Are There Viable Alternatives to Quantum Field Theory and Second Quantization?

[waterfall]

This means you had paid 1/307,000,000 millionth of my salary. Considering the average working load is 2000 hours per year (8 hours per day, 5 days per weeks, 52 weeks per year - 10 days of holidays and furloughs), it means you have a share of 0.23 s per physicist per year. Considering the American Physical Society has 50,055 registered members, you can interview physicists for 20 minutes per year.

I think you spent your allowed time. Please give us our refund.

Peter Woit and Lee Smolin who wrote "Not Even Wrong" and "Physics Wrong Turn" mentioned how half of the billions of dollars of funding were wasted by physicists doing "Recreational Mathematical Theology" in Superstrings theory and how they were sidetracked by "symmetries". There is a third book written by another, does anyone remember or know the title?

 

[Dickfore]

Peter Woit and Lee Smolin who wrote "Not Even Wrong" and "Physics Wrong Turn" mentioned how half of the billions of dollars of funding were wasted by physicists doing "Recreational Mathematical Theology" in Superstrings theory and how they were sidetracked by "symmetries". There is a third book written by another, does anyone remember or know the title?

What's your point?

 

[atyy]

Now what has this got to do with your lattice idea of spacetime? Maybe you mean at low energies, perturbation is not needed in the calculations? But without perturbation, the magnetic charge of an electron would be different than the measured value. Also how is your statement that "Renormalization is the procedure of figuring out how a quantum field theory with a given symmetry looks like at low energies" fit to the idea of cancelling out infinities?

Great question! The idea of figuring out how a quantum field theory with a given symmetry looks like at low energies makes sense - let's call this the Wilson-Kadanoff renormalization group. The idea of cancelling infinities is nonsensical. So the latter is simply a calculational trick, while the former provides the conceptual foundation. Historically, the trick was discovered first, and was accepted even though it was nonsensical because of its successful experimental predictions. However, Feynman, Dirac and many physicists continued to worry about the nonsensical subtraction of infinities. Around 1970, the discovery of the Wilson-Kadanoff renormalization group gave a conceptual basis to the calculational trick (ie. no infinities are actually subtracted), and physicists stopped worrying about the subtraction of infinities.

A slightly technical, but quite readable if you are patient, history is given in the http://fds.oup.com/www.oup.co.uk/pdf/0-19-922719-5.pdf.

More technical details are found in
http://arxiv.org/abs/hep-th/9210046v2
http://web.physics.ucsb.edu/~mark/ms-qft-DRAFT.pdf (chapter 29)

 

[waterfall]

Great question! The idea of figuring out how a quantum field theory with a given symmetry looks like at low energies makes sense - let's call this the Wilson-Kadanoff renormalization group. The idea of cancelling infinities is nonsensical. So the latter is simply a calculational trick, while the former provides the conceptual foundation. Historically, the trick was discovered first, and was accepted even though it was nonsensical because of its successful experimental predictions. However, Feynman, Dirac and many physicists continued to worry about the nonsensical subtraction of infinities. Around 1970, the discovery of the Wilson-Kadanoff renormalization group gave a conceptual basis to the calculational trick (ie. no infinities are actually subtracted), and physicists stopped worrying about the subtraction of infinities.

A slightly technical, but quite readable if you are patient, history is given in the http://fds.oup.com/www.oup.co.uk/pdf/0-19-922719-5.pdf.

More technical details are found in
http://arxiv.org/abs/hep-th/9210046v2
http://web.physics.ucsb.edu/~mark/ms-qft-DRAFT.pdf (chapter 29)

I have read Zinn-Justins' first chapter as you suggested. It ends with this and producing new questions:

"This modern viewpoint, deeply based on RG ideas and the notion of scale-dependent effective interactions, not only provides a more consistent picture of QFT, but also a framework in which new physics phenomena can be discussed.
It implies that QFTs are somewhat temporary constructions. Due to an essential coupling of very different physical scales, renormalizable QFTs have a consistency limited to low-energy (or large-distance) physics. One uses the terminology of effective QFT, approximations of an as yet unknown more fundamental theory of a radically different nature."

My questions are. First are you 100% certain the Renormalization Group arguments are totally valid? Do 100% of physicists believe in it? Or are there some doubts?

Second about this fundamental theory of a radically different nature? Does it include Superstrings? Or something beyond Superstrings?

