One of the biggest things we know of in the universe, weirdly, is nothing. Between galaxies there is intergalactic space, filled with gas, dust and ionised particles. Most of the time, there’s relatively little distance between them: we’re talking hundreds of thousands of light years that, in the grand scale of the cosmos isn’t so much to make a big deal of. But there are a few big places in our universe that are practically a vacuum, huge expanses of space with near to nothing in them. These are the supervoids and the biggest of them is the Boötes void, a spherical area in space 700 million light years from Earth near the Boötes constellation. Its diameter in the sky is 250 million light years and its volume is a staggering 236,000 cubic megaparsecs. To give you an idea of how much that is, a single cubic megaparsec is the equivalent volume of three cubic metres with 67 zeros after it. Put another way, we’ve been observing other galaxies for hundreds of years (even if we didn’t appreciate exactly what they were at the time), but if the Milky Way had been in the centre of the Boötes void, we wouldn’t have even known about any other galaxies until the Sixties. It’s not completely empty though, 60 galaxies have been discovered in Boötes, but a space this large should contain an estimated 10,000 galaxies. By comparison, our galactic neighbourhood has nearly half the number of galaxies of Boötes in a tiny fraction of the same volume.