8.16 - The Big Bang

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).

Cosmic microwave background radiation as evidence

Cosmic microwave background (CMB) radiation is a faint microwave signal detected from every direction in the sky.

What the Big Bang says about it

• The Big Bang theory explains CMB as leftover radiation from the very hot early Universe.
• As space expanded, this radiation was stretched out to the longer wavelengths of the microwave spectrum.

Why it mattered

• The Big Bang theory predicted this radiation should exist, while rival theories did not.
• Discovering it was the main reason the Big Bang became the accepted model.