[Aardwolf]

Oh hey, and what about wormholes?

If both ends of a wormhole open simultaneously---that is, they have no velocity relative to one another, and thus in either endpoint's IRF they appear to have opened simultaneously---then could any time-travel issues arise out of the travel of a ship through that worm hole?

[Bobboau]

well, their observations come via their eyes, which sense the world by the light which enters them, they are not seeing any objects only the light reflected or radiated off objects, so as I said, I don't know how you would go about disproving C as the speed of event propagation without first finding something that can sense via some FTL method, so we hit a tautologous catch 22, it can't be disproven until l it's disproved. :\

[Liberator]

Granted I've got the Maths of a 12 year old but where does it say that time ceases to flow forward and ONLY forward once you transcend lightspeed?  Even if you somehow manage to accelerate to twice the speed of light, the nearest star is still 2 years away.  Hell, it would take you 3 hours to fly to Jupiter.  So I guess what I'm not understanding is how a ship could be constructed and then appear and destroy itself just by exceeding the speed of light.

[General Battuta]

well, their observations come via their eyes, which sense the world by the light which enters them, they are not seeing any objects only the light reflected or radiated off objects, so as I said, I don't know how you would go about disproving C as the speed of event propagation without first finding something that can sense via some FTL method, so we hit a tautologous catch 22, it can't be disproven until l it's disproved. :\

I think I might need to ship you a relativity textbook.

Granted I've got the Maths of a 12 year old but where does it say that time ceases to flow forward and ONLY forward once you transcend lightspeed?  Even if you somehow manage to accelerate to twice the speed of light, the nearest star is still 2 years away.  Hell, it would take you 3 hours to fly to Jupiter.  So I guess what I'm not understanding is how a ship could be constructed and then appear and destroy itself just by exceeding the speed of light.

Superluminal motion is equivalent to time travel in some IRFs. I can run through the math if you want. It needs high-school-level algebra and a willingness to accept the valid derivation of the Lorentz transformation.

[Aardwolf]

I suggest that this silly little diagram be used from now on whenever these debates crop up:






Now can anybody address my wormholes question?

[The E]

Aardwolf, any form of FTL can be functionally equivalent to time travel. There are no exceptions.

At least, that's what people who know more about the subject keep telling me.

[Aardwolf]

But wasn't non-simply-connected space one of the things that general relativity didn't explicitly rule out?

Granted, I know even less about general relativity than I do about special relativity, but...

[The E]

Look, for the purposes of special relativity, it doesn't matter (much) how you go past c, the fact that you're arriving at your destination faster than the light could have bridged that distance is enough.
There's a reason why wormholes have a traditional place in time-travel-themed SF.

EDIT: Wrongness removed.

Read Wikipedia on the subject.

[Aardwolf]

But if there's a wormhole, then the light (or propagation of events) still reaches the destination faster than anything else possibly could (because the wormhole isn't just a shortcut for a spaceship, it's a shortcut for EVERYTHING)

[The E]

Yes, I realize that after reading up on it.

However, there's one major catch for wormholes: Noone has ever observed one. Yes, they are allowed in the relevant theories, but that doesn't mean they actually exist.

[Aardwolf]

Fine by me!

[General Battuta]

Thing is that while static wormholes do not (normally) allow time travel, it's trivial to accelerate one end and thus create a problematic time machine.

[Aardwolf]

Thing is that while static wormholes do not (normally) allow time travel, it's trivial to accelerate one end and thus create a problematic time machine.

...assuming the endpoints can be accelerated at all. Would the 'acceleration' of an endpoint by gravitation (what with all the details of general relativity that I don't know about) cause any problem?

[General Battuta]

Thing is that while static wormholes do not (normally) allow time travel, it's trivial to accelerate one end and thus create a problematic time machine.

...assuming the endpoints can be accelerated at all. Would the 'acceleration' of an endpoint by gravitation (what with all the details of general relativity that I don't know about) cause any problem?

Yes. Acceleration and gravity are equivalent in all ways including time dilation.

And the endpoints can be accelerated.

[Bob-san]

Yes, I realize that after reading up on it.

However, there's one major catch for wormholes: Noone has ever observed one. Yes, they are allowed in the relevant theories, but that doesn't mean they actually exist.

The real question might be how to observe a wormhole in the first place. For all we could know, they could only form only during special cosmic events and be randomly (at least so far as we could observe) spit you out somewhere else, if it'd even be possible to move through space fast enough to transverse it. And what if you don't reach the other side? What if your particular hole closes before you can get through? Plotting space-time only works when you're using a single plane--it's easy to show how gravity has an effect on a 2D cross-section, but does that really tell us anything? And with 3D technology, can we even accurately observe 4+D events?

[General Battuta]

Yes, I realize that after reading up on it.

However, there's one major catch for wormholes: Noone has ever observed one. Yes, they are allowed in the relevant theories, but that doesn't mean they actually exist.

The real question might be how to observe a wormhole in the first place. For all we could know, they could only form only during special cosmic events and be randomly (at least so far as we could observe) spit you out somewhere else, if it'd even be possible to move through space fast enough to transverse it. And what if you don't reach the other side? What if your particular hole closes before you can get through? Plotting space-time only works when you're using a single plane--it's easy to show how gravity has an effect on a 2D cross-section, but does that really tell us anything? And with 3D technology, can we even accurately observe 4+D events?

Yes. Your concerns about observation are not something to get too worked up over - if wormholes do exist, they have pretty trivially observable characteristics.

For instance there may be massive energy buildups on the Cauchy horizon which render the hole untraversable.

[Aardwolf]

For instance there may be massive energy buildups on the Cauchy horizon which render the hole untraversable.

Dangit, now I gotta go look that one up.

[Herra Tohtori]

Aardwolf, any form of FTL can be functionally equivalent to time travel. There are no exceptions.

Except, conversely, every form of FTL forms a time-space path from point A to point B which isn't dependant on the observation cones based on the assumption that speed of light is the fastest speed information can propagate through time and space.

Or, in other words, if you FTL from point A to point B, you're not actually moving through the space between the points at superluminal speed, you're making the distance shorter - depending on type of travel, the distance via FTL travel can be anything from astronomical units (Star Wars hyperspace) to order of thousands of kilometres (Babylon 5 hyperspace) or just kilometres (FreeSpace subspace) to zero (BSG type FTL jump drives).

FTL can't reverse causality, it just introduces a way for information (and therefore causality) to not be bound on the observation cones that are so commonly used to create "paradoxes".


General Relativity doesn't exclude the possibility of information travelling faster than speed of light in vacuum. It simply states that it is impossible for an object with rest mass to be accelerated by a force to speed of light when confined to the currently known time-space continuum.

Now, what comes to Alcubierre drive in which there technically is no force accelerating the ship, but space-time itself moving the ship on a wave... well, even then it's possible that waves in space-time continuum propagate at speed of light at most, in which case riding the wave wouldn't still quite bring you to superluminal speeds.

Except if you take into account time dilation. Which you can also interpret as making the way shorter rather than ship faster...

[watsisname]

Hey Aardwolf.  You can travel to Alpha Centauri, which is 4.3LY away, in less than a year.  Indeed, you could do it in less than a day.
Without breaking physics or using flashy wormholes.


  Just travel at 0.99etc times the speed of light, and have fun missing out on four years of history.

[Aardwolf]

Yeah but I'd be killed by the acceleration/deceleration.