[Inform] Time Travel

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SoonMinYee

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Sep 10, 2002, 10:49:00 AM9/10/02
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I guess I ask this about Inform since that's what I'm working in but I
suppose it could apply to any language. Has any real good time travel game
been written in any language? What I'm wondering is how hard it would be to
code a game that involves time travel where you "meet yourself." Or,
perhaps, you have to avoid doing this. So, for example, you (as the player)
take certain actions in the beginning of the game. Then later in game you
are sent back in time. Now game logic has "stored" your previous moves in
memory thus making "past version of you" an NPC or something with
pre-determined actions. That NPC follows course you took. You ("future-you")
now has to avoid running into "past-you." Time travel is always fascinating
area for stories but I've found it's rarely done well. Not sure if it's been
tried successfully in IF. I know "TimeQuest" sort of did this at the end but
that limited your moves because you absolutely had to do what your
immediately previous self did (or what your immediate future self indicated
you should do) or else the game ended in 'paradox'.


D. Jacob Wildstrom

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Sep 10, 2002, 12:06:39 PM9/10/02
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In article <wDnf9.64943$Jo.11806@rwcrnsc53>,

SoonMinYee <noe...@noemail.com> wrote:
>I guess I ask this about Inform since that's what I'm working in but I
>suppose it could apply to any language. Has any real good time travel game
>been written in any language? What I'm wondering is how hard it would be to
>code a game that involves time travel where you "meet yourself."

I think the best "time travel" trick was in _Sorcerer_, where the
time-travel was of short enough duration that it didn't run in to most
of the usual glitches. There's a somewhat less elegant time travel
mechanic in _Spellbreaker_. More recent works I can think of involving
time travel (and ramifications of such) are Graham Nelson's _Jigsaw_
and Andy Phillips's (infamously difficult) _Time: All Things Come to
an End_. I don't think you meet yourself in either of them though.

See also http://www.wurb.com/if/genre/27, although this may be a bit
more general than what you had in mind.

+------Archbishop, First Church of Mystical Agnosticism------+
| A mathematician is a device for turning coffee into |
| theorems. -Alfred Renyi |
+------------------------------------------------------------+
| Jake Wildstrom |
+------------------------------------------------------------+

Cryptonomic

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Sep 10, 2002, 12:36:45 PM9/10/02
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Most time travel games that I have seen just rely on the mechanics of time
travel itself and not so much on the perhaps intriguing situations that can
come about via such actions, i.e., the meeting yourself type puzzle. It
sounds like what you are talking about is a lot like what happened in "Back
to the Future Part 2", where Marty McFly went back to the same night in 1955
that he went to in the first movie and he had to avoid running into himself
or interfering with any of his "past" actions. In fact, at one point he had
to save "himself" (his younger self) even though his younger self never knew
this happened.

I suppose in Inform you could use the ChangePlayer routine to change the
player from, say, a PastYou object to FutureYou object or something like
that. I suppose you could then set up the "PastYou" object as an NPC, with
the npc_subway (of the NPC extensions) being set up to be the actions of the
past player. I would guess you would only somehow "trap" Group 2 actions in
Inform that the "previous version of you" had taken. I wonder: could you set
up an array and then each time the PC does an action (in the PastYou
persona), you write that action to the array? Then later you just read back
the array for the former-PC, now-NPC, which the NPC blindly follows? I am
not sure of all the mechanics of how you would do this but it is
interesting. You might also have to have some global variable that would
indicate "state of the world". For example, 0 might mean it is the current
world, 1 might be that the player is in their second visit to the "current
world" - i.e., they are in the past. (In this case, the NPC actions for the
PastYou do not kick-in unless the game state is 1.)

The problem is that time travel offers so many possibilities for variances.
For example, it might be that your PastYou player conveniently finds an item
that is needed. But it turns out that the FutureYou player has to distribute
it there in order for them to find (to have found) it. But if FutureYou
never does that then, in reality, PastYou should never have seen it. But
there is no way you can know what the player is "going to do" later unless
you severely constrain the puzzles such that they "must" do a certain action
even if they barely realize they are doing it. Of course, you could also
just opt for the: "You generate a space-time paradox..." ending. I think
'free-form' time travel games would be very difficult to do and be
consistent unless there are a lot of constraints on what can happen and on
how it can happen.

An interesting game in the graphical adventure genre was "Day of the
Tentacle" where you had three players at three different time periods and
they could help each other out by doing certain things in each time period.
But the idea of changing history was not really a major concern in that
game. So you might do something like that. It would sort of reminiscent of
the "All Good Things" episode of "Star Trek: The Next Generation", where the
same character had to interact in such a fashion in three different time
periods as to stop the formation of a space-time anomaly. (That episode was
quite flawed in some of its time travel mechanics, but it still made a good
story I suppose.)

There was an IF game awhile back (available on http://www.the-underdogs.org)
called "Guardians of Infinity: To Save Kennedy" that deals with purposely
changing history. (The game is a nightmare to play, in my opinion.) You
might also check out the graphical adventure "Kronolog", which has a Nazi
change-the-world plot. The graphic adventure "Mission Critical" also dealt
with time travel of the changing history sort. But, again, none of these
really dealt with a situation where you were going back over the game world
where "you" had previously been - at least not to any great extent. The main
one I have seen do that is "TimeQuest" and, as you mentioned, that was only
done by forcing you to take the appropriate action immediately during that
turn or generating a paradox that ends the game.

- Cryptonomic


Franco

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Sep 10, 2002, 2:39:58 PM9/10/02
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"SoonMinYee" <noe...@noemail.com> wrote in message news:<wDnf9.64943$Jo.11806@rwcrnsc53>...

I'm mostly a lurker here, and can't help you with examples, but I find
this an extremely interesting concept and would very much to see such
a game completed.

Lucian P. Smith

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Sep 10, 2002, 2:38:10 PM9/10/02
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SoonMinYee <noe...@noemail.com> wrote in <wDnf9.64943$Jo.11806@rwcrnsc53>:
: I guess I ask this about Inform since that's what I'm working in but I

: suppose it could apply to any language. Has any real good time travel game
: been written in any language? What I'm wondering is how hard it would be to
: code a game that involves time travel where you "meet yourself."

While others have mentioned 'Sorceror', you should also check out the
(TADS) game 'Common Ground'. It's not a time travel game, but you do play
characters that see what former PCs have done. If that makes any sense.

http://www.ifarchive.org/if-archive/games/tads/Ground.gam

-Lucian

Gregory W. Kulczycki

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Sep 10, 2002, 3:49:27 PM9/10/02
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This is the first thing that came to mind when I read this question also.
In Act I you play a teenage girl, who interacts with her stepfather and
mother. In Act II you replay the scene as the stepfather, and in Act III
you replay the scene as the mother. I think Stephen Granade used some
sort of device to record the actions of the girl so that the scene made
sense when you replayed it as the stepfather and mother.

Anyway, it takes less than an hour to play and the (TADS) source code is
available at:

http://www.ifarchive.org/if-archive/games/src/tads/Ground_src.zip

Also, you can find some comments from the author about the 'recording &
replaying' in the game in this article:

http://brasslantern.org/writers/iftheory/wrong.html

Cheers,
Greg K.

J. D. Berry

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Sep 10, 2002, 4:43:30 PM9/10/02
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"SoonMinYee" <noe...@noemail.com> wrote in message news:<wDnf9.64943$Jo.11806@rwcrnsc53>...

A Baf's guide search under time-travel, 5-star games reveals:

All Roads -- Jon Ingold
Jigsaw -- Graham Nelson
Lost New York -- Neil deMause
The Mulldoon Legacy -- Jon Ingold

Regarding meeting a past you, Infocom's Sorcerer has a younger and older you.
(See Spag #2 for a review.)

