron = a |up> + b |down>, then the state D observes is
a |up > | Asees up> | Bsees up> + b |down> | Asees down> | Bsees down> at least when you can assume that A,B are reliable persons. Then D sees A and B agree as is determined by the quantum *dynamics*. Now indeed, it could be that if A,B and D are doing sequentially this game (with sufficient time for causal communication) then it could be that at the N'th step A records up, B down, D sees A and B record up, A sees B record up. That is the price to pay if you give up realism and still is the reason why I reject this line of thought.

Cheers

Careful

 

[Hurkyl]

I don't see a mechanism in the formalism that does what you say. Could you elaborate?

The analysis from the D system would look like:

(a|1> + b|2>) |A's initial state> |B's initial state> |D's initial state>

If we evolve the state through the measurement of A, we get:

(a|1>|A=1> + b|2>|A=2>) |B's initial state> |D's initial state>

And if we evolve the state through the measurement of B, we get:
(a|1>|A=1>|B=1> + b|2>|A=2>|B=2>) |D's initial state>

(and we get the same result if we do it the other way around)

And then evolving through D's measurement yields:

(a|1>|A=1>|B=1> + b|2>|A=2>|B=2>) |D sees that A = B>

 

[hossi]

Quantum states are not physical objects: they exist only in our imagination.

well, I don't know about you but in my imagination it's the other way round - there exist no quantum states Quantum states are not actually observable, but is that so mysterious? Potentials (thermo, electromagn.) e.g. are (in most cases) also not observable, but still it's handy to work with them.

B.

 

[f-h]

Yes I agreed with that. As I said, there is no paradox and D sees A and B agree. But in RQM what you just wrote down was the analysis of what D sees A see which a priori has nothing to do with what A sees, that's the "problem".

I just saw that hossi pointed out the very same thing in the other thread: https://www.physicsforums.com/showpost.php?p=965093&postcount=70

Nice way to put it. Everybody always hears what they must hear to avoid paradoxes in RQM. You have to consider what "A sees B see" as independent from what "B sees" in the set up of your theory.

 

[Careful]

Yes I agreed with that. As I said, there is no paradox and D sees A and B agree. But in RQM what you just wrote down was the analysis of what D sees A see which a priori has nothing to do with what A sees, that's the "problem".

I just saw that hossi pointed out the very same thing in the other thread: https://www.physicsforums.com/showpost.php?p=965093&postcount=70

Nice way to put it. Everybody always hears what they must hear to avoid paradoxes in RQM. You have to consider what "A sees B see" as independent from what "B sees" in the set up of your theory.

I basically answered that objection, each of your different relative states give different local ``collapse´´ possibilities. To synchronise these possibilities is tantamount to treating all macroscopic systems as classical which brings you back to the realist nonlocal collapses - that is exactly why I thought one year ago ``nonsense´´ when reading this (I am a realist, cannot help it).

Cheers,

Careful

 

[f-h]

Careful, I think we are in complete agreement. According to RQM you do not synchronise of course. Not synchronising does NOT lead to paradoxes, only indigestion and vertigo.

 

[Hurkyl]

You have to consider what "A sees B see" as independent from what "B sees" in the set up of your theory.

No you don't. You make an experiment that detects what A sees B see, and what B sees, and test for a correlation.

In other words, the question as stated is aphysical -- but you can make it physical in terms of the actual experiment where C compares what C sees A see B see, and what C sees B see.

(And the correlation will be 100%)

 

[Hurkyl]

The Rovelli paper makes it sound like some sort of gauge freedom -- I'm not sure what I think of that, but meh.


It's appealing to the theorem that it doesn't matter when wavefunction collapse is applied -- you'll get the same answers out either way. So it's reasonable to posit that the choice is aphysical (and that there is some aphysical freedom in the choice of wavefunction as well).

In other words, collapsing when A saw something, and then evolving to when D watches A and B compare notes is physically the same as just evolving all the way up until D's observation and collapsing there.

 

[f-h]

Hurkyl, I agree with what you say. It doesn't touch my point. I wasn't pointing out a physical question that would require collapse (in this sense) to be consistent. I was pointing out what to me appears to be a characteristic feature of an RQM universe: Universal soliplism.

There is nothing in RQM as presented so far that prevents A from seeing green, B from seeing red, and D from seeing A and B see yellow. And E from seeing A, B see magenta and seeing D seeing A and B see magenta and so on and so on ad inf.

Each of the physical questions asked is consistently answered, every observation is consistent with every observation of an observation.

But the price is the disconectedness of all the experiences/information each system acquires about the other systems.

 

[Hurkyl]

There is nothing in RQM as presented so far that prevents A from seeing green, B from seeing red, and D from seeing A and B see yellow. And E from seeing A, B see magenta and seeing D seeing A and B see magenta and so on and so on ad inf.

Yes there is. It is physically impossible for \omega to see A see green, and to see B see red, and to see D see A and B see yellow, and so on ad inf.


Of course, I know you know that. But you're missing the point -- you don't give up "connectedness of experience/information". What you do give up is the ability to perform the sort of classically inspired external manipulations that you need to use to arrive at the conclusion of a "disconnected experience/information."


