@859frcc45 we can only observe 5% of the universe, 95% is “missing” in a combination of dark energy (68%) and dark matter (27%). We know it is there because observations tell us that the universe is expanding and in order for that to happen it has to have a certain minimum amount of energy/mass. And the amount we do observe is no where near enough. There is a lot of research going on trying to understand this very difficult problem. But it’s pretty exciting!
As Lidunka says, no one really knows what dark energy is. We just know that the universe is expanding, and expanding faster than our current ideas predict. To make our maths work, we need to add in a lot of energy that we call ‘dark energy’ – the name just means we don’t know what it is!
Either an awful lot of the universe (68%) is made up of this unseen dark energy, or our current cosmology theories are just plain wrong. Lots of people are working on figuring this out!
Dark energy came up as a solution to the problem that Lidunka already mentioned – we can only see about 5% of the universe! We also needed a way to explain the fact that the universe’s expansion is accelerating, so it was suggested that maybe there was some sort of energy bound to space, which would cause space to expand, thus making more energy. So if that’s the case, it sort of explains why the universe is expanding faster and faster, but it doesn’t explain what it actually IS, or why it’s acting in the way that it does!
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