How old is the Universe?

Measuring the age of the universe has been a challenging, and sometimes controversial, effort among astronomers, with different techniques yielding different results! 

Depending on how precise of an answer you are looking for, we can provide you with some answers in increasing order of complexity:

If you just want a general estimate for the age of the universe, almost all astronomers would agree that the universe is somewhere between 10 and 20 billion years old. That's a big number and difficult enough for most of us fathom.

For a more precise age, we can go a bit further and say that most astronomers would agree that the evidence points towards an age of a bit less than 14 billion years. 

There are a couple of ways they get to these estimates: 

The first is relatively straightforward: look for the oldest objects you can find in the universe. However old they are, the universe itself must be at least that old. At time of writing of this article, one study has found a very old star in our galaxy that is  estimated to be 13.5 billion years old. That sets a lower bound on the age of the universe itself; it must be older than its oldest star!

A second way of measuring the age of the universe is much more complex, and it relies on the theory of how the universe evolved and some fundamental parameters that describe the geometry and content of the  universe and how fast it is expanding.

Some of the most compelling estimates came from space-based observatories:

• In 2012, studies of NASA's Wilkinson Microwave Anisotropy Probe (WMAP) data and theoretical models for the universe yielded as estimate of 13.8 billion years
• In 2015 and 2018, analyses of the Planck observatory microwave background data also suggested an age of 13.8 billion years.

Both of these estimates rely on a parameter which measures how fast the universe is expanding. There is as much as a 10% discrepancy in estimates of this number, depending on the method used to estimate it. This, in turn, could impact estimates of the age of the universe by at least 100 million years or so.

The next generation of space telescopes, including NASA's JWST observatory, will be important to try and pin down how old the universe actually is, and this is a fundamental part of modern astronomy research.

Whatever the final age determination may be, remember that at least in timescales familiar to humans, it's old! 

There are a lot of resources on the internet that try to put this complex concept into terms a non-expert can understand. For more reading, try the NASA Science/Astrophysics webpages. Also the "It Stars with a Bang" series, although written at a somewhat higher level, has very thorough and approachable explanations of this, and other, complex topics. See this article: "Ask Ethan: How do we know the universe is 13.8 billion years old?"