Jim

Paul Drallos

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Sep 10, 2002, 6:56:32 PM9/10/02
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J. D. Berry wrote:


> A Baf's guide search under time-travel, 5-star games reveals:
>
> All Roads -- Jon Ingold
> Jigsaw -- Graham Nelson
> Lost New York -- Neil deMause
> The Mulldoon Legacy -- Jon Ingold
>

The Hitchhiker's Guide to the Galaxy should also be included.


-Paul

Rob Shaw-Fuller

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Sep 10, 2002, 9:35:09 PM9/10/02
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"SoonMinYee" <noe...@noemail.com> wrote...

> I guess I ask this about Inform since that's what I'm working in but I
> suppose it could apply to any language. Has any real good time travel game
> been written in any language?
[SNIP]


In addition to the other games already mentioned, check out:
1. LASH - Not really "time travel" as such, but awfully darn close. And a
splendid game anyway. Does some neat tricks to twist the player/protagonist
relationship.
2. Photopia - A bit of timeline twisting, along with frequent changes of
character. Personally, I didn't think it was quite as good as some of Adam
Cadre's other games, but many many people *loved* it.
3. Shrapnel - Another one by Adam Cadre, but with a much different "feel"
than Photopia. Again, no deliberate time travel, but certainly includes
some twisted timelines.

I haven't played everything in the archive, so I might be wrong, but I don't
remember any time-travel games that dealt with paradox issues. Therefore,
it's uncharted territory, and you can be the first! :)


-Rob Shaw-Fuller, Frobnitz junkie
robsha...@hotmail.com

SoonMinYee

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Sep 11, 2002, 9:31:53 AM9/11/02
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"Cryptonomic" <cryptonom...@hotmail.com> wrote in message
news:xcpf9.220506$kp.8...@rwcrnsc52.ops.asp.att.net...

> I suppose in Inform you could use the ChangePlayer routine to change the
> player from, say, a PastYou object to FutureYou object or something like
> that. I suppose you could then set up the "PastYou" object as an NPC, with
> the npc_subway (of the NPC extensions) being set up to be the actions of
the
> past player. I would guess you would only somehow "trap" Group 2 actions
in
> Inform that the "previous version of you" had taken. I wonder: could you
set
> up an array and then each time the PC does an action (in the PastYou
> persona), you write that action to the array? Then later you just read
back
> the array for the former-PC, now-NPC, which the NPC blindly follows? I am
> not sure of all the mechanics of how you would do this but it is
> interesting. You might also have to have some global variable that would
> indicate "state of the world". For example, 0 might mean it is the current
> world, 1 might be that the player is in their second visit to the "current
> world" - i.e., they are in the past. (In this case, the NPC actions for
the
> PastYou do not kick-in unless the game state is 1.)

Yes! That exactly what I'm talking about. Having "model world" so that when
player goes through it first time it is the present. Those actions are then
stored. Then the model world state is updated and that means all that went
before is the past. Now if player goes back to that, they are going back to
where they were previously. That's where the problems come in. Like you say,
perhaps NPC-PastYou could be set to do actions and you as PC-FutureYou have
to not get in the way or something like that. Interesting.


Stephen L Breslin

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Sep 11, 2002, 3:53:42 PM9/11/02
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On Wed, 11 Sep 2002 13:31:53 GMT, "SoonMinYee" <noe...@noemail.com>
wrote:
>[...]

>perhaps NPC-PastYou could be set to do actions and you as PC-FutureYou have
>to not get in the way or something like that. Interesting.

Would you want the PC-past character interacting with an NPC-future
character? Or do you envision only the PC-future character interacting
with the NPC-past character?

I suppose you could do it either way, but it would be difficult to do
it both ways without a bunch of cut-scenes.

The main problem, I think, would be that you wouldn't be able to store
the PC-identity so it could be re-played by the NPC-identity, unless
the PC-identity actions already were input by the player. So the
player won't be able to interact with a NPC whose actions he
determined unless he's already determined the actions.

Cryptonomic

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Sep 12, 2002, 9:47:37 AM9/12/02
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"Stephen L Breslin" <bre...@acsu.buffalo.edu> wrote in message
news:3d7f9e5e...@news.buffalo.edu...

> Would you want the PC-past character interacting with an NPC-future
> character? Or do you envision only the PC-future character interacting
> with the NPC-past character?

That would be pretty tricky, I would think. The PastYou interacting with the
FutureYou would, by necessity, constrain the actions of the FutureYou
because you will have to do what you already saw that "you" did. (Unless,
again, you generate those "you generate a paradox..." messages.) Unless the
idea is to design a game where history-tampering is not a major issue, I
suppose you could design interesting puzzles where you have to help
"yourself" - in other words, interact with other versions of yourself. For
example, let us say that the player as PastYou (who would really be
PresentYou for the time being) does some actions. Then at some Point B in
the game, they go back in time. Now the player character is actually
FutureYou and PastYou is the NPC. If you, as FutureYou, decide to interact
with PastYou that is something that should have happened in PastYou's
timeline, which is what I said before about time travel offering
constraining puzzles if you allow interaction.

> The main problem, I think, would be that you wouldn't be able to store
> the PC-identity so it could be re-played by the NPC-identity, unless
> the PC-identity actions already were input by the player.

That is what I was saying about perhaps reading the actions of PastYou into
an array or something. The problem is that this could get cumbersome
depending upon how long it is before PastYou becomes FutureYou and PastYou
becomes an NPC. So, in other words, at a certain point in the game (and it
would have to be localized, I would think) the player character goes around
and does some actions. You trap those actions (or just those that affect the
game world) in some fashion. Then when the player character goes back in
time, you establish an NPC that plays back the characters actions. This
would also be a very time-based sort of puzzle because, of course, each turn
for FutureYou will correspond to one turn for PastYou. (That also brings up
the idea if the NPC goes about its actions regardless of what FutureYou
does - which would be more realistic.

I am reminded of Heinlein's short story "By His Bootstraps" where the
protagonist meets himself a couple times over and even gets into a fighting
match with himself. But all of these actions were constrained because what
happened to Past-Him had to be done by Future-Him. If Future-Him did not do
those actions, then Past-Him would not have experienced them. That is where
I think truly ingenious time travel puzzles would have to come in with
interactive fiction. I think the real goal would be to rely on artificial
boundaries to action but not making the artificial boundaries too obvious to
the player. It is an interesting challenge.

- Cryptonomic


LizM7

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Sep 12, 2002, 9:33:09 PM9/12/02
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"SoonMinYee" <noe...@noemail.com> wrote:
> What I'm wondering is how hard it would be to
> code a game that involves time travel where you "meet yourself." Or,
> perhaps, you have to avoid doing this. So, for example, you (as the player)
> take certain actions in the beginning of the game. Then later in game you
> are sent back in time. Now game logic has "stored" your previous moves in
> memory thus making "past version of you" an NPC or something with
> pre-determined actions. That NPC follows course you took. You ("future-you")
> now has to avoid running into "past-you." Time travel is always fascinating
> area for stories but I've found it's rarely done well. Not sure if it's been
> tried successfully in IF.

I've had an idea for a puzzle revolving around that sort of thing for
a little while now -- you're trapped in some sort of cell, and after a
little while someone comes and opens the door. They have to fiddle
with the lock for a while to get it open - e.g. if you turn this
thing, the door will click; if you pull this latch, the door will
rattle, etc. And then you go on and have the rest of the game ...
until you hit some point in time when you have to go back and open up
the door for your past self. (Hope you remembered that combination!)
-- But while that sort of gimick may have gone over during the '80s, I
doubt that anyone would stand for it today.

- Liz

Daniel Barkalow

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Sep 13, 2002, 12:19:11 AM9/13/02
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On 12 Sep 2002, LizM7 wrote:

> I've had an idea for a puzzle revolving around that sort of thing for
> a little while now -- you're trapped in some sort of cell, and after a
> little while someone comes and opens the door. They have to fiddle
> with the lock for a while to get it open - e.g. if you turn this
> thing, the door will click; if you pull this latch, the door will
> rattle, etc. And then you go on and have the rest of the game ...
> until you hit some point in time when you have to go back and open up
> the door for your past self. (Hope you remembered that combination!)
> -- But while that sort of gimick may have gone over during the '80s, I
> doubt that anyone would stand for it today.

