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From: Laws@SRI-AI.ARPA (Ken Laws)
Newsgroups: mod.ai
Subject: Inside Out
Message-ID: <8606040524.AA04776@ucbvax.Berkeley.EDU>
Date: Mon, 2-Jun-86 13:24:35 EDT
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Posted: Mon Jun  2 13:24:35 1986
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Some thoughts on Pat Hayes' question:

My own intuition is that either  1) the Tardis is simply bigger
inside, as you suggest, or  2) the doorway is a portal to another
dimension or reality that could contain anything at all.  One way
to test the intuition is to ask "What would happen if I cut a
hole through the wall?"  The answer would not completely distinguish
the two cases, since it is quite possible that the entire wall
(inside and out) is a portal that maps between two realities;
cutting a hole would create a new door with exactly the same properties
as the original, which would tell us nothing.  My own guess, though,
is that cutting a hole from outside the Tardis would reveal some
kind of "machinery" or peculiar spatial structure (such as a gel,
crystal, or other "matrix"), while cutting a hole from the inside
would let you out into Gallifrey, Dr. Who's natural environment.

Such portals have been frequent in science fiction, and the exact
properties that we infer for each depends on the author's presentation.
Some conceptions do lead to greater difficulties than others.  In
Robots Have No Tails, Louis Padgett (pseudonym) wrote about a box that
was larger inside [partly] because it mapped into the future and the
universe was shrinking.  This lead to difficulties at the interface:
things put inside would shrink, but only after a few seconds, and it
is not clear what would happen to a single object (such as your hand)
that extended across the portal for that length of time.  I find
Pat's "shrinking" hypothesis untenable for this reason.  Similar
problems arise at the boundary if the doorway is a transporter.

Another such box is the chest that appears in one episode of the
Dungeons and Dragons cartoon on TV.  Move it to a particular place,
open it, and you are likely to find a stairway to an alternate
reality.  (This is rather like the holes in time used in the Time
Bandits movie.)  The D&D chest has the property that the spatial
mapping between realities is fixed and that the portal itself
moves between them.  I assume that the box cannot be moved while
open, which covers the main conceptual difficulty: why can realities
only connect at certain points, and what happens if the box straddles
two such points.

As for something simply being bigger inside, this doesn't bother me.
As we move, we somehow update our internal maps of our surroundings.
As I turn my head, I somehow rotate my mapping of where everything is
relative to my focal direction.  It seems unlikely that I actually
store and update a position vector for every book on my bookshelves;
instead I must be storing relative positions of items in the room and
the relative orientation of myself and the room.  One could argue that
our natural tendency to build walls, and perhaps even our tendency to
build rectangular rooms, arises from the mental savings in building
these maps in hierarchically partitioned modules with related coordinate
frames.  If we store spatial relations in such a manner, it is easy
to see how the spatial relationships inside a box need not be strongly
linked to those outside the box.  Just as we can move the box and its
contents as a whole, we can expand it as a whole (on the inside only!)
without affecting our mapping of the rest of the world.

As for two things not occupying the same space, that's not really true.
It all depends on what you mean by "thing".  A forest and a tree occupy
overlapping space.  Properties such as color and texture certainly
coexist.  Fish and streams seem to interoccupy, and groping around
in streams and holes may be a task for which our spatial decoupling
evolved.  I wouldn't even be surprised if fish were perceptually
bigger on the inside than on the outside, since they disgorge a lot of
"stuff" when you open them up that is perceived at a different level
of detail than is the smooth exterior of a fish.

					-- Ken Laws
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