If you look farther and farther away, you also look farther and farther into the past. The farthest we can see back in time is 13.8 billion years: our estimate for the age of the Universe. But is it correct? Image credit: NASA / STScI / A. Feild.

Ask Ethan: How Sure Are We That The Universe Is 13.8 Billion Years Old?

Very sure. Here’s how we know.

You’ve no doubt heard that the Universe itself has been around for 13.8 billion years since the Big Bang, and that scientists are extremely confident of that figure. In fact, the uncertainty on that figure is under 100 million years: less than 1% of the estimated age. But science has been wrong in the past. Could it be wrong again, about this? That’s the question of John Deer, who asks:

Lord Kelvin estimated the age of the Sun between 20 and 40 million years because his model didn’t (couldn’t) include quantum mechanics and relativity. How probable is it we’re doing a similar mistake when looking at the universe at large?

Let’s take a look at the historical problem, and then jump to the modern-day situation to understand more.

The clusters, stars, and nebulae in our Milky Way are useful for coming up with an age estimate for the Universe, but just as our lack-of-understanding of stellar processes led to big mistakes in our estimate for the age of the Solar System, could we be fooling ourselves about the age of the Universe? Image credit: ESO / VST survey.

Back at the end of the 19th century, there was a huge controversy over the age of the Universe. Charles Darwin, looking at the evidence from biology and geology, concluded that the Earth itself must be at least hundreds of millions, if not billions of years old. But Lord Kelvin, looking at the stars and how…