How did the universe begin?
Dec 30, 2015
• 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]