Quantum realism and fields.

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Quantum realism and fields.

Postby Marshall on May 10th, 2014, 12:46 am 

Or maybe the simplest course at this point is just to look back at the Oxford 2013 Cosmology and Quantum Foundations conference and see how Rovelli proceeded to continue developing the Relationalist ideas in his SECOND talk.
This was the one where he introduced space and time geometry---the first talk was more general, it only included that one slide on spacetime geometry, that I called a "teaser". Here's the second talk:


The title is Cosmology and Quantum Gravity: Loops and Spinfoams

If someone is encountering this fresh, the title of the first talk was "Cosmology and Quantum Theory: the Relational View". It was more general and postponed saying how one can treat geometry in an interactive quantum fashion. If you haven't watched it you might want to go back and catch the first talk (link at the start of this thread.)
Marshall
 


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

Postby owleye on May 10th, 2014, 10:57 am 

I'm holding off on the next lecture until I can better appreciate RQM and its explanation of EPR. The relevant section in the archiv paper is section 4. Relational discussion of EPR experiment, which begins with:

We shall now present a relational discussion of the EPR experiment, compatible with locality. But first, let us get rid of the problem of separability: in the EPR experiment, the two entangled systems interact with two different observers. Incontestably, both get definite outcomes during these complete measurements (in the sense of Dirac). Hence, the particles are separable. Fine - one might say - but what about the EPR correlations?


So Rovelli gets into more detail about the measurements.

4.1 Individual Measurements
Say that A measures the spin of in the direction n at time t0. This is an individual observable, denoted . Suppose B measures the spin of in the direction of n' at time t'0 (individual observable ). Let us denote and () the corresponding outcomes. Because A and B are space-like separated, there cannot exist an observer with respect to which both of these outcomes are actual, and therefore it is meaningless to compare and : A’s outcome is fully independent from B’s, and vice versa.


What Rovelli is emphasizing here is that in the context of the observations, these are independent facts, facts than can't be compared. Note that these ideas have significant meaning to those who understand control theory, wherein what's under control are considered random variables, even if at some lower level all is determined. The idea is that at this upper level it doesn't matter whether the inner dynamics is fully determined, what's important is their interaction and is all that's necessary to maintain the control. (The container of a gas doesn't care about the inner dynamics of each of the gas molecules, only its collisions with the container itself.) This can also be understood to mean that a random variable is any variable in which its source and trajectory is not known in advance.

4.2 EPR Correlations
But these individual measures do not exhaust all possibilities. In the EPR experiment, the composite system α + β is assumed to be in the singlet state. From the relational point of view, this means that some observer, say A herself, has the information that the total spin of α + β equals zero. That is, it has interacted with the composite system in the past and has measured the square of the total spin. Let us call this collective observable .


And it is here that I'm having difficulty understanding this new A as being an observer. What interaction is it referring to? What measurement is this collective suppose to be making? Well, I'm thinking its supposed be some observer gathering information about the original source, which is some singlet state, which then at some later time receives information from some observer (called A in the previous subsection) at the destination. And this is a bit obscure to me.

The measurement of brings new information to A. It determines the change of the relative state of α. Notice that A’s knowledge about α changes (epistemic aspect), and, at the same time, A’ predictions concerning future change (predictive aspect). For instance, A becomes able
to predict with certainty the value of if the interaction is repeated.


Again, this is confusing. The observer A presumably is now a super user who somehow is aware of the experimental setup and is stationed at some destination in which to observe an outcome of the experiment, knowing that it will produce one of two outcomes. And once it has observed that outcome, it can presumably repeat its observation with the same assurance of its reading the same result. I'm afraid I'm not seeing how it is able to repeat its observation. It seems to me that interactions aren't repeatable in that sense. I've got to be missing something here. Now he gets to the other observation.

But there is another observable whose value QM enables A to predict: , namely the measurement that A can perform on β at the time t1, when β is back into causal contact with A. For instance, if

and

then QM predicts that



Again, somewhat confusing. The primes ('s) have been dropped from the beta's and the n's. He then summarizes:

That is, the knowledge of the value of the collective observable plus the knowledge of the individual observable permit to predict the future outcome of the individual observable : it is this type of inference which constitutes the “EPR correlations”. It concerns a sequence of causally connected interactions.


I'm afraid I'm not getting the collective observer idea and its relation to it being causally connected. And I'm a bit lost on the nomenclature signaling the individual and collective observer.
owleye
 


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

Postby Marshall on May 10th, 2014, 11:44 am 

owleye » Sat May 10, 2014 7:57 am wrote:...
4.2 EPR Correlations
But these individual measures do not exhaust all possibilities. In the EPR experiment, the composite system α + β is assumed to be in the singlet state. From the relational point of view, this means that some observer, say A herself, has the information that the total spin of α + β equals zero. That is, it has interacted with the composite system in the past and has measured the square of the total spin. Let us call this collective observable .


And it is here that I'm having difficulty understanding this new A as being an observer. What interaction is it referring to? ...


I think it is referring to the process at the very beginning of the EPR thought experiment where some agency (which could be one of the two experimenters A and B) PRODUCES an entangled pair of particles---say the two originate by a decay process, from a system with spin zero, in such a way that we know that their spins MUST ADD UP to zero for ever afterwards. They have to be produced in the same laboratory, to be entangled that way, but thereafter even if you take them far apart (lightyears apart) their spins will continue to add up to zero.

Obviously it's hard to produce an entangled two-particle state, and can only be done at the particle level where the systems have only a small number of degrees of freedom (like spin) which are governed by conservation laws---e.g. like a particle-antiparticle pair.

But we can imagine that the job of producing the entangled pair is assigned to Alice and so she does it and gives one of the pair to Bob. and then the job of separating the two is done by Bob, who takes his particle very far away. and then the real experiment begins.

I think that is the scenario that is referred to in the paragraph you mentioned.

Otherwise we might picture a more symmetric situation where there is a third unnamed agency, a central lab, that produces the entangled pair of particle and gives one to A and one to B, and then A and B each go off in opposite directions. Then A would not have any special role and would not have interacted with the CREATION of the pair.