I don't think most people would have a problem with it if it's not hard to
get to the first part. If you don't remember the combination, you save
your game, restart, watch that scene again, and write it down. Then you
restore your game and use the information. Doing the wrong thing doesn't
make it impossible to win the game sequence you're playing, you just need
to revisit the past in a separate game. Also, you're not required to use
information your character doesn't have; you're required to use
information your character got and you can look up.

In fact, there are plenty of recent games where a necessary action would
be unmotivated if you forgot the beginning of the game. Replaying a game
is (for me, at least) often necessary to get into the right mindset to
solve later puzzles (generally when I get stuck and give up on the game
for a while, and then come back to it).

-Iabervon
*This .sig unintentionally changed*

Eric Smith

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Sep 13, 2002, 2:09:32 AM9/13/02
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J. D. Berry wrote:
> A Baf's guide search under time-travel, 5-star games reveals:
> All Roads -- Jon Ingold Jigsaw -- Graham Nelson
> Lost New York -- Neil deMause
> The Mulldoon Legacy -- Jon Ingold

Paul Drallos <pdra...@tir.com> writes:
> The Hitchhiker's Guide to the Galaxy should also be included.

And Zork III.

But you don't meet yourself in either HGttG or Zork III. You do in
Sorcerer. Do you in the games J.D. listed?

Dave

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Sep 13, 2002, 6:02:48 AM9/13/02
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> And Zork III.

Actually you do meet yourself in HGttG with the added twist of switching
bodies.


--
David Griffith
dgr...@cs.csubak.edu

Adam Thornton

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Sep 13, 2002, 12:50:05 PM9/13/02
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In article <alsd48$fs54$2...@hades.csu.net>,

Dave <dgr...@peddddgassdfasfdf.edu> wrote:
>Actually you do meet yourself in HGttG with the added twist of switching
>bodies.

And without that, there's one rather, um, *brief* way to meet yourself.

Adam

Jon Ingold

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Sep 13, 2002, 1:27:35 PM9/13/02
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> I've had an idea for a puzzle revolving around that sort of thing for
> a little while now .......

> -- But while that sort of gimick may have gone over during the '80s, I
> doubt that anyone would stand for it today.

Mulldoon had something similar - a little lower-scale, I suppose. And no-one
complained about that; mainly because they'd been beaten into submission by
this point (or, alternatively, stopped playing).

Jon

Alex Watson

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Sep 14, 2002, 7:11:48 AM9/14/02
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Dave spake thusly:

> >> The Hitchhiker's Guide to the Galaxy should also be included.
>
> > And Zork III.
>
> > But you don't meet yourself in either HGttG or Zork III. You do in
> > Sorcerer. Do you in the games J.D. listed?
>
> Actually you do meet yourself in HGttG with the added twist of switching
> bodies.

Does the Arthur thing actually behave as you did while you were him?

Dave

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Sep 15, 2002, 2:20:13 AM9/15/02
to

As Ford, you'll see important things like the following:

Jung lbh nf Neguhe fnl gb Sbeq va sebag bs gur ohyyqbmre.

Vs Neguhe ehaf qbja gb gur cho orsber Sbeq (guhf sbepvat Sbeq gb punfr
Neguhe).

Jung Neguhe qbrf jvgu gur purrfr fnaqjvpu.

Jura Neguhe yrnirf gur cho gb tb lryy ng Cebffre.


V qba'g guvax fhcresvpvny guvatf yvxr zrffvat jvgu gur whxrobk,
nggrzcgvat gb ohl crnahgf, be chapuvat Cebffre ner erpbeqrq.

--
David Griffith
dgr...@cs.csubak.edu

Andrew Pearce

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Sep 15, 2002, 12:33:18 PM9/15/02
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"Dave" <dgr...@asldkodkeokeosubak.edu> wrote in message
news:am18qt$gc82$1...@hades.csu.net...

Wow, I didn't remember Vogon poetry being *that* bad!

Andrew


Dave

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Sep 15, 2002, 2:51:22 PM9/15/02
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Andrew Pearce <mox...@zoom.co.uk> wrote:

> "Dave" <dgr...@asldkodkeokeosubak.edu> wrote in message

[snip]


>> V qba'g guvax fhcresvpvny guvatf yvxr zrffvat jvgu gur whxrobk,
>> nggrzcgvat gb ohl crnahgf, be chapuvat Cebffre ner erpbeqrq.

> Wow, I didn't remember Vogon poetry being *that* bad!

That's not actually Vogon, but from an obscure race that hails from the
thirteenth planet of the Rot system.


--
David Griffith
dgr...@cs.csubak.edu

Uli Kusterer

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Sep 15, 2002, 6:44:23 PM9/15/02
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SoonMinYee wrote:
> What I'm wondering is how hard it would be to
> code a game that involves time travel where you "meet yourself." Or,
> perhaps, you have to avoid doing this. So, for example, you (as the player)
> take certain actions in the beginning of the game. Then later in game you
> are sent back in time. Now game logic has "stored" your previous moves in
> memory thus making "past version of you" an NPC or something with
> pre-determined actions. That NPC follows course you took. You ("future-you")
> now has to avoid running into "past-you."

Well,

as long as you somehow find a way to limit what "future you" does (or
rather, what "past you" sees of them) to some predefined actions, this
would definitely be possible. The trouble is that, without a (real) time
machine, you can't show "past you" the actions of "future you", because
the player hasn't played "future you" yet.

I think it was Escape From Monkey Island (MI4), which had a nice scene
where you're going through a swamp where time and space run irregularly.
At one point, you come to a gate, and on the other side is yourself.
"past Guybrush" has the key, while the lock is on "Future Guybrush"'s
side (IIRC). So you have to give the key to your future self, and your
future self will give you lots of things (a rope, a rubber chicken...).
once you're through, you soon end up on the other side of the fence
again, where you have to exactly repeat what "future Guybrush" did. if
you don't you are sucked into a time vortex, and end up back at the
start of the swamp.

The advantage of this is that they can both randomize this encounter
(so you can't just play it from the walkthrough) while you also get
replayability, because when you return to the beginning, you relive both
scenes (which may happen differently this time).

It was kind of a funny idea, especially because you thought "Oh great,
he gives me a rope!" and only seconds later, you have to give them back
:-) Lots of nice Red Herrings there.

> Time travel is always fascinating
> area for stories but I've found it's rarely done well. Not sure if it's been
> tried successfully in IF. I know "TimeQuest" sort of did this at the end but
> that limited your moves because you absolutely had to do what your
> immediately previous self did (or what your immediate future self indicated
> you should do) or else the game ended in 'paradox'.

Yes, I think physics pretty much prohibits us from doing anything else.
Except if you do something like they do in the comics, where they have
alternate realities, which means if you do something wrong and would
thus change your memories, you just create a branch in the tree of
realities, and your time travel, instead of being a jump to a lower
branch in the same tree, turns out to be a jump to a similar-looking
branch on a different tree.

But that would pretty much mean the player could pretty much do what
they wanted. The same would apply when you take the point that the past
will automatically reconfigure itself whenever you do something wrong.
I.e. the PC's memories would change and she wouldn't even notice she did
something different than the run before, while the player would
remember, because he's "outside time" as far as the game is concerned.

Both these approaches where "you can't do anything wrong" I'd find quite
boring, though.

I guess the option I'd find most intriguing as a player would be the
"God removes you from the time stream because you have created a time
paradoxon"-variety, where you only meet yourself one or two times very
shortly. Imagine the following: Past you was sent to fix a fusion
reactor before it blows, together with NPC Jeff. When you return from
your mission, you find out that NPC Jeff (whose help you benefitted
from) was already dead at the time he helped you (heart attack induced
by teleportation, or whatever). You go back in time, to assist yourself,
to make sure history happened as you remember it.

