rtharbaugh1 said:
..
Wishing everyone a pleasent summer...
Richard
Hi Richard, my best experience of gravity is to stand in our garden in bright sunlight around lunchtime and watch the bees go after the lavender. What I notice is that it [gravity] is keeping me in one place, by a slight pressure on the soles of my feet, and that I am very happy to be there. Sometimes I take a sandwich.
And a pleasant summer to you as well!
Next year in January there will be this
https://www.physicsforums.com/showthread.php?t=119283
A workshop at SantaBarbara organized by or featuring
Martin Bojowald, Robert H. Brandenberger, Gary T. Horowitz, Hong Liu
on "spacetime singularities"
and essentially what they mean to say in the title is not singularities but bounces. these days the singularities are getting repaired and bounces are what replaces them.
a singularity is a fault in the model and if you remove the singularity you get a bounce. "bounce" is just their word for a removed spacetime singularity---I don't know of any other word that is being used much in this context.
they have to have some word for it, and even tho it is not much like a bouncing tennis ball we might as well let them say bounce. or what else do you propose?
Bojowald has accumulated a lot of OCCAMY EVIDENCE (clean economical evidence that doesn't need to assume a lot of extra structure that you could cut away with occam razor) that gravity is repulsive at high density.
the occam point about it is that to get that he just quantizes gravity in a fairly straightforward (Loop) way and gets hi-density repulsion out as a surprise---something he didnt put in by hand.
naturally the other bigname guys like Gary Horowitz and Robert Brandenberger are interested to hear about this because maybe they can use it in telling their various stories. so they set up this workshop where they can question Bojowald and see what they can do with it.
the others mostly have more complicated stringy structures they are thinking about, like a "gas" of branes drifting around and colliding. Wagner would have loved it and pictured it on the stage in one of his operas. People sing while branes collide.
But Bojowald already went ahead and wrote a paper that SHOWS them how to use his hi-density repulsive gravity in the context of colliding branes! He made it easy. The repulsion cushions the collision so they don't actually even have to TOUCH! there is no sign I can see that Bojo believes in branes, he just tossed off the paper to show how you can use quantized gravity (Loop style) to improve other models.
I will get the link. Here it is:
http://arxiv.org/abs/hep-th/0407115
Loop Quantum Gravity and the Cyclic Universe
Martin Bojowald, Roy Maartens, Parampreet Singh
6 pages, 4 figures
Phys.Rev. D70 (2004) 083517
"Loop quantum gravity introduces strong non-perturbative modifications to the dynamical equations in the semi-classical regime, which are responsible for various novel effects, including resolution of the classical singularity in a Friedman universe. Here we investigate the modifications for the case of a cyclic universe potential, assuming that we can apply the four-dimensional loop quantum formalism within the effective four-dimensional theory of the cyclic scenario. We find that loop quantum effects can dramatically alter the near-collision dynamics of the cyclic scenario. In the kinetic-dominated collapse era, the scalar field is effectively frozen by loop quantum friction, so that the branes approach collision and bounce back without actual collision."
Anyway the answer to Wolram question is that the business of repairing spacetime singularities is going GREAT! Progress in all sorts of ways on it. Lots of papers to read if anyone wants to follow the progress in technical detail.
