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#1
May1908, 01:07 AM

P: 2,799

I finally started to read Smolin's Three roads to Quantum Gravity and only read the first two chapters so far. It doesn't contain any math, but it does seem to present a particular choice of reasoning on howto make progress on the matter, which I think is interesting in it's own because it may be a valuable guide in the world of theories and on a very early stage in the reasoning, it may hint us about flaws in reasoning.
I am not sure if anyone else is interested in such things but I will give it a try. My aim is to see if the logic of reasoning used in science can have any constructive outcomes. In chapter 2 Smolin argues that that classical logic, that there is an objectivity to the notion of true and false, is not well designed for the task of quantum gravity. One of the reasons is that due to limited information of each observer (no observer can hold compelte information about everything in the universe at once), and prescription to establish truth or false, would be observerdependent. I agree with that. But then Smolin seems to argue that a measure ofthe rationality of actions/decisions can be construced without the use of an "superobserver" knowing everything at all times. He says it's enough to assume that the observers are honest, and argues that in that way, two observers facing "the same information" will always make the same decision. This makes me suspect, and I am curious to se how he builds onto this later in his reasoning. The problems I see is the feedback, that also "logic of reasoning" of a particular observer is evolved in the observer history. So it could still be that different observers facing the same information, responds differently, becase the very notion of "logic of reasoning" is different. This is what I see as the basis for backgroudn independence at a fundamental level. There seems to be a feedback and selfreference between the way information is processed, and the evolution of the logic of information processing. The reason I find common language analysis of very simple things interesting is that, I think differences in reasoning does have implications when you choose the mathematical formalism later. And at the later stages there is such much details and baggage that it's hard to analyse. Defects in the line of reasoning will propagage throughout the entire constructions. Comments are appreciated. /Fredrik 


#2
May1908, 02:16 AM

P: 2,799

Perhaps Smoling will argue later in the book but, he mentions something that the topos theory formalism is a formalism that naturally resolved the issue of the new logic.
Set aside the abstract definition of topos theory as a mathematical subject, is anyone aware of the logic that Smolin implies exists  that topos theory formalism, somehow would naturally emerge as the natural solution to the problem of replacing classical logic in the context of modelling reality? Is there some paper where this reasoning is lined out explicitly in some way? And how is this exploited to constrain the approach? ie what are the constraints of the topos formalism when applied to strategies? /Fredirk 


#3
May1908, 02:31 AM

P: 2,799

As many times before Baez appears to have made some nice summaries!
If found this page http://math.ucr.edu/home/baez/topos_physics/ which contains the following papers (1) A Topos Foundation for Theories of Physics: I. Formal Languages for Physics  http://arxiv.org/abs/quantph/0703060 (2) A Topos Foundation for Theories of Physics: II. Daseinisation and the Liberation of Quantum Theory  http://arxiv.org/abs/quantph/0703062 (3) A Topos Foundation for Theories of Physics: III. The Representation of Physical Quantities With Arrows  http://arxiv.org/abs/quantph/0703064 (4) A Topos Foundation for Theories of Physics: IV. Categories of Systems  http://arxiv.org/abs/quantph/0703066 Judging from the titltes, theis sounds interesting enough that I have to put Smolins book aside and at minimum skim these papers. /Fredrik 


#4
May1908, 03:47 AM

P: 2,799

Smolins 3 roads: new logic
This is somewhat interesting! just skimming the first paper... to mention one thing a new formalism where "the law of excluded middle need not hold" is intuitively plausible to me. It is in line with my thinking that there is always an uncertainty in the microstructure itself. Because the microstructure (beeing the discrete basis for the analogy of the continuum probability space) is in my thinking itself a sort of state in a series of inductions.
I'll keep reading later when I ahve more time /Fredrik 


#5
May1908, 04:23 AM

P: 1,667

I don't get that : if one observer would have limited information, he or she could say ''I don't know'' :) BTW, the rest you say is true in classical GR too and classical logic works impeccably there. You might want to ask yourself what such philosophy implies in the context of Ockham's razor... 


