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.

Re: Quantum realism and fields.

Postby owleye on May 18th, 2014, 5:21 pm 

I'm afraid I'm not getting this reference to quantum fields, and especially as it was used in considering the double slit experiment.

I want to consider the question relative to the geometry of this field. The first thing I'm not understanding is the relationship of the field to the photon. In my ordinary understanding of fields, of which there are only two sorts, namely EM and gravitational, though I suppose there are fields associated with the strong and weak forces. In these cases a field is a property of some object around which the field extends and as there is some sort of acceleration of that object, so also does the field of that object become affected, and such effects reach some point in the field in a finite amount of time (at the speed of light, I think, and I have the feeling that there is some sort of fundamental particle associated with that propagation, but I can be wrong).

If, however, this quantum field isn't like that, but instead is some sort of medium through which photons pass, new questions arise, relating to the geometry of this field. Such as how polarized light plays itself out? Is every compass direction allowed? And, if not, what makes some directions privileged?

(Note that I'm quite easily shot down here as i recognize that I'm missing something.)
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Re: Quantum realism and fields.

Postby Marshall on May 18th, 2014, 6:15 pm 

We're all vulnerable to being shot down. This thread is aimed at developing intuition about Rovelli's relationalist worldview as presented in that YouTube (and also the second one, if anyone is curious and has time---where he introduces space and time geometry into the picture). I think everybody's intuition is in a pupal stage, we probably all realize we're missing something, and that's good.

Developing intuition, so that the math descriptions MAKE SENSE, is a delicate matter. If what I say isn't helpful to your effort to grow some intuition and make sense of things, just ignore it and describe how you see it. Or if the relationalist view presented in the topic talk doesn't interest you are most welcome to pick some other lecture by somebody else with a different viewpoint to assimilate.

My general take is that theoretical physics has gone out ahead of our ordinary spoken language (and attendant intuition) and there's widespread frustration with it not making sense and it's a worthwhile activity to try to sort things out and adapt how we use certain words and GROW intuitive grasp.

I'll try to respond later today, I have to run to a rehearsal soon. It is 4-6 PM which is in an hour.

Remember the message that Lincoln was giving us about the Higgs field? The Higgs "particle" almost doesn't exist. We should focus on the field, which pervades space, or spacetime if you want to think in those terms.

The "particle" is just a quantum of the field which is useful as a concept in certain applications, e.g. when it materializes in some interaction, and decays into other stuff. It is the Higgs field that does what we care about (helps bestow inertia on other things etc) and is always at work everywhere, and may even have been the field involved early on in inflation (speculative).

Well Lincoln's view seemed very much in line with that of another HONEST POPULARIZER named Matt Strassler . He is a theoretical particle physicist and has an excellent blog "Of Particular Significance". Lincoln might not even be aware of Strassler's blog or that he is in fair agreement, they are in different lines of work. But Strassler was hammering the message think Higgs field, not Higgs particle.

I think it is a widespread attitude among knowledgable honest physics types both experimental and theoretical. the public is too obsessed with particles, should be encouraged to think in terms of the several important fields.

Particles are in many cases just temporary disturbances in fields. Without special assumptions you cannot even say definitely how many of a certain type are present, or how big they are or whatever. Since we are used to thinking of the world in terms of a few very stable particles (that make atoms and molecules) this comes as a shock! So lets not rush this. Let's just gradually think a tiny bit more fieldishly and a bit less particley. And try it out. Or at least I will, nobody has to go along if they don't want to. :^D

Unfortunately I have to get going if I'm not to be late for rehearsal. Should go over some notes first!
Marshall
 


Re: Quantum realism and fields.

Postby Marshall on May 19th, 2014, 2:05 am 

Back again. I've been reading the short (12 page) article *Quantum Field Theory* by Nobelist Frank Wilczek.
It is the closest thing to a "philosophical" discussion of QFT that I have seen. The big ideas of QFT.

He articulates what I've been groping towards as an "ontology of fields".
The field is an operator valued function on (x, t) and it can express many electrons or many of some other particle. Particles are merely EXCITATIONS of the field., and of course they propagate in the field.

Particles as *twangs*in an underlying reality.

He several times expresses the view that the quantum field is the REAL thing and the particles are (often quite temporary) excitations.

http://arxiv.org/abs/hep-th/9803075

The American Physical Society was doing a Centennial volume for year 2000 and invited Wilczek to write this kind of overview. It's not entirely out of reach, parts are accessible.

QFT is the basis of the reigning (he says "regnant") Standard Model of matter.

You can see he has distanced himself from the Schrodinger "wave function" model (just as Rovelli did in his Oxford talk). The "wave function" for a single particle is defined on (x,t) but with more articles it's defined on a multidimensional "phase space". QFT goes a different route. The (x,t) indexing stays the same no matter how many particles are excited in the field.

BTW it seems the photon does not have a Schrodinger "wave function"…as I recall Wilczek mentions this. One almost has to go with quantum fields for that reason alone.

So this is the physical reality I think we have to try to understand: the ontology of QFT and also looking ahead to connecting somehow up with geometry/gravity. So far QFT is (*special*) relativistic quantum field theory. they've only constructed it on fixed, usually flat, geometries---typically the flat geometry of SR.

So what you say about AETHER is perceptive. But there are many layers of aethers. And there is no Michelson Morley problem. All the aethers are Lorentz invariant. After all Maxwell's electromagnetic field was the inspiration for Special Rel. It transforms right , is Lorentz invariant.

So there is one aether for electrons/positrons, another aether for quarks, another one for EM field excitations called "photons". Each one of these aether layers can be twanged as much as you want, excited to more and more numbers of particles.

Wilczek talks about the unlimited number of "degrees of freedom" that any one of these fields (i.e. aethers) has. But I shouldn't be using the word "aether"---that was just a comparison. A field is the basic consituent of reality. A field is LIKE the old aether idea in some limited ways. BTW Faraday believed in fields but did NOT believe in the aether. In a sense Maxwell proved him right. Maxwell's EM field is what waves and ripples travel in, and it (thank goodness) does not have MichelsonMorley problems.

Still just groping. Maybe I'll quote some parts of Wilczek's 12 pager tomorrow. It is the best exposition of the "ontology of fields" idea that seems "regnant" in contemporary physics, and even better Wilczek is talking about *quantum* fields. That was a necessary transition and I was stumbling on the doorsill.

Anyway, it's been an active day--time to turn in. Here's the reference if anyone wants to take a gander.

http://arxiv.org/abs/hep-th/9803075
Quantum Field Theory
Frank Wilczek
I discuss the general principles underlying quantum field theory, and attempt to identify its most profound consequences. The deepest of these consequences result from the infinite number of degrees of freedom invoked to implement locality. I mention a few of its most striking successes, both achieved and prospective. Possible limitations of quantum field theory are viewed in the light of its history.
12 pages, 3 figures. Will appear in Centenary issue of Rev. of Mod. Phys., March 1999.
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Re: Quantum realism and fields.

Postby owleye on May 19th, 2014, 10:15 am 

Thanks, Marshall...

