**From:** Mitchell Porter (*mitchtemporarily@hotmail.com*)

**Date:** Fri Aug 01 2003 - 19:40:55 MDT

**Next message:**Gordon Worley: "Test: SL4 CHAT: Wednesday, 6 August, 9 PM ET"**Previous message:**Doug Keenan: "Re: "Ground-breaking work in understanding of time""**Maybe in reply to:**Tyrone Pow: ""Ground-breaking work in understanding of time""**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ] [ attachment ]

*>Here's the paper cited by the article:
*

*>
*

*>http://doc.cern.ch//archive/electronic/other/ext/ext-2003-045.pdf
*

Thumbs down from me. The basic idea is just Zeno's Arrow: it's not moving

at any instant in time, so it's never moving. Zeno was trying to prove that

motion is an illusion. Lynds, conversely, believes motion is real and that

therefore "there is not a precise static instant in time underlying a

dynamical

physical process", and also no "precisely determined" instantaneous values

of physical magnitudes. I find it peculiar that he does not simply propose

this

as the genesis of the uncertainty principle. The argument is that you can't

simultaneously have an exact position and a velocity; which at least

*resembles*

the uncertainty principle; but instead he says explicitly, they're not the

same

thing. Lynds's uncertainty is something extra.

In any case, the original argument goes nowhere as far as I'm concerned.

It's like an argument that there is no such thing as length, because

individual

points have no length, and adding zeroes just gives you zero. Well, in the

continuum model of space, any line interval of nonzero length is already a

little continuum; and there are infinitely many smaller continuum-intervals

within it; but none of that gets in the way of the individual points having

exact coordinates. An analogous view of continuous time would say that

change exists in any nonzero interval of time, and an instant of time is

just

the limit in which change is zero because the starting point and the

endpoint

are the same moment. This does imply that "process" or "becoming" is

something which involves more than one moment of time, but that should

not surprise anyone.

Julian Barbour's view, which Eliezer mentioned, is a response to the

technical "problem of time" in quantum cosmology. In ordinary quantum

mechanics, Schrodinger's equation takes the form

H psi (is proportional to) dpsi/dt

"H" is the Hamiltonian operator, which specifies the dynamics of "psi",

the wavefunction. The problem in quantum gravity is that you also know

that "H psi=0". This implies that the wavefunction of the universe does not

evolve in time. Barbour's theory is a many-worlds theory without time;

he says that the various spatial configurations to which psi assigns a

probability all exist, without evolving in time, and the perception of time

is just an illusion. I believe that Kant, having formulated the notion that

time was an "a priori form of intuition", had a similar idea - what if each

of "my experiences" is happening to a separate, static monad, rather

than to the one "changing" self?

Personally, I think we do have knowledge of change on a deeper level

than just the use of memory to confirm that "this moment differs from

my memory of the previous moment". If that sort of comparison was the

only way that we derived a sense of time's passage, then I think the

Kant/Barbour idea would be "phenomenologically viable", that is, it would

be an idea about fundamental reality which is at least consistent with

perceived reality. But in fact, it seems to me that perceived reality is

already a process at an unreflective level, and that "moments of experience"

are an artefact of reflection, and that the idea of trying to prove the

reality of time by comparing one moment with another is basically doomed,

precisely because you've already adopted a mode of perception in which

you are filtering out the dynamic aspect of things.

Anyway, apart from the philosophy, I may have a more formal problem with

Barbour's theory. How do you judge the plausibility of a multiverse theory,

given that by definition you are stuck in just one world? First of all,

there

simply has to be *something* in the postulated multiverse corresponding

to what you see; your world must be somewhere in the ensemble.

Second, yours should be an average sort of world, modulo anthropic

considerations. In Barbour's case, this means arguing that his (deluded)

observer-moments, with their (fake) memories, should characteristically

remember a past (which never happened) in which the statistics of events

conformed to ordinary quantum theory - since this is what we see in our

world. In making that argument, does Barbour need to use the probabilities

associated with each world by psi? Because if he does, I think it's fair to

ask what those probabilities actually mean.

Suppose someone said, "In my theory of the multiverse, complex systems

cannot form in most universes." You might object that this would make

our world unusual, violating the second principle above. Now suppose

that the multiverse theorist, instead of arguing anthropically, said, "Yes,

the complex-systems worlds are greatly outnumbered by the boring

ones; but the complex-systems worlds are *more probable*, and that

makes up for it." This way of talking makes no sense. The probability

in question cannot be "probability of existing", since by hypothesis all

these worlds exist equally. So what does it mean?

The only way out which I can see is via the concept of a "measure".

In calculus, a measure tells you how to sum over continua, by assigning

a size to each subset. Any set which consists of a countable number

of points has measure zero and can be ignored (unless there are

delta-functions involved, but let's not go there). If the wavefunction

of the universe can be interpreted as a measure - as the thing which

tells you *how* to count the many worlds - then the "probabilities" are

legitimate, and describe the actual universal prior for that multiverse.

Otherwise, the probabilities are just a nonsensical fudge factor added

to Bayes's formula without justification. (I think this is a familiar

consideration in many-worlds philosophy, but I've never seen it stated

this directly.)

_________________________________________________________________

ninemsn Extra Storage comes with McAfee Virus Scanning - to keep your

Hotmail account and PC safe. Click here http://join.msn.com/

**Next message:**Gordon Worley: "Test: SL4 CHAT: Wednesday, 6 August, 9 PM ET"**Previous message:**Doug Keenan: "Re: "Ground-breaking work in understanding of time""**Maybe in reply to:**Tyrone Pow: ""Ground-breaking work in understanding of time""**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ] [ attachment ]

*
This archive was generated by hypermail 2.1.5
: Wed Jul 17 2013 - 04:00:42 MDT
*