Exactly How Old Is Space?

There’s some important clues in the universe around us that point to the fact that at some point in the past, the universe was tiny. For one, we can look at galaxies and notice that in general they appear to all be moving away from one another. Which means that in the past, they must have been closer together. Keep working backwards, and it would seem that everything must have been really close together at some point in the distant past.

The Big Bang Theory would explain a lot of what we can see in the universe. It would explain why the universe appears to be expanding (all the galaxies seem to mostly be moving away from one another), and it would explain the “cosmic microwave background” radiation that we can observe with radio telescopes.

Using something called the Friedmann equations, which are derived from some of Einstein’s theory of general relativity, cosmologists can make measurements to try to estimate the densities of the material in the universe (including the contributions of dark energy, dark matter, and “ordinary” matter) and then plug them and a few additional measurements in. Using the Friedmann equations, the time since the Big Bang can be worked out.

However, the values that are used with those equations rely on models that to some extent must be assumed to be correct. Based on some high-precision measurements, we think it’s pretty accurate.

There are other ways of figuring the age of the universe that are significantly off from one another, sometimes by quite a lot, but it seems that 13.787±0.020 billion years based on the “Lambda-CDM” model tends to be the most well-accepted by current science.