(At least, if my initial perception of these papers is accurate)

 

[f-h]

"Yes there is. It is physically impossible for \omega to see"

But that's not what I said.

I'll have to ponder this more, I know that what you say is what they are claiming to do, but to me it looks like the way they are doing it leads to the disconnectedness I described.

 

[hossi]

Ah, I think I finally have a vague idea of the interpretation!

Is it that at every point in space and time there is in principle an infinite amount of equally relative observers, each having his own history of observation, each ones history in agreement with quantum mechanics. And though each ones history might be different, no one can tell, cause there is no one who can compare them. And whenever you ask the question whether two histories agree, you have to invoce quantum mechanics, and though the observers have different histories, they hear only an answer that agrees with their opinion.

Is that about correct? Could you give me some feedback?

Does that mean that these histories are kind of classified in the sense that concerning future predictions they have to be identical. I.e. the mouse might be tasty or yukky, but it definately is a mouse and the cat will try to eat it?



B.

 

[marcus]

Ah, I think I finally have a vague idea of the interpretation!

Is it that at every point in space and time there is in principle an infinite amount of equally relative observers,...
Is that about correct? Could you give me some feedback?
...

Hi Biene. Do you want just f-h to reply? or the person you were talking to? Or should somebody else like me also give feedback?

BTW the picture you present seems a bit bizarre to me. In normal QM one does not usually picture so many observers. One may have Alice and Bob and maybe Professor Podolsky----or Wigner's friend inside the box, or maybe a Cat----in any case one has just as many observers as one needs to do the particular experiment or tell the particular story.

In RQM one would have just the same number of observers as in usual QM, I think.

Or perhaps one fewer, because one does not have an Absolute observer who has the Absolute correct state. but let us not worry about a difference of one or two.

the main thing is, I think, there is the same number of observers whether it is usual kind QM or relational QM.

maybe f-h says different?

 

[selfAdjoint]

An infinite sea of unobserved observers?

 

[marcus]

An infinite sea of unobserved observers?

No selfAdjoint. That is not RQM.

I don't know where Hossi got the idea.

I made a recap post to give the essential definition of what RQM is about
https://www.physicsforums.com/showthread.php?p=965312#post965312
it is #72 on the Elephant thread

 

[hossi]

No selfAdjoint. That is not RQM.

I don't know where Hossi got the idea.

Well, I am trying my best I did not mean to introduce more observers as in usal QM, but can't I have a continum of observers not in causal contact observing the same event? Among them Bob and Alice? And at some point they compare their stuff. It's not an infinite sea of unobserved observers, since they do observe each other (or what do you mean with unobserved?). I am having kind of problems finding that plausible, but if anyone could answer my question how Bob and Alice agree on their different measurement histories (before they were in causal contact) otherwise, please enlighten me.



B.

 

[marcus]

... can't I have a continum of observers not in causal contact observing the same event? Among them Bob and Alice? And at some point they compare their stuff...

it sounds like a creative idea. If Niels Bohr will let you have that in usual QM, then I suppose you can have the same setup in Rovelli setup.

RQM tends to equate observers with systems-----there is not much difference.

I have a hard time imagining more than a finite number of systems, and so I can't easily picture more than a finite number of observers (which are quantum systems interacting with other systems)

Biene, maybe the thing is to read Rovelli's paper "RQM" where he talks about what is an observer.

I guess if you can picture a continuum of distinct SYSTEMS not in causal contact (but I cannot) then you can say they are all observers and then you have a continuum of distinct observers.

the main thing is not to make unnecessary difficulty. the RQM is just the usual QM except you dump the notion of an absolute state:
you allow observers to disagree, which we know they do anyway, and you STOP EXPECTING that somehow they are going to agree.

so it is business as usual, except possibly minus a superbeing---comparatively easy and pleasant. I don't understand the face you are making with the tongue

=====================
Biene, I hope all is well with you.

I had a thought after I had gone to bed, and woke up. The thought was that your continuum of observers (which is so alien to RQM as I understand it) is TELLING ME SOMETHING ABOUT MANY WORLDS INTERP.
It is in manyworldsinterp. that one might have a trajectory of observers. actually it would be branching like crazy, going forwards
but if you follow it back it might look like a smooth or almost smooth curve in some Baroque monster space.

So your having this mental picture of a continuum path of observers was a way of helping me understand how manyworlds (which has never interested me so I haven't thought about much) is concretely different from relational. I don't know if you meant it that way, but thanks.

 

[koantum]

In the Quantum Physics Forum there is a thread called https://www.physicsforums.com/showthread.php?p=965424&nojs=1#goto_threadsearch".

Since hurkyl pointed me here, I went through this thread. I find myself in sympathy with what Marcus says in it. Some additional comments:

Well, the question is, are we done if we keep saying let's throw away the excess baggage and take quantum states as epistemological.

If we have thrown away the excess baggage, we are finally in a position to arrive at http://thisquantumworld.com" .

Quantum states are not actually observable, but is that so mysterious? Potentials (thermo, electromagn.) e.g. are (in most cases) also not observable, but still it's handy to work with them.

Only in most cases? The point is: they are nothing but mathematical tools handy to work with.

P.S. I wonder why this thread, which discusses an interpretation of the standard quantum formalism, comes under "Beyond the Standard Model".