Now, both of them work together in different areas of the complex, and
between them there are no connecting gateways. Only in two or three
spots, you'd maybe see each other, and at one time, future You (which
you thought at the time was NPC Jeff) gives you an important code for
opening a door. If you fail to give him that, you both fail.

That would probably work, because it'd be easy to make everything feel
synchronized as long as they don't see each other, and thus it'd give
the player the feeling of being able to influence the past. And in the
end, you have this one paradoxon, which can be undone should the player
make a mistake. That means it's not a "you did something unanticipated
by the programmer -- you die!"-game.

I don't mind if the PC can die in a game, as long as the game provides
clear warnings as to the danger of that situation (and it'd be nice if
there was some hint to the player when he is "past you" that he should
note down the code because it might be needed again later -- at least in
the "easy" version).

Ummm ... not quite my $0.02, but more of my $200, I suppose ... :-)

Cheers,
-- M. Uli Kusterer
http://www.zathras.de

John W. Kennedy

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Sep 16, 2002, 1:41:25 PM9/16/02
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Uli Kusterer wrote:
> Yes, I think physics pretty much prohibits us from doing anything else.
> Except if you do something like they do in the comics, where they have
> alternate realities, which means if you do something wrong and would
> thus change your memories, you just create a branch in the tree of
> realities, and your time travel, instead of being a jump to a lower
> branch in the same tree, turns out to be a jump to a similar-looking
> branch on a different tree.

It's not just the comics; some physicists have proposed this theory
in all seriousness as a way out of the -- to most scientists distasteful
-- notion that quantum events simply happen at random.

--
John W. Kennedy
Those in the seat of power oft forget their failings and seek only the
obeisance of others! Thus is bad government born! Hold in your heart
that you and the people are one, human beings all, and good government
shall arise of its own accord! Such is the path of virtue!
-- Kazuo Koike, "Lone Wolf and Cub: Thirteen Strings" (tr. Dana Lewis)

Magnus Olsson

unread,
Sep 16, 2002, 4:11:36 PM9/16/02
to
In article <jGoh9.77033$e44.2...@news4.srv.hcvlny.cv.net>,

John W. Kennedy <jwk...@attglobal.net> wrote:
>Uli Kusterer wrote:
>> Yes, I think physics pretty much prohibits us from doing anything else.
>> Except if you do something like they do in the comics, where they have
>> alternate realities, which means if you do something wrong and would
>> thus change your memories, you just create a branch in the tree of
>> realities, and your time travel, instead of being a jump to a lower
>> branch in the same tree, turns out to be a jump to a similar-looking
>> branch on a different tree.
>
>It's not just the comics; some physicists have proposed this theory
>in all seriousness as a way out of the -- to most scientists distasteful
>-- notion that quantum events simply happen at random.

Actually, it's more like a way out of the problems caused by the fact
that quantum mechanics allows superposition of states - Schrödinger's
cat being a mixture of 50% "dead cat" and 50% "live cat" - but that
(according to the predominant "Copenhagen interpretation") such
superpositions seem to collapse as soon as an observation takes place;
the "many-worlds interpretation" instead postulates that the entire
universe splits into two. This is particularly popular among quantum
cosmologists, since it allows a sensible (sort of) notion of the
quantum state of the entire universe.

But physicists have actually starting to look seriously at the
consequences of time travel lately, since some solutions to the
equations of general relativity seem to allow you to travel backwards
in time. And the notion of time travel really being a jump to a
different parallel universe is one way of getting away from time
travel paradoxes - if you travel back in time and kill your own
grandfather as an infant, there's no paradox, because the time travel
actually took you to a different universe where you will never be
born.

Any currently active theoretical physicists in the audience are
welcome to rip this to shreds; it's been a while since I was current
on the research.

--
Magnus Olsson (m...@df.lth.se)

L. Ross Raszewski

unread,
Sep 16, 2002, 6:12:41 PM9/16/02
to
On 16 Sep 2002 20:11:36 GMT, Magnus Olsson <m...@df.lth.se> wrote:
>Actually, it's more like a way out of the problems caused by the fact
>that quantum mechanics allows superposition of states - Schrödinger's
>cat being a mixture of 50% "dead cat" and 50% "live cat" - but that

Well, sort of. According to the ideas of superposition, the cat is
100% dead and 100% alive.

Andrew Plotkin

unread,
Sep 16, 2002, 8:31:42 PM9/16/02
to

(70+i*70)% dead and (70-i*70)% alive, wasn't it?

--Z

"And Aholibamah bare Jeush, and Jaalam, and Korah: these were the borogoves..."
*
* Make your vote count. Get your vote counted.

Cryptonomic

unread,
Sep 16, 2002, 9:07:47 PM9/16/02
to

"John W. Kennedy" <jwk...@attglobal.net> wrote in message
news:jGoh9.77033$e44.2...@news4.srv.hcvlny.cv.net...

> It's not just the comics; some physicists have proposed this theory
> in all seriousness as a way out of the -- to most scientists distasteful
> -- notion that quantum events simply happen at random.

And that is what goes back to what I said regarding how "realistic" you want
your game to be if it features time travel. What physicists propose is
called "globally self-consistent time travel" - which means whatever happens
in the past does not change it, but fulfill it. In other words, it makes it
happen as it happened. It only seems odd in the way that it happened because
it required the intervention of something from the future traveling back to
the past. "Causality violation" is considered a 'bad word' in the realm of
the current physics regarding time travel because the very notion of
"changing the past" is ruled out. How much of that you want to force your
reader/player to understand is up to you. For example, you could make some
odd concept like "reality inertia" or something so that the player is
allowed to make certain changes in the past that are "dampened", so to
speak, if they are not major changes. But major changes would kill off the
player; but perhaps those major changes are much harder to do in some
fashion because of overcoming the "inertia" of reality. It is just another
way of constraining player actions, but perhaps one that is not so obvious
as just saying: "You cannot do that! Do you want to generate a space-time
paradox?!"

Meeting your own self, of course, is a much stickier issue unless you are
willing to allow for the idea of your "own" past memories to become
dissociated from the events of your future "self". Some science-fiction
authors do this with abandon. Other stories force a sort of memory "instant
recall". See the movie "Frequency", for example, where changes to the past
are automatically reflected in one person's mind - he just now has
dual-memories. (Why this is true for no one else is never explained.) The
literature and the movies abound with examples of different conceptions of
time travel. The many-worlds interpretation that one person brought up is
actually one thing that is commonly misunderstood because it doesn't speak
to "multiple worlds" at all. It was a quantum description of events that
helped to explain some of the probabilistic nature of wave-particle (or
wavicle, if you prefer) theory. I think it would be interesting to see a
piece of interactive fiction tackle some of those in an interesting way.

- Cryptonomic


Cryptonomic

unread,
Sep 16, 2002, 9:07:51 PM9/16/02
to

"John W. Kennedy" <jwk...@attglobal.net> wrote in message
news:jGoh9.77033$e44.2...@news4.srv.hcvlny.cv.net...
> It's not just the comics; some physicists have proposed this theory
> in all seriousness as a way out of the -- to most scientists distasteful
> -- notion that quantum events simply happen at random.

And that is what goes back to what I said regarding how "realistic" you want

Cryptonomic

unread,
Sep 16, 2002, 9:37:09 PM9/16/02
to

"John W. Kennedy" <jwk...@attglobal.net> wrote in message
news:jGoh9.77033$e44.2...@news4.srv.hcvlny.cv.net...
> It's not just the comics; some physicists have proposed this theory
> in all seriousness as a way out of the -- to most scientists distasteful
> -- notion that quantum events simply happen at random.

And that is what goes back to what I said regarding how "realistic" you want

time travel. I think it would be interesting to see a piece of interactive

Cryptonomic

unread,
Sep 16, 2002, 9:37:11 PM9/16/02
to

"John W. Kennedy" <jwk...@attglobal.net> wrote in message
news:jGoh9.77033$e44.2...@news4.srv.hcvlny.cv.net...
> It's not just the comics; some physicists have proposed this theory
> in all seriousness as a way out of the -- to most scientists distasteful
> -- notion that quantum events simply happen at random.