I'll try to have a look as time permits. I should have paid more attention to the field portion of the Higgs boson when it was being discussed a bit ago. I suppose at the time I regarded the boson as establishing a field, the entirety of it associated with a sea of such bosons in influencing mass. However, it was my impression that not all inertial effects are attributed to such fields. I can be wrong, of course. In any case, in this understanding I think of this field as having a kinship with EM fields, though I wouldn't go so far as to regard it in exactly the same way, as I don't understand bosonic influences and how they might propagate. Note that I am able to think of the particle as a hole in the way I understand Faradave to be expressing his theory. After all, except for influences associated with mass, solid state physics allows electron "holes" to work as anti-electrons. And I do think that it makes sense to associated a photon with a "field" just so that it is capable of interfering with itself as in how the double slit experiment makes that happen. And that such interference can't be understood unless the photon is quantized in precisely the way it is within quantum theory. Despite this, however, we're moving quite far away from the observer-friendly interference pattern, and instead adopting a field perspective. In that scenario, the double slit environment is what caused the interference and produced the pattern, not this new field. In the relational QM, this 'field' would not have any meaning.

Nevertheless, there is probably a reason for having such a field and making it responsible for the self-interference pattern, merely on the basis that if one moves the detecting screen closer or farther away from the double slit, there will be differences in the pattern that is observed. Indeed, if one puts the "eye-point" right next to one of the slits, I believe it pretty much excludes the other slit in its pattern (again I can be wrong, here).

One final comment, and the reason I was thrown a bit, had to do with the ethereal aspect of what I was getting at, which you noticed. If the field is not a relative phenomena (i.e., relative to the photon itself, or to the collection of photons), then it introduces questions about its quantized orientation, and I would think might even impact isometry. See next paragraph.

The quantization of space or space-time (fields?) or even energy/momentum, when one gets down to it, gives me a headache, if taken too far. Space, and space-time, as well as energy/momentum, to me, are continuous properties of the universe. The quantization, however, is what occurs during exchanges ('observations') -- when events transform one thing into another thing or cause things to come into existence as if from nothing at all. (Note the 'as if'.) Packetizing energy and momentum in various configurations are entirely possible, and their possibility is well established in the Standard Model. The packet is the particle of record. However, the continuity of space, space-time, time, energy, momentum, is required in order for the long distances and times in the vastness of the universe to have any semblance of its order to exist within it. My guess is that there is always some energy and momentum somewhere left over from any exchange. It can't all be condensed into quantities of planck's constant, since if it did, I think there would be issues regarding the ability to map out a universe to great distances and times, without some sort of anti-aliasing going on, which to me would be an ad-hoc addition. (I can, of course, be wrong.)
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Re: Quantum realism and fields.

Postby Marshall on May 19th, 2014, 11:09 am 

it was my impression that not all inertial effects are attributed to such fields. I can be wrong...


You're right! I can't recall the percentage but it's been explained to me that only about 5% of the mass of ordinary matter comes from the Higgs field effect on the quarks making up the baryons (protons neutrons in nucleus )

the rest of the proton's mass (95%, if I'm remembering the percentage right) comes from the kinetic etc. energy of the quark gluon soup inside the proton!

This is hard to make sense of but I believe what they tell me.

thanks for your reply!
===================
It's like when you heat a piece of iron it actually weighs slightly more, and gains inertia, so that it would be harder to accelerate. Why? because the atoms in the crystal lattice are jiggling more wildly! like balls attached by springs. they have more kinetic&potential energy. So depending on how much heat you put in, the block of iron gains inertia according to the m = E/c2 rule.

As I recall the author of the 1905 paper about this was thinking along those lines, the inertia added by putting some energy into something, and wrote the rule the way I just did, rather than in the form that is now more familiar.

So the same would go for a box full of gas, if you had sensitive enough scales to weigh it. Putting in heat increases the inertia by just that much.

And apparently the three quarks inside a proton are just very tiny things (compared with the enclosing proton) and they are moving around like crazy, with a lot of kinetic&potential energy according to the "quantum chromodynamics" that Wilczek et al got the Prize for. So most of the mass of the proton is due to the QCD energy, rather than directly to the Higgs field.

The Higgs field only invests the "seed money" of mass (I guess you could say) and the QCD energy does the rest, according to the m=E/c2 rule.

This is what you already said, but I wanted to spell it out in case anybody else is reading thread. :-)
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Re: Quantum realism and fields.

Postby Marshall on May 19th, 2014, 12:17 pm 

owleye » Mon May 19, 2014 7:15 am wrote:...The quantization of space or space-time (fields?) or even energy/momentum, when one gets down to it, gives me a headache, if taken too far. Space, and space-time, as well as energy/momentum, to me, are continuous properties of the universe…


I was especially interested by your last paragraph and will take a while to think about it. I think Wilczek addresses this in part and brings up the scale issue. Other people have said this as well, I don't remember exactly which author I'd be quoting. It seems they don't believe in continuity below a certain scale. Maybe don't DISbelieve either. Agnostic, at least for now.

At the scale most people work at, for all practical purposes you can assume continuity.

But if you push it too far (I think it was Wilczek who made this argument) and assume the continuous geometry of General Rel all the way down to Planck scale, gravity becomes strong in comparison to the rest and the geometry becomes messy. I don't have this down clearly enough…. For some reason you need a scale cutoff . Geometry looks smooth and continuous down to a certain scale, beyond which what it looks like is more a speculative unresolved business.

I agree what you bring up in the last paragraph in above post IS a headache.

It's related to the famous gap between QFT and GR. Present-day QFT is built on a fixed point set (x,t) geometry, typically flat. It's a challenge to try to reconstruct it on a more general geometry such as arises in quantum relativity (quantum GR, or whatever you want to call it). People are working on that. It definitely IS a headache, except that some people are really excited by that kind of headache and like to spend their time exploring the experience :^D.

I think this is where the "boundary formalism" comes in. It is really challenging to bring QFT and GR together (Wilczek avoids going there, he sticks to pure gravityless QFT) and one port in the storm for the people trying to bring them together is to move from field to PROCESS where a process is a bounded region of spacetime, inside of which gravity/geometry is happening and also matter (QFT stuff) is happening. All you have is info and predictions about what you can read on the boundary enclosing the process. And you want a way to find the amplitude. It's analogous to Feynman's path integral approach where you want a "transition amplitude" between some specified initial and final conditions.

My inclination right now is to postpone contemplating the gap between QFT and GR, geometry at extreme small scale, boundary formalism, process language. For the time being I just want to spend some time reading Wilczek's article about QFT, where he doesn't bring in gravity/geometry and leaves the extreme small scale problems alone. But I wobble. It's hard not to veer off into headache-land every now and then.

BTW Wilczek just came out with an article with Larry Krauss where he said that IF the BICEP2 result was right (which it might not be but further studies are underway which will tell) THEN we really are looking at quantum gravity effects that have been enormously magnified by geometric expansion. So, says Wilczek, we are finally able to see down to that hitherto inaccessible scale, and we ought to study it and theorize about it (he is, after all, a theorist). But that's still speculative, BICEP2 results have been strongly questioned and everybody has to wait and see.

