- #1

marcus

Science Advisor

Gold Member

Dearly Missed

- 24,738

- 785

## Main Question or Discussion Point

On 2 October, 5 days from now, Derek Wise will give an online international seminar talk which will be a followup to his June 2012 paper with Stefen Gielen---as I recall a lot of us found that paper very interesting and it topped the second quarter MIP poll.

So I want to review that paper, the better to understand what Derek has to say on Tuesday.

http://arxiv.org/abs/1206.0658

Steffen Gielen, Derek K. Wise

(Submitted on 4 Jun 2012)

Hamiltonian gravity, relying on arbitrary choices of "space," can obscure spacetime symmetries. We present an alternative, manifestly spacetime covariant formulation that nonetheless distinguishes between "spatial" and "temporal" variables. The key is viewing dynamical fields from the perspective of a field of observers -- a unit timelike vector field that also transforms under local Lorentz transformations. On one hand, all fields are spacetime fields, covariant under spacetime symmeties. On the other, when the observer field is normal to a spatial foliation, the fields automatically fall into Hamiltonian form, recovering the Ashtekar formulation. We argue this provides a bridge between Ashtekar variables and covariant phase space methods. We also outline a framework where the 'space of observers' is fundamental, and spacetime geometry itself may be observer-dependent.

8 pages; Essay written for the 2012 Gravity Research Foundation Awards for Essays on Gravitation

Yeah, on our 2nd quarter 2012 MIP poll eleven of us responded and 5 out of 11 voted for Derek and Stefen's paper.

This is to say that if we collectively are reasonably good judge of interesting signficant QG papers then we are probably going to hear more about "Observer Space"

and how the novel concept of a field of observers can help "bridge" between Hamiltonian approach and covariant phase space methods (maybe even get the best of both worlds.)

Lifting to a new contextual structure that may prove more universal/convenient to work in--it sounds like a move mathematics should try on physics now and then.

Derek Wise is a John Baez PhD from UC Riverside who went postdoc to UC Davis (Steve Carlip's group) and thence to Erlangen (Thomas Thiemann's group)

So I want to review that paper, the better to understand what Derek has to say on Tuesday.

http://arxiv.org/abs/1206.0658

**Linking Covariant and Canonical General Relativity via Local Observers**Steffen Gielen, Derek K. Wise

(Submitted on 4 Jun 2012)

Hamiltonian gravity, relying on arbitrary choices of "space," can obscure spacetime symmetries. We present an alternative, manifestly spacetime covariant formulation that nonetheless distinguishes between "spatial" and "temporal" variables. The key is viewing dynamical fields from the perspective of a field of observers -- a unit timelike vector field that also transforms under local Lorentz transformations. On one hand, all fields are spacetime fields, covariant under spacetime symmeties. On the other, when the observer field is normal to a spatial foliation, the fields automatically fall into Hamiltonian form, recovering the Ashtekar formulation. We argue this provides a bridge between Ashtekar variables and covariant phase space methods. We also outline a framework where the 'space of observers' is fundamental, and spacetime geometry itself may be observer-dependent.

8 pages; Essay written for the 2012 Gravity Research Foundation Awards for Essays on Gravitation

Yeah, on our 2nd quarter 2012 MIP poll eleven of us responded and 5 out of 11 voted for Derek and Stefen's paper.

This is to say that if we collectively are reasonably good judge of interesting signficant QG papers then we are probably going to hear more about "Observer Space"

and how the novel concept of a field of observers can help "bridge" between Hamiltonian approach and covariant phase space methods (maybe even get the best of both worlds.)

Lifting to a new contextual structure that may prove more universal/convenient to work in--it sounds like a move mathematics should try on physics now and then.

Derek Wise is a John Baez PhD from UC Riverside who went postdoc to UC Davis (Steve Carlip's group) and thence to Erlangen (Thomas Thiemann's group)

Last edited: