9.2 Astrophysics - Cosmology

When we observe light from distant galaxies, we find something strange. The patterns of light (their "spectra") are shifted towards the red end of the spectrum.

This is called Red-Shift. It is a version of the Doppler Effect for light.

Red-shift tells us that the galaxies are moving away from us.

Crucially, the further away a galaxy is, the more its light is red-shifted. This means the further galaxies are moving away from us faster.

This observation is the main evidence that the entire universe is expanding.

The Big Bang Theory is the leading scientific model for the origin of the universe.

It states that the universe began from a single, extremely hot and dense point (a "singularity") about 13.8 billion years ago.

This point then "exploded" and has been expanding and cooling ever since, forming the stars and galaxies we see today.

Source: Pixabay

There are two key pieces of evidence that support the Big Bang Theory:

1. Red-Shift: The fact that all distant galaxies are moving away from us proves the universe is expanding, just as the theory predicts.
2. Cosmic Microwave Background Radiation (CMBR): This is faint radiation (in the microwave part of the spectrum) that is found everywhere in the universe. It is the "afterglow" or leftover heat from the initial Big Bang, which has cooled down over 13.8 billion years.