Why do stringy people don't like LQG?

[tom.stoer]

Hi,

I know a couple of arguments why the loopy guys don't like string theory (perturbative quantization, background dependence, too many statements w/o proof, mysterious M theory, ...)

But can anybody tell me why stringy people don't like loop quantum gravity?

I mean serious arguments, not something like "Witten doesn't like it, either" or "string theory is the only game in trown". Why is the string community convinced that LQG is just wrong? What are the physical or mathematical reasons?

Thanks
Tom

 

[ccdantas]

I don't know whether I can answer to that, mainly because I am not certain whether the question is 100% true for "stringy people" to begin with (as well as the other way around-- I mean, it's quite a strong, generalized question).

Meanwhile, you may want to take a look at these:

http://arxiv.org/abs/0705.2222 (Ashtekar's FAQ on LQG; see second part of this paper)

http://arxiv.org/abs/hep-th/0501114 (Loop quantum gravity: an outside view by H. Nicolai et al.)In any case, there is one point that I often think about: how far a "crash" of two schools is involved here. String theorists mostly coming from particle physics; LQG theorists mostly coming from general relativity.

 

[ccdantas]

I hope new generations are more open minded and the "string wars" something of the past. I mean, that the younger ones could be wise enough to see possible benefits of certain techniques from both schools/approaches and amplify their vision towards a theory of quantum gravity.

 

[tom.stoer]

Thanks for the hint - I already know both papers :-)

The first one is rather helpful in order to understand the main open topics in LQG - nevertheless it's a LQG perspective. I mean all open issues are somehow technical and Ashtekar is very optimistic that they can be solved. I don't think that this is really the reason why you distrust the whole approach.

The second one has been answered by Thiemann: http://arxiv.org/abs/hep-th/0608210 (Loop Quantum Gravity: An Inside View). Unfortunately I do not know if there is a response from Nicolai. Thiemann claims that most technical problems mentioned by Nicolai are solved or some progress is made at least.

Nevertheless - thanks for the reminder; I will study the papers carefully a second time.

 

[Haelfix]

The string wars thing is old and boring and this post is just going to bait yet another rehash, with more or less laymen or nonspecialists (very few LQG or String theorist are active here) offering opinions about the merits. I suggest you look back a couple years ago for countless posts on the internet/usenets for the various arguments or pseudo arguments involved.

Distler/Motl/CosmicVariance/Notevenwrong/Asymptotia/physics.research and so forth. The scientific content was actually minimal and the noise/confusion extreme outside of a few back and forths on Distlers blog where there was actual specialists from both sides present, so good luck.

 

[Civilized]

The string wars thing is old and boring and this post is just going to bait yet another rehash...Distler/Motl/CosmicVariance/Notevenwrong/Asymptotia/physics.research and so forth.

I think that Motl/Woit are both far too extreme in their positions to have any constructive dialog. And constructive dialog is what will need to happen to mend these fractures in the theoretical physics communities.

I hope new generations are more open minded and the "string wars" something of the past.

I agree, and I think that in such a mathematical science we should be able to come to more of a consensus about how funding is allocated to the various branches of research; there may not be new experimental input for a long time.

with more or less laymen or nonspecialists (very few LQG or String theorist are active here) offering opinions about the merits.

For better or worst most specialists are too busy working on their speciality to participate in these kinds of discussions. But I don't think that demerits the discussion, since the "string wars" is mostly fought on the battleground of public opinion, and as goes public opinion so goes to some extent scientific funding.

For example, I don't know whether this is true, but since Lubos Motl left Harvard around the same time as Woit's and Smolin's books appeared, I have a theory that he was "let go" (failed to get tenure) in part because it was a particularly disfashionable time to be doing string theory, and that this is what fuels the anti-lqg comments on his blog.

Another way to see the ongoing relevance of the string wars is by looking at the comments that are left by laymen on the articles on the various websites that aggregate technology and science news. Articles about string theory still cause heated debates, the laymen are carrying on the war. Even the TV show "Big Bang Theory", which is as close as most folks come to modern physics, portrays (circa 2009) the strings vs loops debate as sufficient to destroy a romantic relationship (haha, "what will we raise the children to believe?)

The point is that public opinion matters, this is why the NSF funded the production of "The Elegant Universe" TV special in the first place. And right now, public opinion is mostly negative towards string theory, and I am worried that there is a lot of doubt and distrust of theoretical physics in general, and if people are looking down on theoretical physicists instead of looking up, then the world has its values system upside-down and that's dangerous.

Having so far argued only for the existence of this thread, which I hope will be pleasant and specific, in my next post I will raise some answers to the bold question in the OP.

 

[Max™]

I'm a fan of the LQ side due to the importance of GR in it's formulation.

I love the mathematical aesthetics of string theory, it is intoxicating.

I can fully understand why people wouldn't want to leave the conformting grips of string theory.

It is so easy to get tangled up in there, so many questions, I get the impression that these people sleep on equations in dorm rooms. So much beautiful math, and it tantalizingly tries to connect to reality.

I'm trying to write something which will be a mix from LQC and Stringy Models pushing a quantized GR with extended temporal interaction.

We're all young, we should be asking new question, and working on these problems on our own if need be.

Fighting just helps people who don't want things to change.

We're all on the same side, the side that seeks to understand all things.

 

[Max™]

The point is that public opinion matters, this is why the NSF funded the production of The Elegant Universe" TV special in the first place. And right now, public opinion is mostly negative towards string theory, and I am worried that there is a lot of doubt and distrust of theoretical physics in general, and if people are looking down on theoretical physicists instead of looking up, then the world has its values system upside-down and that's dangerous.

Non Stringy Person here, offering an honest truce so all sides can understand this.

 

[marcus]

Hi,

I know a couple of arguments why the loopy guys don't like string theory (perturbative quantization, background dependence, too many statements w/o proof, mysterious M theory, ...)

But can anybody tell me why stringy people don't like loop quantum gravity?

I mean serious arguments, not something like "Witten doesn't like it, either" or "string theory is the only game in trown". Why is the string community convinced that LQG is just wrong? What are the physical or mathematical reasons?

Thanks
Tom

This is a constructive post and could be a useful thread especially if the question in bold is interpreted broadly as not limited to string folks but very generally "what do you think are the weak points in the LQG program?" and can you point out any obstacles to progress that you think are insurmountable?

People in the LQG research community are sometimes self-critical and you get internal discussion of what are the most serious problems. We could try to gather some links to that "insider" crit as well.

No need for hostile stuff or ad homs heaping scorn on fellow researchers or defensiveness or handwave dismissal obviously. that wasn't what Tom's opener post invited. Of course not that stuff!

Personally I've found serious critique of LQG helpful, especially if really well informed. So I'd be happy if this thread could blossom into that. I might not be much of a contributor but I'd be an interested reader!

 

[Haelfix]

Sigh, fine. I'll put my 2 cents in for what its worth.

The most obvious reason many HEP people aren't interested in LQG is b/c for a long time it was just about gravity. No standard model, no matter. This isn't just a little problem to be left for another day, in many ways its the whole shebang. The feeling is that even if LQG (or any other theory of pure quantum gravity) was successful, they will have found a mathematical model that is at best only a horribly simplified version of the real world, b/c in the real world there is also matter.