ACH! DUH! I just re-read what you wrote and I see that this is not too different from what you were suggesting might be going on! What I imagined was Alice was around when the singlet state was created and interacted (participated somehow) and so has direct knowledge, a fact. You were also imagining someone who was around then and acquired a fact about the creation of this pair of particles. You just didn't suppose that this person was Alice herself:
Well, I'm thinking its supposed be some observer gathering information about the original source, which is some singlet state,...


That article was written back in 2006, eight years ago! I think Rovelli's philosophical position has clarified since then and he has, moreover, had enough experience stating it that he can do so much more succinctly.
I ought to be able to find a ONE PAGE presentation of the essential resolution of EPR in the Relational context. If one doesn't exist yet, he or one of his grad students/postdocs should write one.

I'll look in the new textbook, maybe there is something in the index:
I have the link to the new textbook here viewtopic.php?f=72&t=27004#p259943
and one can get it by googling "introduction covariant LQG"
Marshall
 


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

Postby Marshall on May 10th, 2014, 1:50 pm 

The online draft of the new textbook is a good source for a lot of topics but I couldn't find relational EPR in the index.

There seems to be a widespread rebellion against the "Super-observer" however. :^D A growing acceptance that there is no unique "official book of facts". I.e. in the quantum version of Realism facts are discrete interactions and one has always to recognize that "it takes two to tango".

So the facts about a system or process are not absolute independent of the others it interacts with.

Just as an example (not to read!) here's a recent paper (2014). They have a section that is "against the Superobserver". The paper is by A.J.M. Medved et al

(Who? Alan Joseph Michael Medved is a South African particle physicist. Here's his profile page: http://inspirehep.net/author/profile/A.J.M.Medved.1)

Here's the paper, again not necessarily to read, just an example of this trend:
http://arxiv.org/abs/1401.5988
Quelling the concerns of EPR and Bell
K.L.H. Bryan, A.J.M. Medved
(Submitted on 23 Jan 2014)
We begin with a review of the famous thought experiment that was proposed by Einstein, Podolsky and Rosen (EPR) and mathematically formulated by Bell; the outcomes of which challenge the completeness of quantum mechanics and the locality of Nature. We then suggest a reinterpretation of the EPR experiment that utilizes observer complementarity; a concept from quantum gravity which allows spatially separated observers to have their own, independent reference frames. The resulting picture provides a self-consistent resolution of the situation that does not jeopardize causality nor unitarity, nor does it resort to ''spooky'' (non-local) interactions. Our conclusion is that EPR and Bell rely on an overly strong definition of locality that is in conflict with fundamental physics.
25 pages

The authors cite the 2006 paper "Relational EPR" and note the similarity of what they are saying (in 2014) to the eight years earlier work by Rovelli and Smerlak.
Everybody seems to have a different way of saying it but it basically comes down to the same way of throwing out the EPR paradox (see also similar articles by Cornell's David Mermin)

I kind of suspect that it is a gradual shift to a QUANTUM ONTOLOGY where the world is "made of" FACTS instead of being made of continuities.
People are gradually shedding their "continuity bias" as the recognition of quantum theory seeps in to our collective awareness.

I noticed that ALL the participants at the Oxford conference, that I heard e.g. in the Q&A discussion were using the word *facts* and emphasizing it as if it was a primitive idea that they ALL shared. It was after all a conference in the Philosophy department, on Cosmology and Quantum Theory, and they were coming from different directions/schools of thought, which though different had all incorporated quantum mechanics in some philosophical interpretation or other. So whatever their differences they were all talking loud and clear about "facts".
Marshall
 


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

Postby owleye on May 10th, 2014, 3:09 pm 

First, there is a parallel idea in cosmology merely from using GR (which I believe has been previously discussed here) wherein one adopts the frame of reference of the CMG in order to be able to regard the proper time measured in some reference frame as importantly connected (in a deep sense) to other inertial frames. In the absence of being able to do that, it might as well be separate disconnected universes. Comparability of proper times (their ages) occurs only when there is some way to compare clocks.

Second, I think if you toss the 'collective observer', what you get is not RQM, but R + QM, which is to say there is the relational, localized treatment of the experiment, removing obstacles to it having a localized understanding, and then add to it QM as a theory, you can account for the results by looking at the the QM portion as merely descriptive and predictive (i.e., epistemic), not ontologically essential. And, as for the reality of that which the "facts" of the observation point to, that implies a weakening of the strong Einstein realism, in that observers aren't necessarily looking at the same element (the singlet in EPR). It may be that they are, but there would be a need to connect it to some knowledge of the initial conditions. And when one does this, the relational aspect then becomes redirected away from the observers, and instead to the initial conditions. It becomes more real, so to speak. Now, if you then retreat back to an earlier time, you can connect all present observations in the way cosmologists (or the totologists in the talk) do as in my first paragraph, the relational aspect might ultimately be withdrawn all the way back to the origin of the big bang, making it relative to that, if not actually absolute.
owleye
 
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Re: Critique of Interactive Realism (Oxford Cosmology&QFdn C

Postby TheVat on May 11th, 2014, 3:39 pm 

No hypothesized classical observer can daunt 'em,
It turns out that Alice and Bob are quantum;

Ontologists rush to turn on their shields,
hoping they still are composed of fields;

But nature, it seems, is Eduard Seurat,
Pointilist and discrete as a cat;
And every brushstroke may be an observer,
logging events with bureaucratic fervor!

Nothing's quite real, not fields or particles,
just interactions with definite articles.

-- Paul N.
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Re: Critique of Interactive Realism (Oxford Cosmology&QFdn C

Postby Marshall on May 11th, 2014, 4:01 pm 

Braininvat » Sun May 11, 2014 12:39 pm wrote:No hypothesized classical observer can daunt 'em,
It turns out that Alice and Bob are quantum;

Ontologists rush to turn on their shields,
hoping they still are composed of fields;

But nature, it seems, is Eduard Seurat,
Pointilist and discrete as a cat;
And every brushstroke may be an observer,
logging events with bureaucratic fervor!

Nothing's quite real, not fields or particles,
just interactions with definite articles.

-- Paul N.


