Can a Living Creature Be as Big as a Galaxy?

Why life is constrained to be about the sizes we see on Earth

By Gregory Laughlin

The size of things in our universe runs all the way from the tiny 10⁻¹⁹ meter scale that characterizes quark interactions, to the cosmic horizon 10²⁶ meters away. In these 45 possible orders of magnitude, life, as far as we know it, is confined to a relatively tiny bracket of just over nine orders of magnitude, roughly in the middle of the universal range: Bacteria and viruses can measure less than a micron…