 

[marcus]

...Since hurkyl pointed me here, I went through this thread. I find myself in sympathy with what Marcus says in it. ...

P.S. I wonder why this thread, which discusses an interpretation of the standard quantum formalism, comes under "Beyond the Standard Model".

Welcome koan (enigmatic Zen saying) tum. Clever handle

I am glad of your sympathy---that we share somewhat of a common perspective.

Why don't you start a thread in QM forum about RQM? I would not want to participate because what interests me is something we have not discussed yet-----THE CONNECTION BETWEEN RQM AND fundamental theories of spacetime-and-matter.

Often called "Quantum Gravity", there are these theories-in-progress which aim at getting a new understanding of spacetime-and-matter.
sometimes called non-perturbative QG, sometimes called BACKGROUND INDEPENDENT QG, these are generally speaking NON-STRING theories seeking the fundamental degrees of freedom of spacetime and matter.
and how matter and geometry interact.

Well, rovelli is a world-leader in this sort of QG. He has deep physical intuition about this class of problems and is unusually clear-sighted. Repeatedly he has been one of those who sees the issues clearly. He doesn't do anything just to do something, to publish a paper.

If he takes the trouble to explore a philosophical question, it is because he thinks there is a PHILOSOPHICAL OBSTACLE TO PROGRESS IN QG.

So I watch RQM in the same forum where I watch other Rovelli work, they are INTERCONNECTED.

======================

SPECIFICALLY there is an important area of discussion in QG called the "PROBLEM OF TIME".
relational QM solves this "problem" very neatly. there are no absolute clocks, there are only natural, which is to say quantum and fallible, ordinary MORTAL clocks.

The blessed Bianca Dittrich once took mercy on Thomas Thiemann and raked his chestnuts out of the fire for him by using Rovelli RQM. Relational QM is central to how people are finding out how to address difficult questions in QG.

because there is no supernatural absolute classical official CLOCK clock, but only natural clock-like things, it is the Heisenberg picture and there are CORRELATIONS between events and readings on these natural clocks.

RQM is about correlations. So RQM is about HOW TIME PASSES IN QUANTUM GRAVITY.
===================

Now keep in mind that what I am saying here is my personal motivation for discussing two sides of rovelli work in the same house. I am not telling you some immutable truths, I am explaining my interest and motivation. I should go back and put "IMHO" in front of all the sentences. Dont quote me and decide for yourself what is right.

but you see, for me, RQM is really really important to the QG context.
it is not just some separate philosophical issue (in which case i would not bother with it since philosophy is not my main concern)

 

[f-h]

Hmmm... RQM is supposed to solve the problem of interpretation of QM, not the problem of time in Quantum Gravity.
While in some sense these seem to be related problems they are very clearly distinct. Particularly there is a whole body of work on relational time spawned by Rovellis concepts of partial and complete Observables and evolving constants of motion, including perhaps most notably so far Dittrich's Thesis, but these work with any odd interpretation of quantum mechanics (or in Dittrichs case it's mostly classical).

The overarching philosophical idea is relationality, but it's different uses should not be confused...

 

[marcus]

there is a whole body of work on relational time spawned by Rovellis concepts of partial and complete Observables and evolving constants of motion,

I know. Have seen several papers. not only by Dittrich. particularly recall one by Bojowald. it is a good line of development IMHO. I am glad you mentioned it.

The overarching philosophical idea is relationality, but it's different uses should not be confused...

You are heartily welcome to keep RQM and QG separate in YOUR mind, f-h.
I am trying to explain to koantum something about where my interest in these things comes from. I do not say that I should or should not make these connections---and I certainly don't tell YOU to make them!
I am saying that I DO draw the connection. And you will kindly refrain from telling me that I should not My motivation and interests are my own business.

 

[marcus]

what is RQM

It may be that some people have not yet had a chance to read the first paragraph of Rovelli 1996 paper called "RQM". this is the paper where he first defined and proposed RQM. This says authoritatively and clearly what I understand to be essential about RQM.

---quote Rovelli 1996 RQM paper---
I. A REFORMULATION OF THE PROBLEM OF THE INTERPRETATION OF QUANTUM MECHANICS

In this paper, I discuss a novel view of quantum mechanics. This point of view is not antagonistic to current ones, as the Copenhagen [Heisenberg 1927, Bohr 1935], consistent histories [Griffiths 1984, Griffiths 1996, Omnes1988, Gell-Mann and Hartle1990], many-worlds [Everett 1957, Wheeler 1957, DeWitt 1970], quantum event [Huges1989], many minds [Albert and Lower 1988, 1989, Lockwood 1986, Donald1990] or modal [Shimony 1969, van Fraassen 1991, Fleming 1992] interpretations, but rather combines and complements aspects of them.

This paper is based on a critique of a notion generally assumed uncritically. As such,it bears a vague resemblance with Einstein’s discussion of special relativity, which is based on the critique of the notion of absolute simultaneity.

The notion rejected here is the notion of absolute, or observer-independent, state of a system; equivalently, the notion of observer-independent values of physical quantities.

The thesis of the present work is that by abandoning such a notion (in favor of the weaker notion of state-–and values of physical quantities–-relative to something), quantum mechanics makes much more sense.