Sources:
google "wilczek quantum field theory" and get
http://arxiv.org/abs/hep-th/9803075

google "wilczek krauss quantum gravity" and get
http://arxiv.org/abs/1404.0634
It's just a 4 page overview paper, which can help non-specialists get perspective. Only 5 equations, which come in the middle section and do not make the surrounding overview paragraphs incomprehensible. I may as well copy the abstract in case anyone's curious:
It is commonly anticipated that gravity is subject to the standard principles of quantum mechanics. Yet some (including Einstein) have questioned that presumption, whose empirical basis is weak. Indeed, recently Freeman Dyson has emphasized that no conventional experiment is capable of detecting individual gravitons. However, as we describe, if inflation occurred, the Universe, by acting as an ideal graviton amplifier, affords such access. It produces a classical signal, in the form of macroscopic gravitational waves, in response to spontaneous (not induced) emission of gravitons. Thus recent BICEP2 observations of polarization in the cosmic microwave background will, if confirmed, provide empirical evidence for the quantization of gravity. Their details also support quantitative ideas concerning the unification of strong, electromagnetic, and weak forces, and of all these with gravity.
Marshall
 


Re: Quantum realism and fields.

Postby dandelion on May 19th, 2014, 4:42 pm 

The QFT paper by Wilczek was a nice read, but I haven’t read on and caught up to the rest of the thread. I read one of his books some years ago. I’m pleased I read a recommendation at the time and I’m grateful to the person who recommended it.

Thinking more about envisaging fields interacting discretely, while unsure of my grasp of incompatibilities involved- I’ve mostly thought of different focus, but wonder how others here might see it, too.
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Re: Quantum realism and fields.

Postby Faradave on May 20th, 2014, 9:57 am 

I've been traveling and have fallen a bit behind, so are my comments.

Marshall wrote:A. one person says the "photon" only exists at interactions, now 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.

That sums it up nicely. B not only seems counterintuitive, if one adopts B, one would have to conclude that something about the barrier and slits caused the photon to interfere with itself which brings us back to fields. Further, it would seem that photon "self interference" would itself constitute an interaction, i.e. action at a distance (from slit to slit). As such, a photon would seem to require its own fields. But as you note below, a photon does not have its own wave equation.

Marshall wrote: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

This is one of the essential elements you’re so good at providing. I would risk saying, A field is a continuous process which interacts discretely. You captured that later,
Marshall wrote: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).

"continuous quantum process" may be an oxymoron ;o) The next step is attempting to model that process. It will be helpful to consider a process as involving at least one fundamental object, undergoing at least one fundamental action. I would further distinguish the object as entailing discreteness (which defines an object, different from other objects) and the process as entailing continuity (which relates to the continuum containing the object).

Marshall wrote: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.

The central issue is this: Do scientific theories and hypotheses refer to real but unobservable entities, forces, and relations?

Wiki: 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?"

As I interpret this,
Realist view: There exists a prevailing, objective reality, which science brings us ever closer to describing.
Instrumentalist view: There are reliable instruments, which give us consistent readings. (Conspicuously ignoring of what those readings might be.)

Marshall wrote:Quantum Realists - 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.

This is insightful but may be ignored at present, as any outside perspective implies additional dimensions.

Marshall wrote: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.

Yes! We have enough to go further. We might examine the Planck constant for clues.

Marshall wrote:My general take is that theoretical physics has gone out ahead of our ordinary spoken language (and attendant intuition)

A few new terms are warranted.

Marshall wrote:It is the Higgs field that does what we care about (helps bestow inertia on other things etc)

I think adding field upon filed is going too far. Inertial mass apart from gravitational mass (different fields?) is a problem for GR which unified them. A gravitational field apart from an electric is a problem which the theory of everything (TOE) wishes to resolve.

Marshall wrote:BTW it seems the photon does not have a Schrodinger "wave function"…as I recall Wilczek mentions this. One almost has to go with quantum fields for that reason alone.

Or drop the photon (and other massless particles).

Marshall wrote:there are many layers of aethers. one aether for electrons/positrons, another aether for quarks, another one for EM field excitations called "photons". Each one of these aether layers can be twanged as much as you want, excited to more and more numbers of particles...

only about 5% of the mass of ordinary matter comes from the Higgs field effect on the quarks making up the baryons (protons neutrons in nucleus )...the rest of the proton's mass (95%, if I'm remembering the%age right) comes from the kinetic etc. energy of the quark gluon soup inside the proton! This is hard to make sense of but I believe what they tell me.


George Musser summarizes this in a simple, 2 min video.

Field segregation is the opposite direction for anyone anticipating a TOE, which seeks to integrate forces (thus, fields). I think it's preferable and more consistent with experience to propose a model which begins with a single force and field (for each particle) than to purport a different universal field for each kind of particle. The latter leaves us the burden of describing what a field actually IS, how it relates to the continuum and what distinguishes one field from another.

edit: fixed quote
Last edited by Faradave on May 20th, 2014, 10:56 am, edited 1 time in total.
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Re: Quantum realism and fields.

Postby TheVat on May 20th, 2014, 10:33 am 

Been away for a week, so catching up here on what seems the mental contortion of positing a universe of continuous fields that interact discretely. This is what drives some to Instrumentalism, no doubt.

I think it's preferable and more consistent with experience to propose a model which begins with a single force and field (for each particle) than to purport a different universal field for each kind of particle. The latter leaves us the burden of describing what a field actually IS, how it relates to the continuum and what distinguishes one field from another.
-- Faradave

If we reach a rock-bottom of ontology then it will be, sui generis, not describable. It would be the foundation of more complex processes that ARE describable but would itself remain in epistemic shadow. We would always refer to it indirectly, as a "force," because our descriptions would be only of interactions, of a force acting upon some observable. On the detector, that discrete whatsit went off there like a curveball, just outside the strike zone. Another went inside and nearly took off the batter's patella. We are watching the cosmic ballgame and only see what happens by a puff of dust from the catcher's mitt, or a patella flying off and hitting the backstop. IOW, we only observe dynamics, we don't observe basic "stuff." If there is a Planckian level at which everything must be modeled discretely, then it really makes no sense to adhere to a classical notion of a field as some kind of background of continuous rubbery bands of tug and stretch. "Field" becomes as much a convenience of math and analogy as "particle." IOW, one might have to give up the word game, so very seductive, and just talk about the measurable interaction. Ontology might be a mirage, in modern physics.
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Re: Quantum realism and fields.

Postby Faradave on May 20th, 2014, 10:52 am 

Paul,
Congratulations and welcome back!

BiV wrote:a rock-bottom of ontology then it will be, sui generis, not describable.

Granted. On the top of my non-existent list of indescribable things is that which isn't. It can be surprisingly useful, particularly when modeling a force. That is, there isn't an interval separation between emitter and absorber of a "photon". A force (pair) can represent a form of contact.

(Recall that Newton's 3rd essentially allows that forces are only observable in pairs, which is not to say that they don't exist unpaired, thus unobservable.)

BiV wrote:Ontology might be a mirage, in modern physics.

Which does nothing to stop us from modeling.
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Re: Quantum realism and fields.

Postby Marshall on May 20th, 2014, 11:46 am 

Hi Dandelion, Faradave, Braininvat! It's strange and neat how your posts fit together. I'm guessing Dandelion was referring to the 2008 Wilczek book *The Lightness of Being* which is highly relevant to both FDave and BiV posts!
dandelion » Mon May 19, 2014 1:42 pm wrote:The QFT paper by Wilczek was a nice read, but I haven’t read on and caught up to the rest of the thread. I read one of his books some years ago...


