The Big Bang is currently the most credible scientific theory on the evolution of the early Universe

The Cosmic microwave background radiationThis is usually the most used piece of proof for the Big Bang theory, and for a good reason. For those who don't know what this is, here is a quick description: Back in 1964, astronomers Arno Penzias and Robert Wilson were testing a new radio antenna. They then noticed something strange- wherever they would point the antenna, they would always get a hum. They tried everything to get rid of the hum, but once they finally exhausted all their possibilities, they came to the conclusion that the hum was of extraterrestrial origin and came from every portion of the Universe. Since this microwave-wavelength light, as said, comes from all portions of the Universe and at the same frequency[1][2][3], we can conclude that whatever emitted this light had to have occupied the entire Universe at some point. The Big Bang theory explains this very nicely: that once the Universe began inflating, it was very dense and homogeneous for a long time, and that only after a certain period of time, light started becaming visible to an observer at a certain distance away from the source(319,000 years after the Big Bang). There is also another very important thing about the CMB- the fact that it is only slightly heterogeneous, which can be concluded from the temperature differences between areas. This proves 2 things:1. The Universe was almost entirely homogeneous for a certain time, thus giving further proof to the credibility of the Big Bang theory.2. There were slight differences in densities in the 'source' of the CMB, and by the Big Bang theory, these differences in density would later determine where galaxies, stars etc. would form. We can observe that this is true even today- we can see that the Universe has a large scale structure and that galaxies aren't just in random positions. No other theory, as far as I know, can explain the CMB.2. The expansion of the UniverseThis is a pretty obvious one. We know that the Universe is expanding since galaxies at greater distances tend to have a greater redshift(reddening due to their moving away from the Earth) which means that distant galaxies are moving away from us. [4][5]Since we know that the Universe is expanding, it is only natural to assume that it was much smaller in the past, thus giving further credibility to the Big Bang theory.3. The abundance of light elements(Hydrogen, Helium)Hydrogen makes up roughly 75% of all baryonic mass in the Universe. Helium makes up around 21% of all baryonic mass. It is obvious that the two lightest elements are by far the most abundant[6], and while some may call this just a coincidence, here is another important piece of evidence: the metallicities of stars based on their age. Metallicity does not necessarily show the abundance of actual metals within a star, but any element other than hydrogen and helium. We have observed that the metallicity of young stars tends to be relatively high, relatively low for old stars in globular clusters and almost nonexistent in ancient stars(example:HE 1523-0901). [7][8]Older stars have a much lower metallicity than new, young stars and we can notice that at some point in the past, the Universe was likely metal-free. This further gives credibility to the Big Bang theory, which states that when the Universe was formed, baryonic mass was composed of only hydrogen, helium and trace amounts of lithium[9] and that heavier elements had to be formed during stellar nucleosynthesis.4. The large scale structure of the Universe The galaxies in the Universe are distributed in a relatively neat way: they are grouped into many interconnected galactic filaments with huge voids in between them. [10] This also supports the Big Bang theory, which says that the Universe was only slightly heterogeneous in the beginning and that these differences in density would determine where galaxies would be concentrated. Gravity would be an unlikely cause, since if this was the only factor, galaxies would likely be either in an almost completely random distribution(like stars inside galaxies) or organized into huge clusters, however these huge clusters would be separated from each other, which does not coincide with observational evidence. [1]. http://aether.lbl.gov...[2]http://www.scientificamerican.com... (never mind the fact that the time frames are slightly wrong since the article was written in 2004)[3]. http://www.bbc.co.uk...[4]http://skyserver.sdss.org...[5]http://wmap.gsfc.nasa.gov...[6]http://en.wikipedia.org...[7]http://burro.astr.cwru.edu...[8]http://www.nature.com...[9]http://astro.berkeley.edu...[10]http://www.universetoday.com...