How Do we Know How Old the Universe Is? [duplicate]

It is common knowledge that the universe is 13.8 ± 0.037 billion years - but how was this calculated?

• It's a best fit to the $\Lambda$-CDM model, which includes a cosmological constant and cold dark matter. If the model is wrong, the number may be wrong. However, since the physics during all but the very first fractions of a second is fairly well understood (maybe with exception of neutrino masses and possible dark matter decay), the number won't change significantly if we should discover new high energy physics. I would venture to guess that the remaining uncertainty after that is mostly in the validity of general relativity. Dec 17 '14 at 17:06
• This should not have been closed as a duplicate. Mar 1 '17 at 18:08