Quantum realism and fields.

Discussions ranging from space technology, near-earth and solar system missions, to efforts to understand the large-scale structure of the cosmos.

Quantum realism and fields.

Postby Marshall on May 6th, 2014, 2:39 pm 

This is a non-confrontational thread. Criticism has to be constructive and cooperative. This is the topic:
http://www.youtube.com/watch?v=TzmykSv6OBY

Ive decided to try out the modifier "interactive" instead of "factual". Facts in Relational quantum context are interactions, so it amounts to the same thing, but saying interactive makes it more explicit. I won't bother to change every occurrence of the word in this thread so far, just start using the new modifier.

Last year there was a conference at Oxford on *Cosmology and Quantum Foundations* at which three main worldviews were presented and compared.

The "relational" or as I will call it the interactive take on Scientific Realism (Carlo Rovelli)
"Many worlds" interpretation of quantum mechanics (Antony Valentini)
"Multiverse" including mathematical universe thinking (Max Tegmark)

This thread is to focus on the first of these. If you want to discuss other professionally researched worldviews please start another thread with a different focus. Here I want to lay out and invite discussion of Interactive Realism.

Another SPCF member called my attention to the conference (which I was not yet aware of) and gave me a link to Rovelli's talk.

In his talk CR says "I consider myself a Realist". A key conceptual point: here FACTS ARE INTERACTIONS.
If there is no interaction--no exchange between two systems--there is no fact. This is where the adjective "relational" originally came in, when this worldview was being presented in the 1990s as an interpretation of Quantum Mechanics.

Here the world is treated as PROCESS rather than STATE. The concept of state is flawed because it is rooted in the idea of *state at a particular time*. But the rates specific natural processes occur depend on where they are viewed from, rates can vary all over the place depending on circumstances. There is no one coherent idea of time that is useful overall in every situation. As the title of a prize-winning FQXi essay put it, "Forget time". So consequently forget STATE.

We still have a meaningful physics of process because we can build an arbitrarily designated clock into the system and log CORRELATIONS between whatever the clock reads and what other facts occur. Rovelli calls the reading of a physical clock a partial observable---it needs to be correlated with other stuff in order to be meaningful and the correlation (not the absolute reading) is what is predicted by theory.

So the focus is on process, and on discrete facts (registered when some type of interaction occurs.) The original 1990s name was Relational Quantum Mechanics.

Cosmology and Quantum Foundations (the title of the 2013 Oxford conference) are really two sides of the same problem of reality large and small--how to think the world as it really is.

What I'm calling Interactive Realism (aka RQM) was first presented in 1990s and was taken over by various Philosophers of Science as a way to resolve various problems and confusions in the interpretation of QM. Rovelli got back to it around 2007 in a paper called "Relational EPR" showing how it resolves the Einstein Podolsky Rosen (EPR) paradox. It's not a bad paper to look at in connection with the video of Rovelli's Oxford talk. It's on arxiv.org, but just google "relational EPR" and you'll get it. Largely non-math and largely common sense.

But the core thing, prerequisite for this thread, is the 2013 Oxford talk. That's our topic.

It should come up if I google "rovelli cosmology quantum foundations" Let's see. Sure, it is the first hit:
Marshall
 
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Critique of Interactive Realism (Oxford Cosmology&QFound Con

Postby Marshall on May 6th, 2014, 3:31 pm 

For convenience in this thread, I may sometimes omit some modifiers like "scientific" in front of Realism, or like "factual" and "relational". It should be clear from context.

One says "Scientific Realism" to distinguish from well-known antique form called "Platonic Realism" which Wikipedia notes is also confusingly called "Platonic Idealism" by some people.

A Realist (as regards modern cosmology and quantum theory) holds that to the extent successful these physics theories refer to reality. Theories can be improved but in an approximate sense they have ontological content.

The reason they are as successful as they are is that they refer to real processes (occurring at various rates involving real stuff and real spatial geometry). In an improvable approximate way, they match reality.

To be satisfactory today I think Realism has to be a quantum Realism as regards physical theory covering all we can see, and we need to be able to assimilate it it intuitively as making sense. So there are some puzzles or seeming paradoxes to be resolved. I think that is what Rovelli is driving at in his 2013 Oxford talk. I'll try to lay some of it out and you can, hopefully, improve on the exposition.
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Re: Critique of factual Realism (Oxford Cosmology&QFound Con

Postby Marshall on May 6th, 2014, 3:57 pm 

The first puzzle he addresses, in the first 15 minutes of the talk, is the problem of quantum cosmology. Quantum theory is conventionally thought to require an OUTSIDE OBSERVER. But in cosmology there is no outside observer, so how can we do quantum mechanics?

People have gotten hung up on that, creative reputable people like Lee Smolin and UCSB's James Hartle. They think that Q theory requires special reformulated foundations in order to treat the universe as a whole, and this has driven a fair amount of contemporary research. The research itself may be highly valuable (say in Smolin's case). I don't want to veer into discussing that. But Rovelli shows, in the first 15 minutes, that the problem may be a non-problem.

The argument is essentially philosophical. Physical theories do not represent ALL possible degrees of freedom of a system, at all possible scales. the theory of a pendulum does not need to involve the molecules in the pendulum.
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Re: Critique of factual Realism (Oxford Cosmology&QFound Con

Postby Marshall on May 6th, 2014, 4:27 pm 

Anybody who watched it (I think some here did recently) is welcome to jump in an continue the summary/paraphrase of the talk. I'll continue as my time permits. Also feel welcome to comment, on any part of the talk that caught your attention, not only on what I've summarized so far.

While i think of it I should also include links to the Scientific Realism thread. It has a good clear definition taken from a Univ. of Michigan webpage that uses material from Jarrett Leplin's book on Scientific Realism. It goes into more detail than we need to in this thread.
http://www.philosophychatforum.com/view ... 60#p259751
http://www.philosophychatforum.com/view ... 60#p259656

Also there's a possibly useful saying about quantum Realism, FWIW:
Interactions are discrete, continuities are inferred.

I have something like a 100 million receptor cells (rods and cones) in my retina. When I look out the window at the redwood tree with tens perhaps hundreds of thousands of little evergreen leaflets projecting from the branches in my view. Each of my retinal cells is EITHER EXCITED OR NOT EXCITED, by the field of light, and each excitation is a fact.
If there is an excitation we can talk about a photon of light being absorbed by a molecule in the receptor cell, a discrete physical INTERACTION at quantum level which triggers a nerve.
So I am being constantly inundated by millions of discrete physical facts.

