Time Travel

[scriven]

The link leads to a study on the time travel suicide that does not dispute my claim against Rowling. Overconstrained or underconstrained, the time travel cannot occur without the existence of a Harry-0 who survived without the aid of a future Harry and then went back in time.

If I understand your argument correctly, you're saying that if an
object interacts with a future version of itself, the future version's
past doesn't include the interaction. What the link shows is that
that's not true in a universe where time travel takes place via the
closed time-like curves of general relativity.

Consider the wormhole example from the link:

http://plato.stanford.edu/entries/time-travel-phys/#6

We have a wormhole with two mouths, 1 and 2. Anything entering mouth
1 emerges from mouth 2 at an earlier point in time.

A spherical ball approaches the wormhole. A future version of itself
emerges from mouth 2, on a collision course. The two strike, sending
the later version careening away and the earlier version into mouth 1.
The ball which enters mouth 1 emerges from mouth 2 before the
collision took place -- and sees a younger version of itself
approaching on a collision course...

The point is that the ball which emerges from mouth 2 has interacted
with its past self. There is no ball-0 that never interacts with a
future version of itself.

 

[Rystil Arden]

If I understand your argument correctly, you're saying that if an
object interacts with a future version of itself, the future version's
past doesn't include the interaction. What the link shows is that
that's not true in a universe where time travel takes place via the
closed time-like curves of general relativity.

Consider the wormhole example from the link:

http://plato.stanford.edu/entries/time-travel-phys/#6

We have a wormhole with two mouths, 1 and 2. Anything entering mouth
1 emerges from mouth 2 at an earlier point in time.

A spherical ball approaches the wormhole. A future version of itself
emerges from mouth 2, on a collision course. The two strike, sending
the later version careening away and the earlier version into mouth 1.
The ball which enters mouth 1 emerges from mouth 2 before the
collision took place -- and sees a younger version of itself
approaching on a collision course...

The point is that the ball which emerges from mouth 2 has interacted
with its past self. There is no ball-0 that never interacts with a
future version of itself.

But there could be a ball 0 that doesn't interact with a future version in one of the quantum-mechanical states of the ball, and that would work no matter what system of time one is using. Unless you make several unusual assumptions about static history, the closed causal loop is a paradox. Any unlimited number of objects can be created from nothingness, for instance.

 

[Henry]

Aetherco's CONTINUUM is the One True Time Travel game. All others are just poor imitations of the real thing.

The biggest problem you run into in time travel games are players who want to screw up All of Time. If you have a means of convincing them that Time travel is necessary, but keeping consistency is necessary too, then time travel is a beautiful tool to put into a game to add spice to it. If a player wants to get away with a lot, then it's more difficult to make it work, so some DM's resort to finicky time gates, plot devices out of the players' control, etc. In order to inject time travel, but without it becoming a big mess.

 

[der_kluge]

Rowling's handling of time travel was actually a case of poor writing, one of her worst. Even were time travel possible, you cannot be saved from certain death by a future version of yourself who would never have existed had you died. Of course, Rowling pulls fallacies and deus ex machinas left and right, so I guess I shouldn't have been surprised by such a blunder.

Oooh yea. Ok, it's Friday. I make it a point not to engage in philosophical discussions about time travel and paradoxes (paradoxi?) on Fridays.

 

[Tom Cashel]

Recently, in fact.

In my D20 game (see link in sig), the PCs have a TARDIS. They arrive at a secret Antarctic research base to rescue one of their own, only to find the base utterly destroyed. No bodies remain. Evidence points to an assault by lots of badass things--all the bullet holes in the buildings are from the inside out.

Well, of course they decide that the only way to save their buddy is to travel back to before this destruction occurred. And no problem, the unknown past can be altered. It's the historical certainties that won't be altered. So while they may be able to save their friend, they realize that there's no way to prevent Zero Station being destroyed. They saw it in ruins: its destruction is a certainty.

So they travel back six days or so. Manage to save the companion. Blow up a little of the base. Interact with the base crew a bit from the safety of their (camouflaged) TARDIS. But, there's a wrinkle: the TARDIS sensors detect a quantum singularity only 181 miles away.

They could leave at this point. But they're curious. Hell, they're terrified. Why is there a black hole on Earth?

