Artist’s logarithmic scale conception of the observable universe. Galaxies give way to large-scale structure and the hot, dense plasma of the Big Bang at the outskirts. This ‘edge’ is a boundary only in time. (Credit: Pablo Carlos Budassi; Unmismoobjetivo/Wikimedia Commons)

How small was the Universe when the hot Big Bang began?

We know it couldn’t have began from a singularity. So how small could it have been at the absolute minimum?

Today, when you look out in any direction as far as the laws of physics allow us to see, the limits of what’s observable extend to truly astronomical distances. At the farthest reaches of our…