An Improved Second Law Defines the Past

It is argued in my blog The Uncreated Universe that existence, in the sense of being a consequence of a divine act of creation, is a meaningless concept. We must not suppose that there are real things that exist and potential things that do not exist - things cannot be distinguished in existential terms. Therefore the present state of the universe does not inherit existence from past states and so from an initial act of creation.

The present state of the universe must therefore be the starting point when we consider its past and future states. The present therefore determines the past rather than, as is usually supposed, the converse.

The extent to which the present determines the future is limited. Indeterminacy at the atomic level and below implies that the future at the familiar level is largely indeterminate and that there are branching alternatives. It is meaningless to suppose that a particular branch will exist and that the rest will not. This is why the future is not completely predictable.

Unlike the future the past is unique. There is a physical principle, that of microscopic reversibility, which implies that the direction of time, as between earlier and later, cannot be determined from behaviour at the atomic level and below. This suggests that past should branch like the future. There must be some overriding principle to make it unique and it is essential for our understanding of the world that its details should be determined.

The Second Law of Thermodynamics is a principle that helps to determine the past but it does so only imperfectly and of itself it is not suitable for defining the past. It merely states that within prescribed confines the amount of disorder in matter will increase with time until equilibrium is achieved, but it does not determine the extent of the increase. It even allows decreases on rare occasions.

There is a non-scientific principle that we invoke when we determine past events. It is that the past shall be chosen in a way that minimises the likelihood that present similarities are pure coincidences. It can be called the Principle of Minimum Coincidence. If we see several identical books on a bookshop shelf we do not suppose that they achieved their similarity by chance. We assume, without knowing the details, that their similarity occurred during the past when they were printed on the same set of presses. The way in which we apply the principle can be more subjective than this example might suggest.

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If we combine the Principle of Minimum Coincidence with the Second Law in its traditional form we get an improved version of the Law. It is the principle by which the unique past is established:

The past is selected from the alternatives offered by retrospective indeterminacy so that the increase in disorder on going from the past to the present is the maximum.

An implication of this is that the past does not contain features that, while being consistent with preceding the present, are unnecessary for preceding the present. The improved Second Law can thus be regarded as the Principle of the Simplest Past. (Compare Occam's Razor.)

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(It may be that there are alternative pasts at the quantum level in the sense that similar alternatives at that level may each give the same maximum increase in disorder as judged from the familiar level. This may explain seeming anomalies like the one concerning the interference of light. Two streams of light from a single source may be brought together so that they interfere when illuminating a surface, even at points where the two streams left the source at different times. But two streams from separate but similar sources do not interfere even when the optical set-up is otherwise the same.)

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The foregoing statement of the improved Second Law may be taken as being basic, the conventional Second Law and the Principle of Minimum Coincidence being derivatives.

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A more complete exposition of these ideas and their consequences can be found on my website

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http://www.uncreated.co.uk/

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