The Mystery of Time’s Arrow


EXCERPT (Julian Barbour): . . . But the reliance on an unexplained initial condition to explain two of the most striking features of the universe—the growth of entropy around us alongside the steady growth of structure in the universe at large—leaves Penrose and others like myself dissatisfied. What drives scientists is the desire to explain and understand phenomena. We all want to emulate the way Charles Darwin explained so much with just four words: evolution by natural selection. In the case of time’s arrow, it is literally a matter of life and death, for we all march together in the same direction from birth to the grave. What is it that puts such striking order into the world?

My collaborators and I have hit upon a potential explanation that relies on law alone. We came to it by chance, and it may or may not be correct. However, it has the merit of showing how at least one time-symmetric law (gravity) always leads to an observed unidirectional growth of structure.[...] the key point is that, because the underlying law does not distinguish a direction of time, the arrows can be reversed and the story reads equally well in the opposite direction. If one considers the complete solution, there is no way in which the law that governs the process enables one to identify a beginning or end of the story. It is quite impossible to say that time flows in one direction rather than the opposite.

[...] The point I want to make is this: All solutions of the model exhibit unidirectional growth of structure out of “chaos.” Very basic elements of the law mean that the growth cannot reverse. The underlying reasons are given in the paper by my collaborators and myself. Moreover, if, as in cosmology, we define the direction of time by the growth of structure, all solutions supply a direction of time even though they are generated by a law that, in itself, does not distinguish a direction of time.

The [...] model questions our instinctive notion of causality, according to which something in the past causes what happens now. ... there is no past that causes and explains any present. Causality does not work that way. Law is the only cause, including the case of the special solutions with only one history. All solutions that obey the law exist in a timeless eternity like paths in a landscape or valleys in a mountain range. It’s wrong to read causality through time into the solutions. Paths simply are. However, they can lead from less to more structured regions. The model proves that law alone, without any special initial condition, may be sufficient to explain time’s arrow.

Now let’s return to our own universe, which exhibits unidirectional change. In the traditional chronology, the early universe was vastly more uniform than today’s. Observations of the microwave radiation that bathes the universe reveal random fluctuations in temperature and mass density of only about one part in 10,000.

Taking this state as an initial condition, cosmologists can explain remarkably well how the present universe with its incredibly rich structure and huge density contrasts came into being. It is therefore very natural to say the microwave background existed before our present universe and through a causal mechanism gave rise to it. It seems utterly bizarre to say the present universe caused the microwave background. But, in the final analysis, this is a conclusion based on instinct, not hard fact—and instinct has often hindered progress in science.

This work is just a start. The fact that all this emerges already from the interaction of just three particles [simplified model] is due to the beautiful simplicity of Newton’s law of gravity and certain architectonic structures it possesses. Einstein’s general relativity has them too but is a much richer theory, so we cannot say yet whether in that case law alone will suffice to create an arrow of time without the crutch of a special initial condition. If it does, though, one of the intuitions that most people, including many scientists, find very hard to shed—that time is real and does flow—may well be an illusion. (MORE - details)
This supposed "work" started with his first book, The End of Time, in 1999, and he doesn't seem to have made any real progress in the meantime. It's more just a fringe theory that attempts to explain away rather than explain.

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