This conclusion derives from the observation that the experimental evidence at the basis of quantum mechanics forces us to accept that distinct observers give different descriptions of the same events.

From this, I shall argue that the notion of observer-independent state of a system is inadequate to describe the physical world beyond the hbar->0 limit, in the same way in which the notion of observer-independent time is inadequate to describe the physical world beyond the c->oo limit.

I then consider the possibility of replacing the notion of absolute state with a notion that refers to the relation between physical systems.[/color][/size]
-------endquote-------

The main idea is to get rid of the notion of an absolute state---an official right set of facts or measurements---because that idea causes trouble in QM and there is no physical evidence that one should expect such a thing. It is an unrealistic expectation.

Also I see that the idea of ABSOLUTE TIME may be an unrealistic expectation. I don't see evidence of any observer-independent time anywhere in the universe. Since the passage of time depends on how deep you are in the gravitational field, the age of the universe as you measure it will depend on how deep you are in your galaxy, and what galaxy and cluster you are in, and the HISTORY of that galaxy and your position in that galaxy. And on a lot of other things having to do with the history of your star and planetary system etc.

One can make a toy model of the universe and define an absolute time for that toy model which will APPROXIMATE a universal time. But that is an approximation, it is still not absolute time.

And when I look for actual evidence of there being absolute time, all the clocks I see are real (ultimately quantum mechanical) devices and all depend on who is observing the clock.

So I agree with what I see in a growing body of papers which is that all we have for sure are the CORRELATIONS between things that one can observe. And time is one of those correlations----between observing the hands of the clock and the natural process like the potatos boiling on the stove.

So f-h you can declare that I am not logical but what I see coming out of RQM is an OBSERVER-DEPENDENT IDEA OF TIME where the observer consults a real quantum clock-device. a natural not absolute clock. and CORRELATES those observations of the clock-like thing with OTHER observations. like potatoes. or the moons of Jupiter.

and you can insist that this (we both know about Rovelli's partial observables) is a SEPARATE BUSINESS and not connected with RQM, but quite frankly I am not so sure of that. I think there may be some connection.

 

[f-h]

There's also Gambini et. al. but that's offtopic here I guess...

---

As a motivation yes certainly I think that is shared by many people, I just wanted to warn that the different kind of relationalities involved, while connected, are different and confusing them might lead to... well, confusion.
Eventually maybe we'll understand that they are all the same after all.

Edit:
Ah I missed your second post, I see we agree.

 

[marcus]

There's also Gambini et. al. but that's offtopic here I guess...

---
.

It is so great! using a black hole as a clock to do a thought experiment by which a theoretical lifetime-accuracy BOUND on all the clocks that can exist is derived. so so beautiful. that paper of Gambini Pullin and maybe someone else

it is hard to think that such a beautiful paper can be offtopic. maybe there is some connection...

 

[f-h]

Actually I was thinking of their earlier work like gr-qc/0101057. "Relational time in generally covariant quantum systems." Gambini+Porto.

 

[marcus]

Actually I was thinking of their earlier work like gr-qc/0101057. "Relational time in generally covariant quantum systems." Gambini+Porto.

Ah. I never read that (or even stared at it hard). It sounds by title to be much more a propos than what I was thinking of. I will get the link to what I had in mind.

Beginning to realize that I WAS confusing two different things----relational time does NOT equal relational QM. You were quite right. but I believe connected even though different. I wish I could ask rovelli or one of your team what is the connection (if any) between r. time and r. QM. thank for alerting me to the confusion

=====================
F-H I expect you have read this one, but I will put the link in case anyone else reads the thread and is curious. I was delighted with this paper

http://arxiv.org/abs/hep-th/0406260
Realistic clocks, universal decoherence and the black hole information paradox
Rodolfo Gambini, Rafael Porto, Jorge Pullin
3 Pages
PhysRevLett.93.240401

"Ordinary quantum mechanics is formulated on the basis of the existence of an ideal classical clock external to the system under study. This is clearly an idealization. As emphasized originally by Salecker and Wigner and more recently by other authors, there exist limits in nature to how 'classical' even the best possible clock can be. When one introduces realistic clocks, quantum mechanics ceases to be unitary and a fundamental mechanism of decoherence of quantum states arises. We estimate the rate of universal loss of unitarity using optimal realistic clocks. In particular we observe that the rate is rapid enough to eliminate the black hole information puzzle: all information is lost through the fundamental decoherence before the black hole can evaporate. This improves on a previous calculation we presented with a sub-optimal clock in which only part of the information was lost by the time of evaporation."

Raphael Porto was at Carnegie Mellon during 2004-2005. He may still be. Someone i think was he posted here at PF for a while, but I haven't seen any sign of him for something like a year.

 

[rtharbaugh1]

Hi

Just a few comments...I will try to keep it crisp.

Quantum states are defined as momentum and position measurements, is that correct?

Momentum involves velocity which involves time, so to say that there is no absolute, preferred time is to say that there is no absolute preferred momentum.

Position involves measuring separation. Two points are necessary, a chosen fixed starting point and a calculated or observed end point. Since there are two points, there has to be a movement between them, hence bringing in time again. And again, no absolute time means no absolute position.

