The Fate of the Solar System and the "Will of God".

Judaism, Christianity and Islam are all fundamentally optimistic religions, insofar as they predict that, after a bit of a rough passage, the Universe ends definitively, with a final Triumph of Good over Evil, an everlasting reward for the good, and everlasting punishment for the bad.

Setting aside the whole question of the justice of everlasting punishment for finite wrong, we have to ask whether or not this picture is actually compatible with what physics tells us is going to happen to the Earth, the Solar System, and our Universe.

There, alas, the picture is far from being optimistic: as far as the Earth is concerned, we know that, because of the steady and relentless increase in the Sun's luminosity over time, in 1.1 billion years' time, the mean annual surface temperature of the Earth will be so hot that there will be no liquid water on the planet - all the rivers, lakes, seas and oceans will just boil away.

The result of that, in turn, given that water vapour is a greenhouse gas, will be a runaway greenhouse effect, causing an even greater increase in temperature. Any living things that have not become extinct because of the loss of liquid water, will be killed off by the huge rise in temperature that follows it.

3.9 billion years later, the Sun will end its life as a so-called 'main-sequence' star, swelling up from a humble 'Yellow Dwarf' into a 'Red Giant'. Mercury, Venus and the Earth will be destroyed in the process, as the Sun will then have a radius of between 1 and 2 astronomical units (AU) - in other words, between 1 and 2 times the average distance, in our era, of the Earth from the Sun, which is 150 million kilometres (93 million miles). Mars may also be destroyed, as its mean distance from the Sun, currently, is 1.52 AU; source: Penn State University.

The Sun will then spend a billion years as a "Red Giant Branch Star", during which time it will lose a third of its mass, and then 200 million years later will suffer something called the "helium flash", followed 140 million years after that by a series of explosions, spaced 100,000 years apart, causing its outer layers to part company from its inner core, the blasted material being expelled into space as far as, and beyond, the orbit of Jupiter. Source: Northwestern University.

What will be left will be a White Dwarf star, similar to Sirius B, composed of electron-degenerate matter, with no nuclear fusion taking place in it. Such stars are incredibly dense, with an average density of about 1 tonne (metric ton) per cubic centimetre (source: Ohio State University).

White Dwarfs are usually composed of carbon and oxygen. The fusion of three helium nuclei will produce one nucleus of carbon-12 (the "triple-alpha process"), the fusion of four of them will produce a nucleus of oxygen-16. Helium is what is fused in Red Giants, being the fuel for nuclear fusion after the hydrogen which was the star's fuel during its main-sequence life, has been exhausted.

Thus will end the Solar System, with its star slowly cooling down, potentially over trillions of years, until it eventually reaches a final Black Dwarf stage, utterly cold and dead. There are, however, no actual Black Dwarfs in our Universe, so it must take a very long time indeed for that process to take place, assuming that it does. (See: Mestel, L. & Ruderman, M.A., 'The energy content of a white dwarf and its rate of cooling,' Monthly Notices of the Royal Astronomical Society 136(1):27-38, May 1967, DOI: 10.1093/mnras/136.1.27, Harvard University.)

None of this seems compatible with the optimistic picture presented by the monotheistic religions, does it? The picture gets bleaker still when we turn to the Universe as a whole, which must occupy our next posting.