Truisms 6

On some days, I'm not even sure about the basic particles... (Though the actual framework of quantum field theory is probably fairly solid, even if it's turtles all the way down.)

In other words...

Basic Concept: Things change. Without which fact the very universe as we know it would not be possible.

Consequence: What pertained earlier may not pertain now, and will not pertain in time regardless of what you do.

Consequence: The location you learned about from a book no longer exists as it was written about in that book.

Implication: What we think we know is often out of date.

Numbers, mathematical and geometric proofs do not change or vary, nor do they appear to be dependent on the existence or absence of a natural world. Perhaps there is more in Aristotle than you are crediting in the above brief statement

Given the example of Heraclitus, and the use of the term "objects" I think the truism is addressing only the behaviour of matter and energy in spacetime - i.e. these things are always in motion relative to something else - but is not suggesting that the laws governing this behaviour are also in flux (they can't be, otherwise the truism and everything else for that matter would be meaningless).

As it is, I think you can reduce the statements to simply follow the river analogy and say,

"Everything is in flux",

because if Einstein had his cards in order, then if one thing is in flux it necessarily follows that everything else is in flux (relative to the first thing).

Or have I completely missed the point (I'm pleading the Friday defence if I have)?

JBB @ 3: Of course numbers change. Sometimes they are even born. "0" for instance. And "pi"...

Once you have set up a schematic formal language like mathematics, so long as you wish things to be coherent, you tend to not revise any axioms or fundamental concepts, but there is conceptual change nevertheless. And anyway I don't think numbers are things...

Heraclitus set the western philosophical project going by asking if we could step in the same river twice. ... But the malign stasism of Aristotle and Plato returned and dominated western thinking for the next two millennia

These are very deep waters (no pun intended). And if I'm not mistaken, that stasism goes back even further, to the Eleatics - Parmenides and Zeno. According to them, there is no change, only the "One". Change is an illusion (sounds like "block time", doesn't it?).

But in any discussion of physical change, philosophy of time is unavoidable. I don't think we're talking about the "change" you observe in an arithmetic number line, when it changes from 3 to 4. That requires a choice in the observer to make the change. Physical change is independent of the will of the observer, and that necessarily introduces a (seemingly objective) focal point for change that we call "now" or the present, dividing past and future events (there is no such point on a number line). Curiously though, there can be no absolute rate assigned to this change - how fast does time pass, one minute per minute? Rates are always based on events relative to other events.

But the present is not required to describe physical phenomena (yet). Most physicists don't even want to discuss it, although Einstein mentioned it briefly by saying that he doubted a theory of the present would ever be possible. The problem for physicists is that a concept of the present cannot be separated from human consciousness (or even the current inertial frame, for that matter). There is no other standard to define what "now" is in the spacetime continuum, except what you think it is. And without the present, the universe is like a static number line without change (block time). Maybe you think of "now" as giant "cursor" moving through spacetime. But can you show me any physical basis for it? So far, the solution for physicists has been to say that "now" is an "illusion". A damn good one though, I must say. And if the present is subjective, then you have no way of knowing whether the "now" you experience (and the change surrounding it) is the same as the "now" that someone else does. Even though we use the word frequently, it may have no objective meaning.

When you write 'Their view was overtaken for a time by atomism, which effectively asserted the Truism above' do you mean by the Epicureans? If so, in what way overtaken? I thought the Epicureans were more a dissenting minority than a dominant philosphical school, hence that statism was alive and well throughout the classical period.

I'd argue actually that these "physical kinds" exhibit their own sort of flux; what better explanation of the wavefunction? The static "particle", at least in the sense of how we treat its existence under most interpretations (an exception, see: David Bohm), contains some amount of necessary ambiguity. The notion of static is always one of a scaling factor, even if it's just that we can't see beyond that scale yet.
As to a "theory of now", the sense I get is it's just of no interest to physicists; why discuss subjective/objective arguments when they're not helpful to anything related to the science of the issue, and potentially destructive of one's street (uh... DOE) cred? Maybe a philosopher of science could shed more light on that.

Jeff: Not my field but I reckon that being here now is just a state of being physical - all physical systems have positions in space and time. We experience the now because we are causal systems that have states at times. We are in a state at t because we were in a state at t minus n, that causally leads to our state at t. Hence we experience the state at t as "now". I can't make that make any more sense,m I'm afraid.

Bruce, Aristotle and Plato were not as popular over the period from Epicurus to Plotinus as they were thereafter. One leading thinker in the atomist tradition was, if memory serves, Chrysippus, whose stoic philosophy was predominant. Unfortunately we lack his writings - they weren't mediated by the Aristotelian and Platonic medieval traditions (as they weren't all that friendly to theism). He looked uncommonly like Daniel Dennett, which may not be an accident.

Kevin, I normally don't do quantum, but I reckon that atoms are stable enough to count as natural kinds. My basic criterion for something being a natural kind is if all members of the putative kind can be interchanged without a difference being made. For that reason, I don't think of living things as forming natural kinds, but a gold atom is a gold atom, isotopes notwithstanding (they merely form subkinds).

That atoms and other particles come into existence or go out of it (or transmute into lead atoms, etc.) is besides the point. The kind remains even if the members individually do not.

all physical systems have positions in space and time. We experience the now because we are causal systems that have states at times. We are in a state at t because we were in a state at t minus n, that causally leads to our state at t. Hence we experience the state at t as "now".

That's what I would think too - it's intuitive, but it assumes the state at t is ontologically real, and t-n and t+n are not, otherwise there's nothing to distinguish any one of the states as "now". The block-timers don't think that way. To them the whole timeline is ontologically real, but they offer no explanation for why we experience a specific moving now.

The main arguments against presentism are difficulties with special relativity (simultaneity in different reference frames), and the inability to assign a rate to the flow of time (even though we perceive such a rate). The arguments against block time include the uncertainty principle and an inelegant coupling with MWI. Most physicists don't actually think too much about it - as Kevin pointed out, it's not helpful to their careers. But AFAIK, it's still an ongoing battle in philosophy of time.

Either way though - whether it's change within the context of dynamic presentism or static eternalism, I would think problems of identity and kinds remain, and are complicated by QM. And it's not only the river that's different when you step in it again, but you're not the same person either.

Posted by: jeff | February 15, 2009 12:30 PM

Maybe you think of "now" as giant "cursor" moving through spacetime. But can you show me any physical basis for it?

Why is 'now' any more problematic than 'here'? - zeroes in time or space (even before invention of zero as a number) relative to an act of communication. Less complicated than verb tenses, but part of the language in the same way.

Why is 'now' any more problematic than 'here'?

Because "now" changes, or appears to change, on it's own without you deciding to move forward in time. That's is not the case with "here". Subjectively, it's motion is also only in one direction and it seems to have a rate (which some say passes much faster as you age). Most physicists think the arrow of time is objective and related to entropy, but none of them talk about a concept of the present.

I did read a rather obscure paper a while ago, which argued that instead of adopting block time - which is essentially viewing time as being space-like, we should view space as being more time-like. In other words, "here" would have special physical meaning, just like "now" does to the presentist. I couldn't see how solipsism could be avoided in a model like that.