Technically (and this is a theorem), at high energies there is no decoupling limit where you can decouple gravity from matter degrees of freedom. Even if you find a nonperturbative finite solution of quantized Einstein Hilbert gravity, there is absolutely nothing that guarentees that any future unknown interaction term(s) does not spoil the nice properties you found as you no longer live in the same universality class.

This isn't strictly a statement about renormalizability vs nonrenormalizability, but the effects are the same. In order to make a prediction about actual experiments in the QG regime, you would need to know (in addition to your gravity solution) all the physics between the electroweak scale and the Planck scale with great accuracy.

Conversely, in this sort of scenario the knowledge of how pure gravity works does not in principle shed any light whatsoever on what's allowed or not allowed in the matter sector and so can't be used to help model builders in their search for beyond the standard model physics.

 

[tom.stoer]

@Marcus: thanks for your your support :-)

@Haelfix: it was definately not the intention to re-start something like the well-known Woit-Motl-... discussions. Waste of time!

Regarding your last statement: the main reason seems to be that loop quantum gravity is only about quantum gravity :-) Yes, that's the limitation of the approach; it is not the intention to develop a ToE. But LQG is - as far as I know - consistent with almost all matter contents (electromagnetic fields and fermions have been investigated; I remember one statement regarding SUGRA).

In general that's a strange argument! Ordinary quantum mechanics does not say a single word about gravity, nevertheless even physicists focussed on gravity take it seriously. So such a limitation does not kill an idea from the very beginning.

Let me clarify my intention: as usual the inside view is mainly focussed on "technical details" (well-defined Hamiltonian etc.). If the loopy guys are able to figure this out, this will not change the way the string community thinks about the whole research program, I bet. So there may be an outside view which criticizes the whole approach - not because of technical problems but because of physical reasons.

That's what I am interested in.

Of course Nicolai's paper could be a good starting point.

 

[MTd2]

For example, I don't know whether this is true, but since Lubos Motl left Harvard around the same time as Woit's and Smolin's books appeared, I have a theory that he was "let go" (failed to get tenure) in part because it was a particularly disfashionable time to be doing string theory, and that this is what fuels the anti-lqg comments on his blog.

Civilized, first of all, excuse me for my behavior that other day towards you.

Secondly, the man went out not really because of the "string wars"... But because of certain "politcialy correct" stuff not related to physics.

 

[Haelfix]

I don't think you understand. LQG or any other pure QG theory may or may not be consistent with adding some arbitrary matter term, one can always do that, but that's not the point.

The point is you cannot say anything about what the resulting theory actually *is* without knowing the full details of all the matter terms and then resolving.

This is a bit subtle, and its hard to say in words. Its a bit like the QCD case, but upside down.

Imagine you happen to live a regime where pure QCD was applicable in a world with only QCD and nothing else, and you had no idea about the *low* energy world and were interested in finding that out. One day, a prophet miraculously handed you a solution of gluon dynamics at some scale that he happened to have solved on his mountain. The problem is you don't know anything about quarks. How many of them there were, and what their nature was.

Absent that knowledge, even though you think you understand the strong force, you still do not have any idea about real QCD. Your predictions would utterly fail an order or two of magnitude into the IR from wherever you started. Now let's say that someone handed you an observation of the top and bottom quarks. You would develop a theory that would work for awhile, but soon enough it would start going haywire again. Its important to note that its not just the new quark terms that are appearing that messes things up, but also the very physics of the gluons themselves are changing in some complicated function that depends on the other interactions that are present and the energy scale being probed. All of a sudden, you would start doubting the very foundation of the gluon dynamics that the prophet gave you in the first place (amusingly in this case: it might morph from a theory of particles to a theory of strings and fluxtubes)

In other words, you cannot solve for these things seperatedly (say solve for the quarks, and then solve for the gluons and then add them together), its much more complicated than that b/c they feedback into each other in extremely complicated ways. Even today, with almost unlimited nuclear experimentation, we still have no idea what real QCD is in the IR.

Now in the gravity case, this is almost infinitely worse, b/c its not just quarks but literally *everything* including physics we might not have even imagined yet. Everything *must* couple to gravity.

 

[humanino]

with almost unlimited nuclear experimentation, we still have no idea what real QCD is in the IR

You just took my job away.

 

[Civilized]

In as much as this thread is a brainstorming effort, I will offer my thoughts in "no particular order, one at a time" so that I don't get overwhelmed trying to order them. Also, even though I do condensed matter I also attend the weekly seminar on particles/strings at my university and so as much as possible I will try to share the opinions I've gleaned off of true string/particle theorists.

(*) LQG does not connect well enough to the rest of modern physics.

One of the things about putting in the extra work to get an article through peer review is that the referees will force you to reference other published articles. This has the side effect of making a researcher spend a good deal of their time connecting their ideas with what other people are doing or have done, even if said researcher does not like doing so and thinks it unnecessary, and has to stretch the applicability of the reference because their idea are so "out there." And so we get some genuine references along with a large number of "BS references" that are only put into satisfy referees.

Sounds like a bunch of BS, right (science in the sense of little "s") ? But guess what, the time-honored journal policies are wiser than any of us who find this exercise pointless, since in the long term this leads to a fully connected network of literature where the truly important connections are highlighted to future researchers and the BS references, if they don't ever pan out in future developments, are just forgotten.

In comparison the LQG community exists almost on a totally separate subnetwork, highly connected within itself, but barely connected to the larger network of physics as a whole. I'm not sure if this state of affairs is necessitated by the nature of LQG (is it really that different then everything else?) or if it is just a result from the near total reliance on ArXiV preprints to communicate results. Put another way, most scientists I know would find life much easier if they could plug away at their own ideas without being forced by reviewers to connect these ideas to other peoples work, but these same scientists know that they can't do this or else they will end up outside the mainstream ( a perhaps loaded sounding but I believe still honest reformulation of this thread's title would be "Why is LQG outside the mainstream?").

I often think about: how far a "crash" of two schools is involved here. String theorists mostly coming from particle physics; LQG theorists mostly coming from general relativity.

I think this is very insightful. Of course string theorist do study GR more than almost any other type of physicists, and likewise I'm sure for loop theorists studying QFT, and so I think this comment really speaks to the approaches (rather than the training) of the two schools.

In particular, the LQG core principles of diffeomorphism invariance and background independence bear a striking similarity to the principles that guided Einstein (and Hilbert) to develop GR. The fundamental starting point for LQG is not just that these symmetries exist in nature, but also that they are good symmetries to guide the development of the theory (just as Einstein used general covariance to guide the development of GR).

String theory does not use such strong symmetries as input, instead it posits that relativistic strings exists and then writes down the most simple Lagrangian that respects Lorentz invariance. One of the immediate consequences is that the Lagrangian turns out to be conformally invariant, which is a symmetry that is comparable to diffeomorphism invariance.

In other words, LQG posits an extreme degree of symmetry, while string theory posits an extremely different kind of matter/field content. The former approach is that taken by GR, and the latter is used in particle theory (for example by phenomenologists studying dark matter).

