The Big Bang Theory

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No, I’m not talking about the sitcom where the main character inexplicitly manages to date very attractive women despite being a socially awkward experimental physics researcher – because that kind of thing happens in every university no doubt! (or maybe it was just my university experience….).

No I am talking about where it all began – the birth of the universe we live in! The big bang was a massive explosion that created all space, matter and time as we know it. It started out from a small point and continues to expand outwards to this day.

So where did this theory come from? Initially the phrase ‘ big bang’ was used in ridicule in the 1940s, as most physicists believe the universe was in a steady state, such that matter was constantly being created and destroyed meaning the universe could have been around for an unlimited amount of time. However, by the 1960s more and more evidence began to stack up in support for this big bang theory.  It had already been proved by Edwin Hubble in the 1920s that most galaxies were moving away, as light that had travelled to our planet appeared redder than when it would have left its galaxy, i.e red shifted. This was because light would take slightly longer to travel in an expanding universe than in a static one. (Incidentally it is the same reason why the sky is dark at night, since most light is so red shifted that it becomes infra-red and we cannot see it with the human eye, hence the darkness)

In 1965, two gentlemen named Arno Penzias and Robert Wilson were working on a radio receiver when they were puzzled by a faint noise signal that they just could not get rid of. It seemed that there was an extra source of microwaves coming from all over the sky, which was equivalent to a few degrees in temperature. What this turned out to be was the last remnants of the big bang, the last embers of the explosion so to speak, what we now know as the Cosmic Microwave Background Radiation (CMBR). Bill Bryson was famously quoted in 2005 as saying:

“Tune your television to any channel it doesn’t receive, and about 1% of the static that you see is accounted for by this ancient remnant of the big bang. The next time your complain that nothing is on, remember that you can always watch the birth of the universe”

The map of the temperature of the universe Cosmic Wave Background Radiation
The map of the temperature of the universe – Cosmic Microwave Background Radiation

So what actually happened during the big bang itself?

Well most of the main building blocks of the universe were formed within the first hour.  Within 1 picosecond (10-12s or 0.000000000001s) the four main forces we know today separated from each other – the ‘strong’ force from the electronuclear force, and the ‘weak’ force from the electromagnetic force. In this time also quarks and anti-quarks start to populate the universe. After 50 microseconds (10-6s or 0.000001s) these quarks bound together to form neutrons and protons. After one millisecond (10-3s or 0.001s) Hydrogen is formed, and 3 to 20 minutes later Helium is formed, thus producing the two main building blocks of stars. During this brief time the temperature has also cooled from a staggering 1-2 quadrillion K to 1 billion K. (K stands for Kelvin which is a different temperature scale that starts at -273⁰C, or ‘absolute zero’)

However, it takes another 380 thousand years for hydrogen atoms to combine to form molecules, only when the temperature has cooled to 3000K, and a further 200 million years for the first stars to heat up when the overall temperature in the universe is 50K.

13.7 billion years later we arrive at this point in time where the temperature of the universe is now 2.726K.

The history of our universe...
Click to expand the history of our universe…

What brought about the big bang you may be asking? Well the truth is we don’t know, and most likely will never know, but we can speculate as to what the future of our universe might be. One theory is that eventually gravity will become the dominant force in the universe and pull everything back into the centre – fittingly known as the ‘big crunch’. This also produces a counter theory that there are multiple universes that are constantly expanding and contracting, in a sort of birth-death cycle. Maybe the cause of the big bang was a previous universe imploding in on itself, before exploding back out again.

Is the Big Crunch around the corner?
Is the Big Crunch around the corner?

Another theory is that the expansion becomes too much and eventually starts to rip the universe apart, scattering it with black holes and particles, or a ‘big chill’. The last theory is a lot nicer to think about – a ‘goldilocks universe’. Where the universe continues to expand forever but slows down to the point where it is just right for us to survive.

For now though we can continue to work on the theory of how an experimental physicist named Leonard gets a beautiful blonde named Penny – now that is one of the great mysteries of the universe!

Punching above his weight....
Punching above his weight….

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