#6
May1908, 04:42 AM

P: 2,799

So those players who consistently refuse to take any risks whatsoever, are IMO doomed! The answer is part of the unpredictable feedback, it's part of the game. Then the next choice is, once you for example found out that the cat is dead  what do you do about it? What do you learn from this new valuable data? :) How do you choose respond to a given answer? What response pattern is of highest utility to You? Of course, we don't know that either :) So we gamble again, the action rules are also evolving... and one would imagine that bad actions are not preseved since they selfdesctruct. /Fredrik 


#7
May1908, 05:03 AM

P: 2,799

Smolins argumentation is not crystal clear to me, and it is still in the early chapters... but I got the feeling that what he means is something like that any two observers will respond to the information that the cat is dead in the same way. That there is somehow a objectively logical action, that is the rational response to this input if the observer is beeing "honest" about what he sees.
But in that case, I disagree with that. Which was my point. But OTOH I am not totally sure that is really what Smolin means. It's early in the book, and it's difficult to express things uniquely. My view is that the observers actions isn't always "rational", because it's difficult to define the measure of rationality. Instead I see it a way where progress is close to unavoidable. The actions that survive are those which are selfpreseving, which means that they have to be in some kind of harmony with their neighbours. (Here I'm thinking of abstract physical systems interacting, not humans). And perhaps an analysis of this logic, will reveal interesting things. I would expect the rational view to emerge in equilibrium  defined at some level of the actions, where local agreement on rationality exists. Edit: So perhaps the most "stable abstraction" here is the emergent rationality. But the rationality is never certain. Specifying the action is analogous the the physical action, it determines the response pattern of the system. But if there is no such level at which there is a truly fundamental, universal action... then perhaps this is the wrong way of asking the questions? Maybe the actions themselves are always in motion too? What kind of formalisms does that lead to? /Fredirk 


#8
May1908, 05:10 AM

P: 1,667




#9
May1908, 05:58 AM

P: 2,799

What is the utility of computing a probability? Then, one asks, how do we know wether the probabilitiy is correct? One way of imagining is to repeat the situation an inifite times and get statistics. But that isn't realistic. For particle experiments it is, but hardly for cosmological scale things. Yet, there seems to be an utility to compute the probability? So if we can't verify in advance if our computer probabitliy is correct, then is there another way to verify it? could there somehow be a more or less unique law of inducing an "expected probability" based on current information? Then the correctness would be a matter of correct induction. So one can imagine that the correctly expected proability, is in violation with what the future shows. How is such a situation handles constructively from the point of view of a theory builder? And how does the computational scheme for these probabilities revise, in the event that the future data is in disagreement with the original guess? If you think this is silly questions, then note the context in which I ask this. I am trying to understand the meaning and utility of physical law, and what the physical basis for that is. There is a strong case of selfreference here which is what makes this complex. But given this problematic situation, what is the best way forward? /Fredrik 


#10
May1908, 06:53 AM

P: 1,667

A good way forward must for sure keep contact with well known and accepted physics and at the same time may scatter may upheld beliefs. People did not accept Einstein in the first place because he came up with the equivalence and covariance principle, but because the first thing he did was to show that the Newtonian limit of GR existed and to show that his theory made new predictions. The latter principles only became important later on although for him, they were the guidelines to this kind of physics. So, I do believe in theories of principle, but you have to choose them wisely and make contact as quickly as possible with the well known laws (even if such reasoning makes plausible extra assumptions). Therefore, starting by throwing away the queen of science  that is logic  does not appear very fruitful to me. 