Beautiful! You put me to shame because at the moment I can only be ploddingly serious, I'm struggling to discover how to talk about ontology in the context of what could be called Quantum Realism (or interactive)

Im delighted by the Seurat pointillist simile. Can't match the wit, but for better or for worse here goes another attempt to talk about Rovelli's form of Realism:

A process has an outside, which is NOT the process. I find that the hardest part of this discussion to be clear about. There have to be other processes which for some reason are distinct, either because they are too small scale to be relevant, or too large scale, or because they are somehow spatially separated.

Processes consist of facts (interactions with the outside.) Reality is comprised of processes. (What we think of as material objects are monotonous processes.)

Spacetime is not a thing, it is a process (specifically, a geometric one).

In the case of a spacetime some of these interactions might be geometric measurements (somebody measuring a radius and a volume, somebody measuring some angles). Or the interactions might not involve a conscious agency: something inanimate might experience the geometry without knowing it. What plays the role of "observer" here does not have to be conscious. It can be called simply an "interactor".

My commerce with, say, a coffee cup consists among other things of millions of quantum interactions of light with the roughly 100 million receptor cells in my retina. A storm of discrete facts, during which the coffee cup sits there with its electrons monotonously sheathing its atoms and scattering quanta of light in my direction.
Marshall
 


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

Postby Marshall on May 11th, 2014, 4:56 pm 

This points squarely at the problem:
Ontologists rush to turn on their shields,
hoping they still are composed of fields;


In CLASSICAL (ie. pre-quantum) physics the ontology is clearly one of FIELDS, and that works out fairly well.

Reality consists of processes, and those processes are fields.
Spacetime geometry is a field (it is not the disposable point set used to define the field on, but the metric tensor field itself)
Matter consists of fields. In particular, solid objects resist intermingling because of the fermionic symmetry of the fields. (electrons refuse to co-habit)

So an ontology of fields works out pretty well. And traditional ontologists, if they have been paying attention, should NOT be hoping that the world is made of "objects and properties" but they should instead be hoping that it is as you say "still composed of fields".
=============

However the physicists (Einstein, Podolsky, Rosen, Rovelli, Bell, Aspect and many others) dug into this and found some trouble. The fields interact in discrete events. they interact as quanta. and the account of the various interactions, which came first, what caused what, etc, depends on the observer.

It seems that the world is still composed of PROCESSES but now a process is described (or determined or maybe even consists of) a WEB OF FACTS.

And if the facts involve interaction with several observers, then it seems you have to wait till sometime in the future when the news from the separate observes has had time to come in before you can construct a combined story and say what happened.

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

Paul N., Owleye and others, which seems like a better rubric for this "Interactive Realism" or "Quantum Realism"?

Which would be clearer to a newcomer? Rovelli is very definite about saying he considers himself a Realist. But it is not strict "Einstein Realism" where there is a Superobserver and a single official Book of Facts. The realism has been relaxed to accommodate many observers, all of whom are now quantum processes themselves rather than being separate classical systems. Any comments from you would be welcome.

(Constructive non-confrontational it goes without saying :^D)
Marshall
 


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

Postby owleye on May 11th, 2014, 5:06 pm 

I've been making some wooly assumptions about the way in which relational QM treats what it treats. Yes, there is a parallel treatment in SR, though it has been related to the meaninglessness of simultaneity, rather than proper time that I'd mentioned. But there are other important aspects of the discussion that needs to be considered, especially as it relates to EPR.

As this theory has been brought to our attention by Marshall, referring to it as Interactive QM, it emphasizes that observers are things which interact with other things.

In the EPR experiment, however, the observer is one who makes a measurement. So, what is a measurement? Surely it is an interaction, but it seems to me to be a specific kind of interaction. For example, in Young's double slit experiment, one might say that the double slit is an observer that interacts with the photon, but I'm hard-pressed to think of it as a measurement.

For the purposes of the discussion, it would seem that measurements are interactions that absorb meaningful information about what it measures. It may just leave a trace, but, in the case of the screen in the double slit experiment, the screen basically absorbs the photon, informing the observer where and when the photon was detected. And this absorption/detection is a measurement that basically prevents it from interacting anywhere else (due to conservation of energy).

In turning to the EPR experiment, however, the measurement reveals only part of the total information content of the source object. From the standpoint of a Sherlock Holmes interpretation of reality, the killer is revealed when all the clues to it have been put in place -- all the bits have the correct up or down state so as to complete the multivariate singlet state that fixes the meaning of that state. For example, if something is meaningful as a sequence of bit values, and is such that we have pinned down all of the bits except the last, we may assume that, if we are observing the total, the remaining bit value is assuredly known without observation.

Now, given this first measurement of the EPR, one may surmise that it forms a sufficient clue, sufficient to lock down the value of the entangled and correlated partner. But it doesn't on its own reveal its source. One may assume there is a source, but this requires other clues to locate, if that is our interest.

We're down to discrete states here, so the analysis is simple, but pool players perform something similar in order to hole a ball and have the cue ball set up for the next shot. They take advantage of the information content as if it were a complete system. (The player, of course, uses foresight in such a way that the work is left to the system after the cue ball is struck.)
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Re: Critique of Interactive Realism (Oxford Cosmology&QFdn C

Postby TheVat on May 13th, 2014, 4:38 pm 

I've been perusing this article on some of the problems with an ontology of fields....

http://www.creatingtechnology.org/papers/field.htm

It gets at some of the difficulties with attaching an individual identity to discrete points in space, but I'm not quite to where I can summarize this (there is a summary at the bottom of the article). The language is a bit different from what I'm used to, but I think there are some useful clarifications in there somewhere on how we talk about particles and fields.
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Re: Critique of Interactive Realism (Oxford Cosmology&QFdn C

Postby Marshall on May 13th, 2014, 7:25 pm 

Hi Brain! Glad you are taking time to post despite imminent 17 May wedding, and moving to LeadSD site of that deep underground neutrino detector! I know we are all wishing you best of luck and hoping the move goes smoothly.

