The Big Bang Was NOT an Explosion
As I said, I am going to go over this whole big bang thing but before I do, there are some things I feel shoud be gone over.
This story starts a long time ago in 1916 with, of course, Einstein and his need to extend his relativity theory to the domain of gravity. But before I go on, I must point out that there was no explosion in the big bang. An explosion would imply that there was some unique point in the universe that could be specified as the centre. But such is not the case, there is no unique viewpoint, essentially, all is relative. From large enough distances the universe looks the same from everywhere. This is called the Copernican principle. More on this later.
Proof of the Expanding Universe
Returning to Einstein we find that he was able to extend the concept of gravity into his relativistic framework thanks to works by Ernst Mach, Emmy Noether - without whose theorem (when helping Einstein and Hilbert who both created a General relativity theory around the same time, she reconciled the ideas of symmetries, conservation and invariance, e.g. symmetry within Lagrangians yield conserved quantities of motion) much of modern physics would not exist, we owe must to this woman - and various other mathematicians. One of the things his General theory predicted was that the universe should be conctracting, Einstein disliked this as he felt the universe should be static and so introduced a constant into his equations. An entity that would keep the universe apart and together, to put it most succinctly.
As the story goes however, Hubble, around 1930, measured red shifts in the light emitted by distant galaxies thus implying that these galaxies were moving away from us. This redshift is similar to the everyday concept of the Doppler shift common in sounds. Just as objects speeding towards you have a higher pitch while having a lower pitch when moving away we see that objects which emit light and moving towards us have the wavelength of their light being shifted into the high frequency spectrum, the light appears bluer. For objects moving away from us, the light appears red since the wavelength of the light is longer therefore of a lower frequency.
Today, it is known that the galaxies themselves are not moving, but rather the space between them is, thus the red shift found in the lightwaves is due to the fact that the lightwaves are being stretched as space itself expands. Take a moment to digest this if this seems strange to you. There are stranger things yet.
Following the story from another direction we find that in 1917 Friedmann, a Russian mathematician found that space could infact be expanding, he proposed that once, a long time ago, everything was once very close together and then began to move away from each other all of a sudden, the so called big bang, as its ridiculers labelled it. Some time after this in the 40's George Gamow, Ralph Alpher, and Robert Hermann predicted that there should detectable radiation throughout the universe whose temperature was later predicted to be about 3 degrees above absolute zero. In the 60's two Engineers from Bell labs stumbled unto evidence of the bigbang. The Cosmic Background Microwave Radiation (CMB). In modern times, everyone has seen and heard it, every time you turn on the television and see all that random black and white stuff that goes sshhshhshssh and that same crackling sound on the radio, thats what you are hearing, the left over energy from the high energy expansion that took place at the same place all over and had no where to go. You are listening to the beginnings of the universe. From every direction, no matter where you look, the CMBR is almost entirely the same. There are areas of variation related to where perhaps clumps existed that would later become galaxies and stars. But how did this CMB thing come about?
The Difference Between Spontaneous Homogenous Loacation Invariant Expansions and Explosions - Plus a bit on the Big Bang Singularity
In the earliest universe, according to the Standard Model (i.e. big bang theory), all of what we see of our current universe, all the matter, stars were once compressed into one infinitely small space, a singularity. That the current theories encounter singularities and infinities: Infinite density, infinite energy and infinite expansion rate means of course, that our theories breakdown in that area. Chances are that there really was no singularity at the origin of the universe. It makes no physical sense that thing would be that way. Singularities by all appearances do not exist in nature, the next time you see it used as real, know that it was done so inappropriately. Nonetheless we can model what happened as early as 5 seconds after the big bang which there was suddenly a massive expansion as explained above. But the important thing to note is that the expansion occurred at the same time everywhere. This so called big bang happened at no single point but everywhere at once. If you search the internet you will not find a more in-depth explanation than that but I will try and give a simple example of this concept that will prove how you are the centre of your universe.
A better way to look at this is to realize that according to relativity the causal universe is the area you can reach (i.e. it is within a light cone which extend in both directions from you into the past and future for infinity, if you are interested in light cones and the concept of time travel I can dig up a post I made once on them) in finite time. That probably is not much help but consider this. Every galaxy sees all other galaxies as moving away from it, it does not consider itself as moving. If we trace the history of that galaxy back to the big bang we see that it has its own "singularity" different from ours. We can do this for all the galaxies and do find that for every point in space there was a "big bang". The next important thing as I continue to emphasize is that space suddenly began to expand, things did not blow up, common examples are that of baking bread or blowing a balloon. If you have points on a balloon the point themselves are not moving, instead the balloon is being stretched. The early universe was very hot - photons, electrons and quarks moved along freely in a superfluid of sorts - and just as any hot object gives off radiation (your light bulb: light, stove: infrared) so did this universe. As the universe continued to expand things slowly cooled and so did the radiation. Since that energy is effectively trapped in our universe with nowhere to go we should be able to detect it everywhere at a much lower tempereature than before, and we do.
Returning to around the time of the big bang, some 300,000 years after the big bang things had cooled down to about 3000 degrees celsius and nuclei began to be able to form, we believe that before this there was an inflation as some kind of dark energy collapsed into energy.
So with General Relativity we model from a few minutes after the big bang and predict how thing will be and our similuations on distributioon are accurate so long as we assume:
o High Energy, High Density Singularity
o Sudden High Energy Expansion
o Quantum Gravity required to explain what happened here
o Grand Unified Theory Required to explain what occurred here
o Lots of Energetic Photons, quarks and neutrinos floating about in a high energy superfluid
o Quantum fluctuations and various other perturbations occur to create bumps in the otherwise smooth and symmetric early universe - these would later form into galaxies and such
o Nucleosynthesis occurs, various matter particles fuse together and begin to form
o Magic Dark Energy Inflation