Dark matter and dark energy are more directly motivated by observations of the real world. Dark matter is apparently needed to account for the gravitational effects that seem to come from parts of space where no ordinary matter is visible, or not enough to explain the tug. For example, rotating galaxies seem to have some additional source of gravitational attraction, beyond the visible stars and gas, that stops them from flying apart. The “lensing” effect where distant astrophysical objects get distorted by the gravitational warping of spacetime also seems to demand this invisible form of matter. But dark matter does not exist in the usual sense, in that it has not been seen and there are no theories that can convincingly explain or demand its existence. Dark energy too is a kind of “stuff” required to explain the acceleration of the universe’s expansion, discovered by astronomers observing far-away objects in the mid-1990s. But it is just a name for a puzzle, without any direct detection.
It seems quite possible that dark energy, and perhaps dark matter too, will turn out to be like Crookes’ “dark space” and “radiant energy”: not exactly stuff, but symptoms of some hitherto unknown physical principle. These connections were exquisitely intuited by Philip Pullman in theHis Dark Materials trilogy, where (the title alone gives a clue) a mysterious substance called Dust is an amalgam of dark matter and Barrett’s quasi-sentient psychomeres, given a spiritual interpretation by the scientist-priests of Pullman’s alternative steampunk Oxford University who sense its presence using instruments evidently based on Crookes’ light mill.
Scientists, of course, are not just making things up, while leaning on the convenience of supposed invisibility. They are using dark matter and dark energy, and (if one is charitable) quantum many-worlds and branes, and other imperceptible and hypothetical realms, to perform an essential task: to plug gaps in their knowledge with notions they can grasp.
From Nautilus, a great publication for all the obvious reasons. This article was perfect. I’d definitely recommend it. If only I could write half as well.