Ultimately I think this is just a difference in approach, not a key reason why "stringy people don't like LQG."

The most obvious reason many HEP people aren't interested in LQG is b/c for a long time it was just about gravity.

Right, even if LQG is not meant to describe the origin of non-gravitational interactions, it will still need to couple to these interactions in a well-defined way. In QFT we have already have a good understanding of how to couple fermions to gauge fields, so that's where the bar is set.

In order to make a prediction about actual experiments in the QG regime, you would need to know (in addition to your gravity solution) all the physics between the electroweak scale and the Planck scale with great accuracy.

This is an even stronger point that I had not heard before, I'd be interested to see how LQG diffuses this criticism.

More later, I for one am really interested in what everyone has to say in this thread.

 

[humanino]

Stringy people like to make things up. It's contrary to the very philosophy of LQG : making sure we need to.

 

[MTd2]

Civilized, did you know that it was recently found that something similar to topological strings were naturally emerging from spin networks?

BTW, you still has not forgave me.

 

[Civilized]

I completely forgive you MTd2, I don't think I organized my thoughts well enough in that thread, now that I see some thoughtful people on this board I am trying to think my posts through more.

did you know that it was recently found that something similar to topological strings were naturally emerging from spin networks?

Do you mean string net condensates (Levin, Wen cond-mat/0407140) ? The work looks interesting, I think I'll read it soon (this subforum seems like a good place to discuss it as well). Of course, even though it involves the word "strings" I believe it is a low-dimensional theory, too low for them to be the quantized relativistic strings of string theory, afaik.

 

[MTd2]

No, civilized, I mean this one:

http://arxiv.org/abs/0905.3627

 

[atyy]

My understanding is that LQG doesn't fit in this philosophy:
1) Einstein gravity is not perturbatively renormalizable, therefore either
2a) gravity is non-perturbatively renormalizable (Asymptotic Safety, CDT)
2b) gravity is emergent (Strings, AdS/CFT, "condensed matter" approaches - the various emergent approaches differ in what else emerges)

But LQG seems to divide the possibilities differently - background independent or not, with background independence being fundamental. Yet LQC, at least in its early days, was not fully background independent. So if LQC is acceptable as an interesting lead, then maybe background independence is not so important after all? Or is LQC not an interesting lead? What is the current situation with respect to LQC and background independence? What is the current situation with respect to LQC and LQG? If background independence is the true dividing line, then what is the flaw in the "either AS or emergence" philosophy? If there is no flaw in the "either AS or emergence" philosophy, then presumably LQG would be like AS - but if so, then why not just research AS?

Of course, this philosophizing may be irrelevant - since Einstein used the wrong philosophy of "general covariance" to get the right theory of general relativity. So maybe background independence is not the true dividing line, but LQG is the correct theory.

 

[suprised]

Ups I didn't mean to ignite another battle, I just answered a question by telling how one of the most prominent and influential particle physicists responded in a discussion.

Point is that it is not so that string physicists "hate" LQG, as far as I can say; it rather seems the other way around, the whole war was started by certain circles to gain more visibility of their field. And indeed, LQG wasn't even on the radar screen for most; it was and I guess, still is, considered a niche field with limited scope. Some of the basic ingredients, like strange quantization procedures that don't even correctly reproduce the harmonic oscillator are considered dubious, and there is to my knowledge even today no convincing proof that LQG does reproduce GR in the long distance limit. LQG seems to be stuck in some kind of "topological phase" and from there is still a large step to be made in order to recover gravity (and the tricks that work in 3d don't apply to 4d).

For these and other reasons this theory does not look compelling and promising to many as of today, certainly it is understood that LQG is work in progress --just like string theory--, and the moment some really convincing breakthroughs would be made, more people would study it. It is simply not so that people "hate" LQG but rather simply don't see a reason to study it; they prefer to do what appears more promising or interesting to them. Until now, as I said, LQG is considered as a side development with some potential (for example in the direction of background independence) but otherwise it is not taken very seriously.

The negative tenor in this usually peaceful cohabitation of theoretical physicists was brought up by fabricating a "controversy" by certain authors of books and reports. If there are negative thoughts on the string physicists side, then because of this spin doctoring and instrumentalization of the general public, as an attempt to compensate for the lack of convincing science. It makes me sad to see the success of this strategy by reading through this forum, where most people do not have sufficient scientific insights in these matters but neverthelss have strong opinions!

 

[Fra]

I mean serious arguments, not something like "Witten doesn't like it, either" or "string theory is the only game in trown". Why is the string community convinced that LQG is just wrong? What are the physical or mathematical reasons?

I personally think that if one really wants to understand the mechanism behind some of this some of the commercial/financial and sociological arguments ARE "serious", in the sense that's it's possibly at least a part of the actual explanation. The competition for financial support of various research strategies unavoidably is a serious point.

In an ideal world I guess everybody could get all the resources they want to do whatever research they want.

But I'm the first to agree that this isn't really very interesting to discuss. This is apparently my impression of the the downside of physics as a proffession.

But it's interesting, that not that many peoples seem seriously interested in discussing strategies without keep referring to the bulk opinion. I've got a feeling that those who are professional physicists to a certain extend have their hands tied, they really can not be too openminded at least officially because then there could be negative effects of the "downside of Science". This is the impression I also got from the personal contacts I've have with those doing string theory professionally. It becomes a compromise.

Anyway given this competition for funding, all this is very expected.

Maybe the "serious" physics arguments aren't really that many, or maybe they are simply subjective anyway. String theorist have their good reasons for their preference, and others have their good reasons for their preferences. Who can judged which has the best arguments?

I think so far (judged from my own non-professional and personal view) neither string theory or LQG (Rovelli style) has convinced me to be worth investing my life in. Maybe the answers is something in between, or something totally different.

Given my relatively infinitesimal experience, I still add fwiw my strong opinions :)

What I like about string theory is that it from a choice of fundamental microstructure and action of reality (string, branes etc) aims to infere all interactions in a unified manner.

What I don't think like is that their is an informational ambigouity in the choice of this action and microstructure (apparently related to the landscape problem). Also it's somewhat ad hoc. If someone would find a more first principle explanation of the CHOICE of strings, and why this is the fundamental action, in a way that yields a navigationg principle in this landscape of their, I would have no problems at all with the extra dimensions and other stuff.

So string theory has a lot of background structure, not only background spaces, but more serious stuff like background logic - it's not that such things can be totally avoided, but the information content of this "background structure" is ignored. In a true inside view approach this doesn't make sense to me.

What I don't like about rovellis LQG (judged from this book) is that his view of diff invarance pretty much goes hand in hand with the pure gravity idea, which doesn't make sense to me since to me I perceived it from my amateruish point of view to the extent he can convey his real ideas that he wants to construct a measurement theory without observers. Or alternatively with only god as an observer. This is what bugs me about the foudnations of rovelli. He tries to construct such a theory while explicitly ignoring some of the fundamental problems of QM, and how concepts like probability, statistics are to make and sense for events that "happen only once" like was mentioned earlier.

So to me LQG also has a lot of background structure, where the information context is left out of the physical interactions, by providing a birds view - a birds view that IMO is not physically justified.

