Astronomers Saul Perlmutter, Brian Schmidt, and Adam Riess received the Physics Nobel Prize in 2011 for their 1998 discovery that the universe is not only expanding, but the rate of expansion is increasing. To see exactly what this means, notice that none of the universes explored here grow in size as fast as our own universe. The best explanation for the accelerated expansion is that 70% of the mass of the universe is made up of a mysterious substance called dark energy that has the effect of anti-gravity.

Dark energy was discovered by observing distant exploding stars called supernovae to see if they were as bright as they were expected to be. They were actually dimmer than expected, meaning that they were farther away than expected. Brightness is inferred from a quantity called the distance modulus, the difference between observed brightness and actual brightness. Note that dimmer objects correspond to larger values of the distance modulus. Distance is inferred by measuring the redshift, z, of the supernova: higher redshifts mean that the light waves travel a longer distance and that the waves are being stretched more by the expanding universe during their journey than waves that travel a shorter distance.

The red curve is our universe with matter=0.3 and dark energy=0.7. The CDF player may take a couple of minutes to load.

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Supernova Data Demo

South Carolina State University, 01/24/2015
This material is based upon work supported by the National Science Foundation under Grant Number AST-0750814. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation.