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."
Is heat death still possible under this theory? (Score:1, Interesting)
Obviously, IANAPBICAT (I am not a physicist but I'm curious about this).
not just loop quantum gravity (Score:5, Interesting)
There's nothing particularly special about loop quantum gravity that makes it possible to avoid having a singularity at the big bang. Loop quantum gravity is just one theory of quantum gravity. The best known theory of quantum gravity is string theory. In pretty much any theory of quantum gravity, the classical picture of the big bang singularity is going to get heavily modified. The conditions of the big bang are pretty much the only conditions under which you really need a theory of quantum gravity (unless you're really clever about finding some other situation, like black hole evaporation, where quantum gravitational effects come in). In all theories of quantum gravity, there's a scale called the Planck scale, and when you go beyond that scale (e.g., the universe is hot enough so that the wavelengths of particles are on the order of the Planck length), mysterious stuff happens. Because of this, it's reasonably plausible that the big bang singularity is eliminated in any theory of quantum gravity.
Old attempts to make a theory of a rebounding big bang (with, e.g., a cyclic universe) had various technical problems, which have been solved in recent years. In a rebounding big bang, there are issues to worry about such as what happens to causality, entropy, and the thermodynamic arrow of time. E.g., you could imagine that a universe cycles through a series of big bangs, and that each cycle is a lot like the one before, or you could imagine that the second law of thermodynamics operates across rebounds, so that each cycle has more entropy than the one before. You could imagine that there could be cause and effect relationships extending across rebounds, or that that could be prevented by the laws of physics. Some people believe that there's an unsolved "entropy problem" in the current standard big bang theory. Here [princeton.edu] is a good FAQ about cyclic models.
Re:Fallacy of the Big Bang Theory (Score:4, Interesting)
What you want is a specific "point" at which the big bang happened. That's not the case. When it happened - it WAS the universe - ie it was every single point at once. As the universe expands - anywhere you look from or to you'll be able to see this background radiation. Of course there will be fluctuations if the expansion of the universe isn't completely uniform - and why should it be? Matter distorts space and time, contributing to this non-uniformity.
If it really is just nodes and links at the bottom (Score:5, Interesting)
A likely scenario is that "somewhere" long unreachable beyond our event horizons, there was a region of network sustaining chaotic inflationary expansion in which a bubble of more conservative physics emerged. Our conservative bubble only exhibits polynomial (near cubic) growth but that was enough to separate it from the exponentially growing seed graph.
My current betting is that Type 1a Supernovae [wikipedia.org], or at least some more precise analogue thereof in our parent cosmos, seed new outbreaks of chaotic inflation in which a new generation of more conservative bubble cosmoses arise, the whole process being susceptible to selection for fecundity and constrained only by the need for a viable history to some initial conditions simple enough to have just happened, presumably for no better reason than because nothing is unstable.
Re:You can go almost 3 times the speed of light? (Score:5, Interesting)
Nope. You can't observe objects whose effective speed in your reference frame - combining inflation with velocity - is greater than C. The light from them never reaches you and light from you can never reach them. From your point of view they're "off the edge". It's as if you and they were each below the event horizon of a black hole relative to each other.
(And sorry about an error in my previous post. The correct buzzword for the stretching of space is "inflation".)
Or at least that's how I understand it. IANAP(hysicist)
Re:You can go almost 3 times the speed of light? (Score:2, Interesting)
It makes no sense, but it's OK because the theory never allows us to loop past each other like on a donut and simultaneously notice that the other person is a lot older than we are.
Re:Does anyone know ... (Score:5, Interesting)
The common view now is that the expansion of the universe is accelerating [wikipedia.org]. As the universe ages, galaxies will be spread further away, and the amount of hydrogen and helium in any given galaxy will start to decrease to the point that it would be difficult to produce any stars. Galaxies will be full of brown dwarfs, white dwarfs, and black holes. Over a long time frame, galaxies will start shedding some of their stars, and black holes will decay via the process of Hawking radiation [wikipedia.org]. Eventually, about a googol years from now, protons will start to decay [wikipedia.org]. As the universe runs out of ways to generate energy, there will be parts of the universe, starting with the large empty gaps left behind by the expansion, that will undergo a phase transition. Once some pockets of the universe undergo phase transition, they will act as seeds that spread the transition to other parts of the universe (like the process of water turning into ice). When the phase transition is complete, the laws of physics will change drastically, and there may be a new seed for a new universe.
As I mentioned earlier, it's WILDLY speculative, so don't take this comment as anything definitive. I just wanted to illustrate one of the many theories out there that share some of the most basic premises of the one in the story.
universe stems from the collapse of a previous uni (Score:4, Interesting)
Read this off http://en.wikipedia.org/wiki/Cosmogony [wikipedia.org] the other day. Kinda similar idea in ways:
What if the big bang was just the explosion of all the crap that was in the event horizon of a black hole from a parent universe?
Questions I have are:
-How could there be such a massive black hole in a parent universe that our universe originated from? Subsequent universes would have smaller and smaller total mass/energy so it couldn't go on forever, and that would mean there was a starting point?
-Wtf is the collapsing of a black hole? I thought they evaporated...
Re:Does anyone know ... (Score:2, Interesting)
Yeah, but then again, you're assuming he actually believes the stuff he spouts off, b/c in this universe, he refuses to debate ANYONE on the facts, and he owns the companies he buys 'carbon credits' from... weird, huh?
Re:Does anyone know ... (Score:1, Interesting)
LQC predicts that the contracting phase of the universe (imagine a tape recording of the universe run backwards if you like) connects to an expanding phase at a critical matter density - so you get a big "bounce" instead of a big "bang". On the other side is a collapsing universe. The universe starts out large, smooth and low curvature/energy density. As you go back in time, the curvature gets large, as does the energy density. LQC says that when the density of energy reaches something near the Planck density (it's much more precise about this than I'm being here) the contraction of the universe stops, and it begins expanding again.
Something that people don't seem to realize here: This is a prediction of the theory. Not the theory itself. A lot of people here talk about theories about what happens near a singularity (even if they don't use the technical term). LQC takes its basic variables, makes the assumptions about how they are quantized (and that is where the theory stands distinct from others, such as WdW and string theories) and then actively calculates what will happen as you approach the singularity. Everyone had active guesses at what happens at the big bang, but LQC has an actual prediction.
It's much like the situation with black hole evaporation - lots of physicists had theories (again more like guesses really) about what happened: stuff came out/went to another disconnection sector of the universe/everything turned into a point, but Hawking's famous work was to calculate a prediction (from quantum field theory adapted to curved space time) that the mass would radiate away over time.
Re:Thanks for furthering your agenda! (Score:2, Interesting)
And then there's me... I can get laid, but only by using a couple of paper clips, a rubber band and a slinky.