What's Causality?

[CoyoteNature]

What is Causality, I mean I know it means the principle of cause and effect, but why is it assumed to be inviolate at least when applied to time travel or faster than light travel.

Is it just a principle you apply to that you assume because the universe wouldn't make sense otherwise?

Really I don't know, seen it been bandyed about in many of books and classes I have taken, but haven't seen anything in terms of real evidence to support that it would have any real value in the real world.

Is it a assumption or real term or what?

[SirNitram]

What is Causality, I mean I know it means the principle of cause and effect, but why is it assumed to be inviolate at least when applied to time travel or faster than light travel.

If your cause happens after your effect, you can potentially have a Grandfather Paradox(You kill your own grandsire). This is considered a bad thing, as then you wouldn't be born. Then you wouldn't have killed him. You see?

Of course, if time travel is allowed, FTL is probably allowed.

[Hotfoot]

The logical thing we commonly assume is that time is absolute, and thus, things can happen instantaneously in all frames of reference. Relativity says that time is, well, relative. The only absolute is the speed of light. If you go faster than that, everything falls apart.

There was a very in-depth thread on this matter not too long ago in this very forum, in which several posters far more knowledgable than I went into extreme depth with the diagrams and descriptions of light cones and so on.

In order to preserve causality and keep FTL, as I understand it, you would need some sort of super-constant, that isn't breakable like Light would be. Of course then, it's turtles all the way down, but meh.

[Braedley]

With all this recent talk of causality, I think it's important to bring up a theory that basically says you don't have ot worry about causality <1>. An extension of this theory says you are who you are because of every quantum event that has ever happened in the past, including those as a result of what a future self has done in the past. This however royally fucks up multiple quantum universes and makes time travel impossible (at least into the past), so we won't worry about it.

This also makes many time travel plots impossible (of the handfull of Stargate time travel episodes, only "1969" would get it right), but that's another thread entirely.

[Ford Prefect]

I'll tell you what causality is, it's a fucking bitch.