
#127
Aug2705, 12:26 AM

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Unfortunately, understanding the above paper requires a certain amount of understanding of "geometric algebra", which is a type of Clifford algebra where the basis vectors are associated with the tangent vectors at a given point of the manifold of spacetime. Carl 



#128
Aug2705, 07:35 AM

P: 416

1) Nobody has measured spacetime curvature directly. 2) Spacetime curvature does not imply curved space. Usual popular image of curved space around Sun is pictorial only. 3) The curved spacetime view is not exclusive. E.g. torsion formulations, CartanEhelers reformulation, etc. 4) The curved spacetime view is problematic on the Newtonian limit. Far from common understanding, nobody has derived the Newtonian limit from GR. This is easy to understand. In the limit c > infinite the curvature of spacetime may be zero like correspond to the Newtonian approach but then, if gravity is curvature, gravity may be zero. Textbook’s derivation of Newton second law is a derivation valid only when c is finite and the approximation is non linear. c finite contradicts Newtonian theory. Ehlers reformulation of GR does not obtain the Newtonian limit (even if Ehlers claims the contrary). His formulation on flat spacetime has problems: I) the splitting of curved derivatives is not unique and additional equations does not contained in GR are needed, ii) the compatibility with Newtonian limit is done invoking “asymptotic flatness”, which is experimentally unsustainable. 5) The geometric approach breaks the unification with rest of forces. 6) Far from standard claims the geometric approach of GR does not explain the misterium of gravity. This is easy to understand. In Newtonian theory, one has an equation for computing the force, but none explaining of underlying mechanism of it. In Einstein (really HilbertEinsteinGrossmann) theory, one has equations for computing spacetime curvature, but none explaining of underlying mechanism of it. GR substitutes the question "How does Earth know that force that Sun does" by "How does Earth know the curvature that Sun does". Far from common statements in GR literature, GR does not explain gravity. The solution is not a geometric approach to quantum gravity. The solution is a forcelike approach to GR that can be quantized more a demonstration of that GR is, strictly speaking, wrong. Regarding your link, not only the choosing of Minkoskian spacetime metric is not correct (related to imposibility for obtaining correct Newtonian limit, that was the source for the search of alternatives like NCG and similar), moreover, i see fundamental difficulties with the "gauge" line element (7.7) that appears to be the basis of all the "gauge" approach. 



#129
Aug2705, 11:21 AM

P: 1,308

At best String Theory can only be an effective theory, not a TOE. This is because there seems to be nothing in String/Mtheory itself that explains where the strings or membranes came from to begin with. What process creates these membranes/strings from the background? I suppose that there was a background without strings when the universe was very, very small, and then at some later time some process gave rise to strings and/or other membranes. How did that happen?
I suspect that if we knew the process by which strings/membranes come into existence, then this might give us constraints on which strings/branes can exist and allow a choice from the landscape. 



#130
Aug2705, 11:28 AM

P: 1,545

I have to disagree on David Hestenes. He cannot be talking about a Euclidean basis while using GR and Riemannian geometry. That is 4D and Euclidean is 3D where time is just a variable. GR/Riemannian is also “Background Independent” as I understand it, and Euclidean would be Background Dependent. While the successful current theories GR and QM are not. At least I think QM is background independent. The ideas that wish to replace or correct GR and/or QM, all seem to get more complex in both their concept and mathematics. Maybe that’s because reality is complex. I still feel that String theory has been successful in showing that 11 dimensions “appear” to be required. Therefore, in my opinion any proposed new theory needs to explain why that appeared to be true. That includes variations on Strings, canonical science, and even Euclidean explanations. RB 



#131
Aug2705, 12:01 PM

P: 416

The strings of string M theory really one would talk of the pbranes are really inmortal on the formulation proposed. In fact some brane inspired cosmology models claim that the big bang was (of course is just a especulation) the outcome of a collision of two 5D branes. 



