How did the universe begin?

• The most popular theory is the Big Bang

• Matter, energy, space and time all started 13.7 billion years ago

• Nobody knows what caused the Big Bang, or even if it had a “cause”

• At first the universe was infinitely hot and dense, smaller than a single atom

• In an instant, the universe expanded very quickly

• Then it settled down to a slower rate of expansion, cooling all the time

• After a few minutes it had cooled enough for protons to form

• It took another 380 000 years to cool enough for hydrogen and helium atoms to form

• The universe became transparent and filled with light

• This is as far back as astronomers will ever be able to see, even with the biggest space telescopes

[Image by NASA]

• Hydrogen and helium were the raw ingredients that were available for making stars form

• Heavier atoms were made inside stars

• Then more stars were born, many of them with planets like our solar system

• These smudges, taken by the Hubble space telescope, are galaxies forming in the early universe

[Image by NASA]

• Whichever way you look out into space, you see galaxies speeding away from us

• The light from these galaxies is stretched out towards the red end of the spectrum

• Measuring this red-shift tells us how fast they are moving

• The further away they are, the faster they are moving away

• So the universe was once much smaller and denser [Image by NASA]

• We can measure faint microwave (heat) radiation coming from space

• This image shows the cosmic microwave background radiation arriving from all directions (the colour is false)

• It’s the after-glow from the Big Bang, when the universe must have been incredibly hot billions of years ago

• It’s existence was predicted from Big Bang theory before it was discovered

WMAP

[CERN]

• Light elements like hydrogen make up most of the matter in the universe, with smaller proportions of heavier elements

• This ties in nicely with what the Big Bang theory predicts we should find

• Like any idea in science, the Big Bang theory is only as good as the evidence that supports it

• So far it has stood up to everything we’ve thrown at it

• But there are big gaps in our understanding

• The LHC experiments recreate conditions 1/100th of a billionth of a second after the Big Bang

• Nobody is sure what we will discover… [CERN]