In that book Wilczek made a serious effort to picture unification based on the welded "multilayer aether" vision of the Standard Model. And his vision is seriously REALIST. It is a premature book and both extremely "literary"and frustrating. Now, from the perspective of 2014 he could write a much better one, and I hope he does. There is more to go on, now.

Back in 2008 he was making a valiant almost frantic effort to envision a unified picture of what is REALLY THERE, which for want of a better term, and somewhat idiosyncratically, he called the GRID. It was unified because it had a SINGLE LAGRANGIAN. (though gravity was still not entirely worked in, he argued that you can almost see how to work in a kind of approximate effective version).

Like some cakes or parfait the unity was many-layered, a kind of rainbow unity of COUPLED layers. The one grand Lagrangian consisted of many terms (many ethers/fields) welded together by their coupling constants.

So Faradave, if you wanted, you could see Wilczek's "Grid" as a single unified field. Just one where the description has several different terms, coupled together.

He also included some balanced criticism of his own Grid vision, in that book. I pulled it off the shelf and flipped thru after I saw Dand's post. He was worried that the LHC when it got started or when it reached design energy would not find SuperSymmetry. He acknowledged the possible *adhoc-ness* of his vision.

Still, QFT and the Standard Model of matter based on it, is a remarkably successful wide-ranging theory. It just keeps on checking with experiment, it won't stop. In 2009 Steven Weinberg gave a lecture at Cern where he warned the String Theorists that nature might not need their "strings" because the QFT might be good all the way to Planck scale. Essentially the same as Wilczek's vision without SuSy and the jazzy "grid" terminology. There is a kind of conservative sense there. Take seriously what experience has shown works really well.

No way am I advocating some particular vision like the non-stringy unification pictures drawn by those two smart guys (the Laureates Wilczek and Weinberg). My personal view is more like what was presented in the 1999 Wilczek paper that Dand just read. No forward looking vision (that's guesswork) but the SIMPLE RECOGNITION THAT THERE IS ROOM FOR REALISM AND THAT modern physics has pretty clearly arrived indeed had already arrived one or more decades ago at an ONTOLOGY OF (quantum) FIELDS.
So no big deal, but we need to be massaging our language and growing our intuition so that kind of thing makes sense to us. That is the basic philosophy of this thread. If you would like to present an opposing view, what you could do is read the 1999 Wilczek paper "Quantum Field Theory" and see what you find wrong with it.

Just google "wilzcek quantum field theory"
http://arxiv.org/abs/hep-th/9803075
Quantum Field Theory
Frank Wilczek
I discuss the general principles underlying quantum field theory, and attempt to identify its most profound consequences. The deepest of these consequences result from the infinite number of degrees of freedom invoked to implement locality. I mention a few of its most striking successes, both achieved and prospective. Possible limitations of quantum field theory are viewed in the light of its history.
12 pages, 3 figures. Will appear in Centenary issue of Rev. of Mod. Phys., March 1999.

I think the two video lectures by Rovelli (to the 2013 Oxford conference on Cosmology and Quantum Foundations) are basically just jumping off from that basis---he tries to make sense of quantumness and to include cosmo and dynamic geometry in the QFT framework. Its difficult, but not a major change of direction.
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Re: Quantum realism and fields.

Postby Marshall on May 20th, 2014, 12:27 pm 

Sorry to be talking so much this morning. It might be better to say that rovelli, rather than trying to put quantum dynamic geometry into the QFT formwork is instead trying to see how to REBUILD the remarkably successful QFT ON A NEW GEOMETRIC BASE namely the quantum geometry theory (call it "QGT") base instead of the fixed prior (x,t) flats.

Maybe rovelli is the Icarus to wilzcek's Daedalus. But either way it means getting QFT and dynamic geometry together, whether you some how cram gravity in to Wilzcek's sandwich, or somehow REBUILD qft on a quantum geometry base. As a theory of PROCESS occurring in a finite bounded region where you can say what transactions went across the boundary but aren't sure what went on inside.

(Like Richard the Great said, the particle can have taken lots of different paths to get from "here" to "there" and maybe it took all of them. So processes can take many different "paths" and you can only pin down what transacted at the boundary.) this is just speculative but one way or another those people seem likely to put QFT together with "QGT". I think.

And it's fun watching :^D
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Re: Starting point

Postby Faradave on May 20th, 2014, 12:58 pm 

Marshall wrote:...what is REALLY THERE, which for want of a better term, and somewhat idiosyncratically, he called the GRID. It was unified because it had a SINGLE LAGRANGIAN. (though gravity was still not entirely worked in...He was worried that the LHC when it got started or when it reached design energy would not find SuperSymmetry.

I've ordered the book and will look at the paper but I am apprehensive because gravitation is what all particles have in common. Thus, a firm grasp of gravitation is the logical foundation for a TOE. I tried to approach this in T2 but when GrayGhost went on vacation, I believe I lost my audience.

The nice thing about starting with gravitation is that it anticipates even dark matter but requires no explicit suggestion of SuperSymmetry. This is indeed the way things seem to be going at present.

Marshall wrote:So Faradave, if you wanted, you could see Wilczek's "Grid" as a single unified field. Just one where the description has several different terms, coupled together.

That is the way I would view it. But I think we can resolve the unified field one step further into a unified field element exhibiting a variety of behaviors ("processes" works just as well) in spacetime. Behaviors would imbue the field with its various observed expressions. The trick is to model gravitation consistently from particle to particle, while allowing the other fields to vary widely.
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Re: Quantum realism and fields.

Postby Dave_Oblad on May 20th, 2014, 6:06 pm 

Hi All,

Been watching the progression of this thread with considerable interest. It sounds a lot like, through deductive reasoning, you are approaching the same conclusions I reached just before joining this Site. I'm thinking that the best way to proceed is to build Models of what you believe Reality must be composed of. Even if you have no experience at Computer Modeling, there are serious issues in many models commonly thought to represent our Reality not so very long ago.

Starting with the Particle Model that some see expressed as resembling a Solar System with Particles orbiting some primary Particle or cluster. All the while exchanging information between components as the Weak or Strong force Particles. Imagine actually trying to do this with some toy blocks and some rules. I tried it.. it doesn't work. Perhaps on the Macro Scale with Planets or such, but not on the Micro-Scales. Try holding a Solar System together with the Planets exchanging Asteroids.. ridiculous... right?

My very first post here, I called it a Matrix.. but a Grid works just as well. I compared Reality to Conway's Life Algorithm. The reason why is.. everything must be connected. This requires we abandon the concept of an Empty Vacuum.. at any Scale. The next issue is such formula(s) that Science commonly uses, such as E=MC2 or E=IR or F=MA etc. These are useful but they have no defining values that anchor them, they are purely Relational. As pointed out, we need a definitive value to give meaning to everything else, which is the Planck Length or Interval. Once the value "ONE" is established, all else can have real meaning by Scale.

