For something a bit more realistic, we are still studying nuclear propulsion in fits and starts since we halted its development in the 60s:
http://www.nasa.gov/topics/technology/features/ntrees.html#....
Some Emerging Possibilities For Space Propulsion
11–20 of 61 posts
Re: Some Emerging Possibilities For Space Propulsion
#12Speaking as a professional physicist, this page feels awfully light on actual information. And as far as I can tell, that's merited: there's not a lot of solid science discussed on this page, or even especially tantalizing ideas for what might come next. They spend a lot of time discussing quantum vacuum energy, but the one short note about its "propulsion implications" includes the comment that "Those particular gra…
How do these "legitimate" ideas for FTL deal with causality? I've always wondered that. People always use causality to argue against FTL, but then readily acknowledge that wormholes or Albicurie might allow it. I'm not getting that disconnect?
Re: Some Emerging Possibilities For Space Propulsion
#13Speaking as a professional physicist, this page feels awfully light on actual information. And as far as I can tell, that's merited: there's not a lot of solid science discussed on this page, or even especially tantalizing ideas for what might come next. They spend a lot of time discussing quantum vacuum energy, but the one short note about its "propulsion implications" includes the comment that "Those particular gra…
How do these "legitimate" ideas for FTL deal with causality? I've always wondered that. People always use causality to argue against FTL, but then readily acknowledge that wormholes or Albicurie might allow it. I'm not getting that disconnect?
I think, definitely not an expert, that when thinking about ways to travel faster than light would not actually involve an object moving through space in the classical sense.
You could look instead of at the means (i.e. moving through space) at the goal: Mass first being somewhere, and then being somewhere else in a relatively short amount of time.
So the solution would be to cross distance at a low velocity, so you don't have all the downsides like getting heavier, requiring insane amounts of energy, but still arriving at a location sooner than a conventional ray of light would.
The concept of a worm hole would be that there would be a path between two points in space, over which matter can travel, that has a shorter physical length than the shortest paths we can come up with now.
So faster than light travel might simply be 'regular' velocity travel over undiscovered paths.
(Note that in a mathematical sense, under the rules we learn in school, there can not be a path between two points that is shorter than a straight line. What we know however that the universe around us does not conform to these rules precisely, we already know for example that space has curves in it.
The key to knowing whether there are paths or if we can create those paths, that are shorter than the ones we experience now lies in understanding the structure of the universe better.)
Re: Some Emerging Possibilities For Space Propulsion
#14[deleted]
Re: Some Emerging Possibilities For Space