"Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is"
Douglas Adams - "The Hitchhiker's Guide to the Galaxy"
"To see a world in a grain of sand, And a heaven in a wild flower,
Hold infinity in the palm of your hand, And eternity in an hour"
William Blake - from "Auguries of Innocence"
This section covers a very broad time scale from the birth of the Universe until it was about one billion years old. The first part is what is known generally as the "Big Bang". So; what is the "Big Bang"? It is the main current theory of the origin of the Universe. A number of cosmologists prefer the brane world theory, but here I discuss only the Big Bang, or more specifically, the "Inflationary Big Bang". I discuss some alternative theories, albeit briefly, in the "Alternatives to the Big Bang" section. I have tried to show the key points in the history in chronological sequence, so I suggest you go through the items at left in the order they are shown under "Early Universe".
Do note that everything from the point of the birth of the Universe up to the hypothesized creation of primordial black holes probably happened in about one millionth of a second!
Through all this time, right up to today, the Universe has been expanding, and continues to expand. It is crucially important to understand that the Big Bang was not some sort of explosion that occurred in a void of empty space; it is space itself that is expanding and moving everything in it. The point of the birth of the Universe was the moment that space and, probably, time were created. Everything in the Universe, including space itself, was contained within that tiny region (according to many theories, all dimensions would have been at the Planck length, but there are other theories). As space expands, it pulls all the matter with it, spreading it apart. OK; all this is scientific theory. We cannot go back and try it again to see what happens! However, the theory fits superbly with observed data, leaving very few gaps most of which I mention as appropriate.
The biggest gap is what happened in the first tiny instant between zero and the Planck time. Personally, I favor the idea that it was a simple Quantum Fluctuation that triggered the expansion. This means that it is quite possible that there are a myriad of universes out there, all triggered by other Quantum Fluctuations, that we would never be able to observe. Maybe. Then not much more than 100 years ago, many eminent scientists did not believe in atoms!
A question often hear is "what happened before the Big Bang?". This question really has no meaning, and is often compared to asking "what is north of the North Pole?". One can not go further north than the North Pole. The moment that the Universe came into being is the moment when space and time came into being. There was no "before"; for "our" Universe. Of course, it is possible that the "egg" from which our Universe "hatched" was embedded in another universe, but that, essentially, has nothing to do with us. That "other universe" could have produced a myriad of offspring universes. Who knows; our Universe could be producing offspring of which we have no knowledge, and of which we will never have any knowledge. Let's face it, our own Universe provides us with more than enough to think about, analyze and explore.
Astronomy & Cosmology -
The Early Universe
(or "What Banged in the Big Bang?")
As an overview, here is a graphical representation of the Big Bang. It contains links to provide more detail about each topic in, generally, the same sequence that I have used in this section.
Here is a complete glossary, which itself has links to yet more detailed descriptions. None of it is overtly mathematical.
There is also a "Big Bang 101" on the NASA website which is an excellent introduction to the concepts.
You may enjoy this amusing, and brief, video "A shorter History of Time" made by Dr Eric Schulman for the National Science Foundation.