#11
May1908, 07:14 AM

P: 2,799

Are you effetively questioning Smolins initial note that a prescription to establish truth or false, would be observerdependent? I am not throwing away logic in favour of madness or chaos, I am just suggesting that if we are to see it from a realistic view, the procedure, say the logical line of reasoning, that deduces the value true or false, are IMO is a physical process, and whatever is evaluating this truthness can't be anything but a part of the universe subject to the same issues as everything. To ignore an apparent issue, is not logical to me either. I rather think that taking a too idealistic view of this, may inhibit a more fundamental awareness. Just for the perspective what is your personal take one these things? /Fredrik 


#12
May1908, 07:42 AM

P: 1,667

It is not because something bewilders you, that you have to take an easy way out and go on the metaphysical tour. Note that this has nothing to do with my comment about the braids in another thread; these comments stand even in the case of MWI like interpretations. 


#13
May1908, 09:30 AM

P: 640

Hi Fra … Careful!
May I join the discussion? I might add a different prospective? Uncertainty would then be base on the “laws of nature”. In a few words …. Is this what we observe? Classically, or at the macro level, two objects can be only be placed beside each other. Two objects cannot occupy the same location/position at the same time. Continuity. At the molecular level, two molecules/objects cannot be placed beside each other. Crystal structures of atoms. At the atomic level, two atoms/objects cannot be placed beside each other. Nucleon structures. Quarks structures are confined. Now … into the unknown … (for me) At the quark level, do we have any evidence that there is a “minimum length”. Do we have a cause for confinement? Do the quarks behave classically? Can they be placed beside each other? Can they occupy the same position/location at the same time? Can a quark occupy two locations/positions at the same time? ========= 


#14
May1908, 11:14 AM

P: 1,667




#16
May1908, 03:29 PM

P: 2,799

Careful, thanks for the contribution but I choose not to comment further because I can't relate to your comments in the intended context. My feeling though is that you either are making fun of the discussion or aren't appreciating the questions or maybe it's because of my poor way of posing them or not I don't know. Either way it's not interesting to I'll drop that.
I don't understand the followup reflection, but what I have in mind suggest that the "laws" themselves aren't the same but they are related in feedback between dynamics of the microstate and the microstructure itself. And this feedback might be able to formulate as and induction principle that may also be subject to change, but less so. But this is immature conceptual ideas only. I am working on finding the formalisms for this, but it's not yet mature and definitely not anyting standard so it's not something that's appropriate to discuss here. (But for sure, my starting points are not continous structures, I start with notions of distinguishability in the context of an observer  which impliticlty replaces the probability space with a discrete microstructure. The continuum approximation is recovered as the information capacity > infinity. Actions are treated combinatorically, but the difference is that the action is part of the mictrostructure. So the action/logic is evolving along with the microstructure.) My starting point is that of reasoning, and my fundamental idea is that there is a strong connection between reasoning and the laws of physics themselves. The seleciton of formalism that realises the idea is the motivation for the thread. In particular I was looking into some thinking of Smolin. I'll try to read up on those papers later and keep reading Smolin. /Fredrik 


