Simulations of Anisotropies in the Cosmic Microwave Background

The universe is expanding. Tomorrow our cosmos will be bigger than it is today. Yesterday, it was smaller. Five trillion days ago--around the time of the Big Bang, the birth of our universe--the hundreds of billions of galaxies that currently populate the heavens were on top of one another in a hot, dense state of matter called a plasma. The remnant glow of this plasma, called the cosmic microwave background (CMB), exhibits faint temperature and polarization patterns that cosmologists study to learn about the properties of the early universe. Below is an interface that allows you to toggle hypothetical physical conditions in the universe and simulate images depicting the resulting patterns in the CMB.

With the current version of Wolfram CDF player (available here), the interface should load in under a minute. For a higher resolution version of the interface, click here.

On the left is a list of six parameters that quantify various properties of our universe. The middle value is the actual value. In the center is a simulated CMB temperature map that changes in accordance with the combination of parameter values being considered. This is a map of a patch of sky slightly larger than your outstretched hand. On the right is a plot that displays deviation from average temperature as a function of angular size. Low l values correspond to large scales. This is called a temperature power spectrum.

The Parameters

  • H - The Hubble constant. This is a measure of the current expansion rate of the universe.

  • Ωbh2 - The physical baryon density. This is a measure of the current density of baryons.

  • Ωch2 - The physical cold dark matter density. This is a measure of the current density of cold dark matter.

  • τ - The reionization optical depth. This is a measure of the time since the first stars in the universe began to turn on.

  • ns - The scalar spectral index. This is a measure of the initial density inhomogeneities in the plasma as function of spatial scale.

  • As(109) - The scalar amplitude (109). This is a measure of the amplitude of the initial density inhomogeneities in the plasma across all spatial scales.

If you have questions or comments about the interface, please feel free to contact David Marulli at