OTOH, if I am so unexperience and ignorant, then I must ask where my confidence comes from. Why hasn't the experts convinced me? I think so far neither string theory nor LQG can claim any superior status, as both are in my very humble and insignificant but still strong opinion still speculative and it's their problem to prove themselves, solve the open problems, suggest new applications that blow us off the chairs.

/Fredrik

 

[tom.stoer]

Thanks fort the replies. I’ll try to summarize some mathematical and/or physical issues leaving asside sociological or financial arguments. I do not say that they are not valid – I only want to stress what may focus is.
[my comments in parenthesis]

GR as it stands is not perturbatively renormalizable. Whereas LQG claims that using a different quantization procedure this problem does not show up, the HEP/string physicists insist on the possibility of perturbative calculations. So the claim is that this is not only a failure of the method but of the whole theory; it is not that a different quantization procedure is needed, but that a different approach (strings) of formulation of interacting "quantum field theories" is required.
[I cannot understand this claim; for me it’s the quantization method that fails, not the whole theory.]

A stronger argument is the fact the quantization methods used are not so straight forward and may be ill-defined. Several new ingredients not well understood in different contexts are used. Let me list a few:
The algebra of constraints is solved step-wise with newly constructed or restricted Hilbert spaces.
The algebra of constraints does not close off-shell. Instead the algebra closes only within a certain (physical) sub-space of the kinematical Hilbert space. Therefore one may lose the control on gauge anomalies.
[I do not know if this has changed with Thiemann's master constraint approach.]
The diffeomorphism constraint is rather obscure. Classically this constraint generates infinitesimal diffeomorphism transformations, but quantum mechanically the infinitesimal transformations and the corresponding operators cease to exist.
The Hamiltonian constraint is not well-defined: it seems to be regulator dependent and has some severe ambiguities due to the very definition of quantum operators, not only due to their ordering.
[I agree; the ambiguities of the Hamiltonian constraint are one major weakness of the theory. One would have to check rather rigorously if this spoils the consistency of the whole approach. One ambiguity, namely the Barbero-Immirzi parameter seems to be quite well understood in the meantime; it corresponds to the theta-angle in QCD.]

There's no physical IR limit. or let’s phrase it differently: there is no proof that LQG has GR as its low-energy limit.
[I agree; that is one major weakness up to now. I have to admit that I haven't studied Rovelli's papers on the graviton propagator; maybe there are some additional insights on that topic.]

Arguments from Haelfix: There is no decoupling limit for gravity and matter degrees of freedom in the UV. Therefore new (currently unknwon) interaction terms could spoil the UV properties of LQG. In order to make a prediction in the QG regime, one would need to know all the physics (quantum gravity plus ordinary matter) between the electroweak scale and the Planck scale.
[It should be clear from the beginning that LQG focuses on gravity w/o any attempt to unify other forces with gravity, so this limitation is well-known. The argument seems to be valid only if we are forced to use a different class of theories (e.g. strings). If we assume that the structure of the matter theory remains valid (besides some additional technicalities like GUT, SUSY etc.), then LQG + matter theory (whatever it is) remains a mathematical well-defined framework.
With ordinary gauge theories LQG should be consistent. For SUSY and SUGRA there are claims that the theory is consistent, too, but I do not know many papers on this subject, so perhaps further investigation is needed.
I agree that if we are forced to consider a different class of theories (e.g. strings) in order to unify all interactions including gravity, then the LQG approach may cease to be a consistent framework for that new theory. It does neither provide any inside, if such a theory is required, nor how it could be constructed. As LQG is formulated today these ideas will come from the matter sector w/o any reference to gravity.
I fully agree that LQG it is incomplete in that sense.]

So there are basically three weaknesses in the LQG approach
- quantization ambiguities, especially in the Hamiltonian constraint
- missing IR limit; GR not recovered in the low energy limit
- no approach towards a unification of gravity with other forces

Tom

 

[Demystifier]

But can anybody tell me why stringy people don't like loop quantum gravity?

I don't think that it is true that stringy people don't like loop quantum gravity, at least not for majority of string people. It would be more correct to say that they are not interested in it. For example, they are also not interested in solid-state physics, but it does not mean that they do not like solid-state physics.

So, why they are not interested in it? Not because they think that it is wrong (most of them do not have a strong opinion regarding its correctness), but because they do not find it very promising in the program of finding the "theory of everything" (i.e., the theory with a power to unify all interactions). In other words, stringy people find loop quantum gravity not ambitious enough for their taste.

 

[ccdantas]

Someone wrote (excuse my lack of proper quoting):

"For better or worst most specialists are too busy working on their speciality to participate in these kinds of discussions."

I wonder how many of them really know about this forum. I know of a very few coming eventually here, but I wonder how interesting it would be if they participated a little more. This would not take "so much" of their time. I can tell it from my own (professional) perspective (although I am not an expert in quantum gravity).

I think there is a moral duty for the professional researcher to spend a small fraction of his/her time in order to share and discuss their research in a more accessible manner. PF is a good instrument for that matter.

 

[tom.stoer]

@Demystifier: I agree that LQG is incomplete in that sense. But I think it provides insights regarding new technical aspects how to quantize classical systems, how to address background independence, how to do non-perturbative claculations, ... Therefore they should not ignore it - but this is something I should write in Marcus' thread :-)

@ccdantas: Perhaps they are discussing it elsewhere: in their offices, on the phone, ... definately NOT here, NOT in "not even wrong", not in "the reference frame", ... The web has been abused too much in the past

 

[marcus]

I don't think that it is true that stringy people don't like loop quantum gravity, at least not for majority of string people. It would be more correct to say that they are not interested in it. For example, they are also not interested in solid-state physics, but it does not mean that they do not like solid-state physics.

So, why they are not interested in it? Not because they think that it is wrong (most of them do not have a strong opinion regarding its correctness), but because they do not find it very promising in the program of finding the "theory of everything" (i.e., the theory with a power to unify all interactions). In other words, stringy people find loop quantum gravity not ambitious enough for their taste.

I have to compliment this post. It seems perceptive and reasonable--always hard to confirm broad statistical statements ("majority of string people") based on personal impressions, without some objective stats--but I really suspect you are right. Not that LQG is unambitious, but that a majority of stringfolks and their adherents think of it as such.

On the other hand some stringfolks seem to be drawn by recent results in LQG and allied approaches. I would say it is the highly visible exceptions that stand out, and are potentially influential.
Per Horava is a recent example. I would not suggest for a moment that he thinks the various approaches to 4D QG are right. But Horava and his followers cite non-string QG results which the Horava approach duplicates.

We see examples of a movement of people out of conventional extra-dimension string, as if tempted by the recent spate of results in nonstring 4D QG---people shifting attention to such things as 4D Sugra, Horava, Asymptotic Safe gravity (UV fixed point),...

I have to go but will get back later this morning.
Anyway I would like to agree with what you say about the state of mind of bulk rank-and-file of ordinary string researchers.

