Supergravity Back In Vogue !?!

[maddog]

So as I understand it that the old theory of Supergravity has come back around again and now become popular again. This was from the late 70's and early 80's. What is Supergravity you ask ? Well think of a the notion of supersymmetry applied to gravity. You can look up supersymmetry on wiki for an in depth. The basics of supersymmetry is that among Fermions and Bosons both have a similar super-partner of the opposite type. So for every Fermion, there exists a Boson superpartner and for every Boson, a Fermion as a superpartner. So Supergravity would for the graviton (Boson) have a superpartner - gravitino (Fermion)

 

There is an article in the current issue of SciAm May 2012 discussing redressing using the Feynman Diagram process to work out gravity as well as the other forces. That is with an old principle brought back again, called Unitarity. By using this an infinite number of possible solutions can be reduced to a simpler small finite value. Their findings has loops of gravitons behave like doublets loops of gluons. It is likely the doublets that reinvigorates supersymmetry to be reconsidered.

 

What I find odd is that Supergravity was disenfranchised back in the early 80's (as explained by Michio Kaku) as requiring the wrong number of dimensions (even not odd). It has been considered as at 11-dimension to work out gravity (odd). Of course I have heard of an alternate idea of using a different group working in 12-dimensions (even again).

 

Interesting.

 

maddog

Edited May 2, 2012 by maddog

[CraigD]

Bern, Dixon, and Kosower’s 5/12 SciAm article on "unitarity" alternative to Feynman diagram calculations is interesting.

 

Alas, I can only distantly spectate the kind of physics math they’re describing – and while I’ve had some excellent spectators guides to Feynman’s perturbation approach, I haven’t yet, so need to keep my eyes peeled for some about the unitarity approach.

 

I’m reminded of a common comment the folk who can do this math make about string theory: that it’s “22nd century physics, but we only have 20th century math”. It appears that something similar can be said of the good 'ole Standard Model: it’s 1950s physics, but 21st century math still isn’t enough to calculate it well enough to explain gravity.

[maddog]

Alas, I can only distantly spectate the kind of physics math they’re describing – and while I’ve had some excellent spectators guides to Feynman’s perturbation approach, I haven’t yet, so need to keep my eyes peeled for some about the unitarity approach.

The Superposition of wavefunctions by Feynman is mostly what is covered in Quantum Field Theory which is 2nd yr grad physics. What I think makes this tougher than undergraduate QM is the Schroedengers equation deals with a full 3-D coordinate system. Partial DifEq is not my strong suit.

 

I’m reminded of a common comment the folk who can do this math make about string theory: that it’s “22nd century physics, but we only have 20th century math”. It appears that something similar can be said of the good 'ole Standard Model: it’s 1950s physics, but 21st century math still isn’t enough to calculate it well enough to explain gravity.

For both String <M> Theory or the normal Standard Model, independent of what century math, Quantum Gravity (QG) will always be just over the hill, just beyond our reach, until what is acknowledged is some 'sacred cow' assumption [maybe even very fundamental] that 'everybody' just knows to be 'true' is found out to be the LIE it really is. I just wish I could put my finger on what it was.... :doh:

 

Personally this is a time of convergence of ideas. One where it might be that what it will take is some combination of M-Theory, Loop Quantum Gravity (LQG), Twistor Theory, and now maybe lets bring back SuperGravity (like Supersymmetry ever went away).

 

maddog

[CraigD]

For both String <M> Theory or the normal Standard Model, independent of what century math, Quantum Gravity (QG) will always be just over the hill, just beyond our reach, until what is acknowledged is some 'sacred cow' assumption [maybe even very fundamental] that 'everybody' just knows to be 'true' is found out to be the LIE it really is. I just wish I could put my finger on what it was.... :doh:

This impression I got from their Article is that BDK are hoping that an essentially simple quantum field theory, in the way that QED was simple, will be possible as a result of improvements in mathematical approach – that the expedient but ultimately restrictive use of perturbation approach that worked adequately for QED simply “poisoned” folks’ thinking on how to approach “quantum gravito-dynamics” (QGD), and that the sacred, LIEing cows that need abandoning aren't old, fundamental assumptions, but a new (or new-ish, as post-QGD quantum gravity thinking goes back at least to ca 1980) meta-assumption: that a simple, do-for-every-particle-what-photons-do-for-charged-ones particle – for lack of a better term, graviton – approach can’t work.

