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How Old is the Universe?

Astrophysicists tell us the universe is 13.8 billion years old, but how do they know that? Everyday Einstein explains how we determine the age of our universe from ancient stars and relic radiation left over from the Big Bang.

By
Sabrina Stierwalt, PhD,
Episode #146

From very precise maps of the CMB made by space probes like WMAP and the Planck satellite, astronomers and physicists measure these parameters. From them, the determine an estimate of the age of the universe within the theoretical framework of Lambda Cold Dark Matter cosmology, which includes our understanding of what components make up the universe.

This method finds the age of the universe to be 13.8 billion years old, plus or minus 37 million years. This uncertainty in the age, which is relatively small compared to a total time of 13.8 billion, comes from the uncertainties associated with measuring each of the three cosmological parameters.

To put this age in perspective, the age of our Solar System is only about 4.5 billion years. Certain isotopes that were created with the Solar System, like potassium and uranium, offer clues as to the age of our Solar System. These isotopes undergo radioactive decay, and thus, offer a very accurate measurement of the time elapsed since their formation.

The fact that the age determined by the CMB is consistent with the minimum ages calculated for the oldest star clusters and white dwarf stars tells us astronomers that we are on the right track. Keep in mind, though, that we are defining the age of the universe as the time that has elapsed since the Big Bang. None of our observational evidence can tell us what may have happened before the Big Bang—a question that may be better answered by a theoretical astrophysicist or even a philosopher, rather than an observational astronomer.

Until next time, this is Sabrina Stierwalt with Everyday Einstein’s Quick and Dirty Tips for helping you make sense of science. You can become a fan of Everyday Einstein on Facebook or follow me on Twitter, where I’m @QDTeinstein. If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.com.

WMAP image of CMB courtesy of nasa.gov.

Hubble Space Telescope Deep Field courtesy of nasa.gov.

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About the Author

Sabrina Stierwalt, PhD

Dr. Sabrina Stierwalt is an extragalactic astrophysicist at the California Institute of Technology and Adjunct Faculty at the University of Virginia.

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