 

[ccdantas]

Perhaps they are discussing it elsewhere: in their offices, on the phone, ... definately NOT here, NOT in "not even wrong", not in "the reference frame", ... The web has been abused too much in the past

You do not understand. I do not mean discussing their research technicalities and progress over blogs and forums, I have never discussed my own research using the internet (namely, webs, blogs, forums) with my collaborators, but only in our offices or by emails/telephone, evidently. I am talking about science outreach.

Also, I do not mean they should be disussing over "abused" blogs; they can have their own blogs for that matter; or they can use PF, which I believe is well moderated (I could be in error, though).

 

[ccdantas]

Wouldn't it be nice to have some "ask a quantum gravity theorist"/ "ask a string theorist" section here? Or would it be a bad idea??

I also think Demystifier has a point here. And again I wonder whether this issue has something to do with the different "origin schools" (string theory -- particle physics; quantum gravity -- GR), as I posted previously.

 

[marcus]

Christine, a thread like this is interesting because it gives us a sampling of what the current stereotypes are. But there is no permanent substance.
There are always some string hangers-on who express resentment of LQG. It is good to give a listen now and then, but we have better things to do than argue with them.

There is too much that is exciting going on in LQG and allied approaches for me to want to waste even half an hour engaged with negative poorly-informed bickering.

 

[Demystifier]

@Demystifier: I agree that LQG is incomplete in that sense. But I think it provides insights regarding new technical aspects how to quantize classical systems, how to address background independence, how to do non-perturbative claculations, ... Therefore they should not ignore it - but this is something I should write in Marcus' thread :-)

I certainly agree with that. If someone would convincingly show that these methods are usefull in string theory as well (in fact, I think that some not very successfull attempts in that direction already exist), I am sure that stringy people would start to use it.

 

[ccdantas]

There is too much that is exciting going on in LQG and allied approaches for me to want to waste even half an hour engaged with negative poorly-informed bickering.

?

Sorry, I do not understand you. Have you really read my previous posts? Did I ever suggest that people wasted their time with " negative poorly-informed bickering"? I was just suggesting that researchers should do a little more outreach activities, that is all.

Oh, well. It must be a language problem or something. It appears that I always have to explain myself again and again about simple statements, I am often misunderstood. Oh well. Good bye.

 

[George Jones]

Wouldn't it be nice to have some "ask a quantum gravity theorist"/ "ask a string theorist" section here? Or would it be a bad idea?? :bugeye

This is exactly one of the things for which Physics Forums is meant: questions by laypersons, undergrads, and grad students answered by knowledgeable people. For me, it's a disappointment that more of this doesn't happen in the Beyond the Standard Model Forum (BSM), because it does happen in the other forums here, even without special sections.

Christine, a thread like this is interesting because it gives us a sampling of what the current stereotypes are. But there is no permanent substance.
There are always some string hangers-on who express resentment of LQG. It is good to give a listen now and then, but we have better things to do than argue with them.

There is too much that is exciting going on in LQG and allied approaches for me to want to waste even half an hour engaged with negative poorly-informed bickering.

I don't see the relevance of this to Christine's comment. If questions about about either LQG or string theory are not welcome in BSM, then BSM should be shut down.

Criticism about any approach should be allowed, but Faction A should not be allowed to overwhelm and derail a useful thread by Faction B. A balance has to be struck, and a reasonable level of civility should be maintained.

I would like to see more string theory posts and discussion. This should not be read as "I would like to see fewer posts about loop quantum gravity and other approaches."! Far from it.

Shutting down BSM has been discussed by the Mentors in the past, as BSM often causes Mentors more grief than it's worth.

Oh, well. It must be a language problem or something. It appears that I always have to explain myself again and again about simple statements, I am often misunderstood. Oh well. Good bye.

I understood what you wrote, and I think other people did as well, as what you wrote in post #29 was quite clear.

 

[MTd2]

This kind of fierce disputes happen because phyisics beyond the standard is almost like a religion in the neolithic: everything goes, as long as it fits reality as we know it right now, but unless we lived in a Star Trek level of technology, we wouldn't be able to test any of them...

People should face that physics beyond the standard model theories is mostly mathematics based in physics. It is much more likely that they eventualy will be broven as right as when the orbits were considered the result of the drag of vortexes of ether than when anti particles were found as solutions of the dirac equations because, the former, like strings and LQG, have just too many assumptions of things never seen. That doesn't mean these are all useless, because, even in the simple example of ehter, it inspired many scientists to keep the development of much of the mathematics of fluid dynamics.

 

[Fra]

In any case, there is one point that I often think about: how far a "crash" of two schools is involved here. String theorists mostly coming from particle physics; LQG theorists mostly coming from general relativity.

I too think this is a very important point. In general I think there are different strategies to formulating and solving problems, that are related to once choice of philosophy of science as well.

Due to my own angle, this is something that usually strikes me as I've read papers from various researchers. There is a clear difference in reasoning that somehow constitutes the context where problems are formulated, and strategies for solving then are justified.

I think this relates to what Demystifier called different levels of ambition. I'm not sure there is necessarily an objective level of ambition, but for sure I think that the differences in reasoning and formulating the problems explains some of the disagreements.

From my perspective, the reasoning outline by LQG but also the one outlined by string theory, simply doesn't aim to answer My questions. So to me it's simple, I don't prefer the respective strategy for the I think quite rational reason that it doesn't seem to be the answer to a question I asked.

That said, I find FRAGMENTS of reasoning on both camps very interesting. This is why I like this forum. I have to say I've gained a lot of insight by trying to undertand how very different various people think about these matters. To me these differenes are not problems, instead they are food for thought, because no matter how much I disagree with my enemy, there is usually still a different logic of the other camp, and it's interesting to learn about it.

IMHO, rovelli's logic and treatment of probability doesn't appear that thoughtful as he explicitly avoids these questions, of physical basis of probability. What I really have a hard time to understand, is someone like Rovelli can ignore such an important point, and then invest so much on that foundation? He seems well aware of it, but for some reason he assigns is little physical significance. I find this strange. And given Rovelli's excellent initial reasoning in the RQM paper, this was both dissapointing and surprising. From my point of view, this was a broken line of reasoning on rovellis part.

I think there would be a way to continue his reasoning, and not ignoring this problem in a way that is more in line with the evolving law that smoling talks about.

All this is just talk. But I think this general like of reasoning, and shool of thought is really prior to the "mathematical problems". A mathematical problem exists only within a given framework and if the discussion is on the choice of framework, and as long as this choice is under debate, the problems at hand are more that just mathematics. Once you have formulated a mathematical prolblem, it's not a physical problem anyway IMHO. Then you have already made most of hte physical choices.

/Fredrik

 

[marcus]

Sorry, I do not understand you. Have you really read my previous posts? .

I must apologize! Looking back at my post I see that it seems as if I objected to your idea in post #29. This was not intended.

 

[tom.stoer]

I agree that it would be very helpful for us if there would ba a sound discussion of string- with loop-oriented insiders in this forum (or at a different place in the web). Perhaps the meeting in Marcus' new thread is a good starting point. In addition I would really like to see something like the "outside-view" - "inside-view" discussion Nicolai and Thieman had on LQG.

Every couple of years it's time to put the most relevant topics and open issues on the table and try to collect opinions from a different "school" or different perspective.

