**Matti Pitkanen** (*matpitka@pcu.helsinki.fi*)

*Wed, 29 Sep 1999 07:47:26 +0300 (EET DST)*

**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ]**Next message:**Lancelot Fletcher: "[time 832] RE: [time 825] Chu spaces, causality, local systems... quantum laws of form? ..."**Previous message:**Stephen Paul King: "[time 830] Re: Does a fundamental time exist in GR and QM? The thinking of others..."**Next in thread:**Lancelot Fletcher: "[time 833] RE: [time 830] Re: Does a fundamental time exist in GR and QM? The thinking of others..."

On Wed, 29 Sep 1999, Stephen Paul King wrote:

*> 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
*

*> >it.
*

*> >
*

*> >>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!
*

*> >
*

His seems to be typical attitude of a theoretician confined

into the bounds of GRT. There is intellectually extremely challenging

problem but in the narrow confies of GRT it reduces to

a purely technical problem and so no progress occurs. Same

is the situation in neutrino physics. People are toying with same

un-succesful attempts to solve solar neutrino anomaly

and other anomalies and refuse to jump out of a system.

By the way, Feynmann has written some rather nasty comments about these

General Relativists travelling to they conferences and meetingsand

compared them to worms doomed to creep along the surface of apple.

*> >>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.
*

*> >
*

*> >
*

*> >
*

*> >
*

*> >
*

*> >
*

*>
*

*>
*

**Next message:**Lancelot Fletcher: "[time 832] RE: [time 825] Chu spaces, causality, local systems... quantum laws of form? ..."**Previous message:**Stephen Paul King: "[time 830] Re: Does a fundamental time exist in GR and QM? The thinking of others..."**Next in thread:**Lancelot Fletcher: "[time 833] RE: [time 830] Re: Does a fundamental time exist in GR and QM? The thinking of others..."

*
This archive was generated by hypermail 2.0b3
on Sat Oct 16 1999 - 00:36:42 JST
*