Hence it seems inevitable to me that once one accepts SR's assertion of no absolute clock, one must accept that there is no absolute position or momentum. So the universe of space, like the universe of time, has to be relational.

I am glad to see that the notion of an observer has been added to the idea of object. Both are required for any measurement. Has anyone considered that the relationship between the observer and the object adds a necessary third term? So the observer having state O sees the object having state B, as I look at a drawing of a three dimensional still life. The drawing is not the object, but a limited dimensional representation of the object. So I would assert that every measurement has an observer, a relational screen, and an object, making three necessary conditions to any event.

I apologise for barging in like this, but as I read these threads, the same thoughts keep coming back to me, as outlined above. Careful, your position seems to me to be that of a rationalist, not of a realist. How do you account for the irrationality of measurement in your idea of a real (hence absolute?) universe?

Thanks,

Richard

 

[marcus]

off the cuff reaction, Hi Richard, the idea of absolute time has been undermined in two or maybe more stages
1905 SR is still fairly simple, you give up absolute simultaneity but they can still define position momentum energy straightforwardly----and they have lorentz transformations readymade maps to map one persons perspective consistently to another persons

(physists resourceful buggers, can often manage to give up something that looks essential and still make do---still find a way to define what they want to, even with that piece missing)

second stage 1915 GR FURTHER undermined idea of absolute time by having clocks tick at different rates depending on how deep in gravitational field. this is worse. this is a harder problem. you don't have offtheshelf readymade lorentz translator-maps to interpret between different perspectives---it is not so flat and linear and simple any more.

but still at any point the curved 1915 GR space is APPROX flat and they cling tight to mother and are still able to define things locally. at least locally for one observer, in his surroundings, things still feel like the old safe familiar world.

(so again the resourceful little rascals find a way to give up something and still make do---they cope with it OK)

(however spacetime itself is getting less real, it is losing a kind of comforting absolute existence, so there is a kind of giddy feeling about it even though the appliances still work)

now Richard the QG theories are still IN DEVELOPMENT and you and I can simply not predict how they are going to cope with the next stage. We can speculate, but our speculation may not be very useful. All I can say is they will probably develop a new theory of QG that is a picture of space time and matter which is relational and interactive, and it will answer the question

WHAT IS MOTION?

I know this is an important unanswered basic question because several times Rovelli has posed this question at the end of papers. he doesn't say such things needlessly.
============
In case you WANT me to try to speculate, I will. Simply disregard the following if you don't want to hear rash speculation.

Space or spacetime will be found to be a web of relations (like inside outside, next to, between, above below and all stuff like that) and matter will be found to be topological TANGLES OR DEFECTS of some sort in that web of spatial relations. So geomtry and matter will turn out to be the same thing, and it will be relational.

and it will be DYNAMICAL that is the web or network of relations will evolve, and matter and geometry will interact in the course of that: maybe sometimes tangles will appear and disappear as matter exists and unexists. or maybe defects migrate like they do in crystals (just an analogy)

and the dynamics will involve some kind of localized swapping "MOVES" performed on the network, where nodes are relinked in simple ways by removing old links and reconnecting with new ones. You may have heard of "pachner moves" it doesn't have to be pachner moves (the details and jargon don't matter) it can be some other repertory of basic local little modifications of the network

by local swapping around of edges and vertices in the graph, pieces of matter will be able to propagate thru the graph.

so even tho there is no microscopic space or time, and even tho ordinary space and time are merely "epiphenomena" that "emerge" as patterns in larger scale, the clever rascals will STILL have retained an idea of MOTION, they will throw out nearly everything and they will STILL be able to cope and still be able to define mother (which is for physicists is motion) even with this severely reduced set of tools and assumptions.

now that is probably or undoubtably wrong because it is just an off the cuff story. but something like that story might happen.

Anyway, I say TRUST THEM. they always find a way. It makes it very amusing to watch doesn't it?

 

[hossi]

it sounds like a creative idea.

the main thing is not to make unnecessary difficulty.

I don't know if you meant it that way, but thanks.

Hi marcus, well, glad to hear my remark was good for something I didn't mean to make things difficult. I had only the last Rovelli paper to stare at and I thought the whole story is probably more general than having Alice and Bob.

I have a hard time imagining more than a finite number of systems, and so I can't easily picture more than a finite number of observers (which are quantum systems interacting with other systems).

You have the usual A and B observer, not in causal contact, say at time t_0. When they come in causal contact, say time t_1 they can both be observed by observer C. Each of them can tell a different story, but they will never disagree. However, you could have infinitly many observers C_i on the same slice on position x_i, each measuring A and B. I don't see why these observers could not also be at the same place. Or, if you don't like that, let them move to the same place after having made their measurement. Then you have infinitly many stories about the 'same' event at one place. Okay, in case the measurment is either +1 or -1, they can not really be that different. But make that an arbitrarily long series of +/-1 and you have arbitrarily many stories to tell.



Also, you are thinking discrete variables. Take a scattering experiment where the measured quantity is the angle of the outgoing particle (relative to some axis). At each angle-element you have an observer, who either gets the particle or he doesn't.



B.

PS: the dwarves say hello.

