"We should ask - is it possible to be at one part of space ''A'' and then in part ''B'' faster than it would took light traveling in a line?"
No.
You can, however, bend space so that the shortest path between A and B is shorter than you'd expect, so that you can arrive faster than a light ray would have if you assumed a flat metric.
This is actually the same thing as what you said, I'm just being pedantic.
This is the trick behind Alcubierre drives, Krasnikov tubes, wormholes, etc. You'll still never outrun your headlights; you're just making a path between A and B that's speedier than would be possible for a light ray in flat space.
"Possible", however, is meant only in the mathematical sense - AFAIK, there are no *practical* FTL solutions. That is to say, solutions that don't require either
>A: Impractically large amounts of exotic mass-energy (more than, say, a large moon's worth) >B: Impractically large densities of exotic mass-energy (denser than, say, neutronium) >C: Impractically fine feature engineering (needing to squeeze that mass-energy into structures thinner than an atom)
There are definitely solutions that avoid one or two of these problems, but AFAIK none avoid all three. (For more information on FTL solutions and their theoretical plausibility or lack thereof, I refer you to this paper: "The Quantum Inequalities Do Not Forbid Spacetime Shortcuts" arxiv.org/abs/gr-qc/0207057)
Ethan Nguyen
Yes, but near-lightspeed travel is really hard for lots of other reasons and I don't really consider it feasible enough in the near-ish term to worry about practical problems when so many more basic engineering problems required to do it have yet to be worked out. I was just objecting to the claim that large space colonies were impossible.
Justin Ramirez
you are wrong
first, space is very very empty so depending on where you travel the odds are as good as zero of such a thing to ever occur
second, you can easily take measures against this
but yeah, I doubt large scale space colonies will ever exist due to their infeasibility
and near light speed travel wont ever exist for the same reason. I doubt we will ever reach the technological level for it
Alexander Campbell
>There are definitely solutions that avoid one or two of these problems, but AFAIK none avoid all three. (For more information on FTL solutions and their theoretical plausibility or lack thereof, I refer you to this paper: "The Quantum Inequalities Do Not Forbid Spacetime Shortcuts" arxiv.org/abs/gr-qc/0207057)
Help me out here. I'm code-monkey, not a physicist. He's overcoming QM related objections to effective FTL. But what about GR+causality? I've skimmed the PDF looking for this, but I don't seem to see it. Even if he's 100% correct about QM, wouldn't effective FTL still break causality because of the relativity of simultaneity?
Lincoln Foster
Actually, he's just avoiding those concerns. There actually are spacetimes that let you take FTL shortcuts without running into time travel issues, so he's only constructing those.
As I understand it, causality is only an issue if you can actually form a closed timelike curve - if there exists a path from some point on a worldline to some point in that worldline's past. If no such paths exist, then there is no way to send information back in time to yourself, or otherwise meddle with your own past in any way. Paradoxes are avoided and causality remains intact.
For instance, when considering wormholes, Krasnikov only examines the case where the wormhole mouths are displaced in more distance than time. Suppose you have a spacetime containing only a wormhole with one mouth on Earth and one mouth on Alpha Centauri, four light-years away but with the Earth end three years of time ahead of the Alpha Centauri mouth.
In this case, going from Earth to Alpha Centauri will put you four light-years away, but three light-years in the past. Sending a message from Alpha Centauri to Earth through the wormhole will simply send it to the same time you left, but slightly later - no causality violation, everything working as normal. Sending that message *not* through the wormhole will arrive a minimum of four years later, or a year after you left - so not so much a time machine or a time capsule.
Likewise, if you start at Alpha Centauri and go to Earth, you'll arrive at Earth three years in the future, and again sending a message through the wormhole will arrive just after you left (no problem), and sending one through flat space will arrive at AC at a minimum seven years after you left (no problem)
Brody Mitchell
And in case it's not obvious, relativity of simultaneity doesn't come into play here, because no matter what the fastest non-wormhole path between the mouths is the straight-line light-ray path between them through normal space. No more complicated path involving outside observers moving at high velocities can possibly get information from one mouth to the other any faster, and so if paradoxes can't arise in this case, they won't arise in any case involving only one wormhole with spatial separation greater than temporal separation.
When you have multiple wormholes, then things get tricky (see also: Roman ring), which is why the paper is only considering one at a time.
Jayden Ross
>flying >the internet >cars >cellphones
Jaxson Cruz
Evidently they ARE used for bullet points, because they were used for exactly that purpose in the OP
Are you that fucking dumb, stubborn, both, or is this bait?
Nolan Rogers
>space junk wrecks your moonbase
detection equipment, armor / shielding, point defense etc. float a zumwalt with railguns around the base or something.
> plow into an asteroid at lightspeed
there'd be a bow wave as you distort spacetime.
so you'd imagine the size and mass of the object you're encountering versus the mass of the craft times the inherent energy to achieve propulsion then times some compression figure based on the "thickness" of spacetime that is being distorted and you've had something like the amount of energy a spaceship would have in a field around it as it compresses spacetime through some sort of mass effect generation, enabling "faster than light" travel.
but then because you aren't really travelling faster than light, you're just bunching up space into folds and jumping small gaps point to point so you're much less likely to plow into anything anyway as you aren't really travelling very far.