And that is what goes back to what I said regarding how "realistic" you want

time travel. The many-worlds interpretation that one person brought up is
actually one thing that is commonly misunderstood because it doesn't speak
to "multiple worlds" at all. It was a quantum description of events that
helped to explain some of the probabilistic nature of wave-particle (or

wavicle, if you prefer) theory. I think it would be interesting to see a

L. Ross Raszewski

unread,
Sep 17, 2002, 3:46:48 AM9/17/02
to
On Tue, 17 Sep 2002 00:31:42 +0000 (UTC), Andrew Plotkin <erky...@eblong.com> wrote:
>Here, L. Ross Raszewski <lrasz...@loyola.edu> wrote:
>> On 16 Sep 2002 20:11:36 GMT, Magnus Olsson <m...@df.lth.se> wrote:
>>>Actually, it's more like a way out of the problems caused by the fact
>>>that quantum mechanics allows superposition of states - Schrödinger's
>>>cat being a mixture of 50% "dead cat" and 50% "live cat" - but that
>
>> Well, sort of. According to the ideas of superposition, the cat is
>> 100% dead and 100% alive.
>
>(70+i*70)% dead and (70-i*70)% alive, wasn't it?
>

Well, the important thing is that "50% dead and 50% alive" implies
that the cat is "in some state between life and death", which isn't a
superposition. The cat is *both* dead *and* alive. That's why it's a
"super"position as opposed to just our normal everyday mundane
positions.

(I should crosspost this to alt.games.xtrek to get a list of super and
mundane positions.)

Christos Dimitrakakis

unread,
Sep 17, 2002, 5:03:31 AM9/17/02
to
I only have to say one thing that is important:

http://www.arxiv.org

And this is my ranting:

Well, some particles do travel backward in time. They are called
anti-particles. (Think positron, a.k.a anti-electron). For some people,
time is just a measure of rate of change. Nothing more. Einstein's theory
of relativity is a good mathematical model of space and time, but this is
all that it is: a mathematical model. If you transform all of the
equations, for example into a kernel space, they will be making no
physical sense whatsoever, but they will still work.

So, what does it mean to move backwards in time?
Feynman suggested that anti-particles are really only just normal
particles, just moving in a different direction time. Previous experiments
show that if a particle and an anti-particle collide, a photon is emitted
and they are both anihilated!

However, from the point of you of the particle, Feynman explained, it is
moving forwards in time, until it suddenly collides with this powerful
photon. It absorbs the photon, causing it to change direction in time.
(Anyway, the only way you can detect anti-particles is to collide them
with normal particles)

What this also means, is that the particle can never ever influence it's
"previous" self, because, really, there is only just ONE self as far as
the particle is concerned. However we, as external observers, might see
multiple manifestations of the same particle. (going backwards and fowards
through time). Of course, it will make no difference to us, since all
particles look the same anyway. Oh, and this might have something to do
with entanglement too, but I am not sure.


> consequences of time travel lately, since some solutions to the
> equations of general relativity seem to allow you to travel backwards
> in time.

I can only talk about Feynman and his pro

Cryptonomic

unread,
Sep 17, 2002, 8:02:28 AM9/17/02
to

"John W. Kennedy" <jwk...@attglobal.net> wrote in message
news:jGoh9.77033$e44.2...@news4.srv.hcvlny.cv.net...
> It's not just the comics; some physicists have proposed this theory
> in all seriousness as a way out of the -- to most scientists distasteful
> -- notion that quantum events simply happen at random.

And that is what goes back to what I said regarding how "realistic" you want

Uli Kusterer

unread,
Sep 17, 2002, 9:25:52 AM9/17/02
to
Cryptonomic wrote:
> And that is what goes back to what I said regarding how "realistic" you want
> your game to be if it features time travel. What physicists propose is
> called "globally self-consistent time travel" - which means whatever happens

Crypto,

I think your message got distributed over time :-(

I'm seeing it 5 times here, two from 3:07, two from 3:37 and one from
14:02...

Can I borrow that time machine of yours...?
-- Uli

Greg Ewing

unread,
Sep 17, 2002, 10:14:59 PM9/17/02
to
Uli Kusterer wrote:

> Crypto,
>
> I think your message got distributed over time :-(
>
> I'm seeing it 5 times here, two from 3:07, two from 3:37 and one from
> 14:02...


Careful! If what was said before about anti-particles
is right, two of those posts may actually be anti-posts,
travelling backwards in time after having been bounced
by some news server in the future. Don't let any of them
touch, or who knows what might happen!

--
Greg Ewing, Computer Science Dept,
University of Canterbury,
Christchurch, New Zealand
http://www.cosc.canterbury.ac.nz/~greg

Uli Kusterer

unread,
Sep 18, 2002, 2:12:42 AM9/18/02
to gr...@cosc.canterbury.ac.nz
Greg Ewing wrote:
> Careful! If what was said before about anti-particles
> is right, two of those posts may actually be anti-posts,
> travelling backwards in time after having been bounced
> by some news server in the future. Don't let any of them
> touch, or who knows what might happen!

So, to mis-quote Ivanova:

No boom today. Boom yesterday. It's always boom yesterday. (?!)

-- Uli "tongue lost somewhere in cheek" Kusterer

Uli Kusterer

unread,
Sep 18, 2002, 2:13:09 AM9/18/02
to
Greg Ewing wrote:
> Careful! If what was said before about anti-particles
> is right, two of those posts may actually be anti-posts,
> travelling backwards in time after having been bounced
> by some news server in the future. Don't let any of them
> touch, or who knows what might happen!

So, to mis-quote Ivanova:

Magnus Olsson

unread,
Sep 18, 2002, 4:11:53 AM9/18/02
to
In article <I5Bh9.1026$t%6....@nwrddc02.gnilink.net>,

L. Ross Raszewski <lrasz...@loyola.edu> wrote:
>On Tue, 17 Sep 2002 00:31:42 +0000 (UTC), Andrew Plotkin
><erky...@eblong.com> wrote:
>>Here, L. Ross Raszewski <lrasz...@loyola.edu> wrote:
>>> On 16 Sep 2002 20:11:36 GMT, Magnus Olsson <m...@df.lth.se> wrote:
>>>>Actually, it's more like a way out of the problems caused by the fact
>>>>that quantum mechanics allows superposition of states - Schrödinger's
>>>>cat being a mixture of 50% "dead cat" and 50% "live cat" - but that
>>
>>> Well, sort of. According to the ideas of superposition, the cat is
>>> 100% dead and 100% alive.
>>
>>(70+i*70)% dead and (70-i*70)% alive, wasn't it?

Depends on the relativ phase of the dead and live cats :-).

>Well, the important thing is that "50% dead and 50% alive" implies
>that the cat is "in some state between life and death", which isn't a
>superposition. The cat is *both* dead *and* alive.

Actually, the *wave function* of the cat is a linear superposition
(vector sum) of the wave functions for dead and live cats. What that
means for the actual cat itself is a matter of interpretation - in the
Copenhagen interpretation, the cat is neither dead nor alive until
it's observed. Which of course is very unsettling to common sense, and
philosophically unsatisfactory, which has led people to look for
alternative explanation, such as the many-worlds interpretation (which
I personally happen to find even more unsettling).

So all phrasings are to some extent misleading. Quantum mechanics makes
sense only in a QM framework.

>That's why it's a
>"super"position as opposed to just our normal everyday mundane
>positions.

I don't think so; "superposition" means just one thing put on top
of another, i.e. the sum of two wave functions.

>(I should crosspost this to alt.games.xtrek to get a list of super and
>mundane positions.)

Perhaps we should invite the distinguished guest speaker, Dr. S. Moose,
and his amanuensis Mr. S. Makane as well?

