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<\/div>It can be hard to wrap our minds round the very large and the very small. Ron Koeberer\/Millennium Images, UK<\/p>\n<\/div>\n<\/figcaption><\/figure>\n<\/p>\n
Imagine setting off on a spacecraft that can travel at the speed of light<\/a>. You won\u2019t get far. Even making it to the other side of the Milky Way<\/a> would take 100,000 years. It is another 2.5 million years to Andromeda<\/a>, our nearest galactic neighbour. And there are some 2 trillion galaxies beyond that.<\/p>\n The vastness of the cosmos defies comprehension. And yet, at the fundamental level, it is made of tiny particles<\/a>.\u201dIt is a bit of a foreign country \u2013 both the small and the very big,\u201d says particle physicist Alan Barr<\/a> at the University of Oxford. \u201cI don\u2019t think you ever really understand it, you just get used to it.\u201d<\/p>\n Still, you need to have some grasp of scale to have any chance of appreciating how reality works<\/a>.<\/p>\n Let\u2019s start big, with the cosmic microwave background<\/a> (CMB), the radiation released 380,000 years after the big bang<\/a>. \u201cThe biggest scales we\u2019ve measured are features in the CMB,\u201d says astrophysicist Pedro Ferreira<\/a>, also at the University of Oxford. These helped us put the diameter of the observable universe at 93 billion light years.<\/p>\n At the other end of the scale, the smallest entities are fundamental particles like quarks. Yet quantum physics<\/a> paints these as dimensionless blips in a quantum field, with no size at all. So what is the shortest possible distance?\u2026<\/p>\n<\/p><\/div>\n