Time is the increase of order, not disorder (Towards a new arrow of time)

C C Offline

EXCERPTS (Julian Barbour): Two of the most established beliefs of contemporary cosmology are that the universe is expanding and that the direction of the arrow of time in the universe is defined by ever-increasing disorder (entropy), as described by the second law of thermodynamics. But both of these beliefs rest on shaky ground. In saying that the universe is expanding, physicists implicitly assume its size is measured by a rod that exists outside the universe, providing an absolute scale. It's the last vestige of Newton's absolute space and should have no place in modern cosmology. And in claiming that entropy is what gives time its arrow, physicists uncritically apply the laws of thermodynamics, originally discovered through the study of steam engines, to the universe as a whole. That too needs to be questioned.

In the absence of an absolute space and external measuring rods, size is always relative - relative to a measure of distance internal to the system. Starting from the simplest case, a triangle, what we find is that the internal measure of size produces a ratio which also happens to be related to a mathematical measure of complexity that intriguingly plays the central role in Newtonian universal gravitation. Applying these findings to the universe as a whole, we find that Newton’s theory of gravity, contrary to what physicists believe, contains within it an intrinsic arrow of time. This provides a strong hint that the direction of time is not defined by an increase in entropy, but by an increase in structure and complexity.

[...] A better way to think of the expansion of the universe is by illustrating the galaxies as coins stuck on the balloon's surface. The coins can have different sizes, but the ratio of their sizes does not change as the balloon gets larger and the separations between the coins gets larger relative to their diameters. The expansion of the balloon here is measured by a relative change in the distance between the coins, compared to the unchanging size of the coins themselves. This is much closer to how things are in our actual universe. Since galaxies are dynamical and their relative sizes change over cosmological timescales, the image is not perfect but is near enough the truth. What has actually happened in the history of the universe is that its most fundamental constituents - nucleons, atoms, molecules - have maintained a constant ratio of their sizes and so too, to a reasonable accuracy, have rocks, planets, stars, all the way up to galaxies.

The way to make sense of the expansion of the universe, therefore, is by measuring the changes in the distances between the centres of the galaxies relative to the distances defined by the diameters of nucleons, atoms, molecules etc. We should think of the latter as the measuring rods of the universe. What needs to be emphasized is that these ‘measuring rods’ exist within the universe, not outside it. We have no access to an absolute measure of space outside the universe. The most fundamental fact is that the shape of the universe is changing. The only justification for saying that it is expanding is that things within it, above all nucleons, atoms, and molecules but also to lesser accuracy macroscopic objects like planets and stars and even whole galaxies, have for billions of years kept constant sizes relative to each other while the separations between the galaxies have been increasing relative to those 'measuring rods'.

It might seem pedantic to emphasize the relativity of size. However, shape is a much more fundamental concept and, as I will explain, fascinating interconnections are revealed if we describe the evolution of the universe exclusively as the change of its shape, rather than its size... (MORE - missing details)
Kornee Offline
The 'only relative size ratios matter' argument fails right there at the example of dots or pennies stuck on an expanding balloon. Even allowing for the redshifting of light owing to cosmic expansion, round trip radar ranging times are growing in an 'absolute' sense. Only if the speed of light expanded in sync with Hubble growth would there be a conundrum. But c doesn't do that.

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