Maybe this is self-evident to everybody and hardly needs saying. still I personally find it helpful to recall e.g. in connection with the part of Rovelli's talk where he recalls Heisenberg story about what helped inspire his invention of Quantum Mechanics---the Night Park story about the intermittence/discreteness of phenomena. It probably comes shortly after minute 15 in the video (after the quantum cosmology puzzle is dealt with)
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Re: Critique of factual Realism (Oxford Cosmology&QFound Con

Postby owleye on May 6th, 2014, 4:51 pm 

I viewed the YouTube talk by Rovelli in its entirety. He went through the material very fast for my slow mind, one also limited by my limited background in quantum theory, but I was able to absorb some of what he says and found it eye-opening. Thanks for the topic.

There was a part that I had considerable trouble with, when he got around the the 'eye-shaped" space diagram in which I seem to remember his reference to Schrodinger's wave equation being bounded by it. Since the wave equation has complex number values to it, I suppose the equation was a projection onto the real plane, but I can't be sure. And, of course, I can't even be sure of the point he was making with it. My mind raced to the possible implication that space itself is affected by the propagation of the wave. And with that I probably lost Rovelli's thread.
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Re: Critique of factual Realism (Oxford Cosmology&QFound Con

Postby Marshall on May 6th, 2014, 6:09 pm 

A brave and determined attempt, and you got most of the way through, Owl. Thanks! That diagram IS as you say a flat projection. Just a schematic sketch not meant to portray reality.

It's meant to remind the audience of a way of formulating quantum theory as TRANSITION AMPLITUDES from a "before" and an "after" (the lower and the upper layers) with the filling in between being all the possible "paths" nature could take to get from one to the other. The theory gives a way to calculate the "sum over histories" or the "path integral".

I think it was Richard Feynman who first developed the "path integral" style and who persuaded people that you didn't need the Schrödinger equation or wave functions or anything else if you just knew how to calculate the amplitude of the system evolving from here to there.

I forget where that "eye diagram" comes in the lecture. If you tell me what minute it is, I can go to it and make sure we are talking about the same thing, Owl. The diagram is kind of like two pancakes with a fat layer of cream cheese between them. Only the before and after are observed or measured. they are phenomena pancakes. the filling is the unobserved cream cheese of all different histories that might have happened to get from initial to final measurements.

(which cream cheese by the merciful grace of our lord Faraday and his son Feynman we are humbly able to calculate the amplitude of in certain cases, amen)
Marshall
 


Re: Critique of factual Realism (Oxford Cosmology&QFound Con

Postby TheVat on May 6th, 2014, 7:25 pm 

Marshall, re
The reason they are as successful as they are is that they refer to real processes (occurring at various rates involving real stuff and real spatial geometry). In an improvable approximate way, they match reality.



I think this is the sticking point in the clash between realism and instrumentalism. One objection to the above is that there are other reasons for success of a physics theory besides that the theory "match reality." To assert that there is a match with reality is to invite critics to point out a certain circularity in the statement. To embrace realism from consistent measurements is, in a sense, to wish your ontology into existence.

The success of a theory, especially one regarding unobservables, is that it is able to predict certain indirect measurements, certain experimental outcomes, even as the reality of the unobservables remain mysterious. "Unobservable" is a modern term which is a close relative of Kant's noumenon, that which has an essential nature that cannot be accessed in the perceptual formalisms of our neural structure. Gravity waves, virtual particles, gauge fields, etc. are all more or less in the noumenous realm of unobservables. Some we may someday find a way to observe, some are arguably destined to be inherently unobservable and remain disputed as to their ontic status, IMO.

I'm urging caution in any ardor to "assimilate intuitively" that which makes sense but may or may not point to a deep physical reality. After all, a "mind field" could present to us the whole range of geometries and spaces and fields that we presently take in through our scientifically augmented perceptions and yet still conceal its essential nature as some kind of overarching field of mathophile mentality. I think this possibility, however small, has moved me towards a more instrumentalist perspective. Not to say that I'm turning into Bishop Berkeley and placing us all in the divine mind field, just that I don't want to join a headlong rush into realism.

But I can't fault a guy for trying! And I'll keep following your factual version of realism to see if I can gain a better grip on its ontological slipperiness.
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Re: Critique of Interactive Realism (Oxford Cosmology&QFound

Postby Marshall on May 6th, 2014, 7:56 pm 

Glad to see you Vatski, a little extra caution often helps. We are sort of at the Michael Faraday stage where he sprinkled the iron filings and saw the "magnetic curves". This was the year that BICEP reported seeing swirl patterns in the microwave sky---imprints (it is said) of gravitational waves on the ancient light coming to us from year 370,000.
a kind of iron filing sprinkle

Tell me, which sounds better?
Factual Realism
Interactive Realism
Quantum Realism

I want to try out some terminology besides "Relationalism". I know there are reasons for skepticism (always) and caution. but also one has to try things and Rovelli says loud and clear "I consider myself a Realist".

So I say, well, what if he's right? What sort of Realist is he? Certainly not a Platonic Realist (on which see the Wikipedia article)! Which of those terms sound better or seem more correct to you?
Marshall
 


Re: Critique of Interactive Realism (Oxford Cosmology&QFdn C

Postby Marshall on May 6th, 2014, 10:07 pm 

Hi again, BraininVat,
One of us indicated privately a preference for Interactive Realism (over Factual) and AFAICS it means the same thing since in this context facts are interactions---they don't exist independently or in God's eye.
Something has to bump something, or be absorbed or be emitted, or exchanged between neighbors, for there to be a fact.

I decided to try the Interactive modifier, but only from here on: I won't go back and change every occurrence.

When we weigh our skepticism and caution to judge if it is sufficient, two other things to consider are UNIFICATION and SIMPLICITY.

You watched that 20 minute FQXi conference talk (January 2014 Puerto Rico) I think.
google "zeroth thermodynamics rovelli" to get the YouTube of it.
There was a VENN DIAGRAM of three circles, with a central intersection region which is what we want to find our way to:

Quantum theory
General Relativity
Thermodynamics

I think it is important that Thermodynamics is included. It's not so often acknowledged that Thermo does not compat with GR, that intersection in the Venn diagram is something various people are working on andI think it is a fertile problem. What they find themselves being forced to do, in order to get a simple joining of GR and Thermo could turn out to be helpful in unifying other parts of the picture.

Practical simplification seems to be one of Rovelli's strong points. You saw in the Planck Star case how the model resolved the information paradox and the firewall absurdity that had been troubling folks. And sure the model can be WRONG, it is even checkable by observations (which is a good thing, not a bad). The signature feature is that it is simple.

What I'm saying boils down to this. As the Wiki and UMich material on SciRealism said, it is an attitude that people can apply to some things and not to others. Some physics theories smell like there's a trace of truth, others are stale---give them to the Instrumentalist. One is OPEN to believe something points towards a better approximation of reality, and one can be selective about where one invests such belief.

So when exercising choice there are some things to think about and they include unification and simplicity and recovering prior successful theory---whatever it is has to closely approximate SR and GR numerically where those apply, and so on. You can probably think of appropriate considerations quicker than I can.

Here is the 20 minute talk with the three-way Venn diagram in it:
http://www.youtube.com/watch?v=4Qy5Vdzps3g
Marshall
 


Re: Cosmic field lines

Postby Faradave on May 6th, 2014, 10:26 pm 

Marshall wrote:This was the year that BICEP reported seeing swirl patterns in the microwave sky---imprints (it is said) of gravitational waves on the ancient light coming to us from year 370,000.
a kind of iron filing sprinkle

And now a magnetic fingerprint of our galaxy as well. Faraday would be pleased, indeed.
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Re: Critique of Interactive Realism (Oxford Cosmology&QFdn C

Postby Marshall on May 6th, 2014, 10:57 pm 

beautiful technique, like Faraday's iron filings again. the galaxy's magnetic field will tend to align dust grains (imagine them as oblong) and warm objects radiate infrared. But warm oblong objects radiate directionally polarized infrared. So the polarization pattern appears in the light and shows us the alignment of the dust! And that in turn shows us the galactic magnetic field that aligned the dust!!

http://www.sciops.esa.int/index.php?pro ... hed_Papers

the main paper:
http://arxiv.org/abs/1405.0871
Planck intermediate results. XIX. An overview of the polarized thermal emission from Galactic dust
by the Planck Collaboration: ...
(Submitted on 5 May 2014)
This paper presents the large-scale polarized sky as seen by Planck HFI at 353 GHz, which is the most sensitive Planck channel for dust polarization. We construct and analyse large-scale maps of dust polarization fraction and polarization direction, while taking account of noise bias and possible systematic effects. We find that the maximum observed dust polarization fraction is high (pmax > 18%), in particular in some of the intermediate dust column density (AV < 1mag) regions. …

Thanks for spotting this!
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Re: Critique of Interactive Realism (Oxford Cosmology&QFdn C

Postby Marshall on May 6th, 2014, 11:17 pm 

A key quote from the paper:
==quote http://arxiv.org/pdf/1405.0871v1.pdf ==
The linear polarization of the thermal dust emission arises from a combination of two main factors. Firstly, a fraction of the dust grain population is non-spherical, and this gives rise to different emissivities for radiations with the electric vector parallel or orthogonal to a grain’s long axis. Secondly, the rotating grains are aligned by the interstellar magnetic field, probably with differing efficiencies depending on grain size and composi- tion (Draine & Fraisse 2009). While the details of this process remain unclear (Lazarian 2003, 2007), there is a consensus that the angular momentum of a grain spun up by photon-grain interactions (Dolginov & Mitrofanov 1976; Draine & Weingartner 1996, 1997; Lazarian & Hoang 2007; Hoang & Lazarian 2008) becomes aligned with the grain’s short axis, and then with the magnetic field via precession (e.g., Martin 1971). The end result is that, if we look across magnetic field lines, the rotating grain will have its long axis orthogonal to the field lines, and accordingly dust emission will be linearly polarized with its electric vector normal to the sky-projected magnetic field.

A related phenomenon occurs at near-UV/optical/NIR wavelengths, where the light from background sources becomes lin- early polarized as a result of dichroic extinction by the aligned dust grains (Davis & Greenstein 1951). Since extinction is higher for light vibrating parallel to the grain’s long axis, i.e., perpendicular to the field lines, the incoming light will be linearly polarized with its electric vector parallel to the sky- projected magnetic field. In fact, historically, the optical polarization caused by dust extinction led to the prediction that thermal dust emission would be polarized in the millimetre and sub- millimetre domains (Stein 1966)
==endquote==

I had better post the YouTube talk that is the topic of this thread. the title is:
Cosmology and Quantum theory: the Relational view
http://www.youtube.com/watch?v=TzmykSv6OBY

In this talk, Rovelli says "I consider myself a Realist"

so I want to explore what does it mean to be Realist concerning Relational Quantum Theory.
==================================
Footnote sort of thing: BTW in the paper "Relational EPR" (just google the title) the authors say that Relationalism, which they show resolves the EPR paradox and considerably simplifies Quantum Theory reality, involves a slight relaxation of strict Einstein Realism.

each observer only has the facts in his past lightcone
observers can compare notes and reconcile their facts (but only by communicating or getting together, information does not leap superluminally from one to the other)

there is no supernatural super-observer who has a book listing ALL the facts (if I remember right this was the notion in strict Einstein Realism which they wanted to relax). Don't have a perfect memory---it was a 2007 paper or so. Someone might want to have a look and correct this summarized recollection.
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Re: Critique of Interactive Realism (Oxford Cosmology&QFdn C

Postby owleye on May 7th, 2014, 9:42 am 

Marshall..

First, thanks for the clarification. I won't be returning to the talk, interesting as it is, so the best I can do for referencing the "eye-shaped diagram" is that I think it is roughly half-way through. Perhaps a better description is an elongated sine wave truncated at its troughs, y=0, rotated around the horizontal axis, of which we see only its profile.

I think I understood when I was thinking about projections that it was referring to amplitudes, this being how the linear product carries out its mapping in many of its descriptive accounts. I recall something like this in my readings of differential geometry when we were discussing the geometry of space-time.

But the introduction of complex numbers in equations also informs me that there's something about it that reflects a relationship between some reality (insofar as it deals with real numbers) and its emergence from the complex domain that underlies it. I see this in control theory, where the complex domain represents the underlying mechanics under which something can be considered "under control". And, of course, this fits with the notion of this "eye-shape" being a boundary condition for such things as photons, that I believe Rovelli wants us to consider. (I'm sure I'm reading a lot into it, perhaps more than I should. Note Quine's "To be is to be the value of a bound variable."

With respect to the main point of the talk, namely what you want to focus on, I'm afraid I can only be among the audience here. The concept seems to me that because entities of a certain size, relative to the things that affect them, and are called observers, exist, and especially so in cosmology, that a relative basis for considering them is crucial for understanding how the universe has to be depicted. It may be, according to Rovelli, that there are levels of such relativity, and that different observers in different circumstances do not observe the same event (or something like that -- I'm afraid I couldn't follow the point), but there is nevertheless a reality to them nonetheless.