 

[waterfall]

I have read Zinn-Justins' first chapter as you suggested. It ends with this and producing new questions:

"This modern viewpoint, deeply based on RG ideas and the notion of scale-dependent effective interactions, not only provides a more consistent picture of QFT, but also a framework in which new physics phenomena can be discussed.
It implies that QFTs are somewhat temporary constructions. Due to an essential coupling of very different physical scales, renormalizable QFTs have a consistency limited to low-energy (or large-distance) physics. One uses the terminology of effective QFT, approximations of an as yet unknown more fundamental theory of a radically different nature."

My questions are. First are you 100% certain the Renormalization Group arguments are totally valid? Do 100% of physicists believe in it? Or are there some doubts?

Second about this fundamental theory of a radically different nature? Does it include Superstrings? Or something beyond Superstrings?

I remember reading in Lisa Randall's "Warped Passages" about the Hierarchy Problem and how one of the purposes of supersymmetry was to render the Higgs particle not equivalent to the Planck Mass sort of by making the masses of the superparticles cancel out with them. How come Renormalization Group theory was not applied in this case? Why do physicists have to propose Supersymmetry to handle the infinities issues?

 

[strangerep]

I'm trying to learn what Haag's theorem is, and googling brings up articles by Fraser, and Earman and Fraser. It looks as if Haag's theorem only needs Euclidean invariance, so it would seem to apply to non-relativistic QFT. Does Haag's theorem apply in the non-relativistic QFT used in condensed matter? If Haag's theorem doesn't apply, is it because Euclidean invariance is broken by the lattice?

I looked at some of the Fraser/Earman papers several years ago and got the impression that they're more philosophers than physicists (being in the Dept. of History and Philosophy of Science at Pittsburgh). They seemed to be most interested in exploring the fact that, in infinite dimensions, there can exist unitarily inequivalent representations of the CCRs -- and one certainly doesn't need full Poincare relativity to explore that. The textbooks of Umezawa et al ("Thermofield Dynamics & Condensed States" and "Advanced Field Theory") contain useful introductions to inequivalent reps.

For Haag's theorem in a relativistic context, there's always Streater & Wightman's "PCT, Spin, Statistics, and all that". But the first exposition of Haag's theorem that I could actually follow (including the proof) was in Barton's little-known book:

G. Barton,
Introduction to Advanced Field Theory,
Interscience, 1963.

He also has a chapter near the end with some interesting remarks and speculations about the role of unitarily inequivalent representations in full QFT.

 

[atyy]

@waterfall, supersymmetry isn't meant to solve the problem of infinities, it's meant to solve the "naturalness" problem. It's not primarily a mathematical problem, more a problem of explaining why some parameters in the standard model have to specified so precisely to match experimental observations. There's a discussion of this on p6 of the Zinn-Justin chapter. The Wilson-Kadanoff viewpoint that non-renormalizable theories are acceptable effective field theories, and that renormalization is just a way to see how they look like at low energies, underlies two different approaches to quantum gravity: string theory and asymptotic safety. A further argument for the Wilson-Kadanoff viewpoint is the gauge/gravity conjecture in which the renormalization flow is transformed into a spatial dimension.

@strangerep, thanks for the references! I came across an interesting comment in Rivasseau's "From Perturbative to Constructive Renormalization" in which he says the same formal series can be derived in spite of Haag's theorem, by a method given by Epstein and Glaser, but also further indicates that actual meaning should be given by Euclidean field theory, checking if the Osterwalder-Schrader axioms are satisfied, and analytically continuing to Minkowski space. I think one of the problems in LQG is choosing between unitarily inequivalent representations due to Haag's theorem. Apparently Thiemann's master constraint programme tries to use dynamics to choose the appropriate representation. There seems to be an analogy with a particle on a circle.

 

[strangerep]

I came across an interesting comment in Rivasseau's "From Perturbative to Constructive Renormalization" in which he says the same formal series can be derived in spite of Haag's theorem, by a method given by Epstein and Glaser,

If you're not familiar with the Epstein-Glaser method, try Scharf's book:

G. Scharf,
Finite Quantum Electrodynamics -- The Causal Approach,
Springer, 2nd Ed., 1995. ISBN 3-540-60142-2

(Make sure you get the 2nd edition -- it has a lot more stuff than the first.)

