Explicit embedding of gravity+Standard Model in E8 (new Lisi paper)

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  • #51
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The basic fact to focus on, at this point, is that some worldclass people think it is interesting enough to have a select workshop on it. These are potential contributors to the theory.
Given the reputations and track record of the people at the workshop, it would be arrogant for any of us to pretend we can call the outcome.
This is exactly the type of attitude one should have when doing physics.

Hooray for authority!
 
  • #52
marcus
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Heh heh
unusualname, you might want to read again the statement of purpose:
http://www.birs.ca/birspages.php?task=displayevent&event_id=10w5039

I was interested to see that Bertram Kostant is one of the participants.
http://www-math.mit.edu/people/profile?pid=136
MIT math faculty 1962-1993, so way emeritus now. Has shown an interest in Lisi-E8. There seems to be a video of his talk at Banff, somewhere at the Banff workshop's website, but I haven't seen it.
Born 1928. He participated in an Oberwolfach workshop last year, so keeps active.
http://en.wikipedia.org/wiki/Bertram_Kostant
I think if Kostant is in the group photo he might be the white-haired fellow in the second row standing just behind the front-row guy in the bright red shirt. Could be wrong about that being Kostant, but sure about the other two.
http://temple.birs.ca/gallery/10w5039/groupphoto?full=1 [Broken]

Key thing is that Lisi E8 has captured the interest of some really top mathematicians. Significant development.
 
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  • #53
marcus
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... I didn't see the media going nuts when Connes' proposed a solution to the standard model based on attaching a discrete structure to spacetime, or when Verlinde proposed his entropic model for gravity earlier this year...
Neither did I, but so what? Media hooraw is no indication of the real interest of a development. Media didn't pick up on Asymptotic Safety conference last year either: Steven Weinberg, Roberto Percacci. At least not as far as I know.

Or Horava (if you think that is still interesting.)

Or CDT.

Mass media reaction can in some cases be informative about other things and may be worth watching selectively---but I tend to ignore it most of the time.

Banff workshop now is a different kettle of fish. Far more significant than the media fuss of 2 years back.
 
  • #54
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Heh heh
unusualname, you might want to read again the statement of purpose:
http://www.birs.ca/birspages.php?task=displayevent&event_id=10w5039
I did it says:

blah blah blah
...
A mathematical study of these questions is interesting for its own sake, and may provide some constraints on the structure of the physical theories that can be built using E8.
...
blah
See, clearly just getting the physics angle in for funding purposes :wink:
 
  • #55
marcus
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http://garrettlisi.com/albums/MtRundle.mov [Broken]

unusual, from a certain perspective that is a very intelligent interpretation!

It has to do with how math relates to physics. The way the tools progress cannot always be sharply distinguished from the work done using them. I tend to listen up when people like Joe Wolf say something's interesting or may have potential. I participated in a seminar led by Joe Wolf and George Mackey sometime around 1968 as I recall, based partly on Mackey's current work (Induced Representations of Groups and Quantum Mechanics, 1968). It left me with great respect for Wolf, his integrity, his intuitive sense of what was both mathematically and physically interesting. Mackey too of course (he passed away in 2006).

People like that don't have to promise what they don't know for sure, to get funding. They certainly aren't promising anything here. I would tend to interpret the Banff statement in a straightforward way, without any cynical spin. But it all depends on one's background, how one takes things.

http://www.birs.ca/birspages.php?task=displayevent&event_id=10w5039
 
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  • #56
marcus
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... (I think he mistitled his recent paper, even he agrees), he should be happy that his work has aroused so much interest and some real mathematics has grown from it, and I wish him the best of luck.
...
I think this strikes a good note! In fact I think it is a win-win situation for everybody whatever happens to the theory. I too am (very) happy the workshop took place and wish Garrett and the rest the best of luck.

Just to keep things in perspective, there has been a proliferation of new approaches to quantum gravity and unification, just since 2006.

LQG put on new footing---both the canonical and covariant versions, and the application to cosmology as well.

Asymptotic safe gravity has emerged as a strong research direction--the first major workshop on it was November 2009--applications to cosmology

Causal dynamical triangulations now much more visible since 2006.