Now I recognized long ago that Conway's Life doesn't have the complexity to support a Reality like ours. But the Grid in that program has continuity.. which must Exist for information to connect between places. Faradave called this a Unified Field Element. Well, not long ago, I came across something from our Mr. Lincoln called Preons. A potential structure many many times smaller than the smallest observed Particle. So call it a Unified Field Element or Preon.. same thing in my book.

Next issue is the belief that Matter creates Fields. I see it's being toyed with that we may have the roles reversed. That Fields may be all that Exist and they in turn define Particles. It's so much easier to see an Electron as a Distortion in a Field that travels alone through a Field.. but when captured by an Atom.. becomes a Shell surrounding the Atom. A Shell makes so much more sense.. getting rid of the old model of an orbiting Electron. Now if we take this to the 4Th Dimension, Particles (quarks etc) begin to look more like Braided World-Lines and an Electron, when joining with this Particle Cluster, becomes a surrounding spiked "Tube", along the Temporal Axis.

The final step is then to stop looking at Reality as Substance and see the Braided World-Lines as Informational Geometry formed by the Logic of the Unified Field Elements or Preons (your choice).

Faradave proposed in his T2 post a reasonable Guide to understanding the 4Th Dimension. My only difference would be to substitute a 4D Fractal Dragon for his Sphere. This then provides Controlled Algorithmic Growth in placing Preons. Spheres are really hard to do Mathematically ;^P

For what it's worth...lol.

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Dave :^)
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Re: Quantum realism and fields.

Postby Marshall on May 20th, 2014, 7:55 pm 

Dave_Oblad » Tue May 20, 2014 3:06 pm wrote:...
My very first post here, I called it a Matrix.. but a Grid works just as well. I compared Reality to Conway's Life Algorithm…
...
For what it's worth...lol.
...


You're in good Stockholm company, Dave. Wilczek says in his book that his first thought was to call his unified picture The Matrix. But then he says the sequels were so bad he got disgusted. :^D
"The Grid" was his second choice.

Plus, he says, the Grid kind of "powers existence". Particles arise from it (as he thinks) and so it is like our familiar electrical power grid. So he decided that the word had some of the right connotations and went with his second choice.

Please everybody be warned. That 2008 book is, I fear, flawed and a bit dated. I'd feel bad for mentioning it if anyone bought it and was disappointed. As I said, I think Wilczek could write a much better one today---there's been conceptual and experimental progress since 2008 which he could build on. It exemplifies something, but I don't want to seem to be recommending it! I mention it because it shows that he was making a bold attempt at an INTUITIVE unified geometry-and-matter sandwich back 6 years ago. It shows he felt the same need that some of us feel now. It illustrates something I think needs to be done.
And he dared 6 years ago to write that kind of popular non-math unification book *without featuring string theory* which was still popular with the public then, remember?
He guessed, I think rightly, that string was heading into a deadend and he tried to foresee what might come to light at the LHC. He tried to see which way the Standard Model success was pointing us, and put it all together.
It's a stimulating, imaginative, but ultimately frustrating book, and I think there should be better ones now.
I respect Wilczek a lot. He'd be my choice to write something more up to date, say in the next two or three years.
LHC was shut down for upgrade and is now, I think, gradually being turned back on. there might be some new results in 2015. Several other projects are looking for B-mode swirls in the ancient light--to see whether or not to confirm BICEP.
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Re: Minutia

Postby Faradave on May 20th, 2014, 11:21 pm 

Marshall wrote:That 2008 book...I'd feel bad for mentioning it if anyone bought it and was disappointed.

Not to worry. The used paperback (with shipping) cost me $4 from Amazon. And 2008 is "recent" for my library. I'm still collecting Asimov, Wheeler, Feynman and Gamow editions. Thrilling as ever!

Dave_Oblad wrote:So call it a Unified Field Element or Preon.. same thing in my book.

I can understand your impression and would like to make a distinction. As fields have potentially infinite extent (they grow without bound at speed limit c), I consider the most simple and useful element of an infinite field to itself be infinite, i.e. ray-like.

True, by its own perspective, the field element, as with any light-like trajectory has zero length. But in the rest frame of any real (massive) observer, the field element is indefinitely long. Preons, by contrast, would be observed, as you note, to be very very tiny, i.e. point-like.

I agree that planetary orbits for electrons are out. "A more accurate analogy might be that of a large and often oddly shaped "atmosphere" (the electron), distributed around a relatively tiny planet (the atomic nucleus)."
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Getting back on topic?

Postby Marshall on May 21st, 2014, 3:32 pm 

Faradave » Tue May 20, 2014 8:21 pm wrote:
Marshall wrote:That 2008 book...I'd feel bad for mentioning it if anyone bought it and was disappointed.

Not to worry. The used paperback (with shipping) cost me $4 from Amazon. And 2008 is "recent" for my library. I'm still collecting Asimov, Wheeler, Feynman and Gamow editions. Thrilling as ever.


I hope you like it! Not a bad deal either, at that rate. Even though I'm not a collector myself, I can see the point, with those authors.

How would you characterize the thread topic, at this point?

In a general sense it is about Quantum Realism---upgrading our intuition so that "QF on QG" (quantum fields on quantum geometry) makes better sense.

It's also in the context of Astro/Cosmo so what we are discussing should mainly be professional research (conference talks, journal articles) as opposed to personal theory. For QFT I simply posted the link to Wilczek's 12 page paper. Do you have another online source you'd like to add?
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Realism => Quantum Fields on Quantum Geometry

Postby Marshall on May 21st, 2014, 6:39 pm 

There are several key quotes to get one's head around, in that Wilczek 12-page "QFT" article
http://arxiv.org/abs/hep-th/9803075
Here is one on page 2.

==quote page 2 of "QFT" ==
Undoubtedly the single most profound fact about Nature that quantum field theory uniquely explains is the existence of different, yet indistinguishable, copies of elementary particles. Two electrons anywhere in the Universe, whatever their origin or history, are observed to have exactly the same properties. We understand this as a consequence of the fact that both are excitations of the same underlying ur-stuff, the electron field. The electron field is thus the primary reality. The same logic, of course, applies to photons or quarks, or even to composite objects such as atomic nuclei, atoms, or molecules.

The indistinguishability of particles is so familiar, and so fundamental to all of modern physical science, that we could easily take it for granted. Yet it is by no means obvious. For example, it directly contradicts one of the pillars of Leibniz’ metaphysics, his “principle of the identity of indiscernables,” according to which two objects cannot differ solely in number. And Maxwell thought the similarity of different molecules so remarkable that he devoted the last part of his Encyclopedia Brittanica entry on Atoms – well over a thousand words – to discussing it.
==endquote==

To paraphrase, the electron field is a layer of the primary reality. It pervades all spacetime. All electrons are excitations of this field. that is why they're the same.

The quark field is another part of the primary reality. It pervades all spacetime. Each type of quark is a type of excitation of this field. That is why all quarks of a given type (top, bottom, strange…) are the same.

The electromagnetic field is another layer of the primary reality. It pervades all spacetime. Photons are excitations of this field, having different frequencies and polarizations. All photons of the same type are the same.

It looks to me like Wilczek is PHILOSOPHICALLY ON THE BALL to point out that this seemingly obvious fact is non-trivial. It requires an explanation. (Maxwell realized that too.) The explanation is that the quantum FIELD is the basic "ur-stuff" of Reality and the reason these things are all the same is that they are excitations (quanta) of the same field.

