We can't see it and we can't feel it, but we can test for it.
Guess, what is it?
Easy to answer, ladies and gentlemen let me introduce you Mr. Dark Energy.
Scientists think that this sneaky and unknown form of energy makes up around 67% of the universe. The rest is made up of dark matter (27%) and normal matter (only 5%). Come to think of it, maybe it shouldn't be called "normal" matter at all, as it is such a small fraction of the universe :)).
Dark energy explains why galaxies don't just drift apart but instead accelerate away from each other. You can think of it as a repulsive gravity that pushes matter apart.
Let me tell you more about when and why dark energy was first hypothesized.
Everybody knows that the universe is full of matter, everywhere, and the attractive force of gravity is supposed to pull all matter together. Then came 1998 and the Hubble Telescope observations showing that, a long time ago, the universe was expanding way more slowly than it does today. So the expansion of the universe has not been slowing down, as everyone thought, but it has been accelerating !!! .
NNo one expected this, no one knew how to explain it. But something was causing it.... the dark energy. . So now you know the story of dark energy and where it comes from.
How it works, however, is still a mystery?
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