According to theoretical physicists, a quarter of a gram's worth of matter should release five kilotons of energy if it comes into contact with its anti-matter counterpart. Yet we don't see this happening on Earth or elsewhere in space. What's going on?

Indeed, it's a bit of a conundrum, especially considering that every particle in the universe should have an antithetical counterpart — an oppositely charged chunk of matter.

As physicists Tara Shears explains in this Royal Institution video, it's a mystery with roots in the Big Bang. Anti-matter, while not a major player in the cosmos today, did have a crucial role in the formative moments of the universe, giving it the structure — and matter/anti-matter imbalance — we see today.