Is there more to gravity than gravitons?

This is an intriguing paper by Padmanabhan:

From Gravitons to Gravity: Myths and Reality

I saw this paper back in 2004, when it was submitted, but failed to see reactions to it at that time. In the comments section of a post about string theory over at Cosmic Variance, the issue of gravitons came about and made me wonder again about that “semi-classical” work by Padmanabhan. I wonder whether the issues raised by Padmanabhan are indeed correct and if so, how would they be interpreted in string theory.

Back to physics, back to research

Today is a very special day for me. My request for a transfer from the electronics division (where I was working since 2004) to the materials division was accepted about a month ago, and today was my first day in the new division. Now it is for real: I have a full-time research, permanent job position in physics!

Life is strange and full of surprises. I am happy.

Polchinski, Smolin, Polchinski, …

Now the machine seems to be running. A scientific public debate is going on over the blogosphere between Smolin, author of The Trouble with Physics, and Polchinski, a string theorist who reviewed his book recently.

(Click here for a previous posts on this issue).

Ashtekar on Recent Advances in LQG

In order to assist navigation through Ashtekar’s recent advances in LQG (see his paper, Loop Quantum Gravity: Four Recent Advances and a Dozen Frequently Asked Questions), I have built the following list with links to papers on each research line mentioned by him.

Mathematical foundations
http://arxiv.org/abs/math-ph/0407006
http://arxiv.org/abs/gr-qc/0504147

Planck scale physics near the big bang singularity in FRW cosmologies

http://arxiv.org/abs/gr-qc/0505032

http://arxiv.org/abs/gr-qc/0602086
http://arxiv.org/abs/gr-qc/0604013
http://arxiv.org/abs/gr-qc/0607039
http://arxiv.org/abs/gr-qc/0612104
http://arxiv.org/abs/gr-qc/0612101

Effective matter theories obtained by integrating out gravitational
degrees of freedom
http://arxiv.org/abs/hep-th/0502106
http://arxiv.org/abs/hep-th/0512113

Recovery of the graviton propagator starting from a non-pertubative, background independent theory
http://arxiv.org/abs/gr-qc/0604044
http://arxiv.org/abs/gr-qc/0508124
http://arxiv.org/abs/gr-qc/0608131

Mathematical extensions of gauge theories using quantum groups

A. Okolow, Representations of Quantum Geometry, PhD Thesis, University of Warsaw (2005)

The Master Constraint program
http://arxiv.org/abs/gr-qc/0305080
http://arxiv.org/abs/gr-qc/0411138
http://arxiv.org/abs/gr-qc/0411139
http://arxiv.org/abs/gr-qc/0411140
http://arxiv.org/abs/gr-qc/0411141

Algebraic quantum gravity
http://arxiv.org/abs/gr-qc/0607099
http://arxiv.org/abs/gr-qc/0607100
http://arxiv.org/abs/gr-qc/0607101

Explorations of the Planck scale geometry in symmetry reduced midi-superspaces
http://arxiv.org/abs/gr-qc/0412028
http://arxiv.org/abs/gr-qc/0406087
http://arxiv.org/abs/gr-qc/0402096
http://arxiv.org/abs/gr-qc/0506093
http://arxiv.org/abs/gr-qc/0607053

Ramifications of quantum geometry for dynamics of matter

http://arxiv.org/abs/gr-qc/970519

Ideas on black hole evaporation and information loss

http://arxiv.org/abs/gr-qc/0509075
http://arxiv.org/abs/gr-qc/0509078v2

Phenomenological developments in quantum cosmology

http://arxiv.org/abs/gr-qc/0102069
http://arxiv.org/abs/gr-qc/0202077
http://arxiv.org/abs/gr-qc/0304074
http://arxiv.org/abs/gr-qc/0601085

Ernst Mach, a pan-mathematician?

I will take forever to go through the 600+ pages of “A History of Mechanics”, by Rene Dugas. My hunsband gave me a copy as a gift last year and from a quick browsing it was evident that the book provided a scholarly, chronological overview of mechanics that I have never found elsewhere. With so many books to read, I wonder when will be my time to go through this monumental work.

Anyone interested in foundational issues of physics should go some day in his/her life through the history of this giant pillar — mechanics. There are several surprising facts along this fascinating endeavor. The notion of inertia pervades the history of mechanics and is very intriguing by itself.

Ernst Mach is well known for having influenced Einstein in the development of his general relativity theory, which includes, among others, his ideas on the origin of inertia. This is something I will write about some time in the future. However, in a recent browising of Dugas’ book, have found the very curious passage (page 444, my boldface):

In the terminology of modern philosophy, Mach, reducing science to a well-formed language, would be called a pan-mathematician.

This was the very first time I ever met such a reference to Mach! Unfortunately, Dugas closes the section about Mach in his book exactly at this point with apparently no further explanations about what he means by Mach as a pan-mathematician. I googled around and found nothing. Well, the form “pan” evidently refers to an all-inclusive form, that is, Mach would be seen today as someone who embraces the whole of mathematics. What does this mean?

Dugas refers to Mach’s philosophy of expelling “all mysticism” from science by the use of an “economic” principle. So perhaps Dougas is raising an issue here concerning mathematics as a means of the necessary “economic language” that Mach advocates.

In his book (page 444), Dougas quotes the following passage from Mach (I suppose, from his Science of Mechanics):

According to us all science has the mission of replacing experiment. Consequently it must remain partly in the domain of experiment and must partly go beyond this, always awaiting corroboration or denial from the latter. Where it is impossible to corroborate or deny, science has nothing to do. It always moves in the domain of incomplete experiment… The agreement between theory and experiment can always be improved by the perfection of observational techniques.

It is interesting that Mach does not mention in particular the role of mathematics in the context raised by Dougas (as far as I see). But if we “must partly go beyond this” (ie, the domain of experiment, as Mach states) there is no way to do it without mathematics.

The whole problem then resides in the notion of “partly”.

And today this is certainly the fundamental issue of… er.. pan-quantum gravity.