That action-at-a-distance idea (the non-local resolution to the EPR, should it occur) need not be considered, according to Rovelli. Instead, we should rely on this bifurcation concept in which small effects on larger objects act relationally. This may be a reach, but there's a sense in which the observer is created by these small effects, not so much in the sense in which it might lead to the evolution of life, which might well be the result, but rather that the information it receives from the cosmos becomes something on which the observer has a relationship, giving it relationship properties at the scale of the observer, respecting the objects in which the information is associated. (This is all pure mush and feeds my own sense in which I, too, am a realist, and not of the Platonic kind. But I try, nonetheless, to make sense of things.)
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Re: Critique of Interactive Realism (Oxford Cosmology&QFdn C

Postby Marshall on May 7th, 2014, 3:49 pm 

owleye » Wed May 07, 2014 6:42 am wrote:... can be considered "under control". And, of course, this fits with the notion of this "eye-shape" being a boundary condition…"
... Note Quine's "To be is to be the value of a bound variable."...


You got the idea from just a brief glimpse around minute 48. Near the end of the hour talk he shows that slide (which is from his SECOND lecture) as a teaser to get people started thinking about quantum gravity (i.e. modern spacetime geometry) which is going to be the topic of his next lecture.

Several times during the first lecture, which we linked to here, he mentions that introducing geometry, in the next lecture, will SIMPLIFY the Relationalist view conceptually and get rid of some indefiniteness. It becomes logically more solid when one can specify a PROCESS by saying that it goes on in a bounded region..

Then instead of conventional "state" of system at a specified "time" what takes the place of the traditional "state" idea is the boundary. We imagine interacting at the boundary, establishing boundary facts, before and after the process. All the facts---interactions that affect us---live on the boundary and the quantum amplitude we want to calculate is traditionally called "transition amplitude" but the idea has been generalized. (it doesn't matter but this is Robert Oeckl's "general boundary formalism" for quantum field theory and quantum gravity, or for quantum theory generally.)

I like the quote from Quine---the root of "to define" is "to bound", an unbounded being must either be rather vague or a contradiction in terms, mustn't it?

I appreciate your watching the video! It basically sketches what the Relational view of QM is.
The separation between system and observer can EITHER be a real boundary (as discussed in second lecture where we get into geometry) or it can be one of scale. Scale is not the only way to identify/distinguish an observer interacting with a system.

I'll get the link to the second lecture in case anyone is curious to see a sketch of quantum gravity (for philosopher of physics, not specialist physicist, audience)

The title is Cosmology and Quantum Gravity: Loops and Spinfoams

Note that the title of the first talk was Cosmology and Quantum Theory: the Relational View.
IOW it was much more general and actually omitted saying how one can treat geometry in an interactive quantum fashion. There was only that "teaser" slide around minute 48, from which one couldn't really deduce much since so out of context.
Marshall
 


Re: Critique of Interactive Realism (Oxford Cosmology&QFdn C

Postby dandelion on May 8th, 2014, 9:40 am 

This thread with the explanation of different facets of the theory and consideration of their use as titles is really helpful. For a start, the explanation of the use of the term process rather than state was very helpful because I hadn't really understood that, and I think the explanation in the fourth post of quantum reality supports my understanding of that apect. Thank you very much!
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Re: Critique of Interactive Realism

Postby Marshall on May 8th, 2014, 11:18 am 

Hi Dandelion, welcome to SPCF! I'm happy to see a new person interested in this topic which is one where physics and philosophy seem to meet in a kind of mutually supportive way. Just to recall the topic, in case I stray away from it too much in what I say next, here's a bit from the initial post:
Marshall » Tue May 06, 2014 11:39 am wrote:This is a non-confrontational thread. Criticism has to be constructive and cooperative. This is the topic:
http://www.youtube.com/watch?v=TzmykSv6OBY

Ive decided to try out the modifier "interactive" ... Facts in Relational quantum context are interactions, so it amounts to the same thing, but saying interactive makes it more explicit….
Last year there was a conference at Oxford on *Cosmology and Quantum Foundations* at which three main worldviews were presented and compared.

The "relational" or as I will call it the interactive take on Scientific Realism (Carlo Rovelli)
"Many worlds" interpretation of quantum mechanics (Antony Valentini)
"Multiverse" including mathematical universe thinking (Max Tegmark)

This thread is to focus on the first of these….


One thing that makes me very optimistic about a cooperative trend between physics and philosophy-of-science is that this meeting on Cosmo and QF was sponsored and hosted by the PHILOSOPHY DEPARTMENT. In fact it was part of a series of meetings held alternately at Oxford and Cambridge. BOTH of those universities Philosophy departments (which I think are probably leading ones) are interested in learning about and examining Physics world views. One should always be cautious about optimism and this trend might fail to gather strength and die out, so I won't say anything more about it here.

What I want to talk about, briefly, right now is the role of Heisenberg Uncertainty Principle, which one could almost call the "Heisenberg EXISTENCE Principle" in Relationalist or as I'm calling it Interactive Realist thinking.

A friend who is interested in these half-physics half-philosophical issues recently wrote to to me and put it intuitively this way:
==excerpt from private message==
...regarding ...heisenberg uncertainty principle,... there is a standard argument for the stability of atoms because of quantum theory. the electron cannot fall into the nucleus because HUP forbids it to be too localised without zipping away. i would see the cosmological bounce and the core of the planck stars as possible manifestations of the very same thing. as you say, nature does not like to be pinned down too precisely. discreteness and therefore the area gap is a manifestation of the same: in the classical phase space, a system cannot be squeezed in a region smaller than hbar (hbar has the dimensions of phase space ...). so we cannot have an eigenvalue of the energy of a harmonic oscillator, or of the electron in a coulomb potential, or of the area of a region, or of the volume of a symmetric universe, so small as to require the corresponding state to be squeezed in too small a region of phase space. ...
==endquote==
Marshall
 


Re: Critique of Interactive Realism (Oxford Cosmology&QFdn C

Postby Marshall on May 8th, 2014, 12:02 pm 

The basic intuitive idea here is that existence is ROBUST because of hbar. It doesn't collapse into singularity. Atoms do not collapse. If a star tries to collapse it bounces. If the universe were to try to have a "big crunch" it would bounce.

==side comment==
I suspect (though just a non-expert watcher of professional research, not a participant) that this existential resilience principle is even stronger than the Second Law of Thermodynamics.

If to comes down to choosing between hbar and (the usual increase of) entropy, I bet on hbar.
==back to main discussion :^D==

Some readers might be wondering "why should atoms collapse?" This goes back to an observation about Maxwell equation made around 100 years ago. Accelerating motion of charge radiates away energy. If you have some ideal zero-resistance wire and make some charge oscillate back and forth in it (or flow around and around a loop of it) then that is an ANTENNA and it radiates (accelerating charge emits "photons" and loses pep, the acceleration eventually tires out and dies). It is a reciprocal interaction: some incoming radiation can be absorbed by an electron and cause it to jump, to accelerate (as happens in receiving antennas).