So what in the contemporary (quantum) picture corresponds to ONTOLOGY OF FIELDS? The focus has to be on DISCRETE quantum INTERACTIONS and on PROCESS.
"field" sounds too classical like Maxwell circa 1850 electromagnetic field, or Einstein 1915 gravity-geometry field. they were smooth curvy things. Their TRUTH still abides but we have to be prepared to describe them in an approximate way that employs discrete interaction.
By a web of facts.
A photon only really exists at the point when the electromagnetic process interacts with a molecule in a cell in my eye, or when the process triggers a photomultiplier tube, or when an atom bumps down to ground state and EMITS a photon.
Quanta are part of the language by which we describe emission and absorption events. I recall you articulating this clearly in one of your posts, so I'm repeating that in part.

In Rovelli's new textbook (still just an uncorrected draft, now at Cambridge U P) there is some discussion of what I'm calling "quantum realism" and "ontology of process" early in the book around section 2.4.2 and 2.4.3 and also later in "applications" around page 241. But it's quite sketchy.

At the risk of getting temporarily off track I want to accumulate a bit of bibliography about FUNDAMENTAL DECOHERENCE. I'll explain why in a moment.
http://inspirehep.net/record/781938 (Intrinsic and Fundamental Decoherence: Issues and Problems)
http://inspirehep.net/author/profile/B.L.Hu.1 (profile of Bei Lok Hu)
http://inspirehep.net/record/674573 (Fundamental decoherence in quantum gravity) 12 cites
http://inspirehep.net/author/profile/J.A.Pullin.1 (profile Jorge Pullin)
http://inspirehep.net/author/profile/R.Gambini.1 (profile Rodolfo Gambini)
http://inspirehep.net/record/653376 (Realistic clocks, universal decoherence and the black hole information paradox) 38 cites
http://inspirehep.net/record/645205 47 cites
http://inspirehep.net/record/712912 38 cites
http://inspirehep.net/record/735013 25 cites
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Re: Critique of Interactive Realism (Oxford Cosmology&QFdn C

Postby Marshall on May 13th, 2014, 7:48 pm 

One reason Fundamental Decoherence is interesting is to explain the direction of time.
(despite reversible physics)
We could understand the direction time flows if we could understand how it happened that expansion began with what looks to us like a very low entropy state.

Now increasingly researchers are coming towards the BOUNCE picture of the start of expansion and one of the qg approaches that has been working on that picture the longest time (over 10 years) is Loop (which represents processes discretely as a "foam" of vertices edges faces a bit like honeycomb or soap suds in the sink).

So we could understand the direction of time in a Loop context if we could understand why the Loop bounce (a robust feature of the theory) results in low entropy state.

Recall from "Planck star"discussion that a collapse and bounce is a *shortcut to the distant future* Seen from outside it could take billions of years but to a participant it only takes a second. He falls in, undergoes extreme time dilation, and bounces out, discovering *surprise* that it is billions of years later.

the basic reason is that gravity s turned on its head (becomes repellent) during bounce so that the DEFINITION OF ENTROPY CHANGES and things evolve towards a blank slate instead of toward an incrteasingy marked and messy one.

What Gambini Pullin Fundamental (very slow) decoherence could give us is a OUTSIDE CHECK because there is an analogous fading of information on a billion or trillion years scale as seen from the outside which they prove based on the premise that there is no ideal clock, and no ideal time. *There is only the time kept by actual physical clocks which are quantum mechanical and have limits on accuracy.*

Eugene Wigner was the first person to notice this fundamental limit on the accuracy of real clocks.
OK so that's it for now. Just wanted to get the biblio links written down so I can go in and study this at leisure, when time permits.

Have fun! Keep us posted about life in Lead town!
Marshall
 


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

Postby Marshall on May 13th, 2014, 8:59 pm 

BTW I was watching a presentation given by Sanford Undergrd Research Facility (SURF) about the new LUX
(large underground xenon) facility, I gather for detecting WIMP dark matter.

The presenter pronounced the name of the town "Leed" instead of "Led" to rhyme with head.

I thought Lead SD was called Lead because of a lead mine. What's going on? Is that guy changing the traditional pronunciation to put a new spin on it (because they now have some of the leading cosmic matter detectors and are "world-leaders" in their branch of physics)?
Marshall
 


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

Postby TheVat on May 14th, 2014, 10:11 am 

Hi, Marshall. We are actually going to be in Rapid City, not far from Lead. "Lead" is pronounced "Leed" because it doesn't refer to the element lead (the mine there was a gold mine), but a mining term that refers to a geologic thing that leads into a major deposit of ore, IIRC. It's a common confusion, and aids the detection of outsiders (just like the pronunciation of "Willamette" in Oregon).
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Re: Critique of Interactive Realism (Oxford Cosmology&QFdn C

Postby dandelion on May 16th, 2014, 1:17 pm 

Snip- [quote="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.
==endquote==[/quote]

Hi Marshall, and thank you! It sounds like a happy interaction!

Sorry for the time and that I haven't learnt to quote properly.

Snip- [quote Marshall » May 8th, 2014, 4:18 pm

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==[/quote]



Some things I’ve read regarding this give me the impression that the HUP could be responsible for some fuzziness.

There is a lot to take in in this thread, which I’m enjoying, so this post isn’t well ordered.

Snip-[quote="Marshall » May 8th, 2014, 9:02 pm
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.[/quote]

Was it here?
http://nipslab.org/nic-at-qs13/location/


snip [quote Marshall » May 6th, 2014, 7:39 pm


Here the world is treated as PROCESS rather than STATE.



[/quote]


I have still been thinking about this comment. Searching for more about this, I was looking at Rovelli (1996), and although it is somewhat out of context, as it involves discussion of information, and perhaps it is not in line with more current considerations, on page 11 it is written, “In place of the notion
of state, which refers solely to the system, the notion of
the information that a system has about another system
has been introduced.”
And also, from page 10, ‘I will denote a process of acquisition of information
(a measurement) as a “question” that a system
(observing system) asks another system (observed system).
Would this suggest the term “process” also stresses an interactive description?

Incidentally, the sentence following the explanation of absence of the term state, reads, “I view this notion very concretely:
a piece of paper on which outcomes of measurements are
written, hands of measuring apparatus, memory of scientists,
or a two-value variable which is up or down after
an interaction”. Does this suggest that the paper upon which it is described, or a person describing such a process, theirself, could be a part of the process they describe?


