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Next: 12. Measurements and Other Up: 11. Two Stages of Previous: 11.3 `Gauge' Invariances


11.4 Quantum Substances

  We saw above that there can only be propensities for actual events if the Schrödinger wave function does have discrete branches that have little or no interference with each other. It is only for a time interval following collisions or fragmentations that discrete and non-interfering branches are formed, and actualising begins to be possible. This has the important consequence that propensity fields, as the distribution of propensities for actualising, do not exist continuously through all times. This is in direct contrast with what we assumed in chapter 10, although we were careful to qualify our statements there with the reminder that the `quantum substances' postulated there were not guaranteed to last forever. Now it seems that they hardly last from one actual event to another! Propensities for actualising still form a field of finite duration, and so can still with some validity be called `substances', but they are hardly the `ultimate substances' which (if they exist) would persist through many events.

Any properly-persisting substances could perhaps be constituted from the propensities for virtual events. The trouble with this proposal is that virtual events occur continuously in time. The propensities for virtual events are presumably between the times of successive virtual events, by analogy with propensities for actual events, but that would leave only zero time intervals for them to exist! In the language of quantum field theory, we are trying to identify the `bare' particles -- those that exist before and between any virtual events or processes. According to the renormalisation process above, however, these `bare' particles do not necessarily have to have definite masses or charges.

    It this point I am at a loss when it comes to identifying the `propensities for virtual events': those propensities that must constitute the `underlying quantum substances'. I am tempted to look not at those propensities that exist between successive virtual events, but at some more long term `propensity to follow a least action principle', such as the propensity to satisfy equation (11.3). This propensity would be more like a disposition, however, in being deterministically rather than probabilistically satisfied. Whether this proposal can be successfully elaborated will have to remain a subject for further investigation.  

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Next: 12. Measurements and Other Up: 11. Two Stages of Previous: 11.3 `Gauge' Invariances
Prof Ian Thompson


Author: I.J. Thompson (except as stated)