So intuitively the electron orbiting the nucleus of an atom should gradually radiate away all its orbital energy and spiral in to the nucleus. Matter would be millions of times smaller and would stop having chemistry, it wouldn't hold up anything and life would be no fun :^D. Probably I didn't need to say that because anybody who might be reading here already knew it.

HUP is what keeps that collapse from happening. And other similars. For succinct intuitive summary, look back at the previous post.

Notice that we are talking about INTERACTIONS. If the proximity of two things shrinks to zero so that their relative position is evermore precisely determined, then their RELATIVE MOTION becomes extremely undetermined. The electron cannot REST in the lap of the nucleus, it has to continue buzzing around. Because of hbar. hbar is the minimal distance scale of the combined position and motion picture called "phase space".
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Re: Critique of Interactive Realism (Oxford Cosmology&QFdn C

Postby owleye on May 8th, 2014, 1:47 pm 

Marshall...

There are two things I want to get into respecting your last post. The first one, in this post, will be on the concept of collapse, which will include a bit about the bounce effect. My comments are principally for my own growth and as such correspond to a trial on my part to which error is surely one of its parts. The second will be on constituency in a discussion of particles (of particle physics) and will be a separate post. And I draw attention to this initially from the notion of a wave-function collapse, which may or may not be the same usage as above, but requires me to address existence in a different way.

The use of 'collapse' in how you use it, I think, could be taken in its everyday sense. Buildings collapse. Marriages collapse. The idea being that there is stability within something that exists but where conditions might arise in which whatever maintained the equilibrium is disrupted in some way. Beams soften. Glue gives way. And these may be such as to destroy it, reducing it to rubble, reduction being the key thing. How this is manifest differs depending on how the bonds are broken.

So, this analogy can be taken to the atomic level wherein it might be assumed that the atom is held in some sort of equilibrium by various forces operating on its constituent elements. Presumably by way of analogy, one might imagine that conditions could arise that would disrupt that equilibrium. And this surely is the case, except that what we find is the collapse occurs in bundles or packets and not uniformly. And this, I believe, is what Marshall is referring to, respecting the limits of collapse. That it produces a bounce effect, however, requires an additional explanation.

And I suppose this has to mean that while energy is exchanged in packets, there remains a dynamic aspect to it. In other words, energy is still a continuous function, but that packets resist in some way to additional energy infusions until they reach a certain packet amount and only then is there an actual exchange. Up to that point resistance would be released in the reverse direction in accordance with principles of conservation of energy and momentum.
owleye
 


Re: Critique of Interactive Realism (Oxford Cosmology&QFdn C

Postby owleye on May 8th, 2014, 2:34 pm 

This post begins with what constitutes existence. Particle physicists refer to existence as comprised of energy bundles or packets. The problem with doing so is that energy is a property, not an entity. And although a packet or bundle might be thought of as an entity, it seems to exist in name only. Consider a photon, a particular packet of energy determined by its frequency, "packaged" by Plank's constant. However, though it has a frequency, there really isn't anything that varies There's no there, there (unlike, say, with sound waves). Photons have no constituency.

Despite this, photons enter into interactions with observers as if they have an indeterminate, though bounded existence, producing patterns that have been understood to be probabilistically accounted for, but at each individual instance represents a collapse of its (the photon's) wave function. However, if I have it right, Rovelli redirects our understanding of it not to the wave function, but rather to the energy exchange that takes place at the observer end. From the standpoint of the observer, photons can exchange their energy only where and when the receiving entity (some atomic or molecular constituent of the observer) absorbs it, altering its structure in some way. And although there are a number of candidate absorbers, conservation laws allow only one of them to take place. It's not that there is any communication needed between places where the packet is exchanged and where it could have been exchanged but wasn't. Rather, it's because, once again, energy exchanges take place only in packets. And this trumps other causal connections. In that interpretation, there is no collapse of the wave function at all. The wave function, while descriptive and predictive, has no particular existence.
owleye
 


Re: Critique of Interactive Realism (Oxford Cosmology&QFdn C

Postby Marshall on May 8th, 2014, 4:02 pm 

Hi Owl, so nice to have a partner in discussion raising points like this. There was a famous lecture by Dirac where he said of the two usual formalisms he thought HEISENBERG's (not using Schroedinger equation) was the right one.
That has been echoed down the years. Rovelli repeats it around minute 15. and gives one of the main reasons.

Heisenberg invented QM in 1925 and Schro came up with wave function in 1926.
H's treatment is essentially to use MATRICES or more generally OPERATORS that evolve in time and can represent *observables* resulting from some measurement. Each observable operator has a "spectrum" of possible outcomes of the measurement.

Schro treatment was POPULAR because it looked back to CLASSICAL PHYSICS OF WAVES. Which physicists were used to and could easily picture mentally.
However it is flawed for a reason that Heisenb. himself pointed out. Only if you have as system with ONE particle is the the Schro wave function defined on space so that it looks like moving hump of "probability amplitude", imitating a classical particle.

As soon as you have a system of TWO OR MORE particles the wave function is no longer defined on space.
If you have say 30 particles then the wave function is defined on a big 90 dimensional cartesian product.

Anyway Rovelli is saying "if we want to be realistic, let's not imagine the world in terms of Schröd wave function!" just use it where convenient as a computation device." And this has been said by others for a long time, going back at least to Dirac's HUNCH that Schro was not the way to go.

This is in line with some things I like that you just said in preceding post:

owleye » Thu May 08, 2014 11:34 am wrote:... However, if I have it right, Rovelli redirects our understanding of it not to the wave function, but rather to the energy exchange that takes place at the observer end.

... Rather, it's because, once again, energy exchanges take place only in packets. And this trumps other causal connections. In that interpretation, there is no collapse of the wave function at all. The wave function, while descriptive and predictive, has no particular existence.


That's right! He redirects our attention not to the wave function but to the INTERACTION, where e.g. a photon is emitted, or scattered, reflected, or absorbed by a nerve ending in your eye. It very often can involve exchange of energy. An observable can however measure other stuff, e.g. geometric facts too, like area, length, angle.

Dirac was speaking at a famous series of summer lectures given annually somewhere in Sicily, I can't remember the name of the scenic spot on the Mediterranean where they hold it. Gerard 't Hooft spoke there one summer recently.
Marshall
 


Re: Critique of Interactive Realism (Oxford Cosmology&QFdn C

Postby owleye on May 8th, 2014, 8:16 pm 

Marshall » Thu May 08, 2014 2:02 pm wrote:That's right! He redirects our attention not to the wave function but to the INTERACTION, where e.g. a photon is emitted, or scattered, reflected, or absorbed by a nerve ending in your eye. It very often can involve exchange of energy. An observable can however measure other stuff, e.g. geometric facts too, like area, length, angle


Actually I was thinking of Young's double slit, where the screen represents the observer. And, if one thinks of the eye, I was thinking of the retina (the rods and cones), each element of which is capable of picking out some range of energies of single photons. The focal point need not be, and possibly even shouldn't be thought of as, a sharp point, but as having a spread.

