Why LQG spin foam vacuum is better than Strings!
‘String theory has the remarkable property of predicting gravity’: false claim by Edward Witten in the April 1996 issue of Physics Today, repudiated by Roger Penrose on page 896 of his book The Road to Reality, 2004. String theory does not predict anything testable about gravity. - Comment on Peter Woit's blog
'... it is thus perhaps best to view spin foam models ... as a novel way of defining a (regularised) path integral in quantum gravity. Even without a clear-cut link to the canonical spin network quantisation programme, it is conceivable that spin foam models can be constructed which possess a proper semi-classical limit in which the relation to classical gravitational physics becomes clear. For this reason, it has even been suggested that spin foam models may provide a possible ‘way out’ if the difficulties with the conventional Hamiltonian approach should really prove insurmountable.' - http://arxiv.org/abs/hep-th/0601129
String theory suggests 10^500 different vacuum states, and although it could provide an empty framework for a (unobserved but speculated) spin-2 gauge boson (graviton speculation), it does not provide any dynamics or testable predictions after 20 years of intense funding and effort! Nature has no strings attached...
posted by nige @ 1:33 PM
2 Comments:
New comment to Dr Motl's blog:
http://motls.blogspot.com/2006/01/review-of-loop-quantum-gravity.html
Dear Lubos,
'... it is thus perhaps best to view spin foam models ... as a novel way of defining a (regularised) path integral in quantum gravity. Even without a clear-cut link to the canonical spin network quantisation programme, it is conceivable that spin foam models can be constructed which possess a proper semi-classical limit in which the relation to classical gravitational physics becomes clear. For this reason, it has even been suggested that spin foam models may provide a possible ‘way out’ if the difficulties with the conventional Hamiltonian approach should really prove insurmountable.' - Page 14 of http://arxiv.org/abs/hep-th/0601129
The reason for the technical problems like an infinite number of potential solutions is simply a lack of connection to reality. This is the same problem which stops string theory from succeeding after 20 years of intense funding, which LQG has not had!
I don't think the aim of science is just to link GR and QFT by some kind of mathematical fiddle of the Feynman path integral, but the broader picture of understanding why gravity is so much weaker, and being able to predict it.
The conventional aim of producing a theory that "predicts gravity" by merely being consistent with unobserved hypothetical spin 2 graviton conjectures is no good.
Maxwell fiddled his theory to fit the facts, but at least his equations allow me to calculate electromagnetic phenomena.
With both string theory and LQG you have a mathematically far more complex and incomplete version of something like Maxwell's aether electromagnetism, but the equations are useless for practical things. You can't calculate Standard Model parameters with them, or anything.
So you are left with the physical picture - 10/11 dimensional strings and 10^500 vacuua. This is why I think LQG spin foam vacuum is more realistic - it is tied to reality.
It's a pity you people are so constrained to only seeing abstract mathematical approaches and technical details of speculative conjectures. Top physicists should be resolving the reasons why Maxwell's equations wrongly predict continuous and not discrete electromagnetic waves for atomic phenomena. Once this is sorted, then you will a correct model for one observable unified force (electromagnetism) which will be a foundation for getting a grasp of quantum gravity. At present, anomalies between real observed physics phenomena and the mathematical models are swept under the carpet. And some people have the cheek to speculate on SUSY and other unobservables.
Nigel
http://motls.blogspot.com/2006/01/who-is-lqg-expert.html :
Dear Lubos,
"We could go on and on and on. String theory reproduces special relativity; LQG does not. String theory is consistent with the existence of other forces and fields (which moreover seem necessary not only according to the experiments but also because of internal consistency of quantum gravity) and it in fact predicts them; LQG does not." - Lubos Motl
Special relativity not exactly a defence of string theory as general relativity is quite different, and anyway special relativity conflicts with quantum field theory:
Quantum field theory is moving towards an ether picture of the Feynman path integral, due to problems with renormalisation in the purely abstract mathematical model. See arXiv: hep-th/0510040 p85, the virtual particles in the vacuum contradict special relativity and imply a Dirac sea as: 'it is not possible anymore to define a state which would be recognised as the vacuum by all observers'. There is evidence that 'string theory' is hogwash as it makes no testable predictions, but its major rival is the 'spin foam vacuum' of loop quantum gravity, which again is a Dirac sea.
General relativity is entirely different to special/restricted relativity:
EINSTEIN REPUDIATED SPECIAL RELATIVITY AS FOLLOWS:
‘The special theory of relativity … does not extend to non-uniform motion … The laws of physics must be of such a nature that they apply to systems of reference in any kind of motion. Along this road we arrive at an extension of the postulate of relativity… The general laws of nature are to be expressed by equations which hold good for all systems of co-ordinates, that is, are co-variant with respect to any substitutions whatever (generally co-variant). …’ – Albert Einstein, ‘The Foundation of the General Theory of Relativity’, Annalen der Physik, v49, 1916.
You can get the equations of "special relativity" from electrodynamics as Lorentz and others did before Einstein. Yes Einstein was the biggest genius of all time, but he ADMITTED SPECIAL RELATIVITY DOESN'T APPLY TO A REAL WORLD WHERE THERE ARE ACCELERATIONS (SEE QUOTATION ABOVE). Which is why general relativity is different. At best, the EQUATIONS of special relativity are the same as those of the correct theory; at worse they are completely wrong and lead to paradoxes by not including acceleration effects. You cannot rely on the framework of special framework since all real motion involves acceleration and thus force.
It is really to be expected that the same people who admire Einstein's early errors as if they were better than his major work in general relativity, are the people who also work on string theory. It is not coincidence. You are just brainwashed bigots. You can't see that physics tied to facts, such as FitzGerald and Lorentz's approach to the equations of "special relativity" a decade before Einstein are MORE BEAUTIFUL PHYSICALLY, because they are connected to reality.
Instead, you ignore the reality of general relativity and the spin foam vacuum which seems to connect the experimental facts of gravity with those of quantum field theory, and you instead try to connect 10/11 dimensional speculation with spin-2 gauge boson (graviton) speculation, by way of unobservable string speculation.
You think speculation is beautiful because the level of maths, or what you call maths, is so technically involved it will not be understood or checked by outsiders. The whole approach of you big mouthed crackpots is insulting, speculative, trivial, unconnected to any reality, and frankly insane.
Grow up!
Nigel
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