Our data on Cosmology isn't solid

Bill Bryson, A Short History of Nearly Everything

  • The difficulty in making final determinations is that there are often acres of room for interpretation. Imagine standing in a field at night and trying to decide how far away two distant electric lights are. Using fairly straightforward tools of astronomy you can easily enough determine that the bulbs are of equal brightness and that one is, say, 50 per cent more distant than the other. But what you can't be certain of is whether the nearer light is, let us say, a 58-watt bulb that is 37 metres away or a 61-watt light that is 36.5 metres away. On top of that you must make allowances for distortions caused by variations in the Earth's atmosphere, by intergalactic dust, by contaminating light from foreground stars and many other factors. The upshot is that your computations are necessarily based on a series of nested assumptions, any of which could be a source of contention. There is also the problem that access to telescopes is always at a premium and historically measuring red shifts has been notably costly in telescope time. It could take all night to get a single exposure. In consequence, astronomers have sometimes been compelled (or willing) to base conclusions on notably scanty evidence. In cosmology, as the journalist Geoffrey Carr has suggested, we have 'a mountain of theory built on a molehill of evidence'. Or as Martin Rees has put it: 'Our present satisfaction [with our state of understanding] may reflect the paucity of the data rather than the excellence of the theory'. This uncertainty applies, incidentally, to relatively nearby things as much as to the distant edges of the universe. As Donald Goldsmith notes, when astronomers say that the galaxy M87 is sixty million light years away, what they really mean ('but do not often stress to the general public') is that it is somewhere between forty million and ninety million light years away — not quite the same thing. For the universe at large, matters are naturally magnified. For all the éclat surrounding the latest pronouncements, we remain a long way from unanimity. One interesting theory recently suggested is that the universe is not nearly as big as we thought; that when we peer into the distance some of the galaxies we see may simply be reflections, ghost images created by rebounded light…
  • The upshot of all this is that we live in a universe whose age we can't quite compute, surrounded by stars whose distances from us and each other we don't altogether know, filled with matter we can't identify (dark matter and dark energy), operating in conformance with physical laws whose properties we don't truly understand.