 

[koantum]

Why don't you start a thread in QM forum about RQM? I would not want to participate because what interests me is something we have not discussed yet-----THE CONNECTION BETWEEN RQM AND fundamental theories of spacetime-and-matter. Often called "Quantum Gravity", there are these theories-in-progress which aim at getting a new understanding of spacetime-and-matter. sometimes called non-perturbative QG, sometimes called BACKGROUND INDEPENDENT QG, these are generally speaking NON-STRING theories seeking the fundamental degrees of freedom of spacetime and matter. and how matter and geometry interact.

Hi marcus, I see now why you opened this thread under Beyond the Standard Model. I won't open a thread on RQM because I have my own axe to grind. Instead I offer below a few comments on passages in the Stanford Encyclopedia entry on RQM from the point of view of the Pondicherry interpretation of quantum mechanics (PIQM). By the way, the PIQM offers significant insights into the nature of matter and spacetime (even if I say so myself) without going beyond the standard quantum formalism. Personally, I feel that a quantum theory of gravity may be a contradiction in terms. (I don’t say it is.) But I fully agree with the need for background independence and http://koantum.blogspot.com/2006_04_10_koantum_archive.html" .

there is no supernatural absolute classical official CLOCK clock, but only natural clock-like things, it is the Heisenberg picture and there are CORRELATIONS between events and readings on these natural clocks.

IMHO (that is, according to the PIQM) QM is truly and fundamentally a probability algorithm describing an objective fuzziness. Not only this fuzziness but also other mathematical features of this algorithm are instrumental in the realization (manifestation, creation, whatever) of the world. For instance, I see the metric properties of the world rooted in the fact that all free particles of the same type "tick" at the same rate anywhere, anytime. (Feynman associates a rotating arrow with each path contributing to the particle propagator. In my dictionary, each time the arrow completes a cycle, there is a tick.) Each particle species could serve as a standard clock. Mass ratios tell us how these clocks are related.

RQM is really really important to the QG context. It is not just some separate philosophical issue (in which case i would not bother with it since philosophy is not my main concern)

I agree, but philosophy is really important for discovering how the mathematical formalism relates to REALITY. Now the promised comments.

Laudisa and Rovelli: The difficulty in the interpretation of quantum mechanics derives from the fact that the theory was first constructed for describing microscopic systems (atoms, electrons, photons) and the way these interact with macroscopic apparatuses built to measure their properties. Such interactions are denoted as "measurements". The theory consists in a mathematical formalism, which allows probabilities of alternative outcomes of such measurements to be calculated. If used just for this purpose, the theory raises no difficulty. But we expect the macroscopic apparatuses themselves — in fact, any physical system in the world — to obey quantum theory, and this seems to raise contradictions in the theory.​

The PIQM adheres to the (IMHO correct) perception of the founders that the theory is an algorithm for assigning probabilities to possible measurement outcomes on the basis of actual outcomes. (In my dictionary, a measurement is any event or state of affairs from which the truth of a statement like "system S has property p" or "observable O has value v" can be inferred.) It resolves the apparent contradictions by a judicious reality assignment, obtained after a rigorous definition of a macroscopic domain (the "macroworld"), which rests on a careful examination of the ontological implications of the quantum-mechanical probability assignments.

L and R: The core idea is to read the theory as a theoretical account of the way distinct physical systems affect each other when they interact (and not of the way physical systems "are"), and the idea that this account exhausts all that can be said about the physical world. The physical world is thus seen as a net of interacting components, where there is no meaning to the state of an isolated system.​

Indeed, there are no systems "as they are" and there is no meaning to the state of an isolated system. However, according to the PIQM the notion of physical systems affecting each other is a classical concept unsuitable for the real world. As said, there is a well-defined macroworld. The properties of whatever lies beyond the macroworld exists only if, when, and to the extent that they are indicated by events or states of affairs in the macroworld ("measurement outcomes").

L and R: the values of the variables of a physical system S... do not express properties of the system S alone, but rather refer to the relation between two systems. ...there is no meaning in saying that... a variable of the system S has taken the value q: rather, there is meaning in saying that... the variable has taken the value q for O, or with respect to O.​

The values of the variables of a physical system S do not express properties of the system S alone, but rather refer to the relation between S and the macroworld. But this is not a symmetric relation. The properties of S are what they are because they can be inferred from what happens or is the case in the macroworld, not the other way round. Saying that a variable of the system S has taken the value q is the same as saying that the possession of the value q is indicated by the goings-on in the macroworld.

L and R: Consider for instance a two-state system O (say, a light-emitting diode, or l.e.d., which can be on or off) interacting with a two-state system S (say, the spin of an electron, which can be up or down). Assume the interaction is such that if the spin is up (down) the l.e.d. goes on (off). To start with, the electron can be in a superposition of its two states. In the account of the state of the electron that we can associate with the l.e.d., a quantum event happens in the interaction, the wave function of the electron collapses to one of two states, and the l.e.d. is then either on or off. But we can also consider the l.e.d./electron composite system as a quantum system and study the interactions of this composite system with another system O′. In the account associated to O′, there is no event and no collapse at the time of the interaction, and the composite system is still in the superposition of the two states [spin up/l.e.d. on] and [spin down/l.e.d. off] after the interaction.​

It's not a question of this or that observer. IMHO, any interpretation of QM that needs to invoke observers has not done its job, which (IMHO) is to understand the world without dragging in observers. It's a question of whether or not a variable belongs to the macroworld. If it does, it indicates and thereby realizes a property of the other system. If it does not, we have a correlation between the possible outcomes of measurements performed on the two systems, and that's all there is. There isn't a property that system A has relative to system B and another property that system B has relative to system A. There are only the properties that are indicated by events or states of affairs in the macroworld.

