3.1 The Big Bang

What is the Big Bang and just how big was it?

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DAVID MITCHELL:

60 Second Adventures in Astronomy. Number one, the Big Bang.

Just how big was the Big Bang? The idea that the universe is expanding as a result of a single explosion wasn't always universally popular. In fact, the term ‘Big Bang’ was coined in 1949 by astronomer Fred Hoyle as a way of sarcastically dismissing it. But thanks to Edwin Hubble we now know our observable universe is expanding. And extrapolating backwards, we can tell that 13.7 billion years ago it was all compacted into one super dense ball. And this singularity expanded and cooled to become everything in the universe that we see around us.

So though the Big Bang involved everything in existence, its beginnings were really quite small. And after measuring the background radiation in the universe, astronomers have worked out that the Big Bang was only around 120 decibels, about the volume of an average rock concert. So while the Big Bang still has a lot to teach us about the universe, we do know-- at least to start with-- it wasn’t particularly big and it wasn’t much of a bang either.

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Scientists have observed that the galaxies in the Universe appear to be moving away from each other. If it were possible to wind time backwards, 13.7 billion years ago, all the galaxies would seem to have come from a single, compacted, super dense region – or singularity.

The singularity expanded and cooled to become every thing in the Universe. It is also important to realise that all the matter in the Universe was created in this instant. Since then, matter has changed form, but no extra matter has been formed. This is the Big Bang theory.

One way of envisaging the expansion of space is to think about the surface of a balloon, with galaxies drawn on its surface. As the balloon is blown up, the galaxies appear to move away from each other. What is happening is that the space between the galaxies is expanding. The distance from the surface of the balloon to its centre is a measure of time. When the Universe starts, the balloon has zero size, and as time goes on, the balloon gets bigger. Because all of space was ‘contained’ in the singularity, the Big Bang happened everywhere in space simultaneously.

The Big Bang theory is illustrated on the History of the Universe Timeline. [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)]

Next, you’ll consider whether the Universe will keep on expanding forever.