Also, I’ve liked the discussion about fields and a web of facts, and look forward to following the links.

Quote Marshall » May 11th, 2014, 9:56 pm

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

Paul N., Owleye and others, which seems like a better rubric for this "Interactive Realism" or "Quantum Realism"?

Which would be clearer to a newcomer? Rovelli is very definite about saying he considers himself a Realist. But it is not strict "Einstein Realism" where there is a Superobserver and a single official Book of Facts. The realism has been relaxed to accommodate many observers, all of whom are now quantum processes themselves rather than being separate classical systems. Any comments from you would be welcome.

(Constructive non-confrontational it goes without saying :^D)[/quote]


They sound good to me, and I think the interaction of two physical systems is well described by “Interactive Realism”, and that they are quantum interactions is also descriptive. Maybe it would be interesting to compare or contrast the realism here with other ideas?

[quote="[Marshall » May 10th, 2014, 6:50 pm

I kind of suspect that it is a gradual shift to a QUANTUM ONTOLOGY where the world is "made of" FACTS instead of being made of continuities.
People are gradually shedding their "continuity bias" as the recognition of quantum theory seeps in to our collective awareness.

I noticed that ALL the participants at the Oxford conference, that I heard e.g. in the Q&A discussion were using the word *facts* and emphasizing it as if it was a primitive idea that they ALL shared. It was after all a conference in the Philosophy department, on Cosmology and Quantum Theory, and they were coming from different directions/schools of thought, which though different had all incorporated quantum mechanics in some philosophical interpretation or other. So whatever their differences they were all talking loud and clear about "facts".[/quote]

I missed noticing this. I’ll take another look.
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Re: Critique of Interactive Realism (Oxford Cosmology&QFdn C

Postby Marshall on May 16th, 2014, 1:58 pm 

dandelion » Fri May 16, 2014 10:17 am wrote:
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.


Was it here?
http://nipslab.org/nic-at-qs13/location/

.


Yes! The Erice Lectures! I couldn't remember the name.
Here is the history of this series
http://www.ccsem.infn.it/em/history/index.html
I think in 2010 was held the 48th in the series. But I am now not sure how often they are held. It could be once every two years or more irregularly

It is a beautiful place, the top of a mountain at the Northwest tip of the island, a place where in earlier times people liked to build temples, castles, monasteries… Here is a photo album:
http://en.wikipedia.org/wiki/Erice

Many great physicists have taught "summer school" courses in their favorite subjects at Erice.

I think Steven Weinberg, Victor Weisskopf, Eugene Wigner, Sidney Drell, Dirac, 't Hooft, Kapitza many others.

But not every year are the topics and the lecturers so outstanding. It is uneven, I guess. I can't find current information (maybe the Erice tradition is dying out!)
Marshall
 


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

Postby Marshall on May 16th, 2014, 2:19 pm 

dandelion » Fri May 16, 2014 10:17 am wrote:...

Also, I’ve liked the discussion about fields and a web of facts, and look forward to following the links.

, which seems like a better rubric for this "Interactive Realism" or "Quantum Realism"?

Which would be clearer to a newcomer? Rovelli is very definite about saying he considers himself a Realist. But it is not strict "Einstein Realism" where there is a Superobserver and a single official Book of Facts. The realism has been relaxed to accommodate many observers, all of whom are now quantum processes themselves rather than being separate classical systems. Any comments from you would be welcome.



They sound good to me, and I think the interaction of two physical systems is well described by “Interactive Realism”, and that they are quantum interactions is also descriptive...


Dandelion, I'm gradually settling down to a preference for the term "quantum realism" where one just has to remind the readers that quantum events ARE interactions. This is where quanta are revealed---e.g when a photon is emitted, or when it is absorbed, or scattered. I do not think of the quanta of a field as existing independently of interactions. While making a long trip from a star to our telescope, the quantum gives up her individual identity and becomes merged with the field. One cannot then any longer trace her progress. The field travels various ways, but there is no fixed path. And then one day a photon is absorbed at the telescope. Again a distinct identity is recovered. But it is a million years later! Who can say what the photon has been doing all that time, or where exactly it has been? :^D Or if it even existed?

I still believe in fields, you see, as the basic constituents of reality. But the fields only INTERACT in quantized events, discretely. So I am at a loss how to imagine fields. How could a continuous thing only interact discretely?

So I use this term "quantum realism" as a kind of fig leaf to cover confusion or as a kind of "I O U" which means "I owe you an explanation" which I don't yet have. Maybe Rovelli will give that explanation, sometime. :^D. Or he did already and I didn't catch it.

Basically "quantum" should be the modifier because (1) it has fewer syllables and (2) quantum IMPLIES interactive, but not the other way around. It is both shorter and more specific.

And any way it doesn't really matter :-) It is just you and me talking. with maybe Braininvat sometimes overhearing a word or two. And so from today I changed the topic heading...
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Re: Quantum realism and fields.

Postby Faradave on May 16th, 2014, 3:46 pm 

Marshall wrote:I am at a loss how to imagine fields. How could a continuous thing only interact discretely?

You have a knack for getting to the essence of things. This question demands an answer but the only way to give one is to break a conventional rule. That's usually not received very well at first. But the reality is that the question brings most of the strain upon convention. The answer is simply "the last straw", so to speak.
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Re: Quantum realism and fields.

Postby Marshall on May 16th, 2014, 4:15 pm 

Faradave » Fri May 16, 2014 12:46 pm wrote:
Marshall wrote:I am at a loss how to imagine fields. How could a continuous thing only interact discretely?

... This question demands an answer but the only way to give one is to break a conventional rule. That's usually not received very well at first. But the reality is that the question brings most of the strain upon convention. The answer is simply "the last straw", so to speak.


I really like how you titled that post "Quantum realism and fields". It opened a small door in my head, somehow. Hopefully we help each other (as you just did) "get to the essence of things".

I decided to go back and rename the thread that. It's simpler.
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Quantum realism and fields.

Postby Marshall on May 16th, 2014, 4:19 pm 

As a reminder of where we started, here's the [retitled] topic 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" 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:
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Re: Quantum realism and fields.