 

[selfAdjoint]

Feynman associates a rotating arrow with each path contributing to the particle propagator. In my dictionary, each time the arrow completes a cycle, there is a tick.

Feynmann's "little arrow" was his popular image for the complex function e^{i\psi t}. The t in there is the famous quantum "absolute clock". If you want it to be particuar to a particle you have to change Feynman's formalism as much as any other.

 

[rtharbaugh1]

Koantum: "I see the metric properties of the world rooted in the fact that all free particles of the same type "tick" at the same rate anywhere, anytime. (Feynman associates a rotating arrow with each path contributing to the particle propagator. In my dictionary, each time the arrow completes a cycle, there is a tick.)"

I had a different impression after reading Feynman's QED. I would say particles experience a tick (that is an advance in their time dimension) only upon some interaction. A particle which does not interact does not experience any advance in time.

I suppose there is not much difference to macroscopic observation. The macroscopic observation system is a huge collection of interactions and any small differences (below the Fermi scale perhaps) quickly average out, so one electron is really pretty much the same age as another in the same system. Maybe neutrinos interact less often than the system average. Maybe a single photon of light does not react at all between its creation and its interaction with our photographic plate. In that sense, traveling photons do not experience time at all, so we can still measure the light of the origin of the universe.

I got the impression from the quote above, Koantum, that you are invoking a kind of standard universal clock? Just wondering, because I have worked very hard to get my mind around the idea that such a clock cannot exist.

Thanks for any interaction...

Richard

 

[hossi]

Only in most cases? The point is: they are nothing but mathematical tools handy to work with.

what about the Aharonov-Bohm effect?

P.S. I wonder why this thread, which discusses an interpretation of the standard quantum formalism, comes under "Beyond the Standard Model

‘The important thing in science is not so much to obtain new facts as to discover new ways of thinking about them.’ ~William Bragg

Anyway, guys, your discussion about the meaning of time is very nice, but I am actually more interested in figuring out what entanglement could or could not have to do with QG. Any opinions on that?



B.

 

[marcus]

...

However, you could have infinitly many observers C_i on the same slice on position x_i, each measuring A and B. I don't see why these observers could not also be at the same place. Or, if you don't like that, let them move to the same place after having made their measurement. Then you have infinitly many stories about the 'same' event at one place. Okay, in case the measurment is either +1 or -1, they can not really be that different. But make that an arbitrarily long series of +/-1 and you have arbitrarily many stories to tell.

PS: the dwarves say hello.

Hello back to the dwarves.

I am glad you got in contact with Satz at realityconditions blog about discussing Rovelli EPR. Better to discuss with him in the relatively quiet peaceful surroundings of that blog---a very good one!

It is risky talking here, one can be yelled at. Even if just joking I do not like such violent joking.

About your uncountable infinity observers, I do not like to push my own point of view which is finitistic. I do not see any evidence that we live in a continuum---a smooth manifold a la Riemann

I don't want YOU to change your ideas! I am happy if you think we live in a 4D differentiable manifold ( when I was in grad school I loved diff. geometry, our teacher was Frank Warner, very good). And I am happy if you think this is in a 10D diff manif too.

But I personally see no evidence of this. I am not even sure the past exists either. Maybe there is just this approximately 3D quantum graph of spatial relations. maybe there is no continuum at all. I try to picture observers as nodes in a graph or as COLLECTIONS of notes that are somewhat separate from the others that surround them.

I guess I can picture an countable infinity of observers, but the idea of a continuum---an uncountable infinity---does not work for me. that is just how I am, a bit like the "constructivist" school of Brouwer maybe, no not really----just finitistic

(like I suspect there might be a MINIMAL MEANINGFUL DISTANCE at least in a rough sort of way, but I don't want to convince you of that, you should go on thinking however you like to think)

So when you produce examples involving an uncountable infinity of observers who necessarily must be able to compare all their different measurments in a finite amount of time----to me it begins to look like an idea for a THOUGHT EXPERIMENT TO DEMONSTRATE THAT WE DO NOT LIVE IN A CONTINUUM on a smooth psRiem manifold. that is, a thoughtexperiment argument by CONTRADICTION. assume that we do live on a smooth manif and arrive at absurd conclusions. and this boggles me a little. and I begin to want to go think about something else more congenial.

this by way of apology.

all the best

 

[marcus]

Rovelli discussion of Consistent QM (Omnes, Gell-Mann others)M

I came across something nice today! It is a one-page discussion and critique by rovelli of the 1980s idea of CONSISTENT HISTORIES qm.

It is thought-provoking and an odd coincidence came up connected to it.

