What Is the Marseille Interpretation of Quantum Mechanics?

[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!

 

[koantum]

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 [sic!] ... 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.

Omnes in his Quantum Philosophy: Bohr always attempted to preserve at all costs the objective character of the science he had helped to found, and we shall see that he was right in doing so. As for the rest, it is nonsense, twaddle, balderdash, and idle fancies (I also have some stronger words in store).​

Apparently these two share the same arrogance.

 

[rtharbaugh1]

Koantum, I liked the idea you put forward that there may be no such thing as a traveling photon. Perhaps it is observers which do the traveling, and the realm of the photon is unmoving. Maybe this will lead to a new way to think about the zero point energy? But what then becomes of the speed of light as a constant? Zero is not very satisfactory as a constant. Or must we then say that all observers are traveling at the same speed relitive to the unmoving photon field? Then what is motion, what is separation, what is space? I suppose velocity and differences in velocity such as we commonly observe would be diffences in direction instead, such as on the light cone.

My doctors have advised me to avoid intoxicants. Champions of homeostatic mediocrity, they prize longevity above all other qualities. Pfah. What good is life without smoke and drink? But perhaps thoughts like these will be proof enough to disolve my sense of self after all, allowing me to achieve the perfectly smooth manifold of the omniscient, omnipresent unobserver.

Nice talking with you, too.

R.

 

[marcus]

Apparently these two share the same arrogance.

but in one case the arrogance may be hollow (I have found his assertions repeatedly to be unreliable)
and in the other case the arrogance may be solid.
Won't swear to it but the latter might be justified opprobrium

Anyhow, a stylistic likeness can conceal fundamental differences
and flamboyant arrogance (as long as it is not cruel) can be amusing.
One tries to be tolerant: appreciate the originality and talent without being misled.

And yeah, I agree with your remark. I am just elaborating on it a little. In fact the Omnes pronouncement about balderdash is priceless Thanks for finding it and sharing it.

 

[marcus]

What good is life without smoke and drink? But perhaps thoughts like these will be proof enough to disolve my sense of self after all, allowing me to achieve the perfectly smooth manifold of the omniscient, omnipresent unobserver.
...

the Mark Twain of quantum gravity

 

[rtharbaugh1]

Hi Marcus

Was it Mark Twain who said that? I was thinking Gertrude Stein. But you flatter me too much, and I am embarrassed to admit I enjoy it. I envy your memory for its accuracy and precision. Mine was cloudy long before I took up the bottle or the cigar. I don't suppose fifth essences will improve it any.

I saw your post about the Oriti book, and VSL. I suppose it has to vary given inflation, depending on the observer. What surface shall one attach oneself to, when tossed like flotsam on the open sea?

A friend asked me a few days ago how scientists can say they are detecting light from the first seconds of the universe, coming into us from way out there. Shouldn't that light have past us by long ago, since it moves away from the center so fast, and we so slow? I mulled over the inflation explanation, then considered curved spacetime, broke upon the thought of inversion. What happens to our sense of space if way out there is the same thing as what is deep within our own origin? It seems one must collapse the bubble to find the center.

R.

 

[marcus]

Hi Marcus

Was it Mark Twain who said that? I was thinking Gertrude Stein.

.

said what? I'm weak on quotes like that. to me, it just sounded like Mark Twain (a kind of ironic realism that allows for some human frailty)

if Gertrude stein said something about smoke and drink what did she actually say? I'm curious.

 

[marcus]

...A friend asked me a few days ago how scientists can say they are detecting light from the first seconds of the universe, coming into us from way out there. Shouldn't that light have past us by long ago, since it moves away from the center so fast, and we so slow? ...

the CMB light is usually dated from when the U was about 350,000 years old (roughly a third of a million years old, not a few seconds)

most lay confusion about mainstream cosmology comes from not realizing that there is no center

the "balloon 2D analogy" is the best, although imperfect.
the CMB light comes from everywhere in the 2D surface of the balloon and it travels every direction IN the 2D surface and is always arriving at every point in the surface from all directions IN the surface

but you have to stretch your mind to imagine a 3D analog. a closed 3D world WITH NO CENTER

tell your friend to watch Ned Wright balloon animation.
http://www.astro.ucla.edu/~wright/Balloon.html
this one just shows just galaxies, there was another that used to show light waves wriggling on the surface as well. As the surface expands, the galaxy dots on it get farther apart. the lightwave snaky things are the CMB---they are always there coming from all directions (in the 2D analog) and they gradually get stretched out (redshifted) by the expansion.

if only lay could imagine a universe where space has no center, so many puzzles would just evaporate, and it is EASY TO DO. you don't have to go to college for godsake to imagine expanding space without a center.

give the guy Ned Wright animation URL, might help. this one has the lightwaves too as well as the galaxies but it is not the best one which I remember from a couple of years ago.
http://www.astro.ucla.edu/~wright/balloon0.html

he used to have a better one that filled the whole screen, can't find it now but will post if I come across it

 

[rtharbaugh1]

Thanks, Marcus.

The smoke and drink quote, or paraphrase anyway, is a favorite among some of my community. At least three people have expressed to me their dissatisfaction with the laws restricting smoking in bars and restaurants. It isn't so much that they want to trample on non-smoker's rights to drink and dine in a smoke-free environment, as that they resent the loss of a freedom to sit in comfort among random friends enjoying the subtle poisens of their choice. I suggested they form a private smoker's club, freedom of association you know, but that did not really ease the pain of severance. They still remember the contemplative joy of abandonment when snuffing out a butt in the last scraps of a plate of eggs and ham, and then the last sip of cooling coffee. I suppose it gives a sense of finality to a meal, unequaled by the presentation of the check or the after-dinner mint. Personally, having already given up tobacco and liquor, I must confine myself to crumpling the paper napkin, throwing it with disdain upon the plate, like a final prayer to the forgotten god, there, it is finished.