--
Magnus Olsson (m...@df.lth.se)

Magnus Olsson

unread,
Sep 18, 2002, 4:28:34 AM9/18/02
to
In article <Pine.GSO.4.31.0209171054040.29951-100000@barasson>,

Christos Dimitrakakis <oleth...@oohay.com> wrote:
>I only have to say one thing that is important:
>
>http://www.arxiv.org

Specific references, rather than just the URL of a huge collection
of research papers, would be more useful.

>Well, some particles do travel backward in time. They are called
>anti-particles. (Think positron, a.k.a anti-electron).

This is a considerable oversimplification. And even if you accept
this at face value, it's not the kind of time travel that was discussed
before in this thread - you can't go back an meet Alexander the Great
by turning yourself into antimatter.

>Einstein's theory
>of relativity is a good mathematical model of space and time, but this is
>all that it is: a mathematical model.

That's true. It's also true of *all* physical theories (substituting
whatever the theory is about for "space and time"). Quantum
electrodynamics (which is the theory that seems to suggest that
positrons are electrons going backwards in time) is also "just" a
mathematical model, and that's all it is.

However, if GR actually allows time travel, then either people will
have to take time travel seriously, or GR isn't such a good model
after all, which is also worth taking seriously. In any case, people
have good reason to look at the implications of time travel.

>So, what does it mean to move backwards in time?
>Feynman suggested that anti-particles are really only just normal
>particles, just moving in a different direction time.

What he observed was that the equations of motion for a particle
moving forward in time and those of an antiparticle moving backwards
in time are identical. This doesn't mean that antiparticles "really"
are particles moving backwards in time. It doesn't mean that they
aren't, either - quantum field theory is "just" a mathematical
model of reality, just as GR; it doesn't tell us what reality
really *is*.

And these equations do not allow for time travel or violation of
causality: you can't send an antiparticle back in time to influence
events in the past.

--
Magnus Olsson (m...@df.lth.se)

Christos Dimitrakakis

unread,
Sep 18, 2002, 7:08:56 AM9/18/02
to
> >http://www.arxiv.org
>
> Specific references, rather than just the URL of a huge collection
> of research papers, would be more useful.
>
Well, it does have a search function. And some people do not know about
arXiv, which is the reason I mentioned it. (comes up on google if you do a
search for 'physics papers' though). Good terms to look up in arXiv:
'curvature space time'
'relativity'
'gravitation'
'quantum gravity'
'exotic matter'


>
> And these equations do not allow for time travel or violation of
> causality: you can't send an antiparticle back in time to influence
> events in the past.
>
>

Influencing events in the past is another matter. I think I mentioned,
however, that an anti-particle can't (influence events in the past).
In the hypothetical scenario where it is possible to send something back
in time by turning it into anti-matter, the problem arises that someone in
the past must have his apparatus ready to do the opposite transformation.

Most people, however, like to use 'worm-holes' as the easy way out.
AFAICU, these require some kind of 'exotic matter' in order to exist.
Doing a search for those terms in arxiv.org produces some particularly
weird papers.


Blah


Paul Drallos

unread,
Sep 18, 2002, 9:14:42 AM9/18/02
to

>>Well, some particles do travel backward in time. They are called
>>anti-particles. (Think positron, a.k.a anti-electron).
>>

This is getting way off topic, but the notion that anti-particles travel
backwards in time is but one interpretation of anti-particles. Years
ago I used to participate in positron scattering experiments and we
regarded positrons simply as electrons with a charge-congegation.

In elementary particle theory (Standard Model) neutral Kayons and CP
violation provide a clear cut distinction between matter and
anti-matter. There, it can be shown that the state <K_L prefers to
decay into positrons rather than electrons. This allows us to give a
convention-independent definition of positive charge.

By convention, we call the more copious species "particles" and CP
violation plays a role is this. We assume that, at the time of the Big
Bang that there are an equal number of fermions and antifermions. As
the universe cools, the mean energies of the constituent particles drop
and they become involved in pair-creation. At some point, the universe
must have gone out of thermal equilibrium at the same time that
CP-violating processes were significant, leading to the eventual
imbalance of particles and anti-particles.

However, the concept of time-reversal invariance is related to CP
violation and it may be this concept that has spawned the 'backwards in
time' interpretations of anti-particles. Elementary particles and
Cosmology is not my field, and it's been more than 20 years since I
studied this stuff in graduate school. I don't follow it much.

That being said, there is a particle called the tachyon which is
generally regarded as traveling backwards in time. That is because the
most striking feature of this particle is that it can only travel
*faster* than the speed of light. So if you want an object that travels
backwards in time, the Tachyon is your man.

-Paul

Magnus Olsson

unread,
Sep 18, 2002, 10:52:38 AM9/18/02
to
In article <3D887C4...@tir.com>, Paul Drallos <pdra...@tir.com> wrote:
>
>>>Well, some particles do travel backward in time. They are called
>>>anti-particles. (Think positron, a.k.a anti-electron).
>>>
>
>This is getting way off topic, but the notion that anti-particles travel
>backwards in time is but one interpretation of anti-particles. Years
>ago I used to participate in positron scattering experiments and we
>regarded positrons simply as electrons with a charge-congegation.

Well, that's the *definition* of charge conjugation: it's the operation
that replaces every particle with its antiparticle.

>In elementary particle theory (Standard Model) neutral Kayons and CP
>violation provide a clear cut distinction between matter and
>anti-matter. There, it can be shown that the state <K_L prefers to
>decay into positrons rather than electrons. This allows us to give a
>convention-independent definition of positive charge.

Well, given a direction of time. You still have CPT symmetry, which
means that physcial laws are invariant if every particle is replaced
by its antiparticle (Charge conjugation), everything is mirrored
(Parity inversion) *and* the direction of time is reversed (Time
reversal).

And this is what "positrons are electrons going backwards in time"
*really* means in quantum field theory: since we have CPT symmetry,
an electron going forwards in time obeys the same equations as a
positron with the oppsite spin going backwards in time.

>That being said, there is a particle called the tachyon which is
>generally regarded as traveling backwards in time.

Wait a minute: tachyons are purely hypothetical particles; there's no
experimental evidence whatsoever that they exist. They're not
explicitly forbidden by any law of nature (except by causality) but
that's about it.

However, if they *do* exist, their defining feature is this:

>That is because the
>most striking feature of this particle is that it can only travel
>*faster* than the speed of light.

And in a relativistic framework, something travelling faster than
light in one frame of reference will be travelling backwards in
time in other frames. And now we're talking about *real* time
travel: if you had a way of creating tachyons, you could actually
send them backwards in time so that they were detected before you
created them.

>So if you want an object that travels
>backwards in time, the Tachyon is your man.

Assuming they exist.

The interesting thing about the general relativity solutions that
(seem to) lead to time travel is that they are solutions for
ordinary matter (a person, say), moving forward in "local" time,
but still ending up at an earlier time than they started out,
for example by going through a wormhole in spacetime (which, let
me hasten to add, is also a hypothetical object).

--
Magnus Olsson (m...@df.lth.se)

Paul Drallos

unread,
Sep 18, 2002, 1:55:04 PM9/18/02
to
Magnus Olsson wrote:


>
> Well, that's the *definition* of charge conjugation: it's the operation
> that replaces every particle with its antiparticle.
>

This is usually true, but actually a misnomer. Not all particles have charge,

yet can still have an anti-particle. For instance, the anti-neutron is

electrically neutral as is the neutron, However, the neutron and anti-neutron

differ by a magnetic moment of the opposite sign. Also, it is an experimental

fact that anti-neutrinos are not identical to their antiparticle.


More generally, if a particle has any atributes beyond momentum and spin,
the anti-particle has the opposite attributes. Usually, this means charge,
but not always.

Although the notion of anti-particles traveling back in time is often a
convienient representation, one must not forget that not everything is
'mirrored'. CPT symetry is not complete. The weak interaction does not
display reflection symetry. There are many other examples of symetry
breaking. The K-meson from my earlier post being one other such example.

since not all interaction obey CPT symetry, that means the the universe
does
NOT look the same to an anti-particle traveling backwards in time.

