Time Travel (A Question)
Andreas Schwarz
to...@eleceng.ee.queensu.ca (Mansour Toloo Shams) writes:
>Hello:
> I would like to know if time travel is possible at least
> in theory (Both in positive and negative direction)?
Maybe this posting is useful. I sometime before thought out for
the same question.
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In the time I read SF literature, I often wonder in the imagination of
some SF-writers in case if time mashine problems called paradoxa.
It seems to me that they imagine the time as a very angry person if
someone meddles in it's sequential flooding.
There were somtimes scenes where the time takes revenge on time
travellers for their heretic doing !
And that hurts my logical understandment.
So I want to post this article for discussion the logical implications
in time travelling - please enjoy and react :) :
Preliminarity in time mashines:
First we want to imagine, that time mashines are reality.
That means, you have a mashine where you can carry somthing
from one point in time to another point in time.
There the first problem will came on :
Our Universe is not static. That means, all time the Earth is turning
around, moving in it's orbit, moving with our sun through our galaxy
and also with our galaxy through the universe.
So if you only change the point of time, you will start on Earth, but
never will reach back , for the Earth will not be on the same place in
universe twice ( or if so it wil a absolutely incalculatible random
event ! ).
That includes, that for use of a time mashine the technology must have
the capability of interstellar travelling, to reach the Earth in another
time, or you have to trigger the travel for part of seconds.
But this was only a technical aspect.
Let us imagine that the mashine works as most sf-writers say ( you start
on earth and you reach earth again - no problems with space ) or even
let magic work or somewhat else.
Anyhow, let's take a look at the logical aspects of time treavelling.
( But I don't want exclude technical aspects completely for I can better
explain what I mean with semi-scientific terms :-)
General Preparations :
If you take a look on the universe, than should be accepted the
following definitions :
M(t) = mass of the universe at time point t
E(t) = energy of the universe at time point t
U(t) = the combination of mass and energy ( such as movements and so )
at time point t ( also called space-time-continuum )
TM1 = mass and energy of a time mashine Nr 1
TM2 = mass and energy of a time mashine Nr 2
so we can say that after a time difference of (t n+1) - (t n)
you get from U(t n) -> U(t n+1).
In the following I want say this when I make the following formula :
U(tn)
------------- => U(tn+1)
d((tn+1)-(tn))
Now we want to take a look on paradoxa:
As paradoxa only can happen ( what a mess with the speak, for paradox
means, something can NOT happen ! :-) in case of travelling back in
time, we only want to look after that.
Now let's say thet t0 will be the starting point of the universe,
t1 the point a time traveller will go to, t2 a time point following
immediate after that, t3 the point in time the traveller will start,
and t4 just the time point immediate after.
So if no travel will happen, you will get this :
U(t0) -------> U(t1) --------> U(t2) --------> U(t3) --------> U(t4) -->
Now let's look for the begin of the travel :
We cannot get the same U(t4) for there something has changed :
we get therefore U'(t4), which is defined as U(t3)-TM1.
U(t3) - TM1
------------ => U'(t4)
d( t4-t3 )
( I don't want to refer about the physical law of static mass/energy of
this universe - that can't be discussed in case of time travelling,
for we never will get the relating facts before we don't HAVE such a
mashine :)
If we now look after the point when the traveller will arrive, we can
see thet there has again something changed :
At point t1 the Universe again will be changed in it's mass/energy for
we have to add the TM1 to the U(t1) and we will get U''(t2).
U(t1) + TM1
------------ => U''(t2) , where U'' not = U or U'.
d( t2-t1 )
And that includes, that U''(t2) never can become U(t3) for U(t3) is only
the result of evolution of U(t2) !
( I use U'' instead of U' for not to give confusions between the
universe that follows after U'(t4) and the universe following U''(t2).)
So I wil try another picture to show this :
U(t0) -------> U(t1) --------> U(t2) --------> U(t3) -------> U'(t4) ->
|
travelling : +--------<---------------<------+
|
U(t1) --------> U''(t2)
And now we come to the point, where ( my opinion ) the most writers make
one completely unlogical mistake.
I say, that a universe wich differ from another universe ( U vs. U' )
never will produce the same future.
Even if the time masine will be damaged my an earth quake and be buried
under million tons of stone so that the traveller will nothing do
against even then the universe has changed and is unequivocal different
from the original one.
The reason is the adding of mass and energy, that adds into the existing
universe forces and objects they were not there before and reacts
different reactions on their existance.
Maybe these two universes will convergate ( I'm sure that they more
realistic would divergate ) to the same PICTURE of universe but in
reality they DIFFER !