But the basic idea of Epstein-Glaser-Scharf is that QFT infinities arise from multiplying distributions by \Theta(t) (step-function) in the time-ordered products. The discontinuity in the step function means that the product is no longer a tempered distribution. The method then revolves around inserting correction terms perturbatively to fix it -- using causality as a guide. But it's quite a few years since I went through the 1st edition of Scharf's book, back when I knew far less QFT and math than now. I really should read the 2nd edition thoroughly some time. :-(

[...] use dynamics to choose the appropriate representation.

Haag also makes a brief mention in his book about how choosing the representation is a "dynamical problem". I guess that means choosing an appropriate time-dependent Bogoliubov transformation, but I don't understand that stuff very well -- and modern LQG even less. :-(

 

[waterfall]

@waterfall, supersymmetry isn't meant to solve the problem of infinities, it's meant to solve the "naturalness" problem. It's not primarily a mathematical problem, more a problem of explaining why some parameters in the standard model have to specified so precisely to match experimental observations. There's a discussion of this on p6 of the Zinn-Justin chapter. The Wilson-Kadanoff viewpoint that non-renormalizable theories are acceptable effective field theories, and that renormalization is just a way to see how they look like at low energies, underlies two different approaches to quantum gravity: string theory and asymptotic safety. A further argument for the Wilson-Kadanoff viewpoint is the gauge/gravity conjecture in which the renormalization flow is transformed into a spatial dimension.

@strangerep, thanks for the references! I came across an interesting comment in Rivasseau's "From Perturbative to Constructive Renormalization" in which he says the same formal series can be derived in spite of Haag's theorem, by a method given by Epstein and Glaser, but also further indicates that actual meaning should be given by Euclidean field theory, checking if the Osterwalder-Schrader axioms are satisfied, and analytically continuing to Minkowski space. I think one of the problems in LQG is choosing between unitarily inequivalent representations due to Haag's theorem. Apparently Thiemann's master constraint programme tries to use dynamics to choose the appropriate representation. There seems to be an analogy with a particle on a circle.

From all these infinities and renormalization thing. It looks like our physics is mainly about interactions between particles. So I think it's true they are just lower limit or classical limit of a completely radical theory. Remember Zinn-Justin's last sentence in the book you shared where it is quoted "One uses the terminology of effective QFT, approximations of an as yet unknown more fundamental theory of a radically different nature."

The radical theory would make possible for example the holodeck in Star Trek where one can manifest any object or make them physical. This is engineering beyond the vacuum. It seems our present physics just focus on the interactions of particles, they don't even know how spacetime is connected to quantum particles. So spacetime could be just a temporary construction, and if we can have access to the more fundamental theory, then we can reprogram spacetime and matter to make possible the idea of Holodeck in Star Trek. This is possible isn't it? You can't make arguments about our mere physics of interactions to judge the limit of what is possible. Do you accept this (and others too)?

 

[strangerep]

[...] the holodeck in Star Trek [...] This is possible isn't it?

You just crossed over into the twilight zone of crackpot speculation.

(Moderators: maybe it's time to close this thread?)

 

[waterfall]

You just crossed over into the twilight zone of crackpot speculation.

(Moderators: maybe it's time to close this thread?)

I'm just asking if our physics is the final.. but I noticed they are mostly based on interactions... on non-interacting quantum fields and renormalization group that is ad hoc. Don't worry. I'm not a star trek fan. But it's just asking if our physics is really the final.. or just the beginning to another chapter like from Newtonian to einsteinian or quantum...

 

[martinbn]

I'm just asking if our physics is the final.. but I noticed they are mostly based on interactions... on non-interacting quantum fields and renormalization group that is ad hoc. Don't worry. I'm not a star trek fan. But it's just asking if our physics is really the final.. or just the beginning to another chapter like from Newtonian to einsteinian or quantum...

What if it is not the final theory? In fact, I don't think that anybody thinks that it is.

 

[waterfall]

What if it is not the final theory? In fact, I don't think that anybody thinks that it is.

It's reported in many news and magazines that when the Higgs will be found found. Physics will be almost complete. But it may be just the beginning.. perhaps we are like starting in Newton stage comparatively and physics would continue to develope the next 400 years...

With non-positive results in Loop quantum gravity and Superstrings, we may be on a wrong foundation and quantum gravity may be more than a century away... you think we can solve it before year 2100?