Postby owleye on May 16th, 2014, 6:51 pm 

In re-reading the ground rules, the reference to 'interaction' over 'facts' is emphasized in accord with the idea that facts are interactions. In thinking about this, I conclude that the reverse is not the case. Not all interactions are facts. From this I'd say that you are broadening the debate. To exemplify this, I'd count the passage of the photon through slits corresponds to an interaction, but my guess is that it wouldn't count as a fact. Then again, maybe I'm not understanding the entirety of what is under discussion. Note that I'm to understand that photon propagation between interactions doesn't have any particular meaning within the theory being discussed. Nevertheless, such a "passage" must have some sort of interaction in order for the later detection signature/pattern to make sense.
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Re: Quantum realism and fields.

Postby Marshall on May 16th, 2014, 7:34 pm 

Hi Owl, you know words evolve as we learn to use them differently. Which should I say?
A. The photon (as a photon) passes thru neither slit, it is the disturbance in the FIELD which passes through both. A photon (the field quantum) occurs at the screen when some field energy is localized and detected and a quantum of the field is absorbed.

B. The photon (as a potentiality carried in diffuse form by the field) passes through both slits. This is is just another way of saying it passes through neither, rather the undulation of the field propagates through both slits and the potentiality to deliver field quantum is realized at the screen when one is absorbed.

I was saying something like this to Dandelion earlier today:
Marshall » Fri May 16, 2014 11:19 am wrote:
Dandelion, I'm gradually settling down to a preference for the term "quantum realism" where one just has to remind the readers that quantum events ARE interactions. This is where quanta are revealed---e.g when a photon is emitted, or when it is absorbed, or scattered. I do not think of the quanta of a field as existing independently of interactions. While making a long trip from a star to our telescope, the quantum gives up her individual identity and becomes merged with the field. One cannot then any longer trace her progress. The field travels various ways, but there is no fixed path. And then one day a photon is absorbed at the telescope. Again a distinct identity is recovered. But it is a million years later! Who can say what the photon has been doing all that time, or where exactly it has been? :^D Or if it even existed?

I still believe in fields, you see, as the basic constituents of reality. But the fields only INTERACT in quantized events, discretely. So I am at a loss how to imagine fields. How could a continuous thing only interact discretely?...


You realize, Owleye, that I certainly do not speak as an authority. I am trying to find my way to a consistent manner of talking that accords with quantum physics textbooks read over the years, forgotten and remembered, old photographs of ripple-tanks showing the rows of water waves propagating through two slits, recombining, interfering positively negatively in a pretty fish-scale pattern. I'm making an effort to believe that the photon loses its identity in the Field while it is traveling (as long as there is no interaction), and that no interaction is possible UNLESS it is discrete, so that a new quantum identity must coalesce out of the Field when there is an occurrence at the screen.
And those bulbous airbrush pictures of electron "orbitals". You don't happen to have links to any of those old illustrations (we both have surely seen them, you working for NASA and all) do you?
Marshall
 


Re: Quantum realism and fields.

Postby Faradave on May 17th, 2014, 12:00 am 

Marshall wrote:The photon (as a photon) passes thru neither slit, it is the disturbance in the FIELD which passes through both.

Either description will do. However, I think more to Owleye's point, while the emitter's field includes the region of the interferometer, the fields associated with the apparatus also include the region of the emitting particle and there is interaction between them, even if no photon is ever emitted.

This is obvious with any two electrically charged objects. They interact, likes repel, opposites attract, even under cold, dark conditions. Interaction occurs, absent orbital transitions. The particles need not even be in orbitals (e.g. two isolated electrons). In this situation, QFT starts pulling virtual particles out of nowhere.

Marshall wrote:I still believe in fields, you see, as the basic constituents of reality. But the fields only INTERACT in quantized events, discretely. So I am at a loss how to imagine fields. How could a continuous thing only interact discretely?


I agree with you about quantized events. But regardless of mathematical prowess, no one is going to understand the wave function until they know what is waving and where it's waving. Now, I'm not going to take my absent friend's position that there is no space. I'm fine with space but I must say that to construe the wave function (Rovelli's slide read, Schrodinger 1926 wave in space), or fields as spatial is begging confusion. That's not their realm!

Marshall wrote:bulbous airbrush pictures of electron "orbitals". You don't happen to have links
Image
Wikipedia has prettier images than this one, including some animated cross sections, but you must scroll down to see them.

Minor edits
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Re: Quantum realism and fields.

Postby dandelion on May 17th, 2014, 5:59 am 

Marshall » May 16th, 2014, 6:58 pm wrote:
dandelion » Fri May 16, 2014 10:17 am wrote:
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.


Was it here?
http://nipslab.org/nic-at-qs13/location/

.


Yes! The Erice Lectures! I couldn't remember the name.
Here is the history of this series
http://www.ccsem.infn.it/em/history/index.html
I think in 2010 was held the 48th in the series. But I am now not sure how often they are held. It could be once every two years or more irregularly

It is a beautiful place, the top of a mountain at the Northwest tip of the island, a place where in earlier times people liked to build temples, castles, monasteries… Here is a photo album:
http://en.wikipedia.org/wiki/Erice

Many great physicists have taught "summer school" courses in their favorite subjects at Erice.

I think Steven Weinberg, Victor Weisskopf, Eugene Wigner, Sidney Drell, Dirac, 't Hooft, Kapitza many others.

But not every year are the topics and the lecturers so outstanding. It is uneven, I guess. I can't find current information (maybe the Erice tradition is dying out!)


It looks stunning!
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Re: Quantum realism and fields.

Postby dandelion on May 17th, 2014, 6:10 am 

Marshall » May 16th, 2014, 7:19 pm wrote:
dandelion » Fri May 16, 2014 10:17 am wrote:...

Also, I’ve liked the discussion about fields and a web of facts, and look forward to following the links.

, which seems like a better rubric for this "Interactive Realism" or "Quantum Realism"?

Which would be clearer to a newcomer? Rovelli is very definite about saying he considers himself a Realist. But it is not strict "Einstein Realism" where there is a Superobserver and a single official Book of Facts. The realism has been relaxed to accommodate many observers, all of whom are now quantum processes themselves rather than being separate classical systems. Any comments from you would be welcome.



