# Simulation of the Cosmic Microwave Background formation

This simulation shows the formation of the Cosmic Microwave Background (CMB) at a detailed level. Brown spheres are atoms and green balls are photons. Initially the universe is very young and very dense and very hot, and the atoms are ionised and hence opaque to photons. The photons bounce between the atoms, trapped. As space expands, eventually the atoms become neutral (go darker in the simulation), after which the photons just ignore them and fly around undisturbed in all directions. It is these undisturbed photons that form the cosmic microwave background we see today.

This simulation is one of many made during creation of the Australian National University's free online astrophysics courses:

https://www.edx.org/xseries/astrophysics

It was created using the VPython library (vpython.org)

- Kind: Short
- Year: 2015
- Runtime: 1 min
- By: Astronomy Simulations
- Archive: [Wikimedia Commons](https://commons.wikimedia.org/wiki/File:Simulation_of_the_Cosmic_Microwave_Background_formation.webm)
- Licence or status: [CC BY 3.0](https://creativecommons.org/licenses/by/3.0) (as the archive states it)
- Credit: Astronomy Simulations
- Who can watch: Teens profiles and older (the archive gives no rating; placed by Invisible Network from its collection and subjects)

[Watch now](https://invisiblenetwork.ai/watch/archive/commons/74447423?play=1)