From: ingles@engin.umich.edu (Ray Ingles)
Subject: Re: Feedback, Boundary Conditions, and Time Travel (long....)
Date: Sat, 26 Sep 92 02:20:13 EDT
Organization: University of Michigan Engineering, Ann Arbor

In article <1992Sep25.063711.1666@ee.eng.ohio-state.edu> rob@hoster.eng.ohio-state.edu (Rob Carriere) writes:
>>In article <1992Sep24.075920.28976@ee.eng.ohio-state.edu>
>rob@hoster.eng.ohio-state.edu (Rob Carriere) writes: 
>>>Yes.  This is exactly my objection to all the `one time-line' ideas of
>>>timetravel:  Not all feedback systems are stable, and you need some kind of
>>>magic to explain how no unstable configuration ever came to be.
>
>In article <FSy-WYC@engin.umich.edu> ingles@engin.umich.edu (Ray Ingles)
>writes: 
>> I think we have a misconception here. 
>
>I don't think so.  At least your explanation below (deleted) coincided pretty
>well with what I thought you were saying.
>
>> In the 'one time line, no paradoxes' view, feedback is entirely the
>>wrong concept. A much better analogy is boundary conditions.
                               ^^^^^^^
 Okay, fine. I will now use the word 'metaphor' rather than analogy,
so that an exact correspondence between the ideas is not assumed.

>Whether feedback is appropriate depends on whether you posit one or more
>hypertime dimensions.  I don't think boundary conditions cut it under any set
>of assumptions.  After all, we're not talking about boundaries here.  Time
>exists towards both the before and after ends of your loop.

 Yup. You're right. Time exists before and after. The same as space
exists both inside and outside a well. Naetheless, there are things
like boundaries. One can look at things in such a way that knowing
something about the future establishes a constraint on the path history
will take.
 Since you know something about the current state of the universe (though
hardly all) and you know something about a subsequent state, you know
something about what will happen in between.
 This is one way to look at it. Another is to assume that all of time
'already' exists (Damn, I wish English had an extrinsic tense.) in a
direction we don't normally perceive or access. After all, if you travel
into the past, the past must still exist somewhere to go to. The same
for the future. (Indeed, *we* are in somebody's past.) Since, in a sense,
all of history has 'already' happened, your own travel and its consequences
have 'already' been taken into account; they are part of the past you came
from and the future you will go to.
 
>> If you put a quantum particle in an infinite potential well, [...]
>
>And this, I think, is the crux of the problem.  Your wave function needs to

 Sorry. I thought I made it clear that this was not a literal example, but
an analogous illustration. My error.

 [deletions]

>That's my whole point: where's the proof that inconsistencies are indeed
>forbidden?  
>
>SR
 
 Uh, well, actually, it was an *assumption* and labeled as such at the
start of this thread... I have been attempting to show that this is
logically consistent and then exploring the consequences...

Sincerely,

Ray Ingles                  || The above opinions are probably
                            || not those of the University of
ingles@engin.umich.edu      || Michigan. Yet.
Newsgroups: rec.arts.sf.science