Thanks for the comments
> "A sensible view is that the entities at each classical level of the hierarchy (Table 1) are real". While this reflects the normal, and indeed practical, view of physical reality, it is ontologically (physically) incorrect.
• well you are stating the standard fundamentalist reductionist viewpoint. It may or may not be true.
> Because certain existent, but superficial, physical characteristics are deemed to constitute any given 'it' (eg computer, you, etc). That 'it' is then thought to remain in existence, albeit with changes occurring to it, until one or more of the defining characteristics is no longer manifest. However, this just depicts reality at a higher level than the actuality, though it could be correct, in itself, at that level.
• Your definition of actuality. Not mine or for example Feynman's or Anderson's or Schweber's. Yes it is correct at that level. And as that level has causal powers, it is real (see my definition 2). Please look at your computer in order to confirm for yourself that higher levels have causal powers (unless you believe the computer came into existence without cause). Or maybe you claim the computer does not really exist? I can't deal with that kind of obscurantism.
> Physically, that 'it' is a sequence of physically existent states. The higher level of differentiation just giving the appearance of less change than there physically is, and the illusion of a level of persistence to existence which does not physically occur.
• Your definition of existence. Not mine or your bank manager's. This kind of statement reminds me strongly of some Eastern religions. The level of persistence is real, it is the basis of daily life. Assuming of course that daily life exists. If it does not, then physicists and physics experiments don't exist.
> For physical reality to occur, and alter, there must ultimately be a physically existent state at any given point in time. This can be defined as the state of the properties of the elementary particles involved, and their spatial position, as at that point in time.
• This statement has not taken present day quantum theory on board. It is precisely at the particle level that reality is unclear, because of (i) the uncertainty principle, (ii) wave-particle duality, and (iii) entanglement. Many quantum field theorists claim there are no particles, only fields. And string theorists claim they are vibrations in superstrings. Is that "real"? On your reductionist view, it follows that the particles don't exist either: they are "nothing but" excitations of strings (if we believe those exist). A present day view should at least take quantum physics into account, if not string theory (which is not a solid foundation, as it is not even well defined, let alone proven to be right).
> So there is a "fixed set of lower level entities". And, by definition, any "event" could be tracked back to alterations at that level. That is, physically it must be 'bottom up'.
• Well you seem not to have read the party of my essay where I carefully explain that there are often not fixed lower level entities: their nature, or indeed their existence, is dependent on their higher level context. In the case of string theory, the nature of particles depends on the string theory vacuum - a non-local higher context for their existence. Their properties are not invariant, they depend on this vacuum. You are using a billiard ball metaphor that does not apply to "fundamental reality", i.e. the lowest levels of existence we can understand.
> The point here is that while that is physically what occurs, we could never establish it in such detail, and would probably all go mad trying. So, we conceptualise up some levels. But we must maintain ontological/physical correctness about the direction of the process. What is ultimately causing alteration in the properties of elementary particles and hence a change in their spatial position is another issue.
• what process? conceptualisation? Actually we conceptualise down, on the basis of our physics experiments, from the level of daily life to the micro level. That's the real direction of the process of physics theorising. As to "causing alterations" - the heart of causation - ultimately, it is top-down effects that decide what changes in lower level entities will take place, because they set the scene for the lower level actions. That context determines the specific outcomes that occur.
> Another point to bear in mind that what exists is a present (ie that which was physically existent as at a given point in time). Previous existences have ceased (the past) as at that point in time. Successive existences (the future) do not exist.
> In other words, one does not affect the future, what happens is that a present occurs which is different to the one which would have otherwise done so.
• Strange phraseology but more or less in accord with my proposal of an Evolving Block Universe (EBU): see http://arxiv.org/abs/gr-qc/0605049
I did not have space to give all the references I would have liked to include. One that is great is Eddington's book The Nature of the Physical World, which is far deeper than many more recent writings (see his earlier chapters for the relation between physical reality and the mathematical models that some people mistake for reality). I'll put up Feynman's writing on this theme of levels of reality in a separate post.
However you have not responded to my main challenge. How does the existence of computer programs relate to your concept of actuality? Do you claim
• They don't exist? - then their outcomes, such as aircraft designed via computers, are uncaused and just appear magically
• They exist and are made up of elementary particles? - if so what are these particles an din what way do the constitute a computer program>?
• They exist and are not made up of particles? - this of course is my position. Can't see that either of the others makes sense.