So they drop off their rescued buddy at home, and travel to the coordinates of the singularity. There they find a massive stone obelisk/tower. The tower is only the tip of a massive and rapidly-failing construct designed to keep an enormous extradimensional horror inside, run by Lovecraftian Elder Things.

They talk to the Elder Things (those whose minds are up to it at that point), and discover that a tiny bit of the enormous extradimensional horror has escaped into their TARDIS, and is now feeding on the artron energies found in the engine room. They're about to rush out and capture it, when the Elder Thing asks whether there are more pieces of said enormous extradimensional horror at the research base.

"Yes, there's one," they reply.

And are the humans experimenting on my people?

One PC is shaking his head, whispering "Don't tell them..." They know full well that the base crew is performing creative autopsies on the remains of at least half-a-dozen Elder Things. Then they tell the Elder Things so.

Elder Things, of course, freak out.

As they flee the tower, hundreds of Elder Things come flying out of it, into the sky, headed toward the base. Checking the calendar, they realize that this is about the time the attack must have occurred.

...And that they caused it. (see sig link for lots more detail.)

Never have I had a time-loop scenario work out more perfectly. I think the fact that it "just happened," rather than being designed, was the reason it worked so well. Didn't feel forced at all, but it did feel like fate. Fine line.

So my advice is to just let it happen on its own...but it can't happen at all until you give your PCs a time machine.

...some DM's resort to finicky time gates, plot devices out of the players' control, etc. In order to inject time travel, but without it becoming a big mess.

We use the online TARDIS manual. It's treatment of the Whovian "Laws of Time" was perfect for keeping things fun, but within limits.

 

[Falkus]

Unless you make several unusual assumptions about static history, the closed causal loop is a paradox.

But in a type one universe, which Rowling's universe is, closed casual loops are allowed because they've already happened. They're predetermined, you can't change history, because your time travelling self was already part of it when you went back. Rowling's depiction of time travel was a perfect example of a type one universe.

Any unlimited number of objects can be created from nothingness, for instance.

That's what makes them so beneficial for time travellers. Face it, when you've got time travel of any kind, you might as well throw causality as we know it out the window. You can't rely on traditional ideas cause and affect.

 

[Rystil Arden]

But in a type one universe, which Rowling's universe is, closed casual loops are allowed because they've already happened. They're predetermined, you can't change history, because your time travelling self was already part of it when you went back. Rowling's depiction of time travel was a perfect example of a type one universe.



That's what makes them so beneficial for time travellers. Face it, when you've got time travel of any kind, you might as well throw causality as we know it out the window. You can't rely on traditional ideas cause and affect.

Causality works fine if you simply view the multiverse as an infinite number of coexisting alternate timelines, a concept that fits well with the quantum mechanical model, and this doesn't break the laws of conservation.

 

[Falkus]

Causality works fine if you simply view the multiverse as an infinite number of coexisting alternate timelines, a concept that fits well with the quantum mechanical model, and this doesn't break the laws of conservation.

That's a type four universe. It also makes time travel lethal. There's more timelines existing now than there are in the past, because a new one is created whenever a probability wavelength collapses. That means whenever you travel back in time, your molecules merge with countless alternate versions of you travelling back to the same instant, resulting in a nuclear explosion.

 

[Ranes]

I haven't used it in a game but I came across this recently and thought you might find it useful.

http://www.bbc.co.uk/science/horizon/2003/timetrip.shtml

I strongly recommend following the weblinks on that page, especially those relating to Dr Nick Bostrom's stuff. Yes it smacks of The Matrix and yes there is the realist school of philosophy that says there isn't much point entertaining the idea that we might all be just brains in vats being manipulated by, er, something. But there's some zany fun to be had with those links.

IMO, of course.

 

[RSKennan]

That's a type four universe. It also makes time travel lethal. There's more timelines existing now than there are in the past, because a new one is created whenever a probability wavelength collapses. That means whenever you travel back in time, your molecules merge with countless alternate versions of you travelling back to the same instant, resulting in a nuclear explosion.

But at least one 'you' should survive. Then you get to kill all the other yous and take their mojo, and pull all kinds of kung fu stunts, until you're the One.