Before the Big Bang: A Twin Universe? 212
esocid writes "Until very recently, asking what happened at or before the Big Bang was considered by physicists to be a religious question. General relativity theory just doesn't go there — at T=0, it spews out zeros, infinities, and errors — and so the question didn't make sense from a scientific view. But in the past few years, a new theory called Loop Quantum Gravity (LQG) has emerged. The theory suggests the possibility of a "quantum bounce," where our universe stems from the collapse of a previous universe. This may be similar with beliefs of Physicist Neil Turok of Cambridge University who has theorized about a cyclic universe, constantly expanding and compressing."
Re:Fallacy of the Big Bang Theory (Score:5, Informative)
In fact space itself stretches. The separation of the material between pairs of distant (and near) galaxies comes from both their motion through space and the stretching (expansion) of the space between them.
The result is that sufficiently distant galaxies can be much farther apart than they could have traveled - even at the speed of light - through non-expanding space in the time since the big bang.
Re:Fallacy of the Big Bang Theory (Score:3, Informative)
Sure it is. http://en.wikipedia.org/wiki/CMB [wikipedia.org]
Also, http://xkcd.com/54/ [xkcd.com]
Re:Fallacy of the Big Bang Theory (Score:3, Informative)
Imagine space as a slightly inflated rubber balloon. Imagine two dots on the outside of that balloon. Then add air to the balloon, inflating it further.
What you get is two dots that are farther apart, more real distance between them but the same balloon.
Re:You can go almost 3 times the speed of light? (Score:5, Informative)
Consider having two probes going away from Earth at 60%-lightspeed in opposite directions, and they want to communicate with each other. At 120%-c speeds, you might think it's impossible. But each of them could communicate back and forth with Earth at mere 60%-c speeds. If you do the actual math you work out that they appear to each other as moving away at something-like-80%c (that figure is totally made up, but you should get the idea anyway).
Re:not just loop quantum gravity (Score:5, Informative)
Actually there IS something special about loop quantum cosmology - it's theory actively predicts a big bounce instead of a big bang. This comes directly out of the loop quantization of a homogenous and isotropic cosmology. So far all other theories have had to put in a bounce "by hand" - adding extra physics at the singularity in order to get something out of the other side. LQC doesn't do that - it replaces the usual metric and curvature operators with holonomies and flux operators as done in loop quantum gravity (OK, the derivation isn't exact yet, and we've a lot more work to do here).
Once you do this, however (and by using other tricks like using a massless scalar field as your time variable), you see that a contracting branch naturally re-expands once you reach a critical matter density (something like 82% of the Planck density - Ashtekar has a good numerical reason for this IIRC). In these steps you end up replacing the Wheeler-deWitt equation (a continous differential equation) with a difference equation which needs to pick a certain super-selection sector of the theory - in simpler terms the timestep effectively becomes discrete.
The beauty of LQC is that it doesn't need us to speculate about what happens at singularities - it gives us an active way to look at them without needing to invent new physics that only apply there. Sure, it makes a few assumptions - that our basic observables are holonomies and fluxes - but there's no new input directly at the singularity, unlike in other theories (such as ekpyrotic scenarios where two branches are joined artificially across the singularity.
For an introduction, see Martin Bojowald's (one of the founders of LQC) living reviews site:
http://relativity.livingreviews.org/Articles/lrr-2005-11/ [livingreviews.org]
If you have questions, please reply and I'll see what I can do to answer them to the best of my ability. If there's enough interest, I might be able to get an "Ask Slashdot" type of thing put to Ashtekar/Bojowald although it'll probably be their post-docs and grad students who end up answering all the questions
Re:You can go almost 3 times the speed of light? (Score:5, Informative)
Re:You can go almost 3 times the speed of light? (Score:1, Informative)
The speed of inflation apparently isn't limited to the speed of light, which (more-or-less) applies to the transmission of information. There's no way to embed bits into empty space, so there's no limit to the speed of expansion. The question is, is the current rate of inflation a constant, or is it changing? And if it's changing, is that change decaying or accelerating? If the rate is increasing at an accellerating rate, then there will come a time when the space between the earth and the sun is increaing faster than gravity can hold them together. At that point, earth will "gravitationally decouple" and float away. Don't worry, though, about freezing to death. Within a just few hours our atoms will decouple, and we'll all decompose into expanding clouds of gas. And then subatomic particles will get sundered. See http://en.wikipedia.org/wiki/Big_Rip [wikipedia.org] for more details.
Re:You can go almost 3 times the speed of light? (Score:3, Informative)