 

[tom.stoer]

It's reported in many news and magazines that when the Higgs will be found found. Physics will be almost complete.

Standard model (including Higgs) + classical gravity (general relativity) is by no means complete

1) the perturbation series of standard model QFTs does not converge (here I do not mean the infinities in each term but the series as a whole
2) there are problems in the UV, especially for the Higgs
3) gravity is not quantized, but we know that QFT + classical gravity is incomplete
4) gravity itself is incomplete (singularities)

Of course there are additional physical issues like unification, reason for SU(3)*SU(2)*U(1), coupling constants, particles, fermion generations etc.; but even w/o taking these questions into account, the mathematical structure "standard model + classical gravity" is ill-defined.

 

[martinbn]

tom.stoer, a side question about your 1), 4).

1) the perturbation series is an asymptotic series, so the non-covergence is normal. Just like in classical mechanics, say in the work of Poincare, so this by itself is not a problem. Of course there is a difference, in QFT there is no non-perturbative formulation (if i understand correctly).

4) why do singularities mean that gravity is incomplete?

waterfall,

if I understand you correctly you afraid that physicists think that physics is almost complete, and you disagree, but i don't think that is the case, dispite of what some news and magazines may say. Also I get the feeling that you believe that about 80 years ago physics took a wrong turn with QFT and now it is in a dead end street, so they should all stop what they are doing and go back to the begining. That is misunderstanding what physics is and what it has done. Of course I may be completely missing you point.

 

[waterfall]

Standard model (including Higgs) + classical gravity (general relativity) is by no means complete

1) the perturbation series of standard model QFTs does not converge (here I do not mean the infinities in each term but the series as a whole
2) there are problems in the UV, especially for the Higgs
3) gravity is not quantized, but we know that QFT + classical gravity is incomplete
4) gravity itself is incomplete (singularities)

Of course there are additional physical issues like unification, reason for SU(3)*SU(2)*U(1), coupling constants, particles, fermion generations etc.; but even w/o taking these questions into account, the mathematical structure "standard model + classical gravity" is ill-defined.

After a week of understanding the essence of QFT, I just realized how badly is our situation. It's like we were back in the days of Newton. When you don't know QFT. You think i'ts very impressive and we are near to the solution of everything. Isn't it that Steven Weinberg wrote how we soon would have a theory of everything. See:

http://www.math.vt.edu/people/gao/physics/weinberg.html

What would it take to create interacting fields. Maybe we need to find alternatives for the fock space which doesn't even interact. It's quiet bad. We have quantum field theory, but the fields don't interact and we have to use artificial means and ad hoc pertubation series.

I think it's time I should reread Lee Smolin Not Even Wrong and Peter Woit Physics Wrong Turn.. because there is a possibility they may be right and String theory and even Loop Quantum Gravity are just "Recreational Mathematical Theology". I forgot all their arguments.

 

[waterfall]

tom.stoer, a side question about your 1), 4).

1) the perturbation series is an asymptotic series, so the non-covergence is normal. Just like in classical mechanics, say in the work of Poincare, so this by itself is not a problem. Of course there is a difference, in QFT there is no non-perturbative formulation (if i understand correctly).

4) why do singularities mean that gravity is incomplete?

waterfall,

if I understand you correctly you afraid that physicists think that physics is almost complete, and you disagree, but i don't think that is the case, dispite of what some news and magazines may say. Also I get the feeling that you believe that about 80 years ago physics took a wrong turn with QFT and now it is in a dead end street, so they should all stop what they are doing and go back to the begining. That is misunderstanding what physics is and what it has done. Of course I may be completely missing you point.

I'm not saying it's a dead end street. I think it's similar to what happened in General Relativity. Had Einstein not discover certain math technique (I forget if it's differential geometry or tensor calculus), he won't be able to perfect GR and make things lorentz covariant. So I think we have missed the right mathematical tool or language for true QFT instead of the sporatic Fock space that may be just child's play. Now I wonder what is the right mathematicals for fields that indeed interact. It means we have to replace or rather enchance Hilbert Space too with a more superior mathematics. Anyone has any idea what kind of math algorithm for it and if I make sense at all?

 

[tom.stoer]

1) the perturbation series is an asymptotic series, so the non-covergence is normal. Just like in classical mechanics, say in the work of Poincare, so this by itself is not a problem. Of course there is a difference, in QFT there is no non-perturbative formulation (if i understand correctly).