However, in depicting it in the way I did, I was cognizant of the EPR experiments in which Bell's inequality eliminated the possibility of hidden variables. It was in that form the led thinkers to think that causality might have been non-local, the idea being that for some reason there was a need to have the second event (spin X) be contingent upon the first event, its revealing of spin Y. (I know it's more complicated than this, as it requires three apparently independent, but actually correlated, spin values to draw the conclusion that EPR had it wrong. This "interaction' as you call it (though, as I see it, while it might be an appropriate descriptor, I think it hides some of the detail necessary to draw the conclusion), has the effect of drawing off the energy of the photon just because it's an elementary particle. (I agree there may be other interactions besides this one, but I was emphasizing this one because it seemed to me the relevant one which led to this notion of a collapse of the wave-function.)
owleye
 


Re: Critique of Interactive Realism (Oxford Cosmology&QFdn C

Postby Marshall on May 8th, 2014, 9:04 pm 

Owl, it's good you brought up the EPR puzzle. I hope we are both around to celebrate its centennial 20 years or so from now. It's had a fertile effect on physics.
Since this thread is discussing the RELATIONAL (aka Interactive Realist) view of quantum mechanics it would be useful to discuss what EPR looks like in that context.

There is a nice paper on that. Google "Relational EPR" you should get a link to the article on arxiv.org. It shows that the puzzle is solved in Relational context.

For general background (using other notions of quantum reality, not relational) there is the Wikipedia article on the EPR "paradox" http://en.wikipedia.org/wiki/EPR_paradox

I'm busy right at the moment but will try to get back to this in a little while.
Marshall
 


Re: Critique of Interactive Realism (Oxford Cosmology&QFdn C

Postby Marshall on May 9th, 2014, 12:00 am 

I'll try to contrast Relational (aka Interactive) EPR with, on the other hand, a kind of Schro wave function ontology EPR in which there is a Super-observer who gets all the facts non-interactively from wherever.

In Relational EPR there is no fact until there is an interaction, widely (e.g. lightyear) separated observers necessarily have different sets of facts and different accounts, and only LATER get together talk it over combine information, and construct a common story. That takes time, so it's not too surprising it turns out there is no faster than light communication.

In the older picture there is in effect some vast GIGANTIC WAVE FUNCTION spread out so it covers both of the widely separated particles at A and B, and which COLLAPSES instantaneously at point B when Alice makes a measurement at point A. To an Interactive Realist, this wave function is UNREAL and it represents the bogus "Superobserver's" knowledge. It does not represent the two separate collections of facts which the two observers separately experience, and which they will not be able to POOL into collective understanding until they eventually have time to radio each other (limited by the speed of light ) and report, compare notes etc.

If I imagine myself as Superobserver and able to instantaneously see Bob reading his spin detector and at the same time watch Alice reading her spin detector. Then to ME it may seem as if there has been superluminal transfer of info. Information has been sent across, say, a lightyear along GIGANTIC IDEA that Erwin Schrodinger made up. The abstract Superobserver's wave function and it's fabled collapse is serving as an imaginary superluminal telegraph wire. But in Interactive view we don't attribute existence to such a thing and so are not bothered by it.

It's a different interpretation of quantum mechanics (relational QM) which is what Rovelli was invited to the Oxford conference to discuss. A bunch of other Q Foundations people have written about it since the 1990s so it's getting increased attention gradually.

If we reduce it to concrete down to earth observables, each separate observers reading separate instruments at widely separated locations, nothing is communicated. In fact, by Special Rel we cannot say in any absolute sense *which observer made the measurement FIRST* or if they checked the spins at the same time. How you judge the temporal sequence would depend on the relative motion of who is judging it. If you want to introduce the logical construct of a superObs then until you specify that supernatural person's state of motion you can't say who measured their particle's spin first. If there was superluminal sending, was the info sent from A to B? or from B to A?

The basic idea is that there is no official BOOK OF FACTS that says what happened until observers have had time to telephone each other or go visit, and construct a common understanding. FACTS are interactions, so they are RELATIVE to which observer. They live in that observer's past light cone. They only merge collections of facts when they travel to visit each other so they now share the same past light cone and the same facts. SIC TRANSEUNT PARADOXA MUNDI. In my bad Latin "thus depart the obnoxious contradictions of the world" :^D

I hope this is OK, I didn't take the trouble to review the "Relational EPR" article before trying to make a non expert summary. I recall they had a nice quote from Asher Peres at the end, an Israeli Q foundations theorist "grand old man" guy (while he lived). He basically agreed, just said it differently.
Marshall
 


Re: Critique of Interactive Realism (Oxford Cosmology&QFdn C

Postby owleye on May 9th, 2014, 3:14 pm 

Marshall...

This relational orientation has stirred up much thought in my noggin. I'm happy to have it as a topic. I'd lost contact with the EPR stuff since the '90s where I confess I'd not really understood how it could possibly make sense. Naturally, from the science community, even on this board, one would get the response back that well, we have to accept it as it is. There may be no explanatory account, only a descriptive/predictive account. And, of course, not being an insider, I hadn't been in on all the individual interpretations from the theorists (Heisenberg, Bohr, Shrodinger, Dirac) and how there were important distinctions which underlie each of their developments. So, in reading the Rovelli article (the one you referred me to on his interpretation of the EPR experimental data in the light of Relational QM), I found myself trying to read into to what I gleaned from the topic article, where I fastened on a quantized exchange of energy that allowed it all to make sense to me. I'm still trying to do so in the context of EPR, though I don't discuss this in the following.

And yes, it helped me understand Young's double slit idea, but it wasn't so easy to figure out how I should actually connect it with information. I do tend to think of information as it is in the sense of being informative, though I also recognize it when it is referred to as negentropy, or a measure of the orderliness in the universe. However, what I was missing in the account is how it relies on a vocabulary in which it can be communicated. We tend to think of light as communicating information about some object at a distance to us as observers, as if there was a deeper reality in the traversal of light that light passed through in order to bring it to us. Light in that treatment is a particle (as packetized information) traversing a path through space.

However, for all intents and purposes, the only reality to this is the reality of the encounter of light with the observer. And, in consideration of our information processor (our brain) as the observer, that's all it assumes in order to arrive at its formulation of the world (at the scale of importance to us as biological organisms). This can't be a solipsistic account, since evolution wouldn't make sense were that to be the case. In any case, this relational aspect of information and the reality it encompasses has to contend with other accounts in which light impinges on observers that are spatially separated. Is it the same reality? Rovelli asks. Well, its the same reality only if it can be placed within the same light-cone. If not, they have to be considered independent observers observing separate realities. (Which may also be part of the explanation of why a lens is required to capture facilitate the communication of information. I have something in mind here, but at this point only intuitively perceived.)

