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From: KFL@MIT-MC.ARPA
Newsgroups: net.sf-lovers
Subject: Time travel
Message-ID: <4042@topaz.RUTGERS.EDU>
Date: Tue, 15-Oct-85 22:50:15 EDT
Article-I.D.: topaz.4042
Posted: Tue Oct 15 22:50:15 1985
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From: Keith F. Lynch <KFL@MIT-MC.ARPA>

    Date: 10 Oct 85 17:24:00 PST
    From: nep.pgelhausen@ames-vmsb.ARPA

    Has anyone any thoughts on these three distinctions?  Has anyone
    seen a story where all three are brought into play?  (Objective and
    Subjective time are dealt with frequently, but Meta time seems to be
    ignored (and rightly so...it would be a difficult concept....can you
    now imagine traveling in Meta time??? You could travel to
    (objective) 1800 by FIRST traveling back a month in Meta time, to
    "before" the barrier was put up...))

  Isaac Asimov's _End_of_Eternity_ deals with all three.  An interesting
twist is that meta-time seems to be circular.  This is never made explicit
in the story, but is the only way I could find to understand it.  This
story also involves a similar time barrier.
  Note that some concepts of time travel do not require this concept.  For
instance Heinlein's time travel (in _Door_Into_Summer, _Time_Enough_For_Love_,
and _Number_of_the_Beast_) always seems to be in one timeline, i.e. whatever
happened happened.  Time travel in Star Trek seems to work the same way, as
it does in H. G. Wells _The_Time_Machine_.
  Also, there is the stack theory of time, as presented in James Hogan's
_Thrice_Upon_a_Time_, and in John Boyd's _Last_Starship_From_Earth_.  In
this theory, changing the past simply obliterates whatever future comes
from the past having not been changed in that way at that time.

								...Keith