[time 830] Re: Does a fundamental time exist in GR and QM? The thinking of others...

Stephen Paul King (stephenk1@home.com)
Wed, 29 Sep 1999 02:27:44 GMT

On 12 Aug 1999 04:24:22 -0700, baez@charity.ucr.edu (john baez) wrote:

>In article <37B08A95.4B9D9053@dcwi.com>, Ralph Frost <refrost@dcwi.com> wrote:
>>If you would be so kind as to expand a bit on the things you are saying
>>here, I think you might avert some people from going astray.
>While causing others to go still further astray... okay, I'll risk
>>I certainly might be one of those people who would be tempted to read in
>>that what Rovelli seems to be saying agrees with the simplified notion
>>that "experience exists, but time does not".
>I wouldn't want to say whether Rovelli's remarks do, or don't, agree
>with this. The main reason is that physics rigorously shies away from
>talking about "experience", preferring to leave that can of worms to
>psychologists, philosophers, and other brave souls. Physics confines
>itself to the thin sliver of reality that can be accurately quantified.
>The concept of "experience" is not presently part of this thin sliver.
>>_I_ see this as
>>fundamental but I expect you are, however, making reference to much more
>>complicated mathematical expressions, correct?
>In fact it's the notion of "experience" which is the really complicated
>thing, not the mathematical expressions that Rovelli is referring to.
>Mathematics deals only with things that are so simple that they can
>be described with utter precision - so precisely that even a computer
>can deal with them. Most things - like "experience" - are too complicated
>to be described in this way (at least for now). These things may seem
>simple, because we are familiar with them, but as soon as you try to
>describe them in a completely precise way - e.g., to write a computer
>program that can "experience" - the crushing weight of their complexity
>is made apparent. What many people take to be the complexity of
>mathematics is really just the difficulty of learning unfamiliar
>concepts at a high level of precision, no matter how simple they are.
>>At the simple level, heck, maybe mine is just a private notion, I see
>>this "problem with time" as intimately wound into the limited scope of
>>contemporary physics. By NOT accomodating ~consciousness~ [or whatever
>>you want to call it], all the various descriptions and theories in
>>physics make _perfect sense_ for as far as they can go. Yet, when that
>>boundary is breached and one notes that the entire system present us
>>with experience, not time, imo some of the temporal equations and
>>relationships take on a much more "grossly approximate" hue.
>Hmm. I'll just say this: there are lots of mysterious things
>about time, but in quantum gravity, the "problem of time"
>is a very specific technical problem, namely: how to recover a
>theory in which time evolution is described by a 1-parameter
>unitary group as a limiting case of a theory without a Hamiltonian,
>but merely a Hamiltonian constraint. You'll notice that I'm
>throwing around a lot of technical jargon here! I'll give a
>somewhat more simplified description below, but right now I'm
>trying to make a particular unhappy point: I want to make it
>clear that the "problem of time" in quantum gravity can only be
>understood after one has spent a while seriously studying physics.
>It is not the sort of problem that can be translated into everyday
>terms without mangling it almost beyond recognition. It *does*
>have a philosophical aspect to it that can be explained without
>any physics jargon, and it's very important to understand this
>aspect - to "see through all the clutter of technicalities" - but
>unless one *also* understands the technical aspects, one can't
>see that it is a very precise problem, possibly with a very
>precise solution - one is at best dealing with a caricature of
>the problem. In particular, one may be misled into thinking
>that "consciousness" or "experience" play an important role
>in this problem. I'm pretty sure they don't!
>>But the yellow caution flag you throw out is aimed at pointing out that
>>ALL the quantitative relationships do indeed only exist in the temporal
>>models. Is that close to what you are trying to express?
>Not really - I'm not sure I even understand what you mean!
>>If not, can you expand
>>a bit on what you are afraid some people might do, please?
>Listing all the things I am afraid some people might do would make
>this a very long post. However, I suppose the thing I am most
>afraid *you* are doing is thinking that "experience" has much to do
>with the problem of time.
>>> Yes - as long as you keep in mind that "derived versus fundamental"
>>> is not a fundamental distinction.
>>Can you clarify what you mean, here? I keep thinking that folks did
>>their level best to evolve a very good fundamental theory.
>In a theory of physics we typically start with some assumptions and
>derive some conclusions from these. We call the assumptions
>"fundamental" - especially if they are simple and we keep using
>them over and over again in different contexts - and we call the
>conclusions "derived". But as theories change, what was once
>"fundamental" may become "derived", and what was "derived" may
>become "fundamental". This is what I meant by the wisecrack above.
>In particular, the idea that time is represented by a real number
>t is considered fundamental in much of quantum mechanics, but
>will certainly be derived in any good theory of quantum gravity.
>We don't know exactly how this will work yet - and that's the problem
>of time in a nutshell.
>I'll add, though, that there has been a huge amount of progress
>on the problem of time over the last couple of decades, so it's
>not as if we are *completely* floundering around in the darkness.
>In fact, right now I think there are other more pressing problems
>in quantum gravity.

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