#132
Aug2705, 12:19 PM

P: 416

Regarding above link you would read it first before disagree . Already in the abstract you can see that are talking of a flat spacetime not a flat space. See also my post #131. But whereas many of others approaches focus on physical insight, ST is just a mathematical goulash around an initially "beatiful" idea that was discarded in accelerator experiments many decades ago. Things are much more simple: any proposed new theory needs to explain the world like it appears to us. Today we know that the world is 4D and non supersymmetric, therefore the first quantum theory of gravity may be a formulation for 4D and without supersimmetry. Precisely this is the point of LQG and other approaches. If at 2007, supersimmetry is experimentally observed. No problem!! your theory will continue to be correct (as Newtonian mechanics is in Formula 1), simply you will need generalize to supersimmetry. The problem of ST and M theory is that 11D and supersymmetry, and the rest of mathematical gulash, are just a mathematical gulash added to the theory because was internally inconsistent or violated experimental data. For example supersymmetry was added ad hoc in the 80s because string theory without it predicted tachions which were newer observed The aim of physics is to explain universe as it is, is not to develop a theory of "like world would be for me". All on string theory is about things that are not about our universe. Nothing of standard model or of GR is obtained from ST. At the best, one obtains certain models (after of tricks and ad hoc asumptions) that look like but are not equivalent. Almost any young student knows the myth that ST predicts gravity or that GR is recovered in the low energy limit but both of those claims are not true. In fact, causality in ST is defined in a flat metric whereas causality in GR is not. Then what? In the past they say like ST is not 100% compatible with GR and ST is mathematically "beatiful" then the problem may be with GR. In fact, you appears to ignore that only some years ago string theorists claimed that one would do not take GR "too seriously" . Even today some guys claim that one would ignore experimental data of GR in favor of string theory!!! All of this is a nonsense, ST is outside of physics. Those "details" are do that ST was a waste of time or in the words of P.W. Anderson 



#133
Aug2705, 12:23 PM

Astronomy
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PF Gold
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to the ancient alchemists, it appeared that all matter could be explained by combining 4 elements shall we require of all future theories of matter that they explain why that appeared true to the alchemists? 



#134
Aug2705, 12:52 PM

P: 416

You explained better and shorter (= two time better) than my 



#135
Aug2705, 01:31 PM

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thank you kindly however on another matter, I feel a deep attachment to the geometric explanation of gravity and, although I am disinclined to argue with you, I wish you would not so often castigate it with your disapproval but if you must, by your very nature as Juan, then I guess you must 



#136
Aug2705, 01:39 PM

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http://modelingnts.la.asu.edu/pdf/GTG.w.GC.FP.pdf http://modelingnts.la.asu.edu/html/GCgravity.html I think the above link is a better article in its explanation of the theory than the one I originally posted. http://arxiv.org/PS_cache/hepth/pdf/0409/0409048.pdf A typical QFT textbook will deal with the background dependence of the theory by showing that while the calculations do assume a background (in the form of a particular metric), the results of the calculations are compatible with Lorentz / Poincare symmetry. That is, if you assume a different reference frame, your calculation will be different but the final result will be the same. The fact that they have to show this is an indication that the theory is not in itself inherently background independent. From my point of view, this is evidence that the universe does have a "background". It's just that since we're a part of the universe, we have great difficulty figuring out exactly what that background is. My guess is that quarks and leptons are the results of a two stage condensation. The second stage is the combination of left and right handed massless chiral particles to form fermions. This is almost a part of the standard model, the difference being that the standard model requires a Higgs particle to be absorbed (or emitted) at the vertices where left and right handed chiral fermions convert to each other. The first stage of the condensation is one that produces the massless chiral fermions and is beyond the scope of this discussion. But this sort of concept does get back to string theory, or at least to the concept of hidden dimensions, by the fact that if one ignores a condensation of subparticles, (that is, if one only looks at the interactions of the combined system), one will end up with unexplained degrees of freedom. These extra degrees of freedom can be naturally explained through the notion of hidden dimensions. As an example, if two subparticles combine to form a tightly bound composite particle, we will use center of mass coordinates for the composite particle. But there will still be a set of relative coordinates for the two subparticles. Since it is a bound state, the relative coordinates will be compact and therefore will look (mathematically) like a space of compactified dimensions. This gives some hope of determining the topology of string theory from the mechanics of the subparticles. Carl 