I'll ask around for the source of the quote. It might even be Hunter S. Thompson.

R.

 

[koantum]

I liked the idea you put forward that there may be no such thing as a traveling photon. Perhaps it is observers which do the traveling, and the realm of the photon is unmoving...

"One unmoving that is swifter than Mind, That the Gods reach not, for It progresses ever in front. That, standing, passes beyond others as they run."

Isha Upanishad, Verse 4​

Then what is motion, what is separation, what is space?

One thing is sure: not what they seem to be!

It may be relevant in this context that generalized Lorentz transformations can be derived from the principle of relativity alone, without invoking the speed of light or its constancy. These transformations contain a single universal constant K. Since this is not dimensionless (it has the dimension of an inverse velocity squared), only three possibilities exist:

• K>0. In this case the signature of the metric would be ++++, no kind of objective difference would exist between time and a spatial dimension, making a U turn in time would be as easy as making one in space, etc.

In the other two cases (but not in this) there exists an invariant speed: whatever travels with it in one inertial frame does so in ever inertial frame.

• K=0. Galilean relativity, the invariant speed is infinite.
• K<0. Special relativity, the invariant speed is finite.

The existence of an invariant speed is what prevents us from making U turns in time, for it takes an infinite amount of energy to reach it. Its existence causes time and space to be objectively distinct. In my opinion what is more important is the existence of an invariant speed, less important is whether this is finite or infinite.

Now suppose that there is such a thing as an unmediated cause-effect relation. Then it is the invariant speed that determines the temporal relation between cause and effect for any given spatial relation, but there is nothing that travels with that speed! In Newtonian mechanics it will be an instantaneous action at a distance, and in Einstein's world it will be a retarded action.

 

[rtharbaugh1]

said what? I'm weak on quotes like that. to me, it just sounded like Mark Twain (a kind of ironic realism that allows for some human frailty)

if Gertrude stein said something about smoke and drink what did she actually say? I'm curious.

Well, an hour searching turned up an interesting absense of evidence. One google reference attributes a quote to Sartre: "Life without smoke is not worth living." Unfortunately I could not find the actual quote in the link, which is here:

http://www.nycclash.com/AllThoseOpposed.html

What is amazing to me is the huge number of anti-smoking sites that came up. There seemed to be many variations in opposition to the idea of life not worth living without smoke (and drink), but few sites flying the death's head flag of liberty.

By the way, in the above link, the anti-smoking crusade was variously attributed to nazis, communists, and liberals, all of whom seem to think they know what is good for all of us and enjoy imposing their opinions on others.

I was reminded of Einstein's comment on the publication of a book by a hundred physicists who were intent on proving relativity to be in error. Albert said if they were correct, only one would have been enough.

If human culture is a kind of super-being, with its own circulation, brain, and senses, is the profusion of anti-smoking anti-drinking anti-drug anti-caffeine (yes, that is on the list) anti-soda pop anti-anything sites evidence that the culture is in the throws of anti-phyllactic shock? Are we eating ourselves alive in a massive allergic reaction?

In my opinion, nature has her own homeostatic mechanisms. Humans would do well to take a deep breath, and reconsider their actions. Life may well go on more merrily without us.

(neologism, for those who may have missed it: anti-phyllactic shock, from anaphylactic shock, which is what happens when the body goes into self-destruct mode in a misguided attempt to protect itself from, say, p-nuts or bee stings. No pun aimed in your direction there, hossi.)

R

and, in edit, the following:

"Jean Paul Sartre spent many years smoking, giving it up only to take up the "demon" habit for the next 40 years. He stated that a life without smoking was not worth living. "

from the link:

http://www.homeopathy-academy.org/HomeoResearch/Tobacco.htm

But notice that this is an attribution again, not a quote. Later in the same link a relevant quote from Sartre is provided:

"A few years ago, I was led to decide to stop smoking. The beginning was rough, and in truth, I did not so much care for the taste of tobacco that I was going to lose, as for the meaning of the act of smoking. A whole crystallization had taken place. I used to smoke at performances, mornings at work, evenings after dinner, and it seemed to me that in ceasing to smoke I was going to subtract some of the interest of the performance, some of evening dinner’s savor, some of the fresh vivacity of the morning’s work. Whatever unexpected event might have struck my eyes, it seemed to me that it was fundamentally impoverished as soon as I could no longer welcome it by smoking. To-be- susceptible-to-be-encountered-by-me-while-smoking: that was the concrete quality that had been universally spread over things. And it seemed to me that I was going to tear it away from them and that, in the midst of this universal impoverishment, life was a little less worth living..."

Can this be the comment that provoked so much intensity in those who wish to refute it? Did they first have to build it up into a scarecrow so that they could be seen brave and virtuous in the act of defeating it?

And the final irony, Sarte seems to say he regrets not the loss of the pleasure of smoking, but the loss to the world in that he may no longer regard it from under the filter of a rich blue haze!

Sartre was a truly powerful and influential thinker, death to tyrants. He was certainly a contemporary of Gertrude Stein, altho I do not know if he was in her aquaintance.

I guess this commentary is appropriate here, in a thread named for Marseille, a town famed for bistros, smugglers, pirates, philosophers and poets.

r