Question: how did the world begin (the big bang)?

Jess Wade answered on 15 Jun 2015:

This is actually a brilliant question, the topic of great debate and loads of science research. We’re all in agreement it probably happened about 14 billion years ago. That’s 14,000,000,000 years! Then, the entire universe was absolutely tiny, and was hotter than anything we could imagine.

What we do know about the big bang is that it happened very quickly. The universe probably grew from the size of a single atom to a whole galaxy in less than a second! Like you and me, the universe is still growing now, which leaves loads of great astrophysics for you to discover. Over the first three minutes of the unvierse’s life, the temperature dropped to less than 1,000,000,000 C. Still super hot, but this temperature let all of the different material in the explosion start to stick together. When these stuck they formed hydrogen and helium nuclei. These are just the beginnings of hydrogen and helium atoms- without any of their electrons. 300,000 years later, the temperature had dropped to only 3000 C! That’s still way too hot, even with strong sun cream! But at this temperature the atoms could capture electrons and form real life atoms. This made gas clouds of hydrogen and helium, that was the beginning of stars.

When a star is born, there is a little cloud of hydrogen or helium that somehow gets a bit restless. This causes the cloud to contract (squish) and all the hydrogen atoms in it zooms towards the centre. The hydrogens are moving so quickly they gets really hot, and then starts hitting into other hydrogen atoms which are also zooming towards the centre of the cloud. When these atoms hit each other they stick together- which makes more heat and makes more collisions. The hydrogens eventually fuse to make helium (the next one up on the periodic table) and we keep making heavier and heavier elements as more heat is produced.