Space Forum / Astronomy / June 2005

Considerations of Time-Travel in General Relativity.

The first thing one has to understand (perhaps the only
one) is that general relativity, as it is being worked upon,
is a theoretical/mathematical universe with only certain
"claimed" connections with/to reality. If one is going to
consider reality, pure and simple, then the only possible
understanding is this:

  Time travel is impossible because the Past and the
  Future exist(ed) only in the human mind. Only "in"
  the human mind is it possible to consider [sic]
  "going back" to a "place" that never existed, et al.

When one looks out far into outer space one is
seeing objects "as they appeared in the past" (which
is the language or our primitive ancestors coloring our
"present" understanding). But this is no different than
looking at a van Gogh "painting" of petunias: Those
petunias might have (in the confusing language of our
primitive ancestors) existed "in the past" but there is no
way to go "back in time" (into the picture) to smell them
when they were real and fresh because it's less than a
picture of them (so there will be no misunderstandings).

And all the past is a picture (that we retain in our human
memory ONLY of how things that have changed looked once,
before they changed): In reality, those petunias "existed" in
the Present, and they are still "here" (as one might expect).

You can easily tell that the van Gogh canvass itself has
"travelled through time" (or you could decide not to play
such silly games and simply say that it's "here" in the
Present where it has always been). But the petunias he
"once" looked at, and smelled, and painted upon his
canvass... where have they gone? In ideal circumstances
they withered and dropped to the ground and became
part of the dust that is still there. So you could pick up
that dust and hold the petunias in your hand (except
that they have undergone a great amount of physical
change).

But if you could do such a thing, if you could change the
dust back into petunias, then van Gogh's petunias would
join his canvass and "time travel" to our present world/time
(in the confusing language of our primitive Stone Age
ancestors who first grew to believe the superstition that
The Past and The Future have some existence separate from
the so-called Present). Or you could choose not to play such
silly mind games and simply say you have re-constructed the
petunias). In any case, you can see that...

The petunias, in fact, are and always have been here
with us (in the so-called Present). You only need to
know what manner of shape they now have (all things
change over time in shape/place to greater/lesser
degrees), and where they now are. Reverse their changes
and you can smell them again. And the same thing is
true with every bit of the rest of the universe: The Past
does not refer to an existence separate from our Present
but is only a reflection of how our so-called Present is
always in a state of flux--One could no more travel to
"The Past" than one could travel to a clean hankie which
is now full of snoot. [Hint for those "slow" among you:
both dirty and clean hankies are in the present, it's just
that one state of hankie is hidden under the other... but
wash the hankie and you have travelled back in time!!!!]

In any folding hanjie, errr.... universe, any "worm-hole"
connected to what's out there in the distance that looks like
what that place looked like millions of years ago... would
connect to whatever is out there NOW, and then what would
we hook up to indeed...! War of The Worlds stuff no doubt.

... And, of course, the problem with reversing the changes
that a region of the universe has undergone in the course of
millions of years is very much greater than reversing the
changes that a handful of petunias might have undergone
in a handful of years (as horrifically difficult as even that
small a change is going to be to reverse). But if one could
reverse such changes (big and small) one would re-create
the Past (always somewhere in the Present, of course). And
an exact recreation of the so-called "Past" is the same thing
as The Past--namely, the shape some bit or other of the
Present had or has. Then it all merely boils down to access
and price of admission. Everything else is science fiction.

S D Rodrian
http://poems.sdrodrian.com
http://physics/sdrodrian.com
http://music.sdrodrian.com

RE:

from The New York Times:

There was a conference for time travelers at M.I.T.
earlier this spring ... "Traversable wormholes are primarily
useful as a 'gedanken experiment' to explore the limitations
of general relativity," said Dr. Francisco Lobo of the
University of Lisbon ... If general relativity, Einstein's theory
of gravity and space-time, allows for the ability to go back
in time and kill your grandfather, asks Dr. David Z. Albert,
a physicist and philosopher at Columbia University, "how
can it be a logically consistent theory?" ... In his recent book
"The Universe in a Nutshell," Dr. Stephen W. Hawking wrote,
"Even if it turns out that time travel is impossible, it is
important that we understand why it is impossible."