So after the travel we can get this Picture :
U(t0) -------> U(t1) --------> U(t2) --------> U(t3) -------> U'(t4) ->
\
--------> U''(t2) ------> U''(t3) -----> U''(t4) ->
As I just clearyfied, these Universes are different, so such paradoxa
like the murdering of your own grandfather before your father's birth
and the resultined removeing of your existance out of reality are
illusion.
if you reach the point of time, you create a new universe by adding your
mass and energy. Your existance is therefor not depending on the
evolution of this universe since you are the product of another one.
So if you will do tis murdering act, you only prevent the birth of
the pendant of yourself in this universe, but that can't have any
influence on your own existance at all.
We can now speculate what will happen with U, when TM1 has "created"
U'', even how I prefer a model of parallel existant universes.
however, the traveller has now the problem, how to come back, for
if he only travel into the future, he will reach the future of the
universe he created and not the one he leaved.
To rech his origin world, he has to be able to switch between the
universes and that is a complete other theme :-)
Now we will lake a look at the problem that some writers make if they
will initiate the hounting of time travellers by time travelling.
The scene is for example :
one outlaw will escape with a time mashine and a time agent shall
follow him into another time.
Again will the movement into the future will not create any paradoxa.
So we must look at the other destination.
Now the question :
Can the Time mashine Nr.2 ( TM2 ) overtake TM1 ? that means, can TM2
arrive at a point of time before TM1 arrives and wait for it ?
Can TM2 go to a point of time after TM1 landed to prevent what the man
in TM1 want to do or to arrest him ? or can TM2 and TM1 reach at the
same time ?
So we have 3 different cases to study :
For the beginning we have the constellation, that TM1 arrive in the past
at the point of time t2 and TM2 should follow it.
U(t0) -------> U(t1) --------> U(t2) --------> U(t3) -------> U(t4) ->
\
--------> U''(t3) -----> U''(t4) ->
The three cases are now that TM2 arrive at t1, t2, or t3.
1 - t1 :
When TM2 reaches t1, it generates like TM1 at t2, another universe by
adding it's mass and energy. But this new universe differ from the U''
generated by TM1.
TM2 generates the universe U'''.
U(t0) -------> U(t1) --------> U(t2) --------> U(t3) -------> U(t4) ->
\ \
\ --------> U''(t3) -----> U''(t4) ->
-------> U'''(t2) -----> U'''(t3) ----> U'''(t4)->
And because the U'' evolved from U, the passengers of TM1 and TM2 never
will met together !
2 - t3 :
This is in fact the same as before, for the reason universe that comes
the start of TM2 is still U and not U'', so TM2 reachhes t3 and build
U'''' there :
U(t0) -------> U(t1) --------> U(t2) --------> U(t3) ----> U(t4) ->
\ \ \
\ \ -----> U''''(t4)->
\ -------> U''(t3) --> U''(t4) ->
-----> U'''(t2) -----> U'''(t3) -> U'''(t4)->
Same effect as in 1).
3 - t2 :
That 's a special problem :
It concerns the "Heisenbergsche Unschaerferelation" ( I don't know
the english term for that ), wich postulated, that never it will be
practable to measure the speed AND the position of an object at the
same time.
I can't imagine how this can be used or not in this case.
But IF the full equal time is possible, only then TM2 can meet TM1,
for if they will reach at the same time, they create the new universe
together instead of each alone.
U(t2) + TM1 + TM2
----------------- => U'''''(t2)
d( t3 - t2 )
U(t0) -------> U(t1) --------> U(t2) --------> U(t3) -----> U(t4) ->
\
\
-------> U''''(t3) -> U''''(t4) ->
So I have present the whole possibilities that can happen in case of
travel into the past.
Now I'm waiting for response what do you think of it .....
Chiron McAnndra
-------------------------------------
| Munich / Germany |
| E-Mail : chi...@cube.net |
-------------------------------------
ceterum censeo claudiam esse amandam :)))
Matt McIrvin
Well, there are a number of different paradigms that SF writers
use for the resolution of time-travel paradoxes. Here are a few
of them:
(1) Branching universes-- This is what you've described, basically.
It's actually a very popular one, especially among people who really
want to write alternate-history fiction. There are subcategories
of this, too:
(a) When you go home, you go back to your original timeline.
(Gibson and Sterling, "Mozart in Mirrorshades"; Alfred
Bester, "The Men Who Murdered Mohammed," though there there's
an extra surprise in store.)
(b) When you go home, you go to the modified future.
(Very popular.)
(c) When you go home, you go to some other universe than (a) or (b).
There are also a couple of possibilities about history that can
be mixed and matched with (1a,b,c):
(A) History converges to the same future after a modification,
given enough time.
(B) History diverges wildly, even following a tiny perturbation
(you consider this more likely, and so do I).
(2) Changing history does something terrible:
(a) Destroys the universe (bummer)
(b) If you prevent your own birth, you disappear, but the effects
of your actions (including the change to history itself) don't.