Connes NCG, and also Marcolli's recent NCG+LQG paper (Oberwolfach 2010 workshop)

Hermann Nicolai and Chris Meissner's approach to unification (MaxBornXXV 2009 conference)

Verlinde's entropic force gravity (earlier work by Jacobson, Padmanabhan).

Horava's approach (but interest there may have slacked off.)

It is hard to keep track of all the new gambits that are being pursued. And most of these only started having an impact after 2006 or haven't yet really caught on with researchers.
 
  • #57
jal
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Re.: Getting funding

Time is running out!

EROEI (energy returned on energy invested)

If they cannot find something SOON, ... its game over.

Governments are bankrupt and will not be able to dig their way out.

The LHC is the last chance to reveal a path to a new source of energy.
jal
 
  • #58
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Will the gravitons in E8 theory not be plagued by the non-renormalization problems of other quantum gravity attempts?
 
  • #59
marcus
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Will the gravitons in E8 theory not be plagued by the non-renormalization problems of other quantum gravity attempts?
Two of the leading QG attempts are Asymptotic Safety and LQG. They do not have "renormalization problems". What attempts were you thinking of?

Interest seems to have waned in some of the others, but I'm not sure it was because of that, they may have had other problems.
 
  • #60
atyy
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Will the gravitons in E8 theory not be plagued by the non-renormalization problems of other quantum gravity attempts?
Lisi's abstract says his construction is consistent with Nesti and Percacci's GraviGUT ideas. Nesti and Percacci do hope that some of their problems will be solved by pure gravity being asymptotically safe, ie. non-perturbatively renormalizable. However, I'm not sure whether Lisi is also assuming asymptotic safety of pure gravity.
 
  • #61
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atyy basically answered my question, sorry I was vague marcus. I was simply referring to the non-renormalization of straight-forwardly quantizing GR (unless it turns out to be asymptotically safe). I was trying to sort out whether Lisi's approach addressed this problem at all since the renormalizability of stringy gravitons is one of the much publicized advantages of string theory.

I noticed on http://www.science20.com/quantum_diaries_survivor/garrett_lisis_new_e8_paper#comments" a lengthy discussion in the comments between Nesti and Motl. Lubos obviously thinks GraviGUT is "foolish" - do his criticisms have any merit? Nesti seems to have held his own as far as the back and forth goes, but I cannot really evaluate the strengths of the arguments made. Something about mixing diffeomorphisms and Yang-Mills groups.
 
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  • #62
MTd2
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No, they have no merit. You cannot trust him lately, he was even banned from posting on Jacques Distler's blog for not accepting being wrong, intellectually lazy and impolite.
 
  • #63
atyy
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I noticed on http://www.science20.com/quantum_diaries_survivor/garrett_lisis_new_e8_paper#comments" a lengthy discussion in the comments between Nesti and Motl. Lubos obviously thinks GraviGUT is "foolish" - do his criticisms have any merit? Nesti seems to have held his own as far as the back and forth goes, but I cannot really evaluate the strengths of the arguments made. Something about mixing diffeomorphisms and Yang-Mills groups.
There's another interesting discussion between Nesti and Distler and some others here:
http://golem.ph.utexas.edu/~distler/blog/archives/002140.html
 
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  • #65
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No, they are not the same. Distler's calculations are clear and correct. The person you mention built a straw man. This post and thread on another physics problem are enlightening and keep that in your mind, since this is a subject that the person you mention worked on for years:

http://golem.ph.utexas.edu/~distler/blog/archives/002199.html#c032759
 
  • #68
arivero
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Given that the SciAm article will force some revisiting to this paper, let me to add my doubt against spin(11,1) or generically against SO(10) unification models: that it does not fit in maximum supergravity with kaluza klein; SO(10) is the symmetry group of the 9-sphere, and thus it invites to 9 extra dimensions.

Or we can stick with maximum sugra plus SO(10) and a bidimensional space time... after all, bidimensional space times are very in the music of string theory and also of other quantum gravity approaches.

In fact I believe to remember, but I am not sure, that the first appearing of E8 in modern theory was by doing dimensional reduction down to tridimensional or bidimensional space time. For GUT theories, the natural unification was only up to E6.
 

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