Looking up at the night sky, you’re browsing deep into history – but how old is the universe? And can we know for sure? How is the age of the universe calculated?
These are just a few of the many questions stargazing can elicit in the curious human mind. Ever since Nicholas Copernicus’ discovery that the Earth wasn’t the centre of the universe, we’ve continued to unlock secrets of the vast, cold, empty expanse we call home.
But can we calculate how old the universe is? If so, will we ever know or comprehend the sheer enormity of the cosmos?
The universe works like a time machine
Light travels, rather unsurprisingly, at the speed of light, which is about 300,000 kilometres per second. This is incredibly fast and means sunlight reflecting off the Moon only takes about a second to reach us.
However, the Solar System is pretty huge – light from the Sun travels for about eight minutes to reach Earth. The Milky Way galaxy contains billions of stars with enormous gaps in between. Beyond that, the Milky Way is just one hot tub awash in a sea of galaxies.
Instead, we use light years. Contrary to its name, a light year isn’t a unit of time, it’s how far light travels in one year. Therefore a light year is, in fact, a distance.
Proxima Centauri is 4.25 light years from our Sun. This means light leaving our closest neighbour 4.25 years ago is only arriving here today.
We see the Moon how it looked one second ago. The Sun we squint at is the star of eight minutes in the past. And astronomers look millions and even billions of years deeper into cosmological history with each more distant observation.
So how old is the universe?
The universe must be at least as old as the objects we find within it. Using this simple theory, we’ve found faraway stars that are at least 11 billion years old. So the minimum age of the universe is set – but it could be older still.
The expanding nature of the universe throws open many mysteries, such as ‘what is dark energy?’ and ‘how will the universe end?’ But it also helps us discover a more precise figure for the age of the universe.
Oh so small in space and time
The size of the universe is still being analysed. We can only observe a universe 13.8 billion light years in radius – any information from further away simply won’t have had time to reach us yet.
University of Oxford algorithms estimate the size of the whole universe (including that we can’t see) to be at least 250 times the size of the observable universe.
The question ‘how old is the universe?’ is one of the few big cosmology queries for which we have a decent answer.
But even with this, a 2019 study led by Nobel laureate Adam Riess questioned our confidence in the figure 13.8 billion years. As is always the case with science, the more we know, the bigger the can of wormholes.
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