So, how does Rovelli explain the correlation of spins spatially separated? He uses the same QM state equations, which are understood as predictive, but adopts the frame of reference for such prediction to be a kind of observer that assumes the status of a super-user wherein the expectation is that when she obtains the results of the other's observation, it will be confirmed. And, presumably, that's because in this framework, the two are observing the same reality. Thus, the correlation occurs because it was formed in the frame of reference of its origin, despite that the only reality is the reality of the observations at their points of interaction. There just isn't any reality beyond the observations. Presumably light spans space and time between points of interaction, but there isn't any understanding of the real relationship between space, time and the interactions, so they are denied any (absolute) existence. (???)

I don't think I'm getting it. I'm going to continue to work on it from the perspective of my previous post, and perhaps there's a way to merge that approach with what Rovelli is talking about. I can only hope.
owleye
 


Re: Critique of Interactive Realism (Oxford Cosmology&QFdn C

Postby Marshall on May 9th, 2014, 6:33 pm 

Whoa! Time for me to review that 2006 article "Relational EPR". I haven't looked at it for a while and should refresh my memory.
When I google the title I get http://arxiv.org/abs/quant-ph/0604064
You might take a look too. You may be familiar with the usual way journal articles go, some verbal explanation and summary at the beginning and end, sandwiching the technical part in the middle. There's usually something to suit various people's requirements. I don't recall how readable that article is but it likely is at least moderately so. Anyway I'll go take a look.
Marshall
 


Re: Critique of Interactive Realism (Oxford Cosmology&QFdn C

Postby owleye on May 9th, 2014, 7:18 pm 

Marshall » Fri May 09, 2014 4:33 pm wrote:Whoa! Time for me to review that 2006 article "Relational EPR". I haven't looked at it for a while and should refresh my memory.
When I google the title I get http://arxiv.org/abs/quant-ph/0604064
You might take a look too. You may be familiar with the usual way journal articles go, some verbal explanation and summary at the beginning and end, sandwiching the technical part in the middle. There's usually something to suit various people's requirements. I don't recall how readable that article is but it likely is at least moderately so. Anyway I'll go take a look.


Up in the right hand corner it offered a PDF version, which I quickly downloaded. It was a fairly easy read, I think, but I suspect I'm missing something. Let me say in the google page there was a rebuttal from someone at UC Berkeley, which, though I read it, I can't say as I was able to understand it very well. I'm generally a slow reader, especially with new material, so in order to be able to make progress I have to see it from a number of angles and, I think, often come to understand only after other people show me the way. Nevertheless, such secondary readings only work after I've wrestled with it for awhile. Once I'm able to paraphrase it, as you have done, will it make sense to me.
owleye
 


Re: Critique of Interactive Realism (Oxford Cosmology&QFdn C

Postby Marshall on May 9th, 2014, 7:22 pm 

Here are excerpts of the first few paragraphs, to give an idea of where it's going. This won't necessarily answer your question, Owl, but you'll catch the drift and I can try to reply subsequent to that. You may notice down at the bottom of these excerpts that he is footnoting to Wittgenstein, so rooting what he has to say not only in interesting recent physicists like Asher Peres, but also in 20th C. philosophy work:
==quote "relational epr"==
EPR-type experiments, championed by Aspect et al. [1, 2], are often interpreted as empirical evidence for the existence of a somewhat mysterious “quantum non-locality”. For instance, Chris Isham concludes his beautiful exposition of the EPR debate with the words “[...] we are obliged either to stick to a pragmatic approach or strict instrumentalist interpretation, or else to accept the existence of a strange non-locality that seems hard to reconcile with our normal concepts of spatial separation between independent entities” [3]. In spite of seven decades of reflection on this problem, leading to considerable sharpening in its characterization [4, 5], the precise nature of this non-locality —which does not appear to be usable to transmit information, nor does make quantum theory incompatible with special relativity— remains rather elusive.

In recent years, a novel point of view on quantum theory, denoted Relational Quantum Mechanics (RQM), has been discussed by some authors [6, 7, 8, 9, 10, 11, 12]. In this paper, we argue that in the context of this interpretation, it is not necessary to abandon locality in order to account for EPR correlations. From the relational perspective, the apparent “quantum non-locality” is a mistaken illusion caused by the error of disregarding the quantum nature of all physical systems.

[[Owl: Including the quantum nature of an observer, from the standpoint of another observer]]

The price for saving locality is the weakening of realism which is at the core of RQM. This ontological move, as radical as it may appear at first sight, is actually implicit in the historical evolution of the EPR debate.

[[weakening: there are no abstract facts independent of interactions, there are no abstract properties a system can have, absent an observer or interaction with another system]]
...
...
...On the other hand, the Kochen-Specker theorem [16] has questioned the very possibility of uncritically ascribing “properties” to a quantum system. From this perspective, the problem of locality moves to the background, replaced by a mounting critique of strongly objective notions of reality (see for instance [17]).
Here we take this conceptual evolution to what appears to us to be its necessary arriving point: the possibility of reading EPR-type experiments as a challenge to Einstein’s strong realism, rather than locality.

[[challenge to strong realism: there is no Superobserver with a comprehensive universal book of facts. there are separate observers with separate collections of facts, which they can merge when and if they get together and communicate]]

To be sure, the philosophical implications of RQM, especially for what concerns realism, are heavy. We shall briefly comment on these in Sec 4.4. However, the purpose of this paper is not to defend explicitly the relational interpretation of quantum theory, but only to remark that, if one adopts this view, the disturbing non-local features of EPR-like correlations disappear.

Similar criticisms to the notion of “quantum nonlocality” have been recently expressed by a number of authors [19, 20, 21, 22]. In particular, in a recent article [23], Asher Peres concludes his analysis of the EPR problem with a general statement, which, as we shall see below, is precisely the ground assumption of RQM. Thus, if we are inclined to accept RQM as a way to make sense of quantum theory, the EPR correlations can be interpreted as supporting this point of view.


In the context of the EPR debate, [[Einstein's strong]] realism is taken as the assumption that, in Einstein’s words:

there exists a physical reality independent of substantiation and perception”.

We call this assumption “Einstein’s realism”. RQM departs from such strict realism. In RQM, physical reality is taken to be formed by the individual quantum events (facts3 ) through which interacting systems (objects4 ) affect one another. Quantum events are therefore assumed to exist only in interactions5 and (this is the central point) the character of each quantum event is only relative to the system involved in the interaction. In particular, which properties any given system S has is only relative to a physical system A that interacts with S and is affected by these properties.