To me this is a wonderful example of the profoundly important role PHILOSOPHY can play in Physics. People in the pop media are saying Philosophy is useless to Physics. And maybe Plato and Kant and such are not so useful at present. Maybe the conventional curriculum that Majors are taught IS currently a bit out of date and doesn't gear them up to ask insightful questions. I wouldn't know about the current state of academic Philosophy. But it seems clear to me that Wilczek has a natural philosophical talent and that can help him and others do physics. He can see questions that it might not have occurred to someone else to ask. Deep conceptual questions. I think this is really important and want to emphasize it. Physics can suffer from *philosophical blindness* unless there are a few people reflecting on basic concepts as in this example. Rovelli has a statement to this effect in his book Quantum Gravity.
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The Realism of a reasonable person

Postby Marshall on May 21st, 2014, 7:09 pm 



This guy wrote down the first example of a Quantum Field. QED. The quantum version of the Electromagnetic field. So he laid the cornerstone of modern ontology, or the first "layer" of the modern idea of Reality.
Other people have been busy adding other layers.

If you want to think of it as ONE BIG field, of course you can. Each different field is then a dimension of the amalgamated field consisting of all the layers. But I don't see any point to thinking of it that way. A layer cake Reality, or a Parfait is just as good AFAICS.

A major project these days is to realize Geometry as a quantum field (defined independently of any prior geometry) and then to rebuild the existing multilayer structure of reality on that QG basis.
"QF on QG"

Notice how Feynman expresses his commonsense Realism: Finding out more about how Nature IS,
exploring how the world IS.
Of course :^D. Did anybody ever imagine that Feynman was an Instrumentalist?

Folks, I've created a special thread for PERSONAL SPINOFFS FROM THE REALISM AND QUANTUM FIELDS THREAD viewtopic.php?f=39&t=27084
and moved some interesting and colorful posts which I thought present too great a temptation to get us off the main topic.

Please check out the new thread to see a remarkable poem by Dragonfly about Gravity (in part inspired by the "Lightness of Being" book mentioned here) and some illustrations of Dave_O's fractal multiverse concept.
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Re: Quantum realism and fields.

Postby owleye on May 21st, 2014, 8:42 pm 

Marshall...

In reading your last post (the one prior to the Feynman video), I'm afraid the use of the term 'field' loses all meaning for me. For each particle, there's a field responsible for the properties it is endowed with. Unfortunately this tells me nothing. It explains nothing. It is completely uninformative. It claims to explain why the particles are the same everywhere. But as I see it, it is just putting a name to something, as if in doing so it provides an explanatory framework of something we already had a framework for its understanding, namely the standard model.

Bohr speaks of probability waves in describing the passage of photons (or electrons). Ok. It's difficult to establish this as something real. However, pasting a field in its place doesn't automatically remove that difficulty. I thought we were getting somewhere when we referred to the amplitude wave, which is mapped onto real space. If the field corresponds to something that carries this amplitude, perhaps as an emergent effect (on the basis that there's some sea of underlying boson-like entities) that, in their combined action, produces this field in just the right way, well), maybe it can be explanatory.
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Re: Quantum realism and fields.

Postby Marshall on May 21st, 2014, 9:59 pm 

owleye » Wed May 21, 2014 5:42 pm wrote:Marshall...

... framework of something we already had a framework for its understanding, namely the standard model.


Wilczek is trying to help us understand the Standard Model. It is based on Quantum Field Theory, so he is trying out some words on us to possibly help make QFT intuitive. the reason he doesn't talk about "probability waves" or "amplitude waves" is, I think, because that is not the right way to picture QFT or to understand the Standard Model of matter.

Wilczek is one of the architects of the Standard Model and I think he is making an honest effort to make the whole business more intuitive. So I am inclined to listen closely and try to absorb some of that intuition. I do feel its working for me. But people differ! There is no use arguing about what makes sense to this or that person as a verbal translation. I don't want to try to persuade you that Wilczek's words SHOULD make sense to you. they either do or they don't and its fine either way.

Translating a math description of nature into intuitive English is like translating a poem from a foreign language into English verse.

Bohr speaks of probability waves in describing the passage of photons (or electrons)... I thought we were getting somewhere when we referred to the amplitude wave, which is mapped onto real space...


BTW he may well have talked about them but I'm not sure it was BOHR who introduced the "amplitude waves" idea, I thought it was Schrodinger around 1927. Correct me if I'm wrong. There are reasons why the Schrodinger "wave function" is a bad way to think about QM. Rovelli gave some reasons in his talk.
Shro originally defined his "wave function" on space or spacetime. But if there is more than one particle this is impossible..you need multiple dimensions. Like 40 dimensions for 10 particles. Not the world we know and love. Heisenberg seems to have been the first to point out this flaw in the "wave function" picture.

This is probably why the picture of Standard Model matter that Wilczek is trying to give us DOES NOT USE the "wave function" or "amplitude waves" idea. It uses the field, which CAN be defined on space or simple 4D spacetime, is operator valued, and can represent as many particles as you need without huge numbers of extra dimensions.

It's just a different brand of mathematics, one that is more adequate to the job, and so is preferred. Anyway that's my impression.

Faradave mentioned the photon (an important player :^D) does not even have a Schro
"wave function" or "amplitude wave". I've heard that too, but I'm not sure why it is. Because massless? Maybe Faradave will give us a clue to that.
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Re: Quantum realism and "Many Fields".

Postby Faradave on May 22nd, 2014, 1:50 am 

I find this thread interesting and useful for the information which Marshall has graciously summarized. Whether we agree with the content or not is clearly no fault of the messenger.

I suspect personalities which find Many Worlds to be an attractive concept will also be comfortable with Many Fields*. I have no doubt that the talented professors who dedicate themselves to such models are ingenious enough to take them far in terms of explanatory power and accurate prediction. What I doubt is that these are the simplest models possible. My preference is simplicity so, I lean toward less is more.

I sense in the following two passages that a problem with Many Fields,

Marshall wrote:To paraphrase, the [name a particle] field is a layer of the primary reality. It pervades space.

...the picture of Standard Model matter that Wilczek is trying to give us...uses the field, which CAN be defined on space or simple 4D spacetime,


The realm upon which the field is mapped is not a trivial consideration. As soon as we say, "an electron field pervades space" the question must arise as to whose space? "Space" varies with every inertial observer as is evident by different coordinate axes for a stationary observer (x,ct) and a moving one (x',ct').
Image
In that sense, the only agreeable field is an invariant field, i.e. one mapped on regions of spacetime. As I have noted in other threads, we are given such regions. They're called "light cones". It can hardly be considered a personal theory for me to say for instance, that photons only occur on light cones. And that's where an emitter's EM field is. The light cone must similarly be the realm of massless gluons, theoretical gravitons, and to the best of my understanding, the virtual occurrences of W and Z bosons.

Of course, there's nothing new in finding discrepancies between Relativity and QM. In this case, I'm convinced that Relativity will offer the simpler, ultimately unified, field model.


*By this I do not refer simply to the number of fields but to the number of kinds of fields. The Many Fields model being discussed allows a different field for every kind of elementary particle particle and then some. Prior convention has a field associated with each of the four recognized forces and a longstanding effort to unify these (having essentially accomplished this for three, excepting gravitation).