#137
Aug2705, 02:53 PM

P: 1,545

YES WE SHOULD BUT  “ancient alchemists” ideas have been explained as wrong, based on current science. And we do understand how their old view of reality; lead them to think they way they did. So that job has been done. I also understand need for a New Theory to show the old wrong theories to be wrong to make way for a new one. However, loudly proclaiming that GR and QM are wrong is far short of showing them to be wrong. True enough not every idea that falls off the truck should qualifies to set yet another standard that must be disproved of proved by any future new theory. That will always be an individual judgment call. But where rigorous scientific interpretation of observations and rigorous math has been applied to build a view of a theory  some explanation as to why the theory was constructed incorrectly should be proved by a replacing better theory. Just as has been done with Alchemists Theories. If it cannot do so what makes the new theory better? In the worst case view of both GR and QM they have certainly met that standard. But, for all those that have better answers than GR or QM, I've never seen a reasoned explanation as to why GR and QM work so well and are yet wrong. Now I’m no String or M theory expert, in fact I don’t see how they could be correct. But based the quality of the people and the work they have done, I trust and I believe the ideas were rigorously formed. And for me the idea of 10 or 11 dimensions was reasonable reached in this case. So for me I feel they have met the standard. Even though I do not believe in extra dimensions myself I feel it’s only responsible to accept the higher standard. Therefore if I want to show strings to be wrong, and there is something better, I must understand how they made the mistake of assuming the extra dimensions. If I can’t take the responsibility to do that, then why should anyone take a new idea seriously? I just find this a more reasoned and logic approach to the issue rather than just cobbling a bunch of ideas together with no proofs, and no explanations of how the others made the wrong conclusions. Is that easy to do – of course not it's harder, nobody promised easy. RB 



#138
Aug2705, 03:13 PM

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PF Gold
P: 8,147

And "background independent" is a property of the physics together with the geometry, not the kind of geometry alone. If the physics acts on the geometry, and the geometry determines the physics, so there is selfinteraction, then you have background indpendence. 



#139
Aug2705, 03:48 PM

Astronomy
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#140
Aug2805, 07:15 AM

P: 416

I think that once the paper was published you could study it carefully and write a public comment if you consider that GR is still a good approach after of reading my work. If i am wrong you will help to me to understand correctly gravitation . If i am not wrong then I will help to you to understand correctly gravitation. 



#141
Aug2805, 07:39 AM

P: 416

In fact the history of dimensions is 4D, 5D, 26D, 10D, 11D, ... According to B. Greene some string theorists are now working in the posibility of more than one time dimension whereas others claim that the fail of compactification may indicate that there are still unknown 4Dversions of "string" theory. Also the size of strings changes from "chapter to chapter" from "infinitely" small (Planck) to mm range to again "infinitely" small to infinitely large. There is a version that says that compactified dimension are the usual 4D ones, etc. The rest of "theory" is also chapterdependant and even bookdependant or authordependant!! 



#142
Aug2805, 07:57 AM

P: 416

That is not a scientific argument. The "quality" of people is a subjective concept and, moreover, is not guarantee of a good work. Look for example the history of QFT, almost all great guys Schrödinger, Dirac, etc. did the wrong work and a new generation of young people did QFT. In fact, this argument against string theory has been recently used by Dyson. Regarding the "quality" of the work they have done, i could say that the quality is very low, with lot of wrong details that are corrected after of decades. Material known in other fields is introduced decades after in string theory. In concrete points, I can assure that the quality of Seiberg's work on NC geomstry is low, the quality of Schwartz's work on unitarity is low, the quality of Witten's work on QM foundations is low, the quality of Nanopoulos' work on the arrow of time problem is low, etc. It is time for exploring other alternatives. 



#143
Aug2805, 04:59 PM

P: 1,545

I just hope and even expect that a good alternative will prove strings wrong by show how/why it appeared to them there should be multi D's. I'd even expect proving so can be helpful. RB 



#144
Aug2805, 05:00 PM

P: 1,545

Does "The line element of GR is not positive definite" address this issue? The Lee Smolin link (Thanks for finding Marcus) http://arxiv.org/abs/hepth/0507235 Provides a firm argument the GR is “relational” or background independent. At least where “warping” is concerned. Is this generally accepted as the case or is this a “debated point” ? 


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