I agree; this is perhaps not a fundamental issue.

It's not true that there are no non-perturbative tools, but one cannot say that there is a fully developed non-perturbative approach applicable to all questions in QFT; it strongly depeds on the use case.

4) why do singularities mean that gravity is incomplete?

b/c GR is formulated for smooth manifolds w/o boundary and w/o defects; at singularities the theory is no longer predictive; you cannot formulate boundary or initial conditions; you don't know where all the matter goes in a black hole (the Schwarzschild metric is a vacuum solution with a point-like singularity); b/c when combined with QFT a black hole it violates unitarity; ...

 

[waterfall]

I was rereading Lee Smolin "Trouble with Physics". He was saying in the following in page 249 that Loop Quantum Gravity was trying to reinvent QFT?? I thought LQG is all about gravity. How come I don't hear about QFT being redone in LQG formulation?

"This work was made possible by Ashtekar's great discovery that general relativity could be expressed in language like that of a gauge field. The metric of spacetime, then, turns out to be something like an electric field. When we tried to treat the corresponding field lines quantum-mechanically, we were forced to treat them without a background because there was none - the field lines already described the geometry of space. Once we made them quantum-mechanical, there was no classical geometry left. So we had to reinvent quantum field theory in order to work without a background metric. To make a long story short, it took the input of many people, with a variety of skills from physics and mathematics, but we succeeded. The result is loop quantum gravity."

Do you agree we have to reinvent quantum field theory in order to work without a background metric? Btw.. why hasn't anyone told me the answer to the "Alternative to QFT " in my thread question is nothing but Loop Quantum Gravity as Smolin mentioned?

 

[suprised]

I think it's time I should reread Lee Smolin Not Even Wrong and Peter Woit Physics Wrong Turn..

It's amazing how one can mess up every little detail. Sorry, don't be surprised about not gettting answers, it's just too far off.

 

[waterfall]

It's amazing how one can mess up every little detail. Sorry, don't be surprised about not gettting answers, it's just too far off.

What? It's not my idea but Smolin's. Anyway. I converted all texts of Lee Smolin "Trouble With Physics" to speech and I'll listen to it all day and night in my ipod. Here's Smolin main theme or punchline:

"This is the story of a quest to understand nature at its deepest level. Its protagonists are the scientists who are laboring to extend our knowledge of the basic laws of physics. The period of time I will address - roughly since 1975 - is the span of my own professional career as a theoretical physicist. It may also be the strangest and most frustrating period in the history of physics since Kepler and Galileo began the practice of our craft four hundred years ago. The story I will tell could be read by some as a tragedy. To put it bluntly - and to give away the punch line - we have failed. We inherited a science, physics, that had been progressing so fast for so long that it was often taken as the model for how other kinds of science should be done. For more than two centuries, until the present period, our understanding of the laws of nature expanded rapidly. But today, despite our best efforts, what we know for certain about these laws is no more than what we knew back in the 1970s. How unusual is it for three decades to pass without major progress in fundamental physics? Even if we look back more than two
hundred years, to a time when science was the concern mostly of wealthy amateurs, it is unprecedented. Since at least the late eighteenth century, significant progress has been made on crucial questions every quarter century"

 

[Physics Monkey]

What I find amazing is the unbelievable hubris required to equate a few esoteric questions in high energy physics with the progress of all physics.

 

[friend]

Btw.. why hasn't anyone told me the answer to the "Alternative to QFT " in my thread question is nothing but Loop Quantum Gravity as Smolin mentioned?

Does your concern about the right math in physics come from a perception that present math may not be able to give us a complete theory of everything? Or does it seem that the mathematical origins of QFT seem arbitrary? What would prove that we are using the correct math? We would have to be able to derive QFT from deductive logic in order to show that there is even any chance of proving the completeness of physics. Otherwise, our theories will always be contingent on the next experiment confirming their predictions. We can never measure everything, so their always remains the possibility that our theory can be proven wrong by some experiment.

 

[tom.stoer]

LQG is certainly not the alternative
- it's not a complete theory but work in progress (neither mathematically nor physically)
- it's a theory about gravity only; full inclusion of matter is still missing
- it's by no means a theory aiming for unification
- the definition of obervables is not fully understood
- nobody knows how to do simple low-energy scattering calculations
-...