I don't want to turn this into a slug-fest, so I offer this as a peace
offering:
I acknowledge that tachyons are still hypothetical particles. I also
agree
that the general relativity perspective on time travel is more 'practical'
than the anti-particle route.

-Paul


Adam Thornton

unread,
Sep 18, 2002, 3:33:33 PM9/18/02
to
In article <am9cg9$ssc$1...@news.lth.se>, Magnus Olsson <m...@df.lth.se> wrote:
>Perhaps we should invite the distinguished guest speaker, Dr. S. Moose,
>and his amanuensis Mr. S. Makane as well?

I regret to inform you that Dr. Moose is too busy doing other
things--and, alas, by "doing", we mean "doing", and by "things", we mean
"things"--and Mr. Makane is frightened by such large words, his apparent
erudition in the holodeck notwithstanding.

Adam

Magnus Olsson

unread,
Sep 18, 2002, 4:23:46 PM9/18/02
to
In article <3D88BDFC...@tir.com>, Paul Drallos <pdra...@tir.com> wrote:
>Magnus Olsson wrote:
>
>
>>
>> Well, that's the *definition* of charge conjugation: it's the operation
>> that replaces every particle with its antiparticle.
>>
>This is usually true, but actually a misnomer. Not all particles have charge,
>
>yet can still have an anti-particle.

Yes, it's a misnomer. I don't know if the term originated when people were
just discussing electrons vs. positrons, or if the term "charge" simply
should be taken as "quantum number". Anyway, "charge conjugation" in
particle physics means "replace each particle by its antiparticle", *not*
"invert the sign of all electrical charges".

>More generally, if a particle has any atributes beyond momentum and spin,
>the anti-particle has the opposite attributes.

In the case of massless neutrinos in the standard model, particles and
antiparticles actually have opposite spins. But since recent
experiments show that neutrinos do actually have masses, this point
seems moot; I just couldn't resist mentioning it :-).

>Although the notion of anti-particles traveling back in time is often a
>convienient representation, one must not forget that not everything is
>'mirrored'. CPT symetry is not complete. The weak interaction does not
>display reflection symetry. There are many other examples of symetry
>breaking. The K-meson from my earlier post being one other such example.

This is simply wrong, at least according to all experiments I've heard
of. The standard model *is* CPT invariant. What you're saying is that
the weak interaction isn't P invariant, but it is CPT (and, IIRC, CP)
invariant. The K-mesons aren't P or CP variant, but they are CPT
invariant. (CPT symmetry means symmetry under the combined C, P and T
operations, not under each operation separately).

People are looking for CPT symmetry breaking as a sign of non-standard
model physics. For example, superstring theories can violate CPT. As
far as I know, nobody has found any sign of CPT violation; if you do,
I'd be exceedingly interested to hear of those results (and I'm *not*
being snarky here - it would be a great scientific breakthrough).

(If you don't believe me - I've not been working in quantum field
theory for some years now, so I'm not up to date - try doing a web
search for "CPT violation").



>I don't want to turn this into a slug-fest,

Good heavens, no. I had no perception that you were. We *are* gettting
a bit far off topic, though.

--
Magnus Olsson (m...@df.lth.se)

Paul Drallos

unread,
Sep 18, 2002, 4:46:04 PM9/18/02
to
Magnus Olsson wrote:


>
> People are looking for CPT symmetry breaking as a sign of non-standard
> model physics. For example, superstring theories can violate CPT. As
> far as I know, nobody has found any sign of CPT violation; if you do,
> I'd be exceedingly interested to hear of those results (and I'm *not*
> being snarky here - it would be a great scientific breakthrough).
>


Point taken.

-Paul

Magnus Olsson

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Sep 18, 2002, 5:06:14 PM9/18/02
to
In article <amanci$bqc$1...@news.lth.se>, Magnus Olsson <m...@df.lth.se> wrote:
>In the case of massless neutrinos in the standard model, particles and
>antiparticles actually have opposite spins. But since recent
>experiments show that neutrinos do actually have masses, this point
>seems moot; I just couldn't resist mentioning it :-).

Oops - thinko! Of course I meant helicity, not spin (the angular
momentum vector, which in massless fermions is constant, rather than
its magnitude).

--
Magnus Olsson (m...@df.lth.se)

Daryl McCullough

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Sep 18, 2002, 7:24:50 PM9/18/02
to
m...@df.lth.se (Magnus Olsson) says...

>We *are* gettting a bit far off topic, though.

Yeah, but you can learn a lot about physics in rec.arts.int-fiction.
It was from a post of yours that I finally understood that the "open"
possibility in a Big Bang cosmology meant an infinite universe, rather
than a finite one that grows without bound. (I later found out that
that's not necessarily true if you allow for nontrivial topology---if
the universe is a torus, it can be open and still finite)

--
Daryl McCullough
Ithaca, NY

Pissing Bandit

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Sep 18, 2002, 7:55:04 PM9/18/02
to
In article <amanci$bqc$1...@news.lth.se>, Magnus Olsson <m...@df.lth.se> wrote:

<horses' hooves rapidly approaching>

Whoa!

<horses' hooves clattering to a stop>

Ha-ha! Nearly too late!

Gentlemen! Present your Cheerios!

<unzipping>

>>More generally, if a particle has any atributes beyond momentum and spin,
>>the anti-particle has the opposite attributes.
>
>In the case of massless neutrinos in the standard model, particles and
>antiparticles actually have opposite spins. But since recent
>experiments show that neutrinos do actually have masses, this point
>seems moot; I just couldn't resist mentioning it :-).
>
>>Although the notion of anti-particles traveling back in time is often a
>>convienient representation, one must not forget that not everything is
>>'mirrored'. CPT symetry is not complete. The weak interaction does not
>>display reflection symetry. There are many other examples of symetry
>>breaking. The K-meson from my earlier post being one other such example.
>
>This is simply wrong, at least according to all experiments I've heard
>of. The standard model *is* CPT invariant. What you're saying is that
>the weak interaction isn't P invariant, but it is CPT (and, IIRC, CP)
>invariant. The K-mesons aren't P or CP variant, but they are CPT
>invariant. (CPT symmetry means symmetry under the combined C, P and T
>operations, not under each operation separately).

<sound of Manly Lantern Jaw hitting floor>

<shocked silence>

<rezipping>

<broken sobs>

I...I...I Should have Gone to College. Why, oh, Why, Have I Wasted
My Life as a Micturitious Action Hero?

Gentlemen.

Carry <sniff> on.

Neener. Eheu!

<plodding horses' hooves diminishing into distance>

TPB

Jason Etheridge

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Sep 18, 2002, 9:48:00 PM9/18/02
to
Cryptonomic wrote:
> And that is what goes back to what I said regarding how "realistic" you want
> your game to be if it features time travel. What physicists propose is
> called "globally self-consistent time travel" - which means whatever happens
> in the past does not change it, but fulfill it. In other words, it makes it
> happen as it happened.

Assuming time travel is possible and assuming that we have free will (that
things aren't predetermined), I see either multiple universe/timelines
happening or this: time goes through a loop and keeps cycling through
that loop until any paradoxes are resolved (if that happens at all).

So say I go back in time and kill my father before I was born. Then I
was never born, so I don't go back in time and kill my father. So then
I was born, and I go to kill my father... This happens over and over,
possibly forever, until maybe some random chain of events thwarts me
from killing my father.

If things aren't predetermined then maybe they can happen differently
each time they are given a chance to happen. :-) We don't need a
concept like temporal inertia here (the loop will either break after
a finite number of iterations or it won't--the sentients need not be
aware of how long it takes or that it happened at all) but we could
use this sort of temporal momentum in IF if it would make things more
playable (something favorable but random happens through one iteration,
so it happens again through subsequent iterations).

As an aside, one wierd notion that occured to me before is that every
possible moment could exist somewhere in a static universe, and that our
consciousness just hops around from universe to universe making things
appear as if they're really happening. Kind of scary, and lonely, that
thought.

