Continued from Part 1.
A hundred thousand years had passed since the Big Bang, and the Universe was now made up of atoms, hydrogen and helium, bathed in light the colour of sunlight. This gas was far more diffuse than any earthly gas, only about one atom per cubic metre. It was expanding and cooling fast, and continued to do so for a billion years. The light also cooled, which meant shifting towards red and infra-red. One can imagine angels watching and thinking that this Universe was a failure, as its bright Big Bang was fizzling out like a damp squib. But its Creator had something more in store.
The early Universe, even before atoms were formed, was not as chaotic as it may have looked. It had been remarkably uniform, at least since the end of the very short period of runaway inflation – the same all the way through and in every direction.1 And on the large scale it still is today.
If the Big Bang had been simply random, then the energy which streamed out from it would have been chaotic and lumpy. Also space and time would not have been the smooth continuum which we see today; they would have been twisted and mixed up, perhaps a bit like an attempt at a balloon model with parts twisted together randomly, blocking the expansion of the Universe. But the space and time we see is more like a normal balloon with a smooth surface, and the Universe can expand freely.
No one knows why the Universe is so smooth, when this in fact seems to be a very special and extremely improbable state of affairs. Maybe it is a result of the little understood early period of inflation. Some people invoke the “anthropic principle”, that the early Universe had to be like this because if it hadn’t been there would be no humans around now to observe it. But surely the hand of God is in this, even though we don’t know how.
For this uniformity of the Universe is of extreme importance today. If the early Universe had been chaotic, it would have remained so, and no kind of structure or order could ever have emerged, at least by natural processes. Either it would have broken up and disappeared into black holes, or it would simply have remained a chaotic mess.2
But the Universe did not remain uniform for ever on the smaller scale. Maybe a billion years after the Big Bang something new became evident. As the atoms continued to move apart and cool they very gradually started to clump together, the weak force of gravity acting on random density fluctuations. Huge masses of hydrogen and helium began to coalesce into the diffuse and swirling clouds which eventually became the galaxies we now observe. Within these clouds smaller regions of gas started to collapse under gravity into the much denser agglomerations which became stars. The original light had been fading for a billion years, but now the Universe was about to be filled again with light.
To be continued …
1. I.e. homogeneous and isotropic. The primary evidence for this is the very high degree of uniformity of the observed cosmic background radiation. This, amazingly enough, is the light released when atoms first formed after the first 100,000 years of the universe, now cooled to less than 3 degrees Kelvin. This evidence of course tells us only about the finite visible part of the infinite Universe, but it is hard to see how this part could be so uniform if the whole is not.
2. This is an attempt to explain how a high entropy Universe would have remained in a high entropy state, and so that the observed low entropy must imply a very special or improbably low entropy initial state.
by the Nobel Prize winning Turkish author Orhan Pamuk. This is a more highbrow type of novel than I usually read, but I admit to buying it because it was displayed at a bargain price at my local Tesco’s, which is more or less the UK equivalent of Walmart (although not to be confused with its rival Asda, which belongs to Walmart).
by Richard Dawkins was in what otherwise looked like a fiction section. And then a few days later I saw a very similar display in Heffers, the major academic bookshop in Cambridge. Are the staff trying to tell us something about