expansion of the universe

expansion of the universe means that, on large scales, space itself is stretching over time.

That expansion shifts light to longer wavelengths (redshift), which is one key observation in cosmology.

It also explains why ancient radiation like the Cosmic Microwave Background Radiation is now observed in microwaves.

See also

• The Big Bang
• Cosmic Microwave Background Radiation
• Electromagnetic Radiation
• Cosmos