I started a couple of threads like this back in January, or perhaps December; sorry, I can’t be arsed to look it up, as that would be too much like work.
Anyway…the idea here is to see what Dopers know about cosmology. Here are the rules:
Have at it!
Ok, I’ll play.
Um, there are an infinite amount of membranes out there just floating around. When two of them collide, at the point of collision An infinite amount of energy is released, also known as the Big Bang. Every collision creates its own big bang which creates a whole 'nother universe.
… batter up!
At the first moment of the Universe’s conception all that is now the universe was only energy concentrated at a single point. Then the Bang, naturally. Energy began to coalesce into matter as the Universe spread outward and cooled. Further clumping of mass, then stars, then planets etc.
Mind you I’ve read (some proximation of) this. With only my brain, I would probably be thinking:
“… sex. Then food.”
Fiat lux!
With inflation.
It started about 13.5 billion years ago, nearly as a singularity. Its size increased and its temperature decreased at a rate that, on log log paper, would look like a straight line at a slope, except for a brief period where the line jumps at a much greater slope, which is referred to as the inflation.
The various fundamental forces gradually separated out - the strong and weak forces, the electromagnetic force, and gravitation - as temperatures and energy levels fell. At some point (I dunno, maybe 100,000 years into the process) energy became dilute enough to separate out into particles, which let radiation become visible at a distance (though nobody was there to look); this radiation is still visible today, redshifted by cosmic expansion to a blackbody spectrum with a 2.73 millikelvin temperature.
The distribution of matter was originally quite uniform, its only fluctuations being quantum mechanical, but the growth (maybe the inflation phase in particular) made these differences more important, so that they originated the earliest concentrations of mass into stars, much bigger stars (maybe a hundredfold) than we see today. There is some relative proportion of something, I think luminous versus dark matter, that was different then from now to cause this difference.
The overall distribution of matter in the universe has the appearance of the solid part of a foam, with big voids that had early explosions or black holes in them driving matter out of the voids. I think this structure appeared early, is the largest scale structure in the universe, and is visible today in the distribution of superclusters of clusters of galaxies.
How’s that?
It’s okay to go from things you’ve read before. I just don’t want people basing their first post in the thread on knowledge gleaned from Wikipedia. And of course once you’ve gotten past that first thread, you may cite to your heart’s content.
The origin of the universe…14 billion years ago, a very hot, very dense universe started expanding outward–not into space, but actually creating space itself. At first, pure energy (specifically high-energy photons) was continually creating matter and anti-matter through pair creation (simultaneous creation of matter and antimatter), but eventually the universe cooled off (due to expansion) to the point where the average energy of the photons was no longer high enough to turn into the mass-energy needed to create massive particles. Furthermore, the universe went through a short period of rapid expansion very early on, called inflation, in which particle creation/annihilation processes were out of thermal equilibrium because the matter and anti-matter couldn’t reach other before they were driven apart by the expansion. This period of inflation ended, and because the temperature is now too low for pair creation, almost all the matter annihilated with pretty much all the anti-matter, leaving just a small amount of matter left over. (A slight asymmetry in the laws of nature for baryons and anti-baryons made this possible.)
The unstable matter decayed into lower-energy states (lower mass particles) when allowed by the laws of nature, leaving just ordinary matter that we see today (atoms and so forth), dark matter, and some photons (cosmic background radiation).
I’m not exactly sure about the order of things…
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In the beginning there was nothing…
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which exploded! 
All the matter and energy (and space?*) in the universe was mushed together into a single point. I don’t think anybody can know how long it existed like this, where it came from, or what, if anything, came before it. For some reason or another it exploded (The Big Bang) and all the matter and energy began spreading. I’m pretty sure everything was hydrogen at first and all the other elements formed afterwards. Gravity pulled a lot of this hydrogen together and when it gathered in a dense enough mass it would start a nuclear reaction and turn into a star. These stars cluster together in galaxies. Stars helped form all the heavier elements and as they died out their matter became the dust and such that later formed planets, asteroids, beer, and people.
*I think I read somewhere that space, as in the boundaries of the universe itself, is expanding along with the matter and energy. If so I guess at the point of the Big Bang there wasn’t space either, except for what was contained in the singularity. I don’t know, this stuff is fascinating but I need a really smart person who’s fluent in Stupid to make me even halfway grasp it.
I was tought that there was nothing and then it exploded. This mystified me, as anyone with even a passing knowledge of incendiary devices knows that you actually need **something **before there will be an explosion.
Being an artist, I gave up and assumed God left a linseed oil soaked rag in the dustbin.
At first there was nothing, which makes no sense, but it makes more sense than there being something (but we don’t know what or maybe it’s I don’t know what), but then a Big Bang happened and the universe has been expanding ever since which begs the question, expanding into what? I mean, it’s hard enough to imagine the universe never ending, but it’s harder to imagine it ending somewhere–what is past the edge of the universe?
And then I need a drink.
How everything came to be is totally mind-boggling to me. It doesn’t matter if I think about it in atheistic terms, and things just somehow came into being from an explosion, or whatever the scientific term is, or in theistic terms that one or more deities created everything. The fact that we’re here seems impossible to me, except that we are here.
