Saturday, November 04, 2006

Kingdom Thermodynamics 4: The Crunch

Note: This is not completely new material. I realised after I posted it that part 3 of this series was rather long, and so I have split it, making the second half of it into this part 4.

In part 3 of this series I discussed the boundary conditions in time, how they might apply to the universe, and how they relate to causality. I also showed how they are in tension with the biblical picture in which God knows and purposes the future, the final state of the universe.

In this post I will look more closely at the final state of the created universe, and how it compares with the initial state.

We observe that the universe is now not in a completely random state but has some order. The Second Law of Thermodynamics implies that its initial state was even less random, technically with lower entropy than at present. It also implies that the final state of the universe will be more random, with higher entropy.

Cosmologists have observed that the background radiation which they interpret as being left over from the Big Bang is extremely uniform across the sky. This implies that at least from an extremely early stage, if not from the very beginning, the universe expanded isotropically, i.e. in the same way in all directions, to a very high degree of accuracy. This isotropy implies order and low entropy; the very early universe was not in a random state but in an extremely special one. Theologians might see the hand of God in this; cosmologists have sought to explain it with physics, but in a way which would require that the Second Law of Thermodynamics did not apply in the first fraction of a second (actually only something like 10-32 seconds in some expansion theories) after the Big Bang.

My argument here is not in fact at all dependent on the Big Bang theory. It would work equally well if the universe was created in a form similar to its present one, even as recently as 4004 BC. But its initial state, at least once the act of creation was complete and the normal laws of physics took over, must have been not completely random, but with order and so low entropy. It first came into being "formless and empty" (Genesis 1:2 TNIV), Hebrew tohu wabohu; these words may imply a state of chaos, but if so God created order within it during his work of creation before putting it in "bondage to decay" (Romans 8:21 TNIV).

As for the final state of the universe, cosmologists generally assume that it will be highly disordered. According to them, there are two possibilities: either the universe will continue to expand for ever but will gradually become more and more disordered, with entropy eventually approaching a maximum, the so called Heat Death; or the universe will collapse again into a Big Crunch, which, according to most, will be very different from the Big Bang in that it will be highly disordered and anisotropic, a state of high entropy. Both Heat Death and a disordered Big Crunch can be considered as unconstrained; there are no final boundary conditions here.

However, some cosmologists have speculated that at some time in the future, probably at about the time that the universe reaches its maximum size, the Second Law of Thermodynamics will go into reverse, and that entropy will start to decrease, such that the universe will collapse in an isotropic Big Crunch which will look just like the Big Bang in reverse. Thus the history of the universe will be at least in general terms symmetric in time. But these cosmologists have realised, without as far as I know discussing this in detail, that such a reversal of the Second Law would have complex and severe philosophical implications, and for this reason the idea is not a popular one.

Nevertheless, they have an interesting idea which is helpful to illustrate the direction in which I am arguing here. In the standard cosmological model, there are tight boundary conditions on the initial state of the universe, constraining it to be isotropic, so in a state of order and low entropy; but there are no final boundary conditions, as required by the principle of causality, implying that the final state is disordered. But if there will also be an isotropic Big Crunch, that is a final and tightly constraining boundary condition. Now as I have tried to make clear, there is only one law of physics which disallows this, the Second Law of Thermodynamics, and that applies only because of causality. An isotropic Big Crunch is possible only if causality does not apply completely, that is, if at least in principle current events can be caused by future ones, indeed ultimately by the Big Crunch itself.

According to cosmologists, the universe is still expanding, and it will be a very long time before it starts to contract again towards a Big Crunch, if it ever does. So, in the isotropic Big Crunch model, its current state is like a point on the banner quite near to one of the poles, or the distribution of the children soon after they were released and before they were starting to think about going home. That is to say, the universe is still quite tightly constrained by its initial boundary condition, the isotropic Big Bang, but the constraints of the final boundary, the Big Crunch, so far have only a very weak effect. Because of this the universe now operates almost precisely as if there were no final constraints, and so according to causality and the Second Law of Thermodynamics. Nevertheless, if there is going to be an isotropic Big Crunch, one might expect to see very occasional or very tiny deviations from this law, which will gradually grow as the universe moves towards the mid-point of its life. Then it will have a severe mid-life crisis! I will not presume to speculate on how physics will operate around this time. But eventually the Second Law will gradually start to work in reverse as the universe collapses towards the Big Crunch.

Now it is interesting to speculate about this time-symmetric universe. But actually I don't think this is what is going to happen. If the Bible teaches us anything about the final boundary conditions for the universe, those conditions are not an isotropic Big Crunch, but some kind of steady state for eternity. It is interesting that scientists are still unable to decide whether the universe will continue to expand indefinitely or collapse in a Big Crunch. A third and intermediate position may be possible, in which it grows to a fixed size and remains that size for ever; and the current expansion of the universe is at about the right rate to attain this. This steady state is probably a very special and improbable state, similar to the isotropic Big Crunch, but if it is a final boundary condition specified from the beginning, the universe is bound to end up in this state. But if there is such a final boundary condition, causality and the Second Law lose their absolute status, and at some stage will gradually cease to operate.

I have to accept that these ideas, especially the final one, are highly speculative. But I hope you find them interesting.

In the next part of this series I intend to relate these ideas to the coming of the Kingdom of God. I hope there will be less heavy physics and more about God and the Bible.

Note re links to Wikipedia: I provide these as service to readers wanting to read a little more about the subjects in question, not as authorities or references.

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