24.4 - The Big Bang

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).

Microwave radiation from every direction

• Detectors pointed anywhere in the sky pick up a faint glow of microwave radiation.
• It arrives from every direction at a specific frequency.
• This is the cosmic microwave background radiation (CMBR or CMB).
• It doesn't come from any single object - it fills all of space.

CMBR is stretched-out radiation from the early Universe

• CMBR is leftover radiation released shortly after the Universe began.
• When first emitted, it was high-energy, short-wavelength radiation.
• As space expanded, the radiation was stretched along with it to longer wavelengths, reaching the microwave region today.
• Because the Big Bang model predicted this leftover radiation, the CMBR is key evidence supporting the hot Big Bang model.