### LOOP QUANTUM GRAVITY

**Loop quantum gravity is the main alternative to string theory.**

*Loop quantum gravity: a spin foam vacuum QFT (quantum field theory)*

'In 1986, Abhay Ashtekar reformulated Einstein's field equations of general relativity using what have come to be known as Ashtekar variables, a particular flavor of Einstein-Cartan theory with a complex connection. He was able to quantize gravity using gauge field theory. In the Ashtekar formulation, the fundamental objects are a rule for parallel transport (technically, a connection) and a coordinate frame (called a vierbein) at each point. Because the Ashtekar formulation was background-independent, it was possible to use Wilson loops as the basis for a nonperturbative quantization of gravity. Explicit (spatial) diffeomorphism invariance of the vacuum state plays an essential role in the regularization of the Wilson loop states. Around 1990, Carlo Rovelli and Lee Smolin obtained an explicit basis of states of quantum geometry, which turned out to be labelled by Penrose's spin networks.' -

*Wikipedia.*

*Why string theory is a fraud*

According to string theory (there is actually no string theory, because the theorists haven't discovered any workable dynamics yet so it can't make any predictions), everything is composed of vibrating Planck-sized tiny strings with 6 dimensions curled up into a Calabi-Yau manifold or 'insect'. The other 4 dimensions of space-time or 5 dimensions of Kaluza-Klein space-time (for unification of gravity and electromagnetism), make a total of 10 or 11 dimensions. String theorist Edward Witten, who unified 10 dimensional superstrings with 11 dimensional supergravity in March 1995, claimed in the April 1996 issue of

*Physics Today*that 'String theory has the remarkable property of predicting gravity.' In fact, string theory doesn't predict the strength of gravity (or anything else that is scientific, i.e., potentially checkable). All it does is to allow the possibility of a spin-2 (graviton) mode if a dynamical theory can be discovered which fits the perturbative expansion, as Peter Woit points out.

*anon Says:*

Sean Carroll now presents a graph of evidence that dark energy varies with time:

Sean Carroll now presents a graph of evidence that dark energy varies with time:

*http://cosmicvariance.com/2006/01/11/evolving-dark-energy/*

*I love this expert cosmology. The fact that they keep modifying the theory to fit the new observations really shows how expert these guys are. Thanks Peter, for your patience with them!*

A more correct (empirically driven, but still predictive and testable) approach to quantum gravity: http://feynman137.tripod.com/

## 2 Comments:

'A fish cannot comprehend the existence of water. He is too deeply immersed in it.' - Sir Oliver Lodge.

COMMENTS BY AND ABOUT PROFESSOR LEE SMOLIN:

http://www.math.columbia.edu/~woit/wordpress/?p=327#comment-7579 :

Lee Smolin Says:

January 15th, 2006 at 6:49 am

"It is no problem to assess even very independent and creative young physicists, and distinguish those with promising ideas and results from those of non-professionals like the Bugdanovs. Their work is not in a vacuum, it is based on and uses established physics and mathematics and is aimed at solving long standing problems. The work can be judged both on the quality of the work and presentation and the promise of solving outstanding problems. A good test is surprise, is the idea new and potentially signficant? Is it an idea I wish I’d had, that I would like to work on? Has the person pulled off more than once an original idea that had an impact on the field? These are the kinds of tests we use when assessing the promise of young people in quantum gravity and foundations of quantum theory and we seem to have done well with them."

Dr Smolin makes the point that presentation is important. If you compare the professional style presentation of my CERN Document server paper preprint EXT-2004-007, http://cdsweb.cern.ch/search.py?recid=706468&ln=en to my website ttp://feynman137.tripod.com/ , you see that presentation is a severe problem.

If you can upload a paper to some place, it can look more formal than when you are trying to cultivate interest on the internet as a lone site. You have to try to make it as interesting as possible to as many people as you can. I do have a plainer version of the site at http://nigelcook0.tripod.com/ which can be printed out normally if people prefer (but the colourful site is getting more hits).

Dr Smolin's comment about my interest in loop quantum gravity:

Nigel Says:

January 14th, 2006 at 2:18 pm

Some kind of loop quantum gravity is going to be the right theory, since it is a spin foam vacuum. People at present are obsessed with the particles that string theory deals with, to the exclusion of the force mediating vacuum. Once prejudices are overcome, proper funding of LQG should produce results.

http://www.math.columbia.edu/~woit/wordpress/?p=327#comment-7555 :

Lee Smolin Says:

January 14th, 2006 at 4:41 pm

"Actually LQG and related research programs (such as CDT or programs based on quantum information ideas) are progressing rapidly, see for example the talks at the recent Loops 05 conference: http://loops05.aei.mpg.de/

"Lobus’s criticisms have been aswered in detail several places, you might look for example at the FAQ section of my review hep-th/0408048 (although this review needs updating in view of some developments since then.)

"While we would of course be happy with anyone’s contribution to the subject, the fact is that there is a community consisting of about 150 mostly young physicists and mathematicians working in the general area of LQG and other background independent approaches and the results show that many of them are of equal quality scientifically to the best young people in other fields. The only concern I have for the future of quantum gravity is that these people be rewarded for their contributions with positions that will let them continue to contribute; for the present people in these fields have much harder careers than equally accomplished or talented string theorists. This does mean that those who have gone into the field have significantly more courage and intellectual independence, which I believe is one reason so much has been accomplished by relatively few people.

"Thanks also to Nigel for those supporting comments. Of course more support will lead to more results, but I would stress that I don’t care nearly as much that LQG gets more support as that young people are rewarded for taking the risk to develop new ideas and proposals. To go from a situation where a young person’s career was tied to string theory to one in which it was tied to LQG would not be good enough. Instead, what is needed overall is that support for young scientists is not tied to their loyalty to particular research programs set out by we older people decades ago, but rather is on the basis only of the quality of their own ideas and work as well as their intellectual independence. If young people were in a situation where they knew they were to be supported based on their ability to invent and develop new ideas, and were discounted for working on older ideas, then they would themselves choose the most promising ideas and directions. I suspect that science has slowed down these last three decades partly as a result of a reduced level of intellectual and creative independence available to young people.

"Thanks,

"Lee"

It is interesting that Lee Smolin is so generous with his enthusiasm and thanks to others. The first time I've ever really been thanked for doing anything connected to science... It can't last so I'd better make the most of it!

Near the top of http://feynman137.tripod.com, you see a table with two calculations.

In the left column is is the radiation pressure calculation for gravity. In the right is the fluid analogy calculation.

Because the gauge bosons spend part of their time as a perfect fluid of matter-antimatter, the two calculations are equivalent in producing the right result.

If we assume 100% radiation pressure and 0% perfect fluid pressure from the vacuum, we get the same result as assuming 0% radiation pressure and 100% perfect fluid pressure.

Similarly, if we assume say 50% radiation pressure and 50% perfect fluid pressure from the vacuum, gravity is still correctly calculated.

The way the physics of the calculation works, it is irrelevant what the partition is between the pressure contributions from radiation pressure and from perfect fluid pressure.

Both have the same effect!

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