This is totally illogical but is popular anyway (see the "Back
to the Future" movies, which combined this with (1b)).
(c) Does (1)-style branching, but for some reason the universe
thus created is in some cosmic sense Not the Right One, and
must be restored to its original form. Used on Star Trek:
The Next Generation, not very logically.
(d) In many time-travel stories, meeting yourself in the past is
supposed to be a particularly dangerous thing with special
destructive properties (see Doctor Who and a recent Babylon 5
episode). Granted, this could be a fertile ground for paradoxes,
but why is it any *more* prohibited than a dozen other equally
paradoxical things?
(3) Changing history is impossible:
(a) Backwards time travel is impossible.
(b) Universe destroys you preemptively (the animistic
"angry time" scenario you don't like--used nicely,
actually, in a little story by Larry Niven called "Rotating
Cylinders and the Possibility of Global Causality Violation").
(c) The Time Police get you preemptively. The problem is that
Time Police are fallible beings and you need some sort of
backup device to patch up mistakes. Rudy Rucker once
complained about this scenario in a review of a sort of SF
novelty book, a user's guide to time travel. He called it
dreary (I agree) and said that the book allowed for some
branching as in (1) if you manage to evade them: but, as he
said, "why not have it branch lots? *God has the budget.*"
Rucker seems to have regarded (1) and (3c) as the only
real possibilities in time-travel fiction, for some reason.
Of course, if the Time Police are doing something *other*
than just preventing paradoxes, that's a lot more fun.
(d) No matter what you do, events conspire to produce the same
history there always was. This can be used to great effect
in stories resembling frustration nightmares. Little did
you know that there *was* a ruined time machine sitting in
a ditch in 17th-century Florence, but all records of it
were lost; or no matter how many times you try to fire at
your grandfather, the gun jams or the bullet misses, or
you discover that you've shot your grandfather's identical
twin, murdered by a mysterious, possibly insane gunman with
an unusual-looking weapon, according to old stories...
It allows for its own somewhat paradoxical phenomena, as
described, for instance, in Heinlein's "All You Zombies."
Since there are no real time machines, we don't know which of these
would actually pertain, and if they're impossible then it's moot.
However, you can tell from this list that I prefer some to others.
My favorites are the (1) possibilities, particulary (1bB), and
(3a) and (3d). I don't think (3d) has been explored enough; it
takes more skill to build a good story with that possibility than
with most of the others.
--
Matt 01234567 <-- Indent-o-Meter
McIrvin ^ Harnessing tab damage for peaceful ends!
Matt McIrvin
Matt McIrvin <mci...@scws37.harvard.edu> wrote:
> Rucker seems to have regarded (1) and (3c) as the only
> real possibilities in time-travel fiction, for some reason.
Actually, now that I think about it, Rucker himself used the
possibility I call (3d) in his clever story "The Man Who Ate Himself."
Nancy Lebovitz
travel in MANY DIMENSIONS. If I've got it straight, the only time
travel you can do is to move your consciousness to a different
point on your time line.
If you try to travel into the past, you get stuck in a loop--after
you go back, you proceed forward to the moment when you decided to
go into the past.....the only way out is for another time traveller
to convince you to change your mind.
If you go into the future (if I've got it right), you skip part
of your time line, but since your experiences for the part of
it that you skipped are still part of you, you remember them
anyway, but are uncertain whether they're memories or foreknowledge.
Furthermore, travel into the future gives you a glimpse of your
whole timeline, but it's more than a human mind can hold--it doesn't
drive you crazy, but it's no pleasure either.
In case you were wondering, the means of time travel is the
stone from King Soloman's crown. It's more trouble than it's
worth, at least if you're not King Soloman, and maybe even if
you are.
Nancy Lebovitz
calligraphic button catalogue available by email
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Antoine Bonavita
About this time travel stuff, there is a very good books I have
read:
-Anubis Gates by Tim Powers
It's definitely a must. And the theory about time travel is not
bad at all (at least it made sense to me).
There is another one which title I can't remember. The story lead to
the creation of a society where timetravel was so common that everything
kept on changing in your world. Funny stuff but definitely not as good as the
other book.
Cheers.
Antoine.
Andreas Schwarz
> About this time travel stuff, there is a very good books I have
>read:
> -Anubis Gates by Tim Powers
> It's definitely a must. And the theory about time travel is not
>bad at all (at least it made sense to me).
I also read the book - and enjoyed it :-)
But I can't agree with the internal idea.
The book bases on the idea, that histoory is unchangeble.
All time-flips doesn't change anything of the world, moreover they
are NEEDED to create the world we know.
So the book violates the principle of causality.