Then I agree that different perspectives dio not only provide different approaches and insights but additional technical issues as well. The measurment-problem or the time-problem is certtainly a conceptual one in all QG approaches, but the correct Hamiltonian of LQG is very specific to LQG. In any discussion those issues should be kept seperately.

 

[Fra]

The measurment-problem or the time-problem is certtainly a conceptual one in all QG approaches, but the correct Hamiltonian of LQG is very specific to LQG. In any discussion those issues should be kept seperately.

Perhaps in some ways of analysing this, the separation into separate discussions differ too :)

Now I don't represent any major program at all, but from my perspective the various problems of measurement, time and establishing state spaces and evolution operators are related, I don't see them as cleanly separable.

So different schools of thought (not just LQG and string), might not always agree on the separation of subquestions. I personally question the physical (observable) basis of these constraints, and this is I think related although not directly to the measurement and time problems.

To me the construction of physically justified (construtcible) measures/observables, is one of the keys. And I don't understand how that process can separate to for example the understanding of time. But then I don't share rovelli's logic. I think there is confusion between "timless" notions as in the objectively of this timeless notion. Most objectivity seems to be attached to realist, imaginary constructs, that are not subject to scientific inquiry. Some conceptual framework that is assume to just be.

I think it's true that there is no objective time, but this does IMHO NOT imply that there exists a objective notion of "timelessness". Rovelli's logic doesn't attach a physical status to the timeless information. In other words, it's a realist type of information, needed, but that is not subject to measurement processes. I find this to be inconsistent reasoning which is why I don't prefer it.

/Fredrik

 

[tom.stoer]

I don't say that the problem of the Hamiltonian and the problem of time are not related. All what I want to say is (and perhaps this was not clear from my post) that the specific technical details of the LQG Hamiltonian (quantization-, regularization-and ordering-ambiguities) are essential topics for the LQG approach - they don't affect in any way other approaches (as far as we can see). Another example could be string theory: if the finiteness of the perturbation series for one specific string model cannot be proven this affects only string theory - nothing else.

 

[Fra]

I don't say that the problem of the Hamiltonian and the problem of time are not related. All what I want to say is (and perhaps this was not clear from my post) that the specific technical details of the LQG Hamiltonian (quantization-, regularization-and ordering-ambiguities) are essential topics for the LQG approach - they don't affect in any way other approaches (as far as we can see). Another example could be string theory: if the finiteness of the perturbation series for one specific string model cannot be proven this affects only string theory - nothing else.

I guess what you say is that since the choice of question posed, are part of the various programs, it is not straightforward to draw implications of any answers to other programs where the questions asked are somewhat different. This is exactly in line with what I said too.

This is exactly why I think that before we invest in answering a question, it might be a sensible to first discuss the construction and justification of the question itself (before we can answer it). In this respect I feel that some reasonings, ignore what should be important questions, and I see that as very speculative. The risk is that you spend 40 years trying to answer the wrong question, and as per the logic above, the answer to one question is not easily decoded into answering a almost logically unrelated question from another program. That's why I can not overlook these details. I tend to think they might be very important. This is why I first of all evaluate the framework and the way the basic problem is formulated. Here I do not like the way Rovelli reasons. Since I don't share the framework from which he phrases the technical problems of LQG, then the technical details somehow becomes deattached to my reality.

The first time I started reading his book, I read it in a very positive way, and interpreted it to it's advantage, but I noticed that the picture I made for myself - regarding the physical meaning and interpretation of the spin networks (I thought of them first as encoding the observers microstructure) simply wasn't what rovelli was doing.

I have similar views on string theory, where a string ca be constructed in a high complexity limite as the simplest possible measure. But in that interpretation there is no external space the string is embedded in, instead the space is emergent as relations between different strings. i still think if string theory ever makes it out of mathematical toyery something in this direction is the way I can make sense of it. But if that is true, strings are not fundamental, and probably the paramters of the string would be understood from an evolutionary point and there should be no landspace problem.

Although I can relate to both approaches, my different angle makes my reasoning so different that the wayt of reasoning typically seen in those papers, even more so the plain technical papers focusing on isolated mathematical problemes withing the program, simply are not motivated for me.

If LQG or string theory will be part of the future big theory, then I think there certainly are some similar issues that need to be addressed. But I want to start at what is for me, the right end.

I guess I misinterpreted you before.

/Fredrik

 

[Demystifier]

I think it's true that there is no objective time

Do you also think that there is no objective space? Or do you think that the difference between time and space is much more than a difference in the sign of the metric?

Anyway, since you like to see how other people think, you might find this interesting:
http://xxx.lanl.gov/abs/0905.0538 [to appear in Phys. Lett. B]

 

[Fra]

Do you also think that there is no objective space?

That's right. I don't see the physical basis for objective space either.

Or do you think that the difference between time and space is much more than a difference in the sign of the metric?

Yes it's a bigger difference. To me the two questions you ask are not XOR, I say Yes on both.

In my view, time is related to evolution of information. Somehow time is simply a distinguished direction in the "data processing" hierarchy of evolving memory records. But the distingusihed direction is observer dependent, but I think not in a way that allows a timeless transformation. The "timeless structures" rovelli uses are emergent in my view.

My idea (under development) is that the first glance "inconsistency" that is the result of denying objective time and space, are exactly where interactions are encoded and classified, and moreoever the "evolving perspective" is the supposed key to unification. The rational reasoning behind that is simple; actions of each subsystem are depending only on the local information, thus any incompleteness does result in a different action. The problem with this is that the theory is always in motion, you can not carve it in stone. That's where thus microinformation exchange connects to the cosmological scale and the universe at large. I think this connection is there from square one, and I dno't know to pretend it's not.

Anyway, since you like to see how other people think, you might find this interesting:
http://xxx.lanl.gov/abs/0905.0538 [to appear in Phys. Lett. B]

Thanks, I'll check that later!

/Fredrik

 

[Fra]

My idea (under development) is that the first glance "inconsistency" that is the result of denying objective time and space, are exactly where interactions are encoded and classified, and moreoever the "evolving perspective" is the supposed key to unification.

This is clearly similar to the idea behind gauge symmetry, but with the major difference that there is no objective/fixed/universal gauge symmetry that we can use for reasoing without the normal constraints of measurement. It's all about perspectives and there is no master perspective, and thus no universal action.

In short the usually symmetry arguements, as a means of reasoing, and inferring interactions from a master symmetry is still there, BUT, this master symmetry is no master symmetry. It is instead an evolving structure, but there are not metalaw governing this, it's just a sea of opinons of how this evolves, which is exactly what drives interactions and evolution. To understand how that evolves, is I think also the key to unification.

From this I think it's easy to see why I for example like parts of string theory, but also why I really don't like other parts.

Neither string theory nor LQG implements, or even acknowledges these issues, but there are components all over the place. Smolin in his arguments on evolving law does seem to acknowledge at least a part of the problem, which is why I like him, although the solution isn't yet there. But relative to the major programs at least he is IMHO sniffing in the right direction from where we are.

/Fredrik

 

[tom.stoer]

I agree to most what you are saying.

... where a string ca be constructed in a high complexity limite as the simplest possible measure. But in that interpretation there is no external space the string is embedded in, instead the space is emergent as relations between different strings

Is there an article on this idea somewhere?

