- #36
Fra
- 4,173
- 618
comment on #30
Yes I think (background) microstructure of spacetime as I use the word, is conceptually very close to or the same thing as the fundamental degrees of freedom of spacetime, because both are related to some imagined probability measure defined on the imagined set of distinguishable spacetimes. And if you picture the space of spacetimes as a continuum then of course a high measure density around a particular geometry, means that there are more "microscopic freedom" there (you are likely to "spend more time" there, or "draw more samples" from there, during an imagined "random walk").
However, maybe there are some slight differences in a larger context. But at this stage of the discussion I'd think they are interchangable. I guess a difference is that I consider
the _observable_ degrees of freedom to be relative as well. I'm not sure how the see that.
I read this again now, and if I understand you right you are arguing that a possible justification of Loll et all's approach something like "minimum speculation" or "minimum action" and that we should evaluate the options with "low action" first so to speak? And this means that the fewer things we need to change or revise, the less information we need to change, the lower action.
I'm all with you on that principal reasoning, however this reasoning is relative to the current state of accepted information, and the accepted rating system, which may explain our disagreement?
I do not accept the path integral in the sense that it's part of my currently accepted truths. Moreover many of the standard QM axioms simply doesn't make sense IMO, this in particular regards the use of probability theory, and the lack of consistent induction of the probability spaces with measures. I don't find their construction with path integral free of speculation, and from my view it's rate sufficiently speculative to not attract me directly into exactly what they are doing. However, I am still interesting, if those who make the ratings are willing to invest in the evaluations, I am happy to be a curious observer for upcoming papers.
Perhaps one can call this view speculative then ok :) But I see it just the opposite way, because the state of opinion from which that evaluates as speculatie, is speculative itself in the first place - relative to my view.
I see this disagreement as perfectly consistent with my views. There is no reason to expect everyone to agree on every evaluation. As long as I can reach a state of subjective understanding to our disagreement, then I am happy.
( Note that I never claimed anywhere that they are "wrong", because how to we define that measure at this point? and that was also be a style of reasoning too categorical for me.)
Now I am still interested to know if you, regardless of wether you "disagree", understand my point or if you think I am missing soemthing yet, if so I am still very motivated to understand what you mean. Do you consider my line of reasoning, speculative? I mean, not the reasoning about physics, but the reasoning regarding the reasoning?
/Fredrik
marcus said:here is the first paragraph of the second article I gave a link to (Planckian...de Sitter Universe)
==quote==
To show that the physical spacetime surrounding us can be derived from some fundamental, quantum-dynamical principle is one of the holy grails of theoretical physics. The fact that this goal has been eluding us for the better part of the last half century could be taken as an indication that we have not as yet gone far enough in postulating new, exotic ingredients and inventing radically new construction principles governing physics at the relevant, ultra-high Planckian energy scale. – In this letter, we add to previous evidence that such a conclusion may be premature.
==endquote==
marcus said:I am gradually constructing a kind of dictionary: you say BACKGROUND MICROSTRUCTURE and Ambjorn/Loll papers often say fundamental dynamical degrees of freedom of spacetime. In one Utrecht Triangulations paper it began by stating simply that "the goal of nonperturbative quantum gravity is to discover the fundmental dynamical degrees of freedom of spacetime" or words to that effect.
That is how they see their job. And it is not too unlike what you are saying about the quest to determine the "background microstructure" that interests you.
Yes I think (background) microstructure of spacetime as I use the word, is conceptually very close to or the same thing as the fundamental degrees of freedom of spacetime, because both are related to some imagined probability measure defined on the imagined set of distinguishable spacetimes. And if you picture the space of spacetimes as a continuum then of course a high measure density around a particular geometry, means that there are more "microscopic freedom" there (you are likely to "spend more time" there, or "draw more samples" from there, during an imagined "random walk").
However, maybe there are some slight differences in a larger context. But at this stage of the discussion I'd think they are interchangable. I guess a difference is that I consider
the _observable_ degrees of freedom to be relative as well. I'm not sure how the see that.
marcus said:In what I just quoted they use a different phrase: fundamental quantum dynamical principle. I think the aim remains the same and they just use different words.
==================
In this second paper they present a new piece of evidence that they are on the right track------ They make lots and lots of random universes and then a giant superposition of all these universes, and they discover it is S4. Roughly speaking the "wick rotation" of usual de Sitter space. they are often going back and forth between Lorentzian version and Euclidean, substituting imaginary
time for real time and back again.
In doing the Monte Carlo runs, they "wick rotate" in this sense so that complex amplitudes become real probabilities. Only then can they do a random walk, in effect tossing dice or coins to decide which modifications of geometry to do.that part can be a bit confusing. Anyway, according to them, what they got (S4 ) is the Euclidean version of the right thing, namely de Sitter space. So it is the right thing, and it is part of the program "To show that the physical spacetime surrounding us can be derived from some fundamental, quantum-dynamical principle."
===================
This then strengthens the argument, which must be familiar to you from the first paper, that it is PREMATURE to resort to exotic and newfangled structures to represent the microscopic degrees of freedom. Like you said earlier, we do not have to resort to "funny wiggling things". Not YET anyway, because a simple nonperturbative path integral appears to be working.
I read this again now, and if I understand you right you are arguing that a possible justification of Loll et all's approach something like "minimum speculation" or "minimum action" and that we should evaluate the options with "low action" first so to speak? And this means that the fewer things we need to change or revise, the less information we need to change, the lower action.
I'm all with you on that principal reasoning, however this reasoning is relative to the current state of accepted information, and the accepted rating system, which may explain our disagreement?
I do not accept the path integral in the sense that it's part of my currently accepted truths. Moreover many of the standard QM axioms simply doesn't make sense IMO, this in particular regards the use of probability theory, and the lack of consistent induction of the probability spaces with measures. I don't find their construction with path integral free of speculation, and from my view it's rate sufficiently speculative to not attract me directly into exactly what they are doing. However, I am still interesting, if those who make the ratings are willing to invest in the evaluations, I am happy to be a curious observer for upcoming papers.
Perhaps one can call this view speculative then ok :) But I see it just the opposite way, because the state of opinion from which that evaluates as speculatie, is speculative itself in the first place - relative to my view.
I see this disagreement as perfectly consistent with my views. There is no reason to expect everyone to agree on every evaluation. As long as I can reach a state of subjective understanding to our disagreement, then I am happy.
( Note that I never claimed anywhere that they are "wrong", because how to we define that measure at this point? and that was also be a style of reasoning too categorical for me.)
Now I am still interested to know if you, regardless of wether you "disagree", understand my point or if you think I am missing soemthing yet, if so I am still very motivated to understand what you mean. Do you consider my line of reasoning, speculative? I mean, not the reasoning about physics, but the reasoning regarding the reasoning?
/Fredrik