#17
May1908, 04:22 PM

P: 587

I read Three Roads recently and is a bit of an odd book. It is a lot like Penrose's Road to Reality in that it has a lot of little divergences where Smolin takes up a speculative idea and takes it in some direction for a few pages but then moves onto something else without actually arriving anywhere, and does not take the idea up again. Although these divergences are a lot of the time more interesting than the text's main thrusts, it makes it kind of difficult to discern exactly what it is the author thinks. The whole "everything is relative" theme is kind of like that, but:
Anyway to me the important application of this idea in Three Roads actually wasn't the topos bit near the beginning but actually later on, when Smolin gets into an extended exploration of various things related to the holographic principle. In this part of the book Smolin seems to be providing a solution to the "how do we do this?" question: If you have two observers in a relational theory, you cannot objectively or meaningfully define the state of either observer but you can rigorously define and reason about the boundary between those observers. Smolin talks about defining sort of "surface areas" (? so to speak...) between regions in space, and goes on quite a bit about the idea that the information flowing across this boundary actually fully specifies what is happening on either side (though his main focus in doing so is on black holes and the Bekenstein bound). The overall argument, then, seemed to be that since the state of individual observers is not real or at least fuzzily defined, we should just ignore the observers and concentrate on the boundary as the "real" thing for purposes of constructing our theories. To me this approach of using the holographic principle as the solution is actually somewhat familiar, since it is analogous I think to the reasoning in gauge theory local states are arbitrary and inaccessible, therefore we ignore the local states and treat our mechanism for translating between local states as the fundamental object. Right? What is confusing to me about this bit as with much of Three Roads is that I have trouble connecting Smolin's apparent conclusion here with what Smolin himself did afterward, forcing me to question to what degree the conclusions are particularly useful (considering even the author did not in the long run really find a use for them). Smolin presents a compelling argument in Three Roads for the importance of the holographic principle and if one looks at Smolin's papers from the 20002001 period (when I assume he would have been writing Three Roads) one finds a LOT of holographic related work! but to my knowledge he did not significantly work with the holographic principle afterward. In fact the only really recent work in my (limited!) understanding of QG research to seriously apply holographic reasoning of the kind Smolin seems to be arguing for is occurring in the String camp (I am specifically here thinking of the ongoing work on AdS/CFT). Of course, Marcus tends to argue that Smolin is not really relevant to LQG today as regards cosmology (and recently seems to have expressed that Smolin may be in his recent work wandering away from LQG altogether), and I believe he has said a few times that Ashtekar's camp in particular are the people to look at if you want to know what's happening with LQG as applied to cosmology. The topos/holographic arguments in Three Roads, it seems to me, were quite specifically about cosmology (since it is only on the cosmological scale that we really lose the ability to select a preferred "superobserver"), so it is unsurprising that if Smolin lost interest in cosmology he'd not be following up on his cosmological ideas. So perhaps this would be a good point to pick Marcus's memory banks on has the holographic principle turned out to be a useful tool for modern loop quantum cosmology for those who are working in the field today? What about, for that matter, topos? 


#18
May1908, 06:14 PM

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PF Gold
P: 23,124

If someone is organizing a big international conference, they will get Ashtekar to speak on quantum cosmology. they will get Rovelli to speak on the current state of putting together spinfoam LQG with the older canonical LQGnow LQG has become a fusion approach and Rovelli has the largest group working on that. Or they might get Thiemann, or Freidel. But they wouldn't get Smolin! That is neither good nor bad it is just how it is. Smolin has always scouted out where the mainstream hasn't ventured and tries new things and gets others to try new things. Now what I've said just now is basic and rather superficial. I notice you are making a penetrating analysis (involving things I don't know much about, like topoi) and hoping that I can fill in. Unfortunately I must disappoint you. I can't fill in the gaps in this case, and I hope some others will be able to. I have to say that even though Ashtekar (and Bojowald too) exemplify the LQC mainstreamturning out the quantum cosmology grad students and computer modeling and research papersSmolin has been voicing some very interesting IDEAS about cosmology. So you can't ignore him or count him out in that area either. He tends to go after fundamental question, as you pointed out, like What are Laws as contrasted with initial conditions? How can we have quantum mechanics if there is no classic observer of the whole universe? What could be the deterministic ground that undeterministic quantum phenomena arise from? What is the deeper ground that space and matter and laws arise from? Why these numbers and not others? I am certainly getting it somewhat wrong and misrepresentingbut you know the kind of question I mean. That is a valid part of cosmology too, just as much as the more practical computer models of the big bounce they run at Penn State and some insight into the basics there might be a key to unlock stuff. But it's not the LQC mainstream, is all. Let's look at the papers these people have written recently, say since 2005, and see if we can find some direction signs. My impression is that Three Roads is a fascinating book but it was written back in 2001 (correct me if I'm wrong). So it wouldn't give the latest clues as to the directions these people are taking. 


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