There is another issue regarding LQG that might show up in string theory as well (it could be a kind of pattern universal for quantum gravity): Whenever you try to develop such a theory your starting point is a classical theory with certain classical structures (e.g. symmetries). Having defined you quantum theory it seems that your classical structures have changed or even dissappeared. In LQG what dissappears are the manifold and the infinitesimal diffeomorphisms. The problem is that these structure (especially the latter one) are at the very core of the theory! The derivation relies on a structure that does not exist in the final theory! In string theory the same pattern might occur after having defined M-theory in a fully background idependent way.

The ultimate building says that its fundaments do not exist.

So my conclusion is that the naive way of quantizing a classical theory may no longer be valid, but one has to do it the other way round: start from a well-defined quantum theory w/o making any reference to a "classical theory". Unfortunately (as far as I know) such an approach does not exist. No quantization w/o starting from a classical theory is know.

 

[Fra]

Demystifier, I printed your paper yesterday but I haven't gotten around to actually read it yet, but I'll let you know when I have.

Is there an article on this idea somewhere?

If you wonder if *I* have written an article on what I mean with this then, No. But if everything goes as intended, at some point there will be. Also the technical context can not be justified in isolation from the larger picture.

I apologize in advance but here is a vauge rambling on this... just to give a hitn, that's all it's meant. Because I think we're talking about approaches and ways of reasoning here, and comparing programs:

I mentioned this as an illustration that I can see grains of hope in for example string theory, even though I reason completely different.

The very basic idea is that I aim to reconstruct the continuum. Going to back to square one, starting from distinguishable discrete events, characterizing an observer inside view, the continuum has IMHO not yet a physical justification. In particular continuum measures, like probability measures and thus probability spaces.

In this reconstruction, follows together a reconstruction of the continuum mathematics, probability theory (from combinatorics to continuum), and the idea is self-organising measure-complexes, that in my mind are the prototypes of "observers" - which ultimately of course is to explain matter. Ie. matter content of the universe is simple it's population of "observer complexes". The physical action of the matter systems, are inferred from the information processing properties of the observer complexs, which in turn are justified as a result of evolution. The rules for selection are contained here, and even the rules of selection are explained as the only constructive ones. Mass/Energy are related to the "complexity" of the observers. Ie the number of distinguishable internal states - basically memory size.

The simplest (lowest complexity) continuum-like measure might be a string like thing. And the idea is that the strings "mass" are simply distinguishable events, and an distinguihable ordering of the events can emerge as a resolution of fitness selection, this defines let's call it the string position. The size of the string would then somehow be observer dependent. For example one can imagine one string observing another string, and interesting interactions will take place. It might well be that a string observing another string, will end up seeing a membrane instead.

I'm not prepared to explain this now though. For simplicty let's just call it a wild idea I've had for a while, that has developed as My attempt to make any sense of string theory.

My reasoning is strictly an imagine "inside view", where the measures and operations are evolving as a result of the measure-complexes interacts with the environment. Starting from the simplest possible measure-complex, a boolean bit, and then scaling up the complexity, at some point the sea of distinguishable states will be forced to either disintegrate or form structures in the index space. A one dimensional distinguishability-index, can be more unstable than a two-dimensional index, when you understand how the existence of theose structures as "information processing structures" sits in the interaction with an unknown environment.

So in my view there is something that might with some stretch of imagination can come close to a string, but there is no such thing as a fundamental continuum string. Instead the string is composed of discrete degrees of freedom, that mathematically "looks like string" if you don't look close enough.

I picture these processes as a game. As a player in that game I can only try to form my own views of the effective rules, and confirm them by my own success. I think the logic is the same for elementary particles.

So I start with no space. I just start with a distinguishability notion, which if you prefer is 1-D. This structure is uncertain - this defines a direction of dissipation - time. But as this structure is subject to an environment that continously challanges it's very consistency, things will happen to this structure - it evolves.

That's just a hint, if that makes not sense just forget it, it is not meant to be conveyed yet.

But OTOH, it is equally possible to make an interpretation that looks like spin networks to this. Then the spin network could represent the microstructure of the measure-complex, and one could "imagine" two spin networks observing each other. And since a finite spin-network has a finite encoding capacity, evolution will select the fittest one, which sometimes may or may not yield string-like things. I think the action of a spin network as decomposed in the action coming from the inside acting on the environment as one thing, this contains random elements but depends only on the spin network itself. But the reaction from the environement, is the feedback that is principally undecidable and that is the cause of evolution and selection. A system can not maintain an inconsistency against a massive environment indefinitely. It's this destabilisation process I aim to understand, and how it's predicts the actions.

But all this is my, looking at both these programs foundations from a totally different view. I presume a try LQG theorist or a true string theorist would not acknowledge any of this.

Most the technical parts I've done so far are combinatorics, and expressions for actions and information measures, and these mathematical expressions are "solutions" to optimation problems. So a particle, would in my world, represent a measure-complex, who is justified as beeing a solution to a particular optimation problem (data compression effiency).

Another way of putting it, to me physical interactions are reduce to compressed data systems interacting and competing for control, of outcoding the other one, and conquer his memory.

In that space are simply a preferred structure that has formed in the memory structure. The bits of space are simply distinguishable events, no more no less. The fact that different structures encodes different sometimes inconsistent structures, implies that there will be an interaction force between them. (just like in gauge theory)

But there is no objective setting to describe this interaction (here I strongly deviate from the gague interaction logic), instead the incompletness and undecidability here imples a simple uncertainty. This is also in my view, the origin of quantum mechanics.

I do not even think in terms of "classical system" and "quantum". I think there is a common framework, where both of them are natural extremes.

/Fredrik

 

[Fra]

Anyway, since you like to see how other people think, you might find this interesting:
http://xxx.lanl.gov/abs/0905.0538 [to appear in Phys. Lett. B]

Hrvoje, I looked at your paper and what I like about several of your papers is that they are usually fairly clearly written and almost a big pedagogical. I don't think I said that before, but that struck med before with other papers of yours!

But from your paper it seems fairly clear that you have a very different attitude and way of reasoning than I do. When I read that papers the first things that point out to me, are not technical, they are your choice of scientific approach to this entire thing.

Just for fun, I'll comment briefly on the things your wirte that first hits me.

- Your blockuniverse view

This is in direct contrast to my inside view. In short think the root of how it is possible that we see this so differently, lies in our view of science. To me, scientific inquiry are closely related to measurements, and information is also depending on measurements.

I simply don't see the physical basis of the information in the universe implicit in the block universe idea. Who is possessing, and acquiring this information? I object to this abstraction since you seem IMHO to use abstractions that I fail to see how to ever realize in a physical subsystem.

This relates to the philosophy of science in the sense that, sure we consider ourself theorists, but still to me, every element in the model must be at least possibly realisable and testable in a real physical implementation. Otherwise for me it somehow falls outside of science.

Information always has a context, and placeholder. The information in a computer for example can not be maintained if the memory hardware is removed.

If you talk about the wavefunction of the entire universe, I simply doesn't understand what that is, in the context of science. This birds view or gods view, is exactly what I oppose to.