They sound good to me, and I think the interaction of two physical systems is well described by “Interactive Realism”, and that they are quantum interactions is also descriptive...


Dandelion, I'm gradually settling down to a preference for the term "quantum realism" where one just has to remind the readers that quantum events ARE interactions. This is where quanta are revealed---e.g when a photon is emitted, or when it is absorbed, or scattered. I do not think of the quanta of a field as existing independently of interactions. While making a long trip from a star to our telescope, the quantum gives up her individual identity and becomes merged with the field. One cannot then any longer trace her progress. The field travels various ways, but there is no fixed path. And then one day a photon is absorbed at the telescope. Again a distinct identity is recovered. But it is a million years later! Who can say what the photon has been doing all that time, or where exactly it has been? :^D Or if it even existed?

I still believe in fields, you see, as the basic constituents of reality. But the fields only INTERACT in quantized events, discretely. So I am at a loss how to imagine fields. How could a continuous thing only interact discretely?

So I use this term "quantum realism" as a kind of fig leaf to cover confusion or as a kind of "I O U" which means "I owe you an explanation" which I don't yet have. Maybe Rovelli will give that explanation, sometime. :^D. Or he did already and I didn't catch it.

Basically "quantum" should be the modifier because (1) it has fewer syllables and (2) quantum IMPLIES interactive, but not the other way around. It is both shorter and more specific.

And any way it doesn't really matter :-) It is just you and me talking. with maybe Braininvat sometimes overhearing a word or two. And so from today I changed the topic heading...



I like the names, and the description about a photon’s individuality and fields. Ideas like these have concerned me too, but I also have trouble understanding differences or definitions of continuity, contiguity, infinity, discretion, these sorts of ideas.

I don’t know of others like it, but there was a paper about amount of quanta, (from 7th April, I don’t think I have enough posts to link, do I?) which I thought expressed some nice ideas. It contained a brief mention of discretion that was interesting.
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Re: Quantum realism and fields.

Postby owleye on May 17th, 2014, 7:16 am 

Thanks, Marshall (Faradave, as well, as always). Just viewed the 4-episode BBC presentation of "Hard Times" (based on Dicken's novel), in which Honest Stephen, a man of great integrity, though his life ended tragically, yet gave us the enduring words: "It's a muddle."

The slits, like the general concept of 'hole', cannot exist in a positive sense. Their existence depends on that which topologically establishes them. Passage through amounts to the allowance of some interaction with that which surrounds the slits, metaphorically squeezing the available passages down to regions close in size to their wave length.

However, if one considers the field as that which interacts with it (presumably EM fields can't, though gravitational fields can), then such interaction has to be extremely minor in comparison to what the surroundings of the slits present to the photon in its journey. In thinking of things in this way, I'm not entirely sure what you (Marshall) are referring to in your reference to fields.

On the issue of facts, perhaps it is a wiser course to steer clear of that term, unless one wishes to engage in a bit of cleansing of their epistemological usage. Facts are the realm of journalism, and interaction is a sufficiently vague term that unless they qualify as a measurement, or in something detected, or something that has some enduring aspect to them (not to say they can't be fleeting), then perhaps we ought to just leave it at that. Inferences to the best explanation is the current best understanding in philosophical circles of what science provides. And this is how scientists deal with unobservables (in the sense of being observable by humans), such as the passage of the photon through dual slits, and still make progress. Which is not to say that scientists have arrived at the best explanation in this case.

At one time I did keep a file of pictures of the standing waves of orbitals. Mostly, however, I was involved in plotting the potential well in two-d from a set of calculated points. I also recall that IBM researchers had developed some actual pictures.
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Re: Quantum realism and fields.

Postby Marshall on May 17th, 2014, 3:46 pm 

owleye » Sat May 17, 2014 4:16 am wrote:... "It's a muddle."

... In thinking of things in this way, I'm not entirely sure what you (Marshall) are referring to in your reference to fields.

On the issue of facts, perhaps it is a wiser course to steer clear of that term,...


I tend to agree and will probably be saying "interaction" more than "fact".
I will also try not to use the idea of the Schrödinger "wave function". You probably remember Rovelli expressing a strong preference (around minute 15) for the Heisenberg version of quantum mechanics. If there are two or more "particles" the "wave function" is not even defined on ordinary space. Heisenberg was the first person to point out this flaw in the "wave function" idea. Rovelli argued that the Schröd picture is "misleading us" and we should not use it (except as a computational device).

I'll try to clarify what I mean by "field" simply by using the word. That will help me clarify it for myself at least and maybe for others. Let's review the CLASSICAL EM FIELD in the two-slit setup.

You create a wavy disturbance in the Field. It travels towards the barrier where 99% of it is BLOCKED BY INTERACTION. IT DOES NOT INTERACT AT THE SLITS (say 1% of the area of the barrier) so 1% gets thru, and it forms a classical INTERFERENCE pattern on the screen.

The only difference when we go to the Quantum version is that now we say that the Field interacts discretely. Say the plane wave source is only strong enough that it beams 100 photons-worth of energy per second at the barrier, on average.
So on the barrier there are occurring, in one second, 99 interactions---absorption events

In the slits there are no interactions, according to my conception of course, because the slits are empty spaces in the barrier.

And at the SCREEN there occurs one discrete interaction, on average, per second---the absorption of a "photon". Maybe triggering a photocell detector.

We find that the statistics of those events on the screen accumulates so as to gradually build up an image of the classical interference pattern.

Even though only one "photon's worth" of EM energy is getting thru to the screen per second, on average, yet there are still those classical interference lines that Maxwell EM field would show. This is the mystery.
People react in different ways:

A. one person says the "photon" only exists at interactions, not while the undulations in the field are traveling. A field is something that only interacts via QUANTA.

B. another person says that the "photon" exists during its uninterrupted journey. It therefore "must have interfered with itself" because only one photon per second was getting thru the barrier. The "photon" if we think of it as real while traveling WAS ALONE IN THAT SECTION of the apparatus so it had nothing to interfere with besides itself.
Marshall
 


Re: Quantum realism and fields.

