Posted on 05/24/2006 3:59:24 PM PDT by LibWhacker
Scientists use quantum gravity to describe the universe before the Big Bang.
Scientists may finally have an answer to a "big" question: If the Big Bang was the beginning of the universe, what could have caused it to happen?
Using a theory called "loop quantum gravity," a group led by Penn State professor Abhay Ashtekar has shown that just before the Big Bang occurred, another universe very similar to ours may have been contracting. According to the group's findings, this previous universe eventually became so dense that a normally negligible repulsive component of the gravitational force overpowered the attractive component, causing the universe to "bounce" apart. This big bounce is what we now know as the Big Bang. The group published its analysis in the April 12th issue of Physical Review Letters.
"These equations tell us that in fact there is another pre-Big Bang branch of the universe, and then we tried to understand what it looks like," Ashtekar said. "[Surprisingly], the universe again looks very much classical.
"So there is another universe on the other side which is joined to our universe in a deterministic way," he concluded.
Coauthor Parampreet Singh, a postdoc at Penn State, said that Einstein's theory of general relativity describes the current universe very well, but it breaks down when it encounters the extreme density of the universe around the time of the Big Bang.
"[General relativity] gives physical singularities when we ask questions about the physics near the Big Bang," he said. "Unless this problem is solved, or unless a solution of this problem is known, we do not have a complete description of the universe."
Physicists have developed theoretical systems, such as string theory, to unite general relativity with quantum mechanics and explain the very early universe. In the late 1980s, Ashtekar published the first paper on loop quantum gravity, a theory which applies quantum mechanical principles to examine the spacetime continuum. According to his model, there is no continuum: Smooth, continuous space is only an approximation of an underlying quantized structure, one that is made up of discrete units.
Loop quantum gravity also predicts a small repulsive component of gravitational force, which is a non-factor in other theories. At most densities, even the extremely high density of an atom's nucleus, this component has no significant effect. But as density increases, approaching 1075 times the nuclear density, this repulsion begins to dominate. According to the Ashtekar's equations, this appears to be what happened to the universe before ours: As it collapsed, it became so dense that gravity started to, in a sense, work backwards, birthing our universe.
Singh, Ashtekar's postdoc, noted that the group's conclusions are eerily similar to findings published by Princeton researcher Paul Steinhardt two weeks ago. Using string theory, Steinhardt concluded that the universe may be cyclic, with each crunch leading to a bounce.
But Steinhardt said the two papers are only distantly related:
"It is an idealized set-up which does not connect smoothly to realistic cosmology," he said via e-mail about the Penn State paper. "By contrast, our scenario is designed so that it connects smoothly to Einstein gravity and standard Hubble expansion, so that it reproduces the astronomical conditions we observe today."
Ashtekar acknowledge that his work addresses the idealized situation of a homogeneous, isotropic universe, one that is uniform in space and uniform in all directions—the model does not account for heterogeneities such as galaxies.
"This picture does hold up in kind of simple generalizations," he said. "The key question is really if this prediction is going to hold up with more and more realistic models."
You mean, created "again".
Who knows? Perhaps it's the case that it only appears to be expanding and that time may, in fact, be running in reverse at the present moment.
You got me. :)
Karma is a deadly business indeed.
Please read #45, Allan. I know you find Physics boring, but a comment from the Mathematicians would be appreciated. (8)
The density of material at the instant the "big bang" is such that no elements are possible. The universe, post bang, starts as a sea of energy. Initial expansion allows cooling and the formation of subatomic particles. As things continue to cool, neutrons, electrons and then finally elemental hydrogen forms. There is no mechanism to carry over anything from the previous expansion/contraction cycle. Time starts at zero with the bang and there is no significance to time before T=0
The elements from hydrogen to iron are formed in the first generation of hydrogen burning stars. The remainder of the elements are forged by later generations of stars going nova. All the elements present in this universe can be accounted for by thermonuclear processes post big bang.
The expansion/contraction of the universe could have been beating like a cosmic clock for uncountable cycles. Or this could be the first "tick" for all we know. Because nothing can pass through the singularity, not matter, not energy, not information. Time truly starts over each expansion.
You may think of it as the ultimate "Mulligan".
Regards,
GtG
Like you say: Limiting it to ONE additional universe makes no sense. Mathematics can be an endless string....WE interfere with it by putting our own mind limitations to it.
I'm not absolutely sure but I think the Black hole theory has been revised.
He spoke and it was. That's how powerful his word is.
According to this theory, yes. But, since we can't look back beyond the signularity of the Big Bang, this is just another piece of fancy speculation pranching around as "science."
This is no more a theory than my grapefruitcentrism is a theory. Both are hypotheses and neither can be falsified but mine has the advantage of keeping time/space jumpers from falling ill to scurvy.
The heavier elements are formed in the crucible of stars and supernovae.
You are right but there three possible results.
1) not enough matter and the universe keeps expanding without bound
2) too much matter and the universe eventually stops expanding and begins to contract into the "big crunch"
and (kind of like the three bears)
3) just the right amount of matter so that the expansion slows at an ever decreasing rate that approaches (but never reaches) zero. This results in a non-cyclic universe with a finite, bound volume.
Observational data seems to indicate that the rate of expansion is slowing, which eliminates number one. My personal favorite is number three because it seems to me to be the sort of thing G_d might do. Put in just the right amount of mass to blow a permanent bubble of space time.
Regards,
GtG
Now we know where the dirt came from...
Our universe is the sand castle he build to while away a sunny afternoon.
Regards,
GtG
It's big bangs all the way down.
Thanks. But it's probably too late to deploy the ping list.
Just postulate another universe and hope nobody notices?......................
Well put, Publius6961!
Black holes are out of sight...
My question for the creationists (and I'm a believer in Genesis as allegory):
If God is eternal, and the universe is 6000 years old (or 16 billion years old, or whatever), . . . . .
. . . what was God doing for the eternity before that?
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.