To me the only birds view that can be realized, when one observer, observes the only thing it can observe - it's environment, and tries to understnad other subsystems as part of his environment, and in that perspective the first observer has a constrained sort of external view of the other observers. But this view, is not an birds view existing in a matematical universe, it is a highly physical view, constrained by the physical universee as everything else.

Since we are looking to extend QM into QG, it is not obvious that the meaning of wavefunction remains the same, so here I'll take wavefunciton to be a metaphor for the "microstate of the observers microstrucutre", or simply the INSIDE information an observer has about it's own information, that is encoded in the observers SELF.

In this sense, to me it's obvious that information is something that the wavefunction AND the microstructure itself (the physical placeholder of the wavefunction - the memory hardware) is constantly challanged and evolving. Time is then a parameterisation of this flow.

The problem with unitary evolution is that - here I speak from my view - it applies only to the EXPECTED evolution. The actual evolution contains reactions from the environment, and wether they are as per expectations or not depends on how well equilibrated the observer is in it's environment (ie how well evolved it is).

The paradox is is when one things that the actual evolution must conincide with the expected one. The actual evolution is not necessarily a simple unitary one. However, there can still be a sound logic for the deformation of the placeholder for hte wavefunction so that the unitarity is sort of always true in the differential sense.

So to me, the picture you dry to draw, is painted in a scientific context (birds view) that does not have a physical justification IMO. That in short, is how I see your reasoning :) But it's nevertheless interesting to try to understand your reasoning, because there is no doubt that you have your own rational arguments to justfy it.

But let me guess that you have a view somewhat similar to Tegemark, which pretty much places the picture in a mathematical universe context? Ie. an eternal context that exists independent of the physical universe? Then your ideas appear rational also to me.

But I think the Tegemark style of replacing a physical scientific context for a mathematical universe is taken us away from good science, rather than getting closer? The reason why I think so, is because all history suggest that "scientific information" is changing all the time, rather than "accumulating". Sometimes we have revolutions that not only update the information relative to a framework, but sometimes not state change required by new data can maintain the integrity of the framework, and the framework itself breaks down.

That's the interesting situation when the trick is to survive a framework breakdown. One can not afford to start from scratch. Such situations are real, and occur in nature, not just biology but I think also in physics. For example, an observer can evolve as a reusult from interactions, and this is to me the one and same logic as the previously mentioned.

The mathematical universe or block universe idea instead picutres a god domain, where the truth is written in stone. But the question is, if the scientific method is the process by which an frog like us, are probing for this information, then strange questions appears. How can there be interaction between an inside observer, and this gods-domain?

Block universe, mathematical universe, universal symmetries, timeless eternal law, they all have this something in common which I object to.

/Fredrik

 

[Fra]

So my conclusion is that the naive way of quantizing a classical theory may no longer be valid, but one has to do it the other way round: start from a well-defined quantum theory w/o making any reference to a "classical theory". Unfortunately (as far as I know) such an approach does not exist. No quantization w/o starting from a classical theory is know.

I agree with your desire here. To start with a classical theory, and then add some - more or less - ambigous quantization procedure is not the satisfactory level of understanding I am content with.

I would label what I am trying to start with as a sort of intrinsic measurement theory, but where the theory itself, is not just a theory sitting outside the system describing it. This kind of gods view is the root of many problems. Instead, the theory itself is pretty much encoded in the physical systems. So the theory evolves as the observers does.

I think of this as a new framework, from which quantum actions will follow. It's known from normal game theory that quantum games are more efficient, and somewhat similar a system implementing quantum logic is more fit (though it depends on the environment) than a classical system.

The emergence of various logics, is something I'm working on, but I believe that it at least partially is in the direction you look for. Ie. there is no "classical system" to start with. There is just information encoded and manifested by real observer. the classiifcation of classical or quantum is depending onthe action beeing implemented in the system, and in my view there is no fundamental action, instead the action is a result of optimations done during evolution. It's simply the most stable and successful actions that we see in nature. If we can infer the actions we sene in nature, from such a model it would be quite spectactular. I think it can be done.

I believe there is yet a logic to this, yet to understand that will shed new light on the foundations of QM, as well as it's connection to the rest of the physics, in particular mass and inertia (and for sure GR).

/Fredrik

 

[Demystifier]

Block universe, mathematical universe, universal symmetries, timeless eternal law, they all have this something in common which I object to.

Thank you for the clarification of your point of view, which is best summarized with your sentence cited above.

 

[apeiron]

I believe there is yet a logic to this, yet to understand that will shed new light on the foundations of QM, as well as it's connection to the rest of the physics, in particular mass and inertia (and for sure GR).

/Fredrik

Do you not have any cites for your approach?

I think I mentioned CS Peirce and his bootstrapping view of reality. Pansemiosis some now call it.

It is also a logic to be found in systems science, hierarchy theory and dissipative structure theory to various degrees.

We could describe this approach generally as reality emerging from a "sum over observers".

And a key point you may or may not have considered is that this would be a scale-free equilbrium balance. So the "information" is not encoded in local observers (nor globally either) but instead is spread smoothly (that is, fractally) over all spatiotemporal scales.

Where is the observer that is dissipating the uncertainties, dissipating the histories, and so firming up the system? Everywhere and thus nowhere. Equilibrated across every scale and so not existing at any particular scale.

 

[Fra]

Do you not have any cites for your approach?

I think I mentioned CS Peirce and his bootstrapping view of reality. Pansemiosis some now call it.

It is also a logic to be found in systems science, hierarchy theory and dissipative structure theory to various degrees.

Apeiron, of course there are a number of papers worth reading, that have components of relevance to this!

But there since I'm not a professional, and I've had a 10 year break from physics I resume only some years ago, I have not yet published anything myself on this. Also I don't have any incentives to publish anything because I have to. If I think I solve a real problem I will publish. Many research papers concern isolated technical probllems within research programs, that interest everyone in that program and not anyone else. Since I am thinking of something that would be a new way of reasning, it would qualify as a new "program" and since this program doesn't yet exist, there is no context to publish isolated technical issues which anyone would care about.

It's harder, I have to produce a convincing overall picture, and solve at least one real open problem to convince anyone.

I think you are one of a few on here that seem to be somewhat on the same page.
Yes Peirce reasoning is good (although I am certainly no exper on Peirce! I think you know Peirce far better than I do; I am not sure i agree with Peirce all the way). Lee Smolins evolving law is good. Olaf Deryers internal relativity reasoning is interesting. Ariel Catichas idea to infere the laws of physics from the rules of rational inference is also good. The early part of Rovelli's RQM paper is also excellent (but not the finish).

But of course none of them have - to my current knowledge - produced any papers that implements more than what's fragments of what I'm looking for. But they are all worth mentioning as an indication of what I'm talking about.

I think you get it reasonably well Apeiron, and we reached a partial agreement about the general direction I think in previous threads. And some of hte unclairities left, and things that simply need more more work to sort out. The technical work I have done is under progress and I see no meaning in publishing fragments that only makes sense in a larger context. It will be published when I have a strong case, not sooner. Given how critical I am on others work I expect others to be critical on this as well.

/Fredrik