Postby Marshall on May 17th, 2014, 4:08 pm 

SO, to hopefully clear a quantum or two of *muddle*, a FIELD is a process very similar to the classical field of, say, Faraday and Maxwell, except that it only INTERACTS DISCRETELY, instead of along a continuum of contact with other processes. The catch is that almost by definition (1) we don't seem to be able to OBSERVE the field EXCEPT by these discrete interactions (in which a quantum of field energy, say, is converted to some other form e.g. absorbed in a barrier or detector cell).
So I want to review what is meant by REALISM:
Marshall » Sun May 04, 2014 12:05 pm wrote:... a source on scientific realism:
http://www-personal.umd.umich.edu/~deli ... ealism.htm
==quote==

What is scientific realism?
An important strand in the story of the philosophy of science in the past three decades has been a struggle between realists and anti-realists. The debate turns around the most adequate way of interpreting scientific theories that refer to unobservable entities, processes, and properties. Realists maintain that the entities postulated by scientific theories (electrons, genes, quasars) are real entities in the world, with approximately the properties attributed to them by the best available scientific theories. Instrumentalists, on the other hand, maintain that theories are no more than instruments of calculation, permitting the scientist to infer from one set of observable circumstances to another set of observable circumstances at some later point in time. (Important recent contributions to the theory of scientific realism include (Miller 1987), (Leplin 1984), (Putnam 1984), (Putnam 1982), and (Boyd 1984), (Van Fraassen, Churchland, and Hooker 1985), and (Gasper 1990).)

The issue of scientific realism has been one of the central hinges of debate within the philosophy of science for the past thirty years. The central issue is this: Do scientific theories and hypotheses refer to real but unobservable entities, forces, and relations? Or should we interpret theories and hypotheses as convenient systems through which to summarize the empirical regularities of observable entities and processes, with the apparent reference to unobservables as simply a façon de parler ...? Scientific realism maintains that we can reasonably construe scientific theories as providing knowledge about unobservable entities, forces, and processes, and that understanding the progress of science requires that we do so. Instrumentalism denies that it is reasonable to interpret hypotheses as referring to real unobservable entities; instead, a scientific theory should be understood as an instrument ...
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Re: Quantum realism and fields.

Postby Marshall on May 17th, 2014, 4:36 pm 

The above seems representative of what Realism MEANS in a scientific context but as a double check we can get Wikipedia's view. It seems to coincide:
Marshall » Sun May 04, 2014 2:53 pm wrote:Wikipedia's short article on SciRealism, http://en.wikipedia.org/wiki/Scientific_realism :
==quote excerpt==
Scientific realism is, at the most general level, the view that the world described by science is the real world, as it is, independent of what we might take it to be. Within philosophy of science, it is often framed as an answer to the question "how is the success of science to be explained?" The debate over what the success of science involves centers primarily on the status of unobservable entities apparently talked about by scientific theories. Generally, those who are scientific realists assert that one can make valid claims about unobservables (viz., that they have the same ontological status) as observables, as opposed to instrumentalism.
==endquote==
A famous physicist used to have 3 portraits on the study wall in his home at Princeton. One was of FARADAY who conceived and gave us the reality of the field.
You put a horseshoe magnet under a piece of paper. You do not see the field. You sprinkle iron filings. You see "field lines". But you still do not see the field, you see the filings. And yet the field is physically real. Faraday did not believe in an "aether". He thought that field lines could actually penetrate vacuum.

Aether was a good idea in its day and explained some phenomena well. It had some limitations however and was replaced by the electromagnetic field which is in many ways LIKE AN AETHER, but a corrected version which does not suffer from the aether's failings (e.g. it can be Lorentz invariant in accord with relativity). Ideas and beliefs about what the world is made of can get better.

==another excerpt==
Scientific realism involves two basic positions. First, it is a set of claims about the features of an ideal scientific theory; an ideal theory is the sort of theory science aims to produce. Second, it is the commitment that science will eventually produce theories very much like an ideal theory and that science has done pretty well thus far in some domains. It is important to note that one might be a scientific realist regarding some sciences while not being a realist regarding others. For example, one might hold realist attitudes toward physics, chemistry and biology, and not toward economics, psychology and sociology.
==endquote==
Marshall
 


Re: Quantum realism and fields.

Postby Marshall on May 17th, 2014, 5:19 pm 

So Realism would enable us to, if we wished, seriously believe in the existence of a continuous Quantum Field, namely a continuous process which is able to propagate disturbances and which interacts with other processes only sporadically, intermittently, in discrete "amounts" (appropriately called quanta).

As described in those sources on it, the ontology of Realism aspires to perfection and approaches it, we believe, but is not done yet and so is subject to gradual improvement. Jarrett Leplin's book on Sci Realism had a list of tenets like that which one of the sources (the U Mich) quoted IIRC.

The quantum relativists whose work I follow would go further in defining a Quantum Field.

For them there is NO POINTSET CONTINUUM. So there is nothing for a classical field to be defined on. There is only the GEOMETRY of spacetime, and this is itself a PROCESS. One can use 4D point sets as a temporary expedient in representing fields but this is not fundamental. The manifold is just an occasionally useful instrument. (actually this was already the case with 1915 GR, for initiates, the metric on manifold was just a convenient representation of the spacetime process which was what mattered and was what matter fields were defined on)

So the Big Riddle becomes *how do you represent THE GEOMETRY process as a QUANTUM FIELD* which mind you can only interact discretely. The answer presumably lies at the Planck scale.

Rovelli and others discovered that in THEIR version of quantum field geometry there is a kind of "graininess" inherent in geometric measurements---area and volume measurements have only certain discrete outcomes. There is a smallest observable positive area which they found was implied by their axioms, down around Planck scale.

So the fundamental representation of the geometry field has to somehow reflect that discreteness. It has to be somehow foam like or web-like. And therefore (at extreme small scale) the OTHER FIELDS defined ON the geometry acquire similar discreteness.

But this puzzling graininess is (or seems to be) too fine to be OBSERVABLE so one is again thrown into the Wickerpedia basket of Scientific Realism
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