But however it is very good written and fine to read :-)
Chris Dollin
[re the excellent ``The Anubis Gates'']
I also read the book - and enjoyed it :-)
But I can't agree with the internal idea.
The book bases on the idea, that histoory is unchangeble.
All time-flips doesn't change anything of the world, moreover they
are NEEDED to create the world we know.
So the book violates the principle of causality.
But however it is very good written and fine to read :-)
Is this the same principle of causality that allows us to predict
when a radioactive nucleus will decay?
[It's not causality; it's consistency of solutions to predicates]
--
Regards, Kers.
"If anything anyone lacks, they'll find it all ready in stacks."
Chua Seng Leng Terence
I've never really understood the reasons *why* this should happen.
It's not necessarily a paradox - and it doesn't violate either the
conservation of energy principle (because no new matter is being
created, just being shifted around in time) nor the Pauli Exclusion
Principle (it's not no two objects can't occupy the same quantum state
because it's only really *one* object).
--
------------
Terence Chua <lawp...@leonis.nus.sg>
"There's no justice. There's just us."
Tim Poston
: Well, there are a number of different paradigms that SF writers
: use for the resolution of time-travel paradoxes. Here are a few
: of them:
: (1) Branching universes--
I've never liked the assumption that universes branch only forward.
Given the `Many Worlds' quantum attitude, where evything branches all the time
anyway, it makes more sense to assume that time travel is to _a_ future
causally consistent with your present, or to _a_ past similarly consistent.
I've only read one story taking this approach, don't remember author or title;
somebody goes back to ancient Egypt a second time, and finds that the vowel
sounds (unrecorded in their writing) are completely different. You can go
back to any past that _could_ have given rise to your present.
If you change it so that it can no longer give rise to your present
(f'rinstance, give Goliath a submachine gun), you can't go back to it;
but lots of past consistent with your present are still there in the hypercosmos,
giving rise to it. Most of the paradoxes disappear.
BTW, why are time paradoxes so often illustrated by the idea of killing the
m a l e parent or -- even less certainly -- grandparent?
Genetic surveys in US towns have shown a high percentage
of children not related to their mother's time-of-conception husbands.
But I have never seen the mother targeted...
Maybe the Oedipus Complex really does make sense.
I haven't seen a n y kill-an-ancestor fiction by a female writer.
Tim
___________________________________________________________________
Tim Poston Institute of Systems Science, Nat. Univ. of Singapore
Helpscreen, n.: a device for fragmenting an explanation.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Keith F. Lynch
> I've only read one story taking this approach, ...
There's at least one other story which takes the branching-pasts
approach. In Robert Heinlein's novel _Farnham's Freehold_, the 20th
century is very slightly different after our heroes return from 2000
years in the future. A car changed from automatic to manual shift, and
someone went to bed at a different hour one evening.
--
Keith Lynch, k...@access.digex.com
f p=2,3:2 s q=1 x "f f=3:2 q:f*f>p!'q s q=p#f" w:q p,?$x\8+1*8
Alice Holt
>Re: meeting yourself causes destructive effects (2d).
>I've never really understood the reasons *why* this should happen.
>It's not necessarily a paradox - and it doesn't violate either the
>conservation of energy principle (because no new matter is being
>created, just being shifted around in time) nor the Pauli Exclusion
>Principle (it's not no two objects can't occupy the same quantum state
>because it's only really *one* object).
I suppose it all comes down to the old chestnut paradox. What happens if
I use my time transporter to accidentaly transport a big bomb with a short
fuse ten seconds into the past. The bomb goes off ten seconds before I
sent it back, thus blowing up the time machine (and itself, and me).
The time machine nolonger exists to have sent it back in the first place.
BTW, suppose the bomb blows up it's past self. I then get twice the
explosive effect! Where does the extra energy come from? Where does it
go to? How does this conserve energy?
Simon Hibbs
yfc...@castle.ed.ac.uk
Jules
>Re: meeting yourself causes destructive effects (2d).
>
>I've never really understood the reasons *why* this should happen.
>It's not necessarily a paradox
>Terence Chua <lawp...@leonis.nus.sg>
>"There's no justice. There's just us."
>
>
I don't know why it would cause destructive effects, however if you in
fact remain in the same time-line it would be a paradox to meet yourself
in the past, unless of course you remember meeting a future you at some
point in your past. I know I haven't run into a future me yet, Therefore
I know that if I ever do travel back in time I won't bother to stop by
and have a chat with myself. Of course all this goes out the window if
you have infinte alternate time lines, and when you travel back in time
you either create a new time line or shut across to another one in which
your meeting did occur.
I enjoy this group so far and I look foward to presenting some of my own
theories for debate at a future time. Unfortunately, I am at work so I
can't spend the time at the moment.
'Till next time;
David Szemerda