### GRG18 2a

There have been some interesting sessions this afternoon. I can only mention a couple, since the queue behind me is growing. D. Terno spoke about work with E. Livine on quantum causal histories in the context of quantum information. Causal diagrams are constrained by the requirement that one wants QM to work, and there is a natural way to associate allowable diagrams with standard quantum circuit diagrams. The relevant paper is Phys. Rev. D75 (2007) 084001. Later on M. Tajmar spoke about an observed non-classical frame dragging effect on spinning superconducting rings. Vibrational effects were dealt with using a subtraction technique between clockwise and anticlockwise modes. A question at the end prompted the remark that the observed 'magnetic' interaction between the 4 gyroscopes on Gravity Probe B may be due to this quantum effect.

## 4 Comments:

This 'magnetic' interaction between gravity B probes is interesting. Any reference?

Hi Matti. Well, the guy is in Austria so if you google his name you should find something. Sorry, I don't have references handy. There is also an NZ paper on the same topic.

Hi Kea,

Could you give some info on the Penrose talk about twistor strings?

I finally was able to review the slides from Strings 07.

I was very surprised by the paucity of discussion on twistor strings.

About two articles discussed Maximal Helical Violation [MHV].

This 07 talk may peripherally relate to twistor strings.

http://gesalerico.ft.uam.es/strings07/040_marco.htm

1 - Urs Wiedemann [CERN], ‘Jet quenching in string theory and heavy ion collisions’, slide 38/38, emphasizes “Our quest: find catenary’.

Remember that the “Helicoid and Catenoid are two surfaces having the same local geometry” [Isometry].

http://xahlee.org/surface/helicoid-catenoid/helicoid-catenoid.mov

Moreover, they are “Adjoint Minimal Surfaces”. See diagrams for Catenoid, 0 degrees rotation. Helicoid 45 degrees rotation. Helicoid, 90 degrees rotation.

http://www.susqu.edu/brakke/evolver/examples/periodic/adjoint.html

Mathworld: Catenary: “The curve a hanging flexible wire or chain assumes when supported at its ends and acted upon by a uniform gravitational force.”

http://mathworld.wolfram.com/Catenary.html

Perhaps when the ends are not fixed, gravity [G] becomes more helical like the trajectories of planets about suns and stars about galactic nuclei?

2 - I see that John Baez is discussing catenoids in Derek Wise on Cartan Geometry and MacDowell–Mansouri Gravity

a - diagram of ‘’tangent de Sitter spacetime at x [or y] in M’’

http://golem.ph.utexas.edu/category/2007/07/derek_wise_on_cartan_geometry.html#more

It may take a helicoid to get from x to y in M?

b - ‘Exotic Statistics for Strings in 4d BF Theory’, unlabeled figure p5 within Quandle field theory.

http://arxiv.org/PS_cache/gr-qc/pdf/0603/0603085v2.pdf

The Catenoid may suffice when respectively the sun or galactic center is not in motion, but the Helicoid is probably better when these celestial objects are in motion?

3 - Catenoids are also used by:

a - Ingo Runkel, Jens Fjelstad, Jurgen Fuchs, Christoph Schweigert, ‘Topological and conformal field theory as Frobenius algebras’.

figure 3.7, p12, figure B.1, p19, figure B.3, p20.

http://arxiv.org/PS_cache/math/pdf/0512/0512076v2.pdf

a - and [catenoid like] Edward Witten. ‘Three-Dimensional Gravity Revisited, fig 5c, p61 fig 6, p64.

http://www.arxiv.org/PS_cache/arxiv/pdf/0706/0706.3359v1.pdf

Have these authors considered a transformation to the helicoid?

4 - Raphael Bousso [Berkeley], ‘Cosmological Predictions in the Landscape’, slide 10/41 ‘The causal diamond’ resembles the open ends of a catenoid placed back to back like lower part of the above Runkel, et al, figure B.3, p20?

Hi Doug

I might get around to Penrose next week sometime, when I'm back at my computer. Cheers, Kea.

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