--
http://phasefx.home.mindspring.com/
Add xyzzy to your message body if replying by e-mail

Magnus Olsson

unread,
Sep 20, 2002, 11:35:11 AM9/20/02
to
In article <amb3oo$esh$1...@news.fsf.net>, Pissing Bandit <t...@fsf.net> wrote:
>>>Although the notion of anti-particles traveling back in time is often a
>>>convienient representation, one must not forget that not everything is
>>>'mirrored'. CPT symetry is not complete. The weak interaction does not
>>>display reflection symetry. There are many other examples of symetry
>>>breaking. The K-meson from my earlier post being one other such example.
>>
>>This is simply wrong, at least according to all experiments I've heard
>>of. The standard model *is* CPT invariant. What you're saying is that
>>the weak interaction isn't P invariant, but it is CPT (and, IIRC, CP)
>>invariant. The K-mesons aren't P or CP variant, but they are CPT
>>invariant. (CPT symmetry means symmetry under the combined C, P and T
>>operations, not under each operation separately).
>
><sound of Manly Lantern Jaw hitting floor>
>
><shocked silence>
>
><rezipping>
>
><broken sobs>
>
>I...I...I Should have Gone to College. Why, oh, Why, Have I Wasted
>My Life as a Micturitious Action Hero?

Mr. Bandit, take heart: there are many physicists out there - too many,
in fact, but there is only one P... Micturating Bandit.

>
>Gentlemen.
>
>Carry <sniff> on.
>
>Neener. Eheu!
>
><plodding horses' hooves diminishing into distance>

Ladies and gentlemen: at last, a working defense against TPB has
been found: quantum physics. Sharpen your ket vectors, polish up your
spinors, put your cats in boxes.


--
Magnus Olsson (m...@df.lth.se)

Neil Cerutti

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Sep 20, 2002, 4:23:01 PM9/20/02
to

Would singing: "The Sun is a Mass of Incandescent Gas," be enough
of a deterent? Learning physics seems hard.

--
Neil Cerutti <cer...@trans-video.net>

T Raymond

unread,
Sep 21, 2002, 11:41:30 PM9/21/02
to
Neil Cerutti <cer...@trans-video.net> wrote in
news:amg02t$5i2ce$2...@ID-60390.news.dfncis.de:

> Would singing: "The Sun is a Mass of Incandescent Gas," be enough
> of a deterent? Learning physics seems hard.

While it is a giant nuclear furnace, I'm not sure that the tune would
subdue anyone as would a conversation on physics in general.

Of course, more little tunes like that and the average Joe, or Tom,
might happen to pick up a few bits about physics and other sundry
topics. Might not be a bad thing. :)

Tom

--
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Tom Raymond af956 AT osfnDOTorg
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=


-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
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Andrew Plotkin

unread,
Sep 22, 2002, 2:55:29 PM9/22/02
to
Here, T Raymond <ukn...@idunno.org> wrote:
> Neil Cerutti <cer...@trans-video.net> wrote in
> news:amg02t$5i2ce$2...@ID-60390.news.dfncis.de:

>> Would singing: "The Sun is a Mass of Incandescent Gas," be enough
>> of a deterent? Learning physics seems hard.

> While it is a giant nuclear furnace, I'm not sure that the tune would
> subdue anyone as would a conversation on physics in general.

> Of course, more little tunes like that and the average Joe, or Tom,
> might happen to pick up a few bits about physics and other sundry
> topics. Might not be a bad thing. :)

There *were* more tunes like that -- fourteen others on the "Space
Songs" album, and five other albums covering energy, biology,
weather, etc, etc.

Made a great impression on me, when I was a kid. Sadly, except for the
one TMBG covered, they're out of print.

--Z

"And Aholibamah bare Jeush, and Jaalam, and Korah: these were the borogoves..."
*
* Make your vote count. Get your vote counted.

T Raymond

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Sep 23, 2002, 12:20:32 AM9/23/02
to
Andrew Plotkin <erky...@eblong.com> wrote in
news:aml3n1$gvs$3...@reader2.panix.com:

> Here, T Raymond <ukn...@idunno.org> wrote:
>> Neil Cerutti <cer...@trans-video.net> wrote in
>> news:amg02t$5i2ce$2...@ID-60390.news.dfncis.de:
>
>>> Would singing: "The Sun is a Mass of Incandescent Gas," be
>>> enough of a deterent? Learning physics seems hard.
>
>> While it is a giant nuclear furnace, I'm not sure that the tune
>> would subdue anyone as would a conversation on physics in
>> general.
>
>> Of course, more little tunes like that and the average Joe, or
>> Tom, might happen to pick up a few bits about physics and other
>> sundry topics. Might not be a bad thing. :)
>
> There *were* more tunes like that -- fourteen others on the
> "Space Songs" album, and five other albums covering energy,
> biology, weather, etc, etc.
>
> Made a great impression on me, when I was a kid. Sadly, except
> for the one TMBG covered, they're out of print.

I see. Terrible shame I missed that. I could have used the help in
science. This is beginning to remind me of the whole schoolhouse rock
thing. Discussions around here have an odd way of becomming circular.

Adam Thornton

unread,
Sep 23, 2002, 1:10:00 AM9/23/02
to
In article <Xns92926C56C...@209.25.157.130>,

T Raymond <ukn...@idunno.org> wrote:
>Discussions around here have an odd way of becomming circular.

Just before they go pear-shaped.

Adam

Neil Cerutti

unread,
Sep 23, 2002, 10:14:36 AM9/23/02
to
In article <aml3n1$gvs$3...@reader2.panix.com>, Andrew Plotkin
wrote:

> Here, T Raymond <ukn...@idunno.org> wrote:
>> Neil Cerutti <cer...@trans-video.net> wrote in
>> news:amg02t$5i2ce$2...@ID-60390.news.dfncis.de:
>>> Would singing: "The Sun is a Mass of Incandescent Gas," be
>>> enough of a deterent? Learning physics seems hard.
>
>> Of course, more little tunes like that and the average Joe, or
>> Tom, might happen to pick up a few bits about physics and
>> other sundry topics. Might not be a bad thing. :)
>
> There *were* more tunes like that -- fourteen others on the
> "Space Songs" album, and five other albums covering energy,
> biology, weather, etc, etc.
>
> Made a great impression on me, when I was a kid. Sadly, except
> for the one TMBG covered, they're out of print.

There's a filk-song version of, "I am the very model of a Modern
Major General," which recites the table of elements. The only
recorded version I know is by an excellent Barbershop Quartet,
The Gashouse Gang. It's worth hunting down if you're into that
sort of music.

--
Neil Cerutti <cer...@trans-video.net>

Richard Bos

unread,
Sep 23, 2002, 10:36:37 AM9/23/02
to
Neil Cerutti <cer...@trans-video.net> wrote:

> There's a filk-song version of, "I am the very model of a Modern
> Major General," which recites the table of elements. The only
> recorded version I know is by an excellent Barbershop Quartet,
> The Gashouse Gang.

It is, in fact, by Tom Lehrer, and I'd be very surprised if his own
recordings didn't include it.

> It's worth hunting down if you're into that sort of music.

Very.

Richard

Neil Cerutti

unread,
Sep 23, 2002, 10:47:25 AM9/23/02
to
In article <3d8f237d...@news.tiscali.nl>, Richard Bos wrote:
> Neil Cerutti <cer...@trans-video.net> wrote:
>> There's a filk-song version of, "I am the very model of a
>> Modern Major General," which recites the table of elements.
>> The only recorded version I know is by an excellent Barbershop
>> Quartet, The Gashouse Gang.
>
> It is, in fact, by Tom Lehrer, and I'd be very surprised if his
> own recordings didn't include it.

Doh! Thanks for the heads up. I can't believe I forgot that.

--
Neil Cerutti <cer...@trans-video.net>

Magnus Olsson

unread,
Sep 23, 2002, 11:19:24 AM9/23/02