Inflation Theory: A Solution over the Horizon

Paige Yarker. 16 December 2016.

Many people will know of the Big Bang Theory, not the TV show, but the giant explosion thought to have created the universe that we currently reside in. Many people will also know that nothing can travel faster than the speed of light. These two things may seem mutually exclusive, however when mixed together with a sprinkle of observations they cause what was thought to be one of the biggest problems in cosmology.

Out in space there are many things, planets, stars, galaxies, black holes, the list goes on. One of the things out in space that we can observe is something called “cosmic microwave background radiation” (CMBR). This is radiation, which we can observe using radio telescopes, produced about 300,000 years after the Big Bang. This radiation provided valuable insights into the state of the universe in its early life, variations in the medium showing how galaxies could have formed. However, there was a problem: the temperature of the radiation was almost consistent throughout the observable universe. At first this doesn’t seem like an issue though, as nothing can travel faster than the speed of light, two objects on either side of our observable universe should have differing temperatures as there would not have been enough time passed in the universe for the heat information from one object to reach the other. Due to this, the CMBR shouldn’t be such a similar temperature throughout our observable universe because the universe hasn’t been around long enough for equilibrium to be established when the radiation was released.

Temperature fluctuations in the cosmic microwave background radiation (shown as colour differences) Credit: NASA / WMAP Science Team

This problem is known as the Horizon Problem, and Inflation Theory is a solution to it. Inflation Theory proposes that, during the first 10–32 of a second after the Big Bang, there was a period of rapid growth in the universe. This would allow the contents of the universe to reach uniformity before it spread out across the universe, accounting for the constant temperature throughout. The theory was proposed by Alan Guth, and it is a currently accepted theory that is supported by further observations of the universe.


Centre for Theoretical Cosmology, n.d. The Origins of the Universe: Inflation

Cowern, D., 2015. Why is the universe flat?

Krauss, L., 2014. Universe from NOTHING!

Mastin, L., 2009. Cosmic Inflation.

Further Reading:

A Universe from Nothing by Lawrence Krauss

The Elegant Universe by Brian Greene

The Inflationary Universe by Alan Guth