When I gaze up at a starry night sky, struggle as I might, I am unable to see it as other than a great dome patterned with stars. In spite of the knowledge that I have that what I am looking at is a large portion of the universe, and that each prick of light is a sun or a nebula or a galaxy a vast distance away, I still see the same curving ceiling that the ancients saw, who imagined it to be a crystal sphere, surrounding the Earth, or a system of such spheres. I know that it is not that, but that is what I see.
If I struggle to pierce this crystal sphere and to see what I know it is that I am really looking at, my mind revolts. Pushing against my mind’s refusal to see the depth is almost painful. But why should this be surprising? Even at the more mundane distances that exist on Earth, we struggle to comprehend scale. Again, I do not mean that we can not imagine it, but rather that we are incapable of actually experiencing it. Perhaps a measure of this limit is shown by how much more frightening it is to look down from a high cliff than from the window of an aeroplane. I once threw myself out of an aeroplane, but would have found jumping off a cliff with a parachute far more daunting. I suspect that this is because – at least for me – at ‘aeroplane height’ I am beyond my animal capacity to judge height, so that from an aeroplane I see the ground with the same level of abstraction that I see the starry sky.
Our brains and our eyes are simply not designed to see across galactic distances. Perhaps this is a blessing. If it is daunting for us to cope with looking down from a high cliff, then imagine how we would react if we could really experience the true depth of the night sky. If looking down from a cliff gives us vertigo, looking down into the vast and essentially bottomless well of the universe would boost vertigo to an intensity where it must surely explode our brains.