It totally banged.
It’s probably cheating for me to play (cosmology grad student), but I love ruining a bell curve.
So, the true beginning is still very unknown by anyone on the planet Earth. However, we do know that there was one. The very confirmed results of General Relativity, and the observation of the continued expansion of the Universe, force us to conclude that at a point in time about 13.7 billion years ago all of the Universe existed as an object of size less than the Planck length. That object contained everything - space and time, matter and energy. Dark matter and dark energy. It still does contain everything, because what it did was not so much explode as vastly expand. The leading theory as to why this happened has to do with quantum fluctuations of something called the inflaton field. The inflaton field, much like the ambient gravitational field, has its own energy level. The beginning of the Universe, inflation, was when the inflaton field suddenly tunneled to a lower energy state. Parlance for this is that the Universe transitioned from a false vacuum to a true vacuum (ours [discussion still continues as to whether or not our vacuum is yet another false vacuum]).
During inflation, the Universe expanded exponentially, and parts of it were traveling faster than the speed of light relative to other parts (this is ok, since GR says nothing about the relative expansion of spacetime). That solves a number of previously intractable cosmological problems, such as why different parts of the visible Universe are almost exactly the same temperature, and why the Universe appears to be very nearly flat. But the separation of regions in this fashion introduces discontinuities. Regions outside our visible universe may have vacuum of a different “polarity” than ours. In between are anomalies, like cosmic strings, magnetic monopoles, and domain walls. Analysis of the physics of these entities is ongoing.
After inflation ended (which only took a few seconds), there was a “reheating”. The energy of the expansion of inflation smoothly exited into particle showers, creating much of the matter and energy that exist today. Thus it was that other quantities came to dominate the energy density of the Universe: dark energy, dark matter, ordinary matter, radiation, and the spacetime curvature. At first, radiation was dominant, and it was too hot to form baryons like protons and neutrons. It was a quark-gluon plasma, with the leptons (like electrons) thrown in to taste. Cooling happened, and nuclei formed, but everything was still ionized. About 300,000 years after the reheating, it was cool enough for atoms to form, and the nascent Universe became mostly transparent to light. It was at this point that the “surface of last scattering” emitted its light rays. We see it today as the Cosmic Microwave Background, and it has been the single most influential scientific discovery in human history.
Some time later, matter and dark matter began to clump, and dominate the energy density of the Universe. Black holes and galaxies formed through processes that are not well understood. This period constitutes most of the history of the Universe that has occurred so far. About one billion years ago, matter dominance gave way to dark energy dominance, and the expansion of the Universe began to accelerate once more. Save a further radical reworking of our understanding of cosmology, as a result of this we know that the Universe will end not in a bang but in a whimper: everything will expand forever, and lone galaxies will be island universes unto themselves. Cold, dead bastions of the heat and light that once warmed the cosmos will be as dead dusty husks of their former selves.
Have a nice day!
In the begining there was a turtle.
And then another showed up and they mated.
And then BANG!
Turtles all the way down.
[sub]I think the Elephant is the chaperone[/sub]
There could only be a bang if there was something to explode into. I imagine it was more like a pssssssssshooooooooo sound.
An infinitely hot, infinitely dense, infinitely small particle got bigger really fast. The hydrogen inside of it cooled, then coalesced into chunks which combined with other chunks to form larger chunks, lather, rinse, repeat. As chunks grew really big, the hydrogen sort of transformed into other elements. The really big chunks formed stars, the smaller ones formed planets.
In the beginning, the universe was very tiny, although how you measure ‘tiny’ is a little tough in this context, since it was the universe, and there was nothing external to it with which to measure.
Nonetheless, it was certainly crammed together. Possibly it wasn’t there a little while before that, and it’s entire existence occurred due to a momentary and soon to be remedied discrepancy in the cosmic balance sheet of things and antithings coming into existence and canceling one another out again.
So. In the first few small increments of time - and I note there are probably some problems with measuring time, since the entire universe is packed together like a sardines on a neutron star - in the first few increments of time the universe expands, or if you prefer, explodes into existence, first as whatever the fundamental units of matter and energy turn out to be, then coalescing into more familiar toolkit of matter and energy we can identify today.
Possibly the fundamental physical constraints of the universe are also settled at this time, and we could have had a completely different universe if things had been ever so slightly different in the first few mini-moments. After that its just expansion, formation of atoms and whatnot, and eventually coalescence of matter into galaxies, stars, dust and other bits.
The whole universe was in a hot dense state. Then 14 million years ago something something something…
or:
In the beginning God created the heavens and the earth. Now the Earth was without form and void, and darkness was over the surface of the deep. And the spirit of God hovered over the Waters.
And then God said, let their be light. And there was light. God saw the light, that it was good. He divided the light from the darkness. The light he called day, the darkness he called night. Then evening and morning, the first day.
…
On the seventh day, God said, “Looks good. I’ll take a break.” And that’s when all the shit started going wrong.