is causality always necessary

[foofighter]

here's a hypothetical question. lets say that all the problems of FTL travel could be circumvented - except for causality. the question is - wats the big deal? its just an illusion. imagine watching a magician - and viewer A is getting all upset because he is violating reality. "Calm down," says viewer B. its just a trick of the eye. we really know it isn't magic. similarly - why are we so upset if spacecraft X appears to arrive at the destination before leaving, or some similar causality issue with FTL travel (assuming all other factors of FTL are a non issue)? we know in our heads its just an optical illusion created by light's fixed speed, so as long as we keep that in mind, the effects, although superficially confusing, shouldn't ultimately fool us. maybe i'm missing a key piece of the puzzle, does anyone have ideas?

[swansont]

The problems of causality aren't illusions.

[Rasori]

No but it is easy to believe they are and hard for someone without a proper education in relativity to realize why they aren't.

 

It is easy for the layperson (myself included) to think of the speed of light the same way we think of the speed of sound--if something goes faster than the speed of sound, the sound of it will arrive after it does, and it should be the same way with light. It takes a much more indepth knowledge of inertial reference frames and the skewing of spacetime at different velocities to realize this isn't true.

[someguy]

well as i understand it if you managed to move at the speed of light you would arrive instantaneously at your destination from your perspective. so then i guess it would follow that if you could move faster than light it wouldn't just seem like you arrived somewhere before you left. from your perspective that would need to have actually happened to you. so then you would have reverse aged... but if you are aging backwards whose flying your spaceship? how are you gonna stop it again? even your computer would be reverse aging. i don't know how you'd do this even for moving only at the speed of light. the main thing is though, that you can't go the speed of light or faster so imagining what it would be like is sort of a moot point. it's the same kind of impossible like wondering what it would be like to move slower than stopped. there isn't any technology or knowledge that will help you to do that.

[Spyman]

here's a hypothetical question. lets say that all the problems of FTL travel could be circumvented - except for causality. the question is - wats the big deal? its just an illusion. imagine watching a magician - and viewer A is getting all upset because he is violating reality. "Calm down," says viewer B. its just a trick of the eye. we really know it isn't magic. similarly - why are we so upset if spacecraft X appears to arrive at the destination before leaving, or some similar causality issue with FTL travel (assuming all other factors of FTL are a non issue)? we know in our heads its just an optical illusion created by light's fixed speed, so as long as we keep that in mind, the effects, although superficially confusing, shouldn't ultimately fool us. maybe i'm missing a key piece of the puzzle, does anyone have ideas?

For whom is it an illusion ?

 

What if observer A gets so upset so he destroys spacecraft X at the launchpad ?

(After it arrived at the destination, but before departing to the destination.)

Now where did that spacecraft X appear from ?

 

Or if observer C, travelling onboard spacecraft X jumps on spacecraft Y after arrival, and hurries back to the launchpad where he stops spacecraft X from leaving. Now where did that second observer C appear from ?

 

Casuality is necessary to avoid Paradoxes.

 

Some Wikipedia links to read:

http://en.wikipedia.org/wiki/Paradox

http://en.wikipedia.org/wiki/Casuality

http://en.wikipedia.org/wiki/Faster-than-light

http://en.wikipedia.org/wiki/Wormhole