That's a 10^-8 difference in scale at the top end, though if we use the size of the human brain instead that's 10^-10 difference in scale. We're certain, howeve

That's a 10^-8 difference in scale at the top end, though if we use the size of the human brain instead that's 10^-10 difference in scale. We're certain, however, about the Planck length being the smallest scale but not whether "The Observable Universe" is really the greatest distance. If some of the large scale parameters of physics, e.g. the fine structure constant, vary depending on position, then there could be a mathematical limit to the size of the Universe, which could conceivably be 10^10 times the "Observable Universe".