#### marcus

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Martin Bojowald has a bunch of papers 2001-2003 on loop quantum cosmology including ones which dispose of the time zero singularity-----the glitch which was christened the "big bang" but is actually a breakdown of the 1915 einstein equation: GR fails to compute at time zero and by quantizing it Bojowald gets it to compute.

Recently some other people have been following up on some of Bojowald's results so there is a bunch of papers by other people.

Among other things, inflation has been derived from the quantum GR model. I've posted some links in other threads.

Anyway, John Baez often has the most graphic and intuitive way of seeing things and the most simpatico explanation and he describes the bounce at time zero as a turning inside out of the volume------what preceded the "big bang" was a "big crunch" he says.

Here is an exerpt from John Baez "This Week's Finds #167". A complete collection of TWF, including the one containing this passage, is at Baez website.

"...Here's where things get technical, in a way that tickles me pink, but may bore you to tears:

A funny feature of the volume operator in loop quantum gravity is that it's expressed in terms of the square root of the absolute value of a certain quantity. We can think of this quantity as a sort of "volume squared" operator, but with both positive and negative eigenvalues. This always used to puzzle me, and I've put a lot of thought into this issue. Renate Loll has also written a paper about it. I'm delighted to find that in Bojowald's setup, it becomes a real *virtue* of loop quantum gravity, since it allows us to extrapolate our quantum cosmology to negative times - or more precisely, negative "volume squared"!

How can you visualize this? Crudely speaking, negative-volume-squared states of the universe can be thought of as "inside-out versions" of positive-volume-squared ones. So the way I visualize Bojowald's result is like this: the universe shrinks to nothing as you rewind history back to the big bang, and then expands again "inside out" as you go to negative times..."

To read more about this from TWF #167 see

http://obswww.unige.ch/~lbartho/TWF/week167.html [Broken]

Thanks to selfAdjoint for the reference to Baez This Week Finds

Recently some other people have been following up on some of Bojowald's results so there is a bunch of papers by other people.

Among other things, inflation has been derived from the quantum GR model. I've posted some links in other threads.

Anyway, John Baez often has the most graphic and intuitive way of seeing things and the most simpatico explanation and he describes the bounce at time zero as a turning inside out of the volume------what preceded the "big bang" was a "big crunch" he says.

Here is an exerpt from John Baez "This Week's Finds #167". A complete collection of TWF, including the one containing this passage, is at Baez website.

"...Here's where things get technical, in a way that tickles me pink, but may bore you to tears:

A funny feature of the volume operator in loop quantum gravity is that it's expressed in terms of the square root of the absolute value of a certain quantity. We can think of this quantity as a sort of "volume squared" operator, but with both positive and negative eigenvalues. This always used to puzzle me, and I've put a lot of thought into this issue. Renate Loll has also written a paper about it. I'm delighted to find that in Bojowald's setup, it becomes a real *virtue* of loop quantum gravity, since it allows us to extrapolate our quantum cosmology to negative times - or more precisely, negative "volume squared"!

How can you visualize this? Crudely speaking, negative-volume-squared states of the universe can be thought of as "inside-out versions" of positive-volume-squared ones. So the way I visualize Bojowald's result is like this: the universe shrinks to nothing as you rewind history back to the big bang, and then expands again "inside out" as you go to negative times..."

To read more about this from TWF #167 see

http://obswww.unige.ch/~lbartho/TWF/week167.html [Broken]

Thanks to selfAdjoint for the reference to Baez This Week Finds

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