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Asked by anon-187836 to Stewart, Miriam, Marton, Laura, Kathryn, David on 12 Nov 2018.
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David Ho answered on 12 Nov 2018:
This is a great question — and the answer might be a bit surprising. Here’s a pie chart showing what the universe is made up of:
All the “ordinary matter” (basically atoms) makes up less than 5% of the universe! Of that matter, the majority is hydrogen atoms.
Then there’s “Dark Matter”, making up about a quarter. We know that this exists because we can measure its gravitational force. But it doesn’t give off any light or other radiation, and we can’t (so far) detect it in any other way, so we don’t know anything about it. That’s one of the biggest mysteries of the universe facing physicists today!
The rest is “Dark Energy”. Scientists have also observed that the universe is expanding outwards, and accelerating as it does so. To accelerate something you need a lot of energy, but that energy doesn’t fit into any of the other types of energy we’ve got in physics, so we call it “dark energy” like dark matter. Dark energy is another puzzle, it could just be a feature of the universe, but a lot of scientists wonder why there is exactly the amount of dark energy that we observe.
Maybe soon scientists will be able to answer some of these questions — that’s what physicists like me are working on!
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Stewart Martin-Haugh answered on 12 Nov 2018:
David has given a great answer! I would like to add that the matter we see around us is normal matter, and not antimatter. Antimatter is like normal matter, but annihilates matter and turns it into energy. So if we did see lots of it, there would be fairly regular explosions!
We expect the universe to be symmetrical in many ways: if so you would expect the same amount of mater and antimatter. The fact that we don’t is very puzzling. Luckily, we can produce small amounts of antimatter at the Large Hadron Collider: if we measure it we might understand why there’s so little of it.
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