P.S. I would love to explain that the reason photons don't have their own wave function is that there are no photons but I must agree, that belongs in Personal Theories.
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Re: Quantum realism and fields.

Postby Marshall on May 22nd, 2014, 2:25 am 

Thanks for pointing out the omission! I meant to say pervades spacetime. I'll go fix it.
QFT is typically built on Minkowskski (x,t) the spacetime of SR.
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Re: Quantum realism and fields.

Postby Marshall on May 22nd, 2014, 2:26 am 

Thanks for pointing out the omission! I meant to say pervades all spacetime. So I went and corrected the post. So now it is a more faithful paraphrase of what Wilczek was saying.
QFT is typically built on Minkowskski (x,t) the spacetime of SR. So of course a field is defined on the whole domain. Glad someone is giving this a careful reading!

===quote the corrected post===
There are several key quotes to get one's head around, in that Wilczek 12-page "QFT" article
http://arxiv.org/abs/hep-th/9803075
Here is one on page 2.

==quote page 2 of "QFT" ==
Undoubtedly the single most profound fact about Nature that quantum field theory uniquely explains is the existence of different, yet indistinguishable, copies of elementary particles. Two electrons anywhere in the Universe, whatever their origin or history, are observed to have exactly the same properties. We understand this as a consequence of the fact that both are excitations of the same underlying ur-stuff, the electron field. The electron field is thus the primary reality. The same logic, of course, applies to photons or quarks, or even to composite objects such as atomic nuclei, atoms, or molecules.

The indistinguishability of particles is so familiar, and so fundamental to all of modern physical science, that we could easily take it for granted. Yet it is by no means obvious. For example, it directly contradicts one of the pillars of Leibniz’ metaphysics, his “principle of the identity of indiscernables,” according to which two objects cannot differ solely in number. And Maxwell thought the similarity of different molecules so remarkable that he devoted the last part of his Encyclopedia Brittanica entry on Atoms – well over a thousand words – to discussing it.
==endquote==

To paraphrase, the electron field is a layer of the primary reality. It pervades all spacetime. All electrons are excitations of this field. that is why they're the same.

The quark field is another part of the primary reality. It pervades all spacetime. Each type of quark is a type of excitation of this field. That is why all quarks of a given type (top, bottom, strange…) are the same.

The electromagnetic field is another layer of the primary reality. It pervades all spacetime. Photons are excitations of this field, having different frequencies and polarizations. All photons of the same type are the same.

It looks to me like Wilczek is PHILOSOPHICALLY ON THE BALL to point out that this seemingly obvious fact is non-trivial. It requires an explanation. (Maxwell realized that too.) The explanation is that the quantum FIELD is the basic "ur-stuff" of Reality and the reason these things are all the same is that they are excitations (quanta) of the same field.
==endquote==

This is just the first of 5 main principles of QFT he presents in the first 2 and 1/2 pages or so. I should get busy and paraphrase the second one. It's a remarkably compact essay, don't you find?--much food for thought packed into a few pages. And he says it all in words, with virtually no use of math symbols. The marks of someone who really understands what he's talking about.
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Re: Quantum realism and fields.

Postby owleye on May 22nd, 2014, 8:51 am 

I think what I'm missing is something interesting about (say) the electron field that allows me some insight that I don't already get from the an understanding of the standard model, coupled with Maxwell/Faraday field theory. In establishing the field to be primary, where the particle is a mere property of the field, am I gaining or losing something? It seems as if I'm losing something. The advantage that I see of the particle being primary, with the field being a property of the particle is that it can more readily be fit with Relativity theory. In the reverse case, the field would be thought of as having an absolute character, existing independently of the inertial frames that particles are referenced by, characterizing their position so that they are relative to the field, as it propagates through it. While I now read that this field is supposed to fit within a Minkowski space-time framework, I'm not getting anything that helps me see that. I'm not seeing fields as observers. Rather, I'm seeing fields as creators and destructors of the particles they are associated with, one where the particles traverse the field and are affected by it, but not in the way that a Minkowski diagram would help me out with. Indeed, such particles would not be differentiated respecting their speed, only their direction, as I understand it anyway.
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Re: Quantum realism and fields.

Postby TheVat on May 22nd, 2014, 10:03 am 

I think the problem remains that neither particle nor field have really advanced to where we can point to a definitive "Ur-field" in a way that would satisfy the epistemic demands of metascience. The hunger is for a unified field, the mother of all fields, and instead we have shards of broken symmetry. We can do a lot of modeling and talk about particles as perturbations of a field, but what the instruments seem to interact with are things that act like particles when they smack into other things that act like particles. "If it walks like a duck, quacks like a duck....[etc.]" So if there is a foundational case to be made, it has to explain better why ducks aren't really ducks, but tuggy-stretchy-wavy continua of duck force that experience local excitations that seem like discrete ducks. And, for the philosopher of science, saying "you have to accept that the math is the reality" may cause him to balk. Ontology asks for more than surrender to geometry, no matter how cool that looks on paper.

Good question, Owl. Got my motor running this a.m.
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Re: Field dimensionality and location

Postby Faradave on May 22nd, 2014, 11:58 am 

Thanks for the clarification Marshall. I hope you will continue with your summary of Wilczek's paper.

I still find myself at odds with the notion of field as corrected. I don't believe a single universal field region can be construed for both particles and forces.

Marshall wrote:To paraphrase, the electron field is a layer of the primary reality. It pervades all spacetime. All electrons are excitations of this field. that is why they're the same.


First, we must remind ourselves that a light cone is a specific 3-region of spacetime associated with a particular event (e.g. a "particle"). By 3-region, I mean it occupies the dimensional equivalence of 3-space within 4D spacetime. However, a light cone occurs at 45o wrt to space and time.
Image
The Wikipedia image is a favorite of mine but it errs in illustrating only two coordinate axes in the spatial hypersurface, which actually contains three. The future light cone is a different 3-surface.

Faraday fields (aka Gaussian fields), though often described in space, are more correctly described as occupying the future light cone of a particle. It does not therefore seem correct to describe them as "pervading all spacetime" as that would make such a field 4D rather than 3D.

I'm OK if by "pervading" we mean an EM field transcends, crosses or spans spacetime. But then, given the distinction between massive and massless particles, an electron field cannot then be superimposed upon the EM field (as was shown in the Sci.Am. video). The EM field is lightlike, electrons are timelike.

The video describes electrons as "perturbations in an electron field" which can appear in a creation event, disappear in an annihilation event and move within the field. Movement of massive particles is restricted to sub-light speed so, the an "electron field" can't map onto a light cone.

The only place an electron can occupy on its light cone is its vertex. This is why I would say that in considering a field as more fundamental than a particle, a particle may be defined as the vertex of a field.

edit: "its" 2nd last sentence
Last edited by Faradave on May 22nd, 2014, 1:49 pm, edited 1 time in total.
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Re: Quantum realism and "Many Fields".

