# Eli5 How did people figure out how old the universe is?

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I know it’s definitely very complicated but I’m very curious

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One guy, Edwin Hubble, studied the light of stars from faraway galaxies and measured the rate at which they were moving away from us by analyzing the stretching of the wavelengths of light by the Doppler effect (a process called redshift). By determining the expansion rate of the universe, known as the Hubble constant, the age of the universe was calculated

It’s actually not all that complicated. Basically, we observed that everything in the universe is moving away from everything else, which means that the universe is expanding. We measured the current size of the universe and how fast the universe is expanding (and the rate that the expansion is accelerating) and then simply “ran the clock backwards” to find out when everything was in the same place.

The universe is expanding like a balloon. We used something called red shift to calculate the expanding rate. If we reverse the expanding rate. Aka deflate the balloon we are able to calculate when everything was not inflated at all.

We haven’t. To our current knowledge we know it’s *at-least* X years old. James Webb actually stumbled onto some ancient galaxies recently that will bring into question all the stuff we know so far on the subject though.. so

The only certainty about the universe at the moment is that we’re in the baby steps of even understanding it. As of right now you could think of earth and humanity as a bit traveling through an oceanic fiber optic line. It’s there.. in theory it’s real. But in terms of what it “knows” about its surroundings it’s at the whim of something bigger. It’s hard to explain in a way a five year old could get with words. Diagrams would be way easier but as simple as it can be put.. our estimates of the age of our (known) universe is always changing/evolving.