This week I’ll be taking a look at the BBT, which henceforth shall be the abbreviation for the Big Bang Theory, not a Bacon, Beef and Turkey sandwich, although that sounds good (mmmm, bacon). Depending on how you measure it the BBT has been around for 70-80 years and in that time has beaten out all other attempts at answering the question of cosmic origins to become not only the best known but also the most likely explanation. Even though BBT deals with some quite complex concepts it makes several concrete predictions that I think most people can get a handle on. Firstly, in the first moments of the Universe there was intense heat (ie radiation), out of this would have condensed the first atoms. Knowing this we can predict what elements would have been formed and in what relative abundances. The expected ratios turned out to be approximately 75% Hydrogen, about 25% helium and tiny amounts of lithium and beryllium. That this is in fact exactly what we observe is one point for BBT.
Secondly, another consequence of BBT is that once the elements had been formed they would have spent their first years as an ionised gas (a plasma, for those of you who take note of these things) which prevented the transmission of photons of light through space. When the Universe cooled down sufficiently that the ions could recombine the photons were allowed to go on their merry way. This means that space should be filled with the light of that first explosion. The fossilised remnants of this primary event should be our constant companion on our journey through space, where is it? Well, in the time since the BB the Universe has been busy expanding, not just objects moving away from each other but an expansion of space itself. One of the effects of this is to cool the radiation to about 2.7K (-270C). Whereas visible light has a wavelength of 400-700 nanometers and according to the physics of light has a temperature of roughly 3000K, the light from the BB has been redshifted until it is about 1.9 millimeters. This puts it in the microwave region of the electromagnetic spectrum. As such it is now called the Cosmic Microwave Background (CMB) as it is all around us permeating the background of our lives, an invisible backdrop against which our endless revolutions around the Sun play out. Discovered in 1964 it is another point in BBT’s favour.
Thirdly, as a consequence of the ratios of elements formed in the BB and the fact that all other elements are formed either within stars as they burn or as by-products of the death of large stars we would expect these massive gaseous beings to have a higher proportion of Metals (astronomers consider everything above Hydrogen a Metal) in their composition the later in cosmic history they were formed and this is exactly what we see, another point. Obviously the points presented here have been pre-chewed for easy digestion and as such can not convey the complex subtleties that continue to support the BBT the closer you look. I strongly recommend following this up with your own reading, I think you will be surprised. Right, I’m off to make my own BBT, the sandwich not the Theory. Mmmm bacon.
Here’s a timeline of some of the significant events related to the development of the Theory:
http://en.wikipedia.org/wiki/Big_Bang -only one reference. What can I say, Wikipedia Rocks.