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Asked by ilovemydogholly to Claire, Kate, Matt, Rob, Sam on 24 Jun 2013.
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Sam Geen answered on 24 Jun 2013:
The Big Bang is a bad name for it. I know people who refuse to use the words “Big Bang” because that’s really not what it is. There’s no “bang”, no explosion. Instead, it’s the expansion of space. What does that mean?
About a hundred years ago, Edwin Hubble noticed that distant galaxies were moving away from us, and that the further away they were, the faster they were moving. The reason for this is that space is expanding – the universe we all live in is expanding at the same rate everywhere, so galaxies twice as far away are moving twice as fast away from us. It’s not an explosion, it’s not a bang, it’s just the universe expanding all over at the same rate at once. At some point billions of years ago, it must have been very small, possibly zero size. And that’s all the Big Bang is – the universe getting bigger all the time, everywhere at once.
For a while, scientists like Fred Hoyle believed in “Steady State theory”, in which the universe is continuously making matter and expanding. Big Bang theory, by contrast, says that the universe was once nearly zero size, and started billions of years ago. So why don’t we believe in Steady State theory?
One thing is the Cosmic Microwave Background – this is a glow of microwave radiation coming from everywhere. This fits with the Big Bang theory, because at some point the universe was very small and thus dense and hot, and the microwaves are from when it was really hot and bright. Big Bang theory can also explain why there is the amount of hydrogen and helium that we can see in the universe, again because it was made when the universe was very hot, and protons and neutrons formed and came together in certain amounts.
Also say hi to your dog!
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Claire Lee answered on 24 Jun 2013:
Awesome answer by Sam!
Another really cool thing is that the galaxies, clusters, etc that you see across the sky are a picture of what the universe looked like in the first fraction of a second after the big bang.
Right then, when the universe was so small, space was kind of bumpy due to quantum mechanics. These “bumps” were so so tiny, much MUCH smaller than an atom, but then the universe expanded, and the tiny bumps were stretched out into wide hills and valleys.
In the valleys, matter started collecting, so there were places of more dense stuff (valleys) and less dense stuff (hills). Where the matter was more dense, there was a bit more gravity, and that’s where stuff started collecting.
Over many many years these areas became the large clouds of gas that eventually condensed to form stars, galaxies, and galaxy clusters.
So when you look up at the sky and see the patterns of the galaxies in the universe, you are actually looking at (almost) 14 billion years of quantum mechanics 🙂
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