Just 3 paragraphs on page 18 of Rovelli's main paper on RQM---the 1996 paper called "RQM". I will quote about the first THIRD of it as a sample, to get the other 2/3 of the discussion go to "RQM"

---quote---

A class of interpretations of quantum mechanics that Butterfield does not include in his classification, but which are presently very popular among physicists, is the consistent histories (CH) interpretations [Griffiths 1984, Omnes 1988, Gell-Mann and Hartle 1990]. These interpretations reduce the description of a system to the prediction of temporal sequences of values of physical variables. The key novelties are three: (i) probabilities are assigned to sequences of values, as opposed to single values; (ii) only certain sequences can be considered; (iii) probability is interpreted as probability of the given sequence of values within a chosen family of sequences, or framework. The restriction (ii) incorporates the quantum mechanical prohibition of giving value, say, to position and momentum at the same time. More precisely, in combination with (iii) it excludes all the instances in which observable interference effects would make probability assignments inconsistent. In a sense, CH represent a sophisticated implementation of the program of discovering a minimum consistent value attribution scheme. The price paid for consistency is that a single value attribution is meaningless: whether or not a variable has a value may very well depend on whether we are asking or not if at a later time another variable has a value.

...There is a key subtlety in the CH scheme that has rarely being emphasized...

...The key question that, as far as I can see, the consistent histories approaches does not address is: ...[/color][/size]
---endquote---

 

[marcus]

the funny coincidence was that Lubos Motl just joined this thread at Christine Dantas
http://christinedantas.blogspot.com/2006/04/unfinished-revolution.html

where they were discussing Rovelli Smerlak paper, and Lubos said

---quote Lubos---
Concerning relational EPR, someone should try to tell these people that the problems that they are trying to solve have been solved by 1992 and most of them by 1929. Omnes' ultimate paper on interpretation of QM is here:

http://schwinger.harvard.edu/~motl/omnes-interp-qm.pdf

What Rovelli et al. are doing is just completely obsolete and confused diluted version of the insights that have been done properly decades ago, and sometimes it is a good idea to study the work of others, especially if the work of others is superior.

4/18/2006 10:56:05 AM
---end quote---And then Christine said...

"...Thanks Lubos Motl for pointing out the important paper by Omnes..."

So if anyone wants to see what Rovelli is discussing and critiquing in his 1996 paper, they can find a very useful and well-written 1992 REVIEWS OF MODERN PHYSICS article on Consistent Histories by Roland Omnes online at Lubos Motl website!

 

[hossi]

.
I guess I can picture an uncountable infinity of observers, but the idea of a continuum---an uncountable infinity---does not work for me.

well, I never said it had to be uncountable inifinite? anyway, it's been interesting to discuss the paper. I admit I have decided I don't like it. I DO think that the non-locality and the so-called collapse is an interpretational problem that can be solved by understanding the principles of QM, but at least for me this way does not work.

B and her dwarves

 

[koantum]

Feynmann's "little arrow" was his popular image for the complex function e^{i\psi t}...

What's \psi doing up there in the exponent? \psi is related to the propagator \langle\cdots|\cdots\rangle via

\psi(\hbox{here,now})=\int \langle\hbox{here,now}|\hbox{there,then}\rangle\, \psi(\hbox{there,then})\,d(\hbox{there})

and the propagator is a sum over paths each of which contributes a phase factor. How does \psi get into this factor?

what about the Aharonov-Bohm effect?

If you increase the current in the solenoid, the interference pattern shifts sideways. The vector potential is a mathematical tool with the help of which we calculate this effect. Generally speaking, the 4-vector A is a mathematical tool with the help of which we calculate the effects that electrically charged particles have on electrically charged particles.

I had a different impression after reading Feynman's QED. I would say particles experience a tick (that is an advance in their time dimension) only upon some interaction. A particle which does not interact does not experience any advance in time.

There certainly is a sense in which you are right. If I image one and the same particle traveling simultaneously along infinitely many paths from (there, then) to (here, now), I visualize a way of calculating the probability (density) with which a particle last seen there and then is found here if the appropriate measurement is made now. I certainly do not imagine that my visualization has anything to do with what happens between successive measurements.
My point was that ultimately all time measurements are rooted, in general, in the quantum-mechanical probability algorithm and, specifically (in the path integral formalism), in the time dependence of the phases of the amplitudes that contribute to the propagator.

one electron is really pretty much the same age as another

IMHO, the actually existing relations (spatial as well as temporal) are relations between macroscopic events. At any rate, if there were any age (or other) differences between electrons, the Pauli principle wouldn't apply to them.

traveling photons do not experience time at all

Perhaps because there is no such thing as a traveling photon? Why must the causal connection between events (in the classical case) or the correlations between events (in the quantum case) be mediated by traveling objects?

Physicists are, at bottom, a naive breed, forever trying to come to terms with the "world out there" by methods which, however imaginative and refined, involve in essence the same element of contact as a well-placed kick.—B. S. DeWitt and R. N. Graham​

I got the impression from the quote above, Koantum, that you are invoking a kind of standard universal clock? Just wondering, because I have worked very hard to get my mind around the idea that such a clock cannot exist.

Why not? It's not built into spacetime. It's built into the quantum-mechanical probability algorithm: free (or freely falling) particles of the same species tick at the same rate anywhere, anytime.

Nice talking to you!