24.3 - Red Shift

Red-shift is evidence the universe is expanding

• Distant galaxies are receding in every direction, and the further away a galaxy is, the faster it's moving away.
• This is evidence that the whole universe is expanding.

Space itself is stretching

• The expansion happens because space itself is stretching, rather than galaxies flying through fixed space.
• As light travels across expanding space, it's stretched to a longer wavelength.
• Light that has travelled further has crossed more expanding space, which is why more distant galaxies show a greater red-shift.

The balloon model

• As a balloon with spots drawn on it is inflated, every spot moves away from every other spot, and spots that start further apart separate the fastest.
• The surface represents space and each spot represents a galaxy.
• This expansion supports the idea that the universe began from a single hot, dense point.