Where is all the missing matter? That question has plagued astronomers for decades, because the Universe looks emptier than it should, given current theories about its makeup. Most of the Universe (70%) appears to be composed of Dark Energy, the mysterious force which is causing the Universe’s rate of expansion to increase. Another 25% of the Universe is Dark Matter, an unknown substance which cannot be seen, but has been theorized to explain the otherwise inexplicable gravitational forces which govern the formation of galaxies. That leaves Baryonic Matter – all the normal ‘stuff’ like you, me, the trees, the planets, and the stars – to make up just 5% of the Universe. But when astronomers look out into the sky, there doesn’t even seem to be enough normal matter to make up 5%. Some of the normal matter is missing!