 

[waterfall]

Does your concern about the right math in physics come from a perception that present math may not be able to give us a complete theory of everything? Or does it seem that the mathematical origins of QFT seem arbitrary? What would prove that we are using the correct math? We would have to be able to derive QFT from deductive logic in order to show that there is even any chance of proving the completeness of physics. Otherwise, our theories will always be contingent on the next experiment confirming their predictions. We can never measure everything, so their always remains the possibility that our theory can be proven wrong by some experiment.

I have to study deeper the math of QFT to be able to answer that. But I heard from Fredrik that even those with Ph.D. in Physics doesn't mean they are already expert in QFT. So it's kinda heartbreaking. From graduate in college of BS in Physics to Ph.D. I think takes 4 to 5 years more for total of 8 years. And yet they are not yet master in it. Are you a physicist? I'm thinking whether to go back to school and become one. Because there is a possibility our physicists may just miss it all and won't see the light even after 20 years or year 2032. This is because they are doing it blind. They don't have any guiding principle much like when Einstein got the insight about the Equivalence Principle and spent 10 years to perfect it to produce GR. I think I have a guiding principle insight too and just need to find the right math. Actually some have the same guiding principle insight but they are just not trained to math to develope it fully. And physics is just so important to leave it to physicists. Important choices to make maybe not just me.. but also you. So is your course related to physics? What do you make of Smolin and Woit book. Woit book is more mathematical and I think I'll try to understand it deeper after learning here that QFT is good for only free fields and Fock space is none-interacting proving Smolin and Woit is not smoking pots but are partly if not more right in their critique of modern physics.

 

[ofirg]

Why is QFT treated here as its definition only makes sense with perturbation theory?
I understood that the path integral definition ( and the canonical formalism also, at least of you can find an appropriate fock space) doesn't rely on perturbation theory, and we use it simply because we aren't able solve the full theory.

 

[marcus]

Hi Waterfall, your thread about a possible wrong turn reminds me of a different discussion we had here a few years back. A mentor named "SelfAdjoint" took part in the discussion.

https://www.physicsforums.com/showthread.php?t=124999

It began with a poll asking when people thought a wrong turn was made.

 

[juanrga]

Why is QFT treated here as its definition only makes sense with perturbation theory?
I understood that the path integral definition ( and the canonical formalism also, at least of you can find an appropriate fock space) doesn't rely on perturbation theory, and we use it simply because we aren't able solve the full theory.

The «full theory» does not exist as QFT... because only free fields are well-defined.

 

[atyy]

after learning here that QFT is good for only free fields and Fock space is none-interacting

First, the renormalization group shows that theories do not have to be defined at all energies to yield great predictions at low energies. QED is such a theory.

Second, it is not true that only free fields are rigourously defined at all energies. Some nonlinear self-interacting quantum fields have been rigourously constructed in 2 and 3 dimensional spacetimes. The rigourous construction of Yang-Mills theory in 4 dimensional spacetime is thought possible because of asymptotic freedom, but it is still being researched. In fact, the Clay Institute is offering a prize of $1 million for a rigourous construction of Yang Mills theory and a demonstration that it has a mass gap.

http://www.claymath.org/millennium/Yang-Mills_Theory/
http://www.claymath.org/millennium/Yang-Mills_Theory/yangmills.pdf

 

[marcus]

LQG is certainly not the alternative
- it's not a complete theory but work in progress (neither mathematically nor physically)
- it's a theory about gravity only; full inclusion of matter is still missing
- it's by no means a theory aiming for unification
- the definition of obervables is not fully understood
- nobody knows how to do simple low-energy scattering calculations
-...

I have no reason to object to any of these 5 points and don't want to argue about any of this.

But I want to mention what my perspective is on your "certainly not the alternative" phrase.

LQG could well be on the correct path to the alternative even though it is itself not the last step nor does try to be.

The LQG program may be *on the path to unification" because it strives for a new (no-prior-geometry) representation of spacetime. One which takes into account how geometry responds to measurement and interacts with matter.

On the path, because it may happen to be necessary to settle on a quantum theory of geometry (interacting with matter) before one can build a new representation of the whole.

And in particular it may be necessary to arrive first at a testable QG model of early universe cosmology, like that of LQC--something which explains how the big bang occurred, resolves some problems with dark matter and inflation, and predicts various features to observe in the background of ancient light.