8.5 - The Origin of the Universe
The expanding Universe points to a beginning
Nearly all galaxies are moving away from one another, and the more distant a galaxy is, the faster it is moving away.
The balloon model
- Imagine a balloon with spots painted on it: as it inflates, the rubber stretches and every spot moves further from every other spot.
- The balloon's surface represents space itself and each spot represents a galaxy.
- Space is stretching and carrying the galaxies apart, so the whole Universe is expanding.
Working backwards
- Because galaxies are moving apart now, in the distant past they must have been much closer together.
- Following this backwards leads to the conclusion that the Universe began from a single, extremely small region - the starting point for the Big Bang theory.
The Big Bang theory
- The Big Bang theory is the accepted explanation of how the Universe began.
- All the matter and energy in the Universe was once concentrated into a single, tiny region that was extremely hot and dense.
- It then began to expand rapidly - the Big Bang - and space has been expanding ever since.
The age of the Universe
- The theory gives the Universe a finite age.
- Working back from the expansion rate gives an age of roughly 14 billion years (about 13.8 billion years).
Theories change as new evidence appears
- The Big Bang is the best theory available at the moment, not a final answer.
- Science works by testing theories against observations:
- New evidence that agrees with a theory strengthens it.
- New evidence that contradicts a theory forces scientists to change or replace it.
The role of better telescopes
- Modern telescopes can detect new regions of the electromagnetic spectrum.
- Telescopes on satellites above the Earth's atmosphere provide clearer data.
What is still unknown
- Observations of supernovae show that the expansion of the Universe is speeding up.
- To explain what they observe, scientists propose two unknown components:
- Dark matter - Provides extra gravity that holds galaxies together, but emits no electromagnetic radiation so it can't be seen directly.
- Dark energy - Thought to cause the accelerating expansion.
TermDefinition
Big Bang theoryThe theory that all the matter in the Universe was once packed into a very small, extremely hot and dense region, and that the Universe has been expanding from it ever since.
Dark matterAn unknown substance that provides extra gravity to hold galaxies together but emits no electromagnetic radiation.
Dark energyAn unknown component thought to be causing the expansion of the Universe to speed up.