The range of human experience

The middle world is the human-sized world. It’s the world we evolved in, the world we interact with, the world babies investigate with their endless experiments. We learned, as children, that when we drop things they fall, that a thing can only be in one place at one time, that objects are solid and we mostly cannot mush them together, that feathers fall slowly and spoons fall quickly when we drop them from our high chair. The middle world is the world of useful knowledge, it’s the world in which we live and in which our intuitions serve us very well.

But this world is only a tiny slice of the whole of reality. There are galaxies upon galaxies stretching out to infinity in the big world beyond us. And in the small world within any single object, there are molecules and atoms and particles far smaller than we can imagine.

That is the point: we cannot imagine them. We should not hope to be able to. Our intuitions and imaginations, helpful as they are for working out human size problems like whether our neighbour is likely to cheat on his wife or how far away Geneva is from Inverness, are only useful in the middle world. In the very small world, or the very big one, those intuitions are likely to mislead and confuse us. When we find results that seem to make no sense, we should not be surprised or alarmed. ‘Sense’ only belongs to the middle world.

On embarking on this journey through the world of physical phenomena it is extremely important to recognise that our own direct experience of the physical world is miniscule. Consider our spatial experience. Being generous we probably have a feeling for something as small as 0.1mm (10^-4m) and as large as the earth which has a diameter of about 12,000 km (roughly 10⁷m),but, as we shall see, many physical phenomena involving the fundamental constituents of matter take place within distances of around 10^-15m. At the other extreme the visible universe extends to a distance of around 10²⁶m. Similarly, with continuing generosity, our feeling for time may extend down to 1/1000 of a second (10^-3s) through to, if we are lucky, 100 years (about 10⁹s).These figures are to be compared with the time scale of fundamental particle processes which can be as short as 10^-23s and the age of the universe which is around 15,000 million years (about 10¹⁷s). This is not to mention the extreme conditions which occurred in the big bang, when the universe came into being as a result of a gigantic explosion and when formidable changes took place in infinitesimal time intervals. This comparison of human experience in space and time with that of physical phenomena is shown diagramatically [above]. Because of the paucity of our experience in the very small and very large realms of space and time it should come as no surprise if physical processes take place which are completely at variance with our very limited everyday experience and expectations. We shall come across some very strange phenomena which it will be hard to accept as ‘natural’.

It’s now known that our era, the stelliferous era of galaxies and stars and colorful nebulae that don’t really exist, is vanishingly short. This whole stupid dance will last for, at most, a few trillion years; it was winding down as soon as it started. After that, after the stars have faded and the planets have all fallen from their orbits, there will only be black holes, and even these will decay over time. For unimaginable eons there will only be a few scattered particles sailing across a total void. If two happen to meet, a single positronium atom might form, float briefly, and decay again, and this single atom might be the first thing to happen in the entire universe for millions of years. This is where we’re all headed—in the grand scale of things we’re already there—and it will go on for so long that the age of light and warmth and stars and trees and people will seem like a brief flash around the time of the Big Bang. Already, in the short time since Schopenhauer, the entropic rot has spread, the uniformity, the blanketing, the pollination, the strewing of electronic debris across the void, the people on the moon, the tin-can probes on Mars and Venus and comets.