Loop quantum gravity 01

A lecture from the CERN website by Carlo Rovelli (who initially introduced the theory of loop quantum gravity in 1988). Date- 21.08.2008. Source- http://cdsweb.cern.ch/record/1121957?ln=en slides- http://indico.cern.ch/getFile.py/access?contribId=30&resId=0&material...

From wiki-
'Loop quantum gravity (LQG), also known as loop gravity and quantum geometry, is a proposed quantum theory of spacetime which attempts to reconcile the theories of quantum mechanics and general relativity. It preserves many of the important features of general relativity, while at the same time employing quantization of both space and time at the Planck scale in the tradition of quantum mechanics. The technique of loop quantization was developed for the nonperturbative quantization of diffeomorphism-invariant gauge theory. Roughly, LQG tries to establish a quantum theory of gravity in which the very space, where all other physical phenomena occurs, becomes quantized.'

Category:

Science & Technology

Tags:

• Loop
• quantum
• gravity
• cern
• LQG
• carlo
• rovelli

[warthog212]

damn u steve i wanted to go to bed... ah well sleep can wait :)

[frippp66]

"The clarity is devastating, but where is the ambiguity? The ambiguity is in the cardboard box under the stairs." - Monty Python

[CACBCCCU]

The thought I had that nuclear spin could decrease gravitational couplings between nuclei could relate to conditions much like in a cold neutron gas where the molecules are still randomly colliding, which I suppose can eliminate any frame-dragging based on consistent nuclear spin. Singular mass frame-dragging is a sort of amplification of gravitational impact and afaik, like every other GR effect, it is reproducible using a sufficient number of infinitesimal-energy infinite-wavelength gravitons.

[CACBCCCU]

Nuclei spin, though not always with much energy unless excited to do so. Extra spin would affect gravitational couplings between nuclei. I suppose it could reduce the couplings, while GR supposes it would increase them. Anyway, I see applying Newton's 3rd law (gravitational retroreflectivity in matter) as justifying closed loops in gravitational couplings, and despite the lack of anything I'd call extradimensional in any of ithat, it seems to me another way to describe the same thing as LQG.

[CACBCCCU]

My idea of incorporating an equal-opposite (matter retroreflectivity) rule in graviton actions mainly differs from GR in that GR's space, in the case of multiple masses, at the low-energy limit, is fundamentally the superposition of the individual effect of each mass. By this view, at the low energy limit, superposition of gravity wells won't work and what seems to be a form of gravitational entanglement emerges.

[CACBCCCU]

I should've left "might" out of the previous comment. It should be "Another reason, apparently also relating to dark matter and the quantum spin question mentioned with the previous one, involves closed/retroreflective graviton couplings." This drops the conventional presumption of areal flux uniformity, which is circular gravity-well symmetry, in favor of a nonuniform flux emphasizing equal-opposite graviton action. My understanding that is this can give a holographic character to matter.

[CACBCCCU]

@soulskies I guess your issue(?) is with GR. Maybe I'm oversimplifying, but if gravity is gravitons then quantizing GR's spacetime makes no sense. The simplest reason for that is because light paths bend and graviton paths shouldn't. Another is that GR quantization implies a spin-2 quantum with no intrinsic quantum wavelength, which I don't think is realistic or matches what's seen out there. Another reason, also relating to dark matter, might involve closed/retroreflective graviton couplings.

[CACBCCCU]

@soulskies I don't know. Time dilation doesn't seem to be an experientially-realistic concept if pendula speed up in places where light clocks slow down. I think of that whenever the twins paradox is mentioned. One version has the traveler do all the frame-switching at one point, the turnaround on a dime, near lightspeed no less, and then goes on to explain that this is the step that's key to the traveler not aging as much... I really can't convey how stupid it seems in only 500 characters.

[soulskies]

@CACBCCCU it is easy the see that there is only one question there: why do we give the space a manifold structure apriori? that's it. By this choice we can define tangent spaces, vectors, forms, tensor etc. However, dıfferentibility and continuity are very strong assumptions that may not by so natural and evident as it may seem. The time will show us whether the Einsteinian way of thinking is right or not.

[CACBCCCU]

@soulskies "I have a serious question."

Well that's exactly what 500 character youtube comments are for!

Which question?



[soulskies]

I have a serious question. Why we start with a continuous manifold with fixed dimension and require diffeomorphism invariance? By this way we give a topology to the space a priori. Can't we start with a set of points and consider all possible topologies? Can't we require invariance of physics under topology changes? Why is locality seen so important in contrast experimentally verified entanglement? Why we fix which point is a neighbor of which point from the very beginning? Thank you:)

[CACBCCCU]

The issue of dark matter is officially "off the deep end" with a lamestream media vengeance, it's as politicized as curved space. It's vital to general relativity, like Felix needs Oscar, it's more than about paying the rent.