 

This is all hunches and guesswork for me, though, all the worse because my intuition isn’t adequately trained by a real, working understanding of existing theory. For what it’s worth, my hunching tells me that an explanation of mass and inertia – the Higgs mechanism – and one of gravity, must be connected in some profound way, and that one or more of the bosons new to that mechanism, perhaps including some that aren’t in any theory yet, are the same as, or are at least strongly linked to, the graviton.

 

My hunching quickly hits a wall, however, one for which the only way I can see over, under, around or through is an actual or the equivalent of a genuine, PhD-level education in physics. A decade or so of whining at anyone who knew more physics than me to magically make me understand the Higgs mechanism and its various requisite mathematical formalism hasn’t worked very well for me so far, so I expect isn’t likely to suddenly start now. Reading pop science books leaves me feeling somewhat like I do after watching a subtitled movie in a language I know not at all, when, afterwards, for an unconscious moment, I believe I’ve learned the language: with the vicarious sense that I’m as educated and clever as the books’ writers. As with the subtitled-language effect, this feeling lasts not very long, until I actually try to make use the understanding I feel I’ve absorbed, and discover it’s effectively an empty box, marking what I don’t know rather than containing what I do. :(

 

Fortunately (and more than a little, I think, perversely), I enjoy hitting walls and being confronted with terrible gaps in my understanding, so at least I’m enjoying myself :)

[maddog]

This impression I got from their Article is that BDK are hoping that an essentially simple quantum field theory, in the way that QED was simple, will be possible as a result of improvements in mathematical approach – that the expedient but ultimately restrictive use of perturbation approach that worked adequately for QED simply “poisoned” folks’ thinking on how to approach “quantum gravito-dynamics” (QGD), and that the sacred, LIEing cows that need abandoning aren't old, fundamental assumptions, but a new (or new-ish, as post-QGD quantum gravity thinking goes back at least to ca 1980) meta-assumption: that a simple, do-for-every-particle-what-photons-do-for-charged-ones particle – for lack of a better term, graviton – approach can’t work.

I have interpreted the article in the same way. An example of a past "sacred cow" was Newton's notion of Absolute Time.

So something along those lines might be going on. A couple of candidate that I might consider are:

1. Causality
2. "Nothing can travel faster than light"
3. Entropy always increases.

Just to name a few. I reinterpret the second example above as "No thing can travel faster than light" as anything that can must have "no-thingness" as one of its properties. And for the first, what if Causality was only required to be adhered to within the timelike part of the lightcone about a particle. Outside, nothing about causality can be strictly said.

 

This is all hunches and guesswork for me, though, all the worse because my intuition isn’t adequately trained by a real, working understanding of existing theory. For what it’s worth, my hunching tells me that an explanation of mass and inertia – the Higgs mechanism – and one of gravity, must be connected in some profound way, and that one or more of the bosons new to that mechanism, perhaps including some that aren’t in any theory yet, are the same as, or are at least strongly linked to, the graviton.

I like the graviton actually. What I did like about the article is their findings were that they found that a graviton could behave in a loop form of Feynman diagram as a two gluon loops. I am rethinking as what we think of reality as bifurcating into two realities:

One that works out to be Real and one that works out to be it's Complex conjugate (may or may not be real). The interaction between realities happens with virtual particles where stipulation of causality is outside the lightcone.

 

My hunching quickly hits a wall, however, one for which the only way I can see over, under, around or through is an actual or the equivalent of a genuine, PhD-level education in physics. A decade or so of whining at anyone who knew more physics than me to magically make me understand the Higgs mechanism and its various requisite mathematical formalism hasn’t worked very well for me so far, so I expect isn’t likely to suddenly start now. Reading pop science books leaves me feeling somewhat like I do after watching a subtitled movie in a language I know not at all, when, afterwards, for an unconscious moment, I believe I’ve learned the language: with the vicarious sense that I’m as educated and clever as the books’ writers. As with the subtitled-language effect, this feeling lasts not very long, until I actually try to make use the understanding I feel I’ve absorbed, and discover it’s effectively an empty box, marking what I don’t know rather than containing what I do. :(

I am like you in this respect that even though I have warmed up to QCD and its constituant breakdown of particles. The requirement to have a Higgs particle still escapes me. Though I do embrace Supersymmetry in concept. What I'm wondering what if why we don't seem to find the super partners is that is like trying to see something that travels faster than light !?!

 

maddog

Edited May 5, 2012 by maddog