Postby Marshall on May 22nd, 2014, 12:10 pm 

Owl, Brain, partial answer to your questions can be found in the recent (21 May) Faradave post that shows what's technically called a LORENTZ transformation. That is the simple algebraic change of coordinates that is at the heart of Special Rel. The change from (x, t) to (x', t')
Faradave » Wed May 21, 2014 10:50 pm wrote:...axes for a stationary observer (x,ct) and a moving one (x',ct').
Image
In that sense, the only agreeable field is an invariant field, i.e. one mapped on regions of spacetime.. . nothing new in finding discrepancies between Relativity and QM...Relativity will offer the simpler, ultimately unified, field model.
...


A longer name for Quantum Field Theory (which underlies the Std Mdl and is the main topic here) is Relativistic Quantum Field Theory. It gets tiresome to include the modifier so people leave it off.
QFT or if you want to include the reminder "RQFT" is AGREEABLE in Faradave's sense. All the Standard Model "particle" fields are Lorentz invariant.

Faradave was slightly mistaken about this being an example of "discrepancy between quantum theory and relativity" but his basic intuition is right. QFT is a case where Relativity ALREADY HAS OFFERED a simpler, more unified field model.

Faraday's field idea begat Maxwell's equation which begat Special Rel and QFT carries on that tradition.

Faraday got the basic intuition of a world made of a field of "forces" (electric and magnetic).
Maxwell devised an EQUATION relating changes in the electric field to changes in the magnetic field.
It was the only equation that did what Faraday wanted the electricity and magnetism to do, having the changing flow of current in a coil do this and that to iron filings and if you turned a crank electricity would flow in the wire etc etc etc. Max equation had PRACTICAL VALIDITY, but it also had a weird unexpected invariance under certain simple algebra change of coordinates from x,t to x',t' that nobody had ever seen before.
If you have a field on (x,t) space and you alter the direction that time is pointing then you naturally alter the way you measure the time-rate-of-change of the field. You alter the first and second time-derivatives. So then if you want the equation to remain valid with the new coords you have to alter the x direction too! And it turns out you have done a Lorentz transformation.

Nature whispered "field" to Faraday. Faraday told Maxwell to make an equation about the field. The equation said "Lorentz transformation" and that was the heart of what we now call special relativity.
Special Relativity is not about relatively moving "particles" it is basically about FIELDS. It is the essential way that nature's fields are INVARIANT. And it is the triumph of Faraday's original hunch.

this is just my take on the story, after the first cup of coffee this morning, or maybe it was the second. It's meant to address some things you said. There's more to say. Feynman's QED was special relativistic (i.e. invariant under those simple algebra changes called Lorentz transformations) and the subsequent quantum field theories continued that tradition of being Lorentz invariant. That's how fields want to be. I'll get some breakfast and get back later. Faradave, Owl, Brain, liked your response posts a lot!!! Mucho gracias.
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Re: Quantum realism and fields.

Postby Marshall on May 22nd, 2014, 12:59 pm 

I see in the last post I said "(x,t) space". I seem to have an engrained habit of using that little one-syllable word in situations where there are more than 3 dimensions. Like "configuration space" which could have say 40 dimensions, or "phase space" which could have 80 dimensions, or "Hilbert space" which could have countable infinite, or "tangent space" which has exactly as many dimensions as the manifold on which it is built and might be 2D, if the manifold is, or might be 17D if the manifold is.

The relativistic quantum fields of the Standard Model of matter are OPERATOR-VALUED functions defined on Minkowski space, or (x,t) space, or (x,t) spacetime. Hopefully the precise terminology doesn't matter, you know what I mean.

the main thing to understand is that Faraday had this vague idea of field of "forces". what is "magnetic force"? he probably couldn't say exactly. you need special conditions like a piece of certain type of metal in order to observe it. Sometimes it twists stuff around, like a compass needle. sometimes it pushes current along a wire if the wire is moved *across* the lines of "force". The direction of current is not in the direction of the lines of "force"

actually the field is of something you OBSERVE, whose operation depends on the instrument you observe it with.

the field is OPERATOR-VALUED. That is how we finally got clear about Faraday's hunch. He knew it was something-valued, but he did not know what-valued. (I suspect)
Marshall
 


Re: Quantum realism and fields.

Postby Marshall on May 22nd, 2014, 1:24 pm 

Always exciting when central ideas get challenged! A paper came out yesterday challenging the fundamental role of Lorentz covariance, arguing that it was a accidental or "emergent" feature arising from something else.

Physicists and cosmologists are always challenging their own prevailing ideas, I guess it's fun and keeps you young etc etc and is healthy for science etc etc, and most often the challenges go a away after a while (like superluminal neutrinos and the Great Void). But I think it's worthwhile taking a serious look at some of them, just in case. I like this one, on first sight, very much.

I don't want this to derail the thread, but I want you (Owl, Faradave, Brain) to know about this without delay, just in case.
===
http://arxiv.org/pdf/1405.5219.pdf
For over a century, physicists have grappled with the logical foundations of general relativity (GR). Einstein arrived at GR by combining his gravitational equivalence principle with the Lorentz covariance of special relativity. Quantization yields a particle, the graviton, with two transverse, traceless polarizations. The local gravitational degrees of freedom are thus determined by the macroscopic properties of gravitational fields and the assumed space- time symmetries.

Using the formalism of quantum field theory, it is possible to invert this reasoning: GR is the unique Lorentz-covariant theory of a self-interacting massless spin-2 particle, and the equivalence principle results from the form of the interactions in the long-wavelength limit [1– 3]. In this picture, GR follows directly from 1) the local gravitational degrees of freedom and 2) space-time symmetries.

Without question, GR is the most successful extant paradigm for the interpretation of gravitational phenomena. Nonetheless, there are compelling reasons to question the basis of gravitational theory…

In this essay, we survey recent theoretical progress demonstrating that GR can be derived from the local gravitational degrees of freedom without assuming space-time symmetry [4, 5]. Our approach relies instead on the weaker assumption of spatial covariance in the context of the effective field theory of the transverse, traceless gravitons.

By way of phenomenological motivation, the observed cosmic rest frame provides a strong justification for assuming spatial covariance, and the claimed detection of B-modes in the CMB is powerful evidence for the transverse, traceless graviton polarizations [6]. Our result implies that Lorentz covariance is a necessary feature of low-energy graviton dynamics, not a property of space-time: Lorentz covariance is an emergent symmetry of the gravitational sector.
===

Khoury Miller Tolley. I'm somewhat familiar with Khoury and Tolley from earlier papers and PIRSA video seminars. Miller's name doesn't ring a bell. I respect Justin Khoury. He used to do some string research which didn't interest me but I felt respect. He always was part-time into cosmology Maybe he is getting into some new research interests.
http://arxiv.org/abs/1405.5219
http://inspirehep.net/record/1297366
http://inspirehep.net/author/profile/J.Khoury.1
http://inspirehep.net/author/profile/A.J.Tolley.1
Here's a longer (42-page) paper that has the same message, spelled out in more detail:
http://arxiv.org/abs/arXiv:1305.0822
It came out one year ago, in May 2013. I wasn't aware of it at the time. Their approach seems to be related to so-called "unimodular" gravity. I don't want to seem to ADVOCATE any of this but it is a challenge to some of the foundational assumptions taken for granted (e.g. in this thread and generally very widely) so I wanted to share it.
Marshall
 


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