If A can keep track of the sequence of her past interactions with S, then A has information about S, in the sense that S and A’s degrees of freedom are correlated. According to RQM, this relational information exhausts the content of any observer’s description of the physical world.

==some footnotes==
3 “1.1 The world is the totality of facts, not of things” [26].
4 “2.01 An atomic fact is a combination of objects (entities, things). 2.011 It is essential to a thing that it can be a constituent part of an atomic fact” [26].
5 “2.0121 There is no object that we can imagine excluded from the possibility of combining with others” [26].
6 An observer, in the sense used here, does not need to be, say “complex”, or even less so “conscious”. An atom interacting with another atom can be considered an observer.
Marshall
 


Re: Critique of Interactive Realism (Oxford Cosmology&QFdn C

Postby owleye on May 9th, 2014, 8:17 pm 

My apologies for not being clearer. I actually read the part you quoted and understood what was being said. It makes sense to the extent that one can reestablish locality considerations at the cost of a relaxation of some absolute consideration of reality -- one must now only consider it in a relational way, where one can only consider interactions as meaningful. (And whereof we cannot speak we must remain silent: Wittgenstein, which he cited at the end.)

Where I had my difficulties is in how he explained the QM entanglement and correlation through a relativized or relational QM. My own thoughts wander here. In the Young experiment, the first interaction is the double slit, which has the effect of creating a pattern of a certain kind. The second interaction yields that pattern by its encounter with the screen. In the second interaction, I worded it so that the "collapse of the wave function" was unnecessary on the basis that the site of the interaction captured all the energy of the photon, prohibiting it from appearing elsewhere. The first interaction merely established the possible sites for some observer and depended on the geometry of the setup. (I suppose there is also an interaction at the origin as well.)

In turning to spin correlations, what I'm thinking about has to do with a different set of degrees of freedom. I recall when I was at NASA that photons interacting with atoms have a number of possible perturbation effects, e.g., the usual one in which an electron in an outer shell can move to a higher orbital and fall back, releasing a photon that corresponds to the "color' of that jump. Excess energy may go into producing rotation or vibrational states. More energetic particles may have an effect on the nucleus. The atom may fission.

So, what I'm thinking regarding the EPR situation is that the interaction at the origin which caused the object to split into components that move apart from each other determines the pattern of interactions at the observer end. And, if the elephant (using Rovelli's imaginative idea) is considered subject to relational QM, the observer, in accordance with the how it is setup to observe one of the spin's degree of freedom, will prevent its entangled particle from having that same value.

However, I'm not even close to being satisfied by this. Indeed, it's supposed to be handled by way of a relational wave function, which I can't quite put my finger on. The same thing was present in Rovelli's talk on the topic, but it's a bit too technical for me to grasp. I'm even trying to figure out how it relates to the Shrodinger Cat thought experiment. Does the death of the cat depend on the observer?
owleye
 


Re: Critique of Interactive Realism (Oxford Cosmology&QFdn C

Postby Marshall on May 9th, 2014, 11:04 pm 

Hi James,
I wanted to quote some introductory material from that article partly in case others were looking in on the thread. I know you read the article thoughtfully and so what I posted wasn't necessary and didn't really answer your question---just provides context.

BTW did you happen to see footnote #6? It says an observer is ANYTHING that interacts with the designated system. It could be an oxygen atom or an amoeba---doesnt have to be conscious. That means that the terminology is awkward. Maybe it will be revised. Maybe we need a new word like "INTERACTOR" to replace "observer"
owleye » Fri May 09, 2014 5:17 pm wrote:... I'm even trying to figure out how it relates to the Shrodinger Cat thought experiment. Does the death of the cat depend on the observer?


Some definite interaction is what makes something a fact, makes it real. For macro systems there is a huge wealth of possible interactions with the outside world. So it may seem absurd to insist on having at least one specific one. It's only down at quantum level when this gets interesting. The polarization of a photon is not considered REAL until it interacts with something---a dust grain, a lab instrument. In fact the photon itself is not part of reality unless it interacts. It is an ontology of (interactive) facts.

I think that the ancestor physics I was thinking about earlier, GR and QFT, leads one to an ontology of fields. One is led to attribute real existence to the fields that successfully describe geometry and matter..
But this Relationalism (or Interactive Realism as I was thinking to call it) is more AUSTERE, leaner, more spare.

I'll have to think more and try to get clearer about this. Maybe this is a possible "critique" of Interactive Realism (the desired thread topic), namely that it is too austere. I'll give it some time to settle.

It's a fact that when you go from classic GR to a quantum geometry like Loop or Spinfoam QG you no longer have nice smooth fields, you enter a world of tinkertoy graphs, knob and stick, nodes and links. like molecule models. There you have nodes which can be events and links which are relations between the events---or chunks of volume with the legs of the graph being contact areas---a graph representing the discrete information accumulated about the geometry of some region, at the region's boundary where the outside world interacts with it.

Everything, whether geometry or matter, is no longer the fields (we know and love from GR and matter field theory) but has become DISCRETE.
Have to go, also need to ruminate and assimilate some thoughts, back later.
Marshall
 


Re: Critique of Interactive Realism (Oxford Cosmology&QFdn C

Postby Marshall on May 10th, 2014, 12:31 am 

James, when you look at LQG closely you see that the spin network, spin foam language is a way of TRANSLATING THE geometric gravitational FIELD of general relativity INTO A WEB OF FACTS and allow it to evolve by a discrete process.

So what has happened is that the ontology of fields has been discretized and resolved into discrete facts.

In a way it is analogous to what happened earlier in Quantum Electrodynamics.

The Maxwell equation and the electromagnetic field was the beautiful field theory par excellence. Everybody poster field, pride and joy. When it got its quantum version, what did you see? FEYNMAN DIAGRAMS.

Spinfoams are often referred to as the "Feynman diagrams" of quantum GEOMETRY dynamics aka quantum gravity.

they describe a process that is resolved into discrete events

So I need a different name for what's developing from contemporary physics: not an ontology of fields and not an ontology of facts (which would refer back to Wittgenstein's Tractatus!) but rather
an ontology of fields resolved into discrete facts.

I'll try looking at it from that angle for a while.

There's a part of a young Austrian guy's thesis (Wolfgang Wieland) that was just posted in March which sketches the outlook for defining matter on (not "spin", more efficiently labeled) foams.
That is the next step---the spin foam is their quantum substitute for the continuous field that describes space and time geometry, so how to have matter live on that? How to embed matter Feynman diagrams in a "quantum geometry dynamics" Feynman diagram foam.

It's just a page of non-technical outlook writing at the end of his thesis. I have the link if anyone wants to see it.. I'll go back and take another look. Lot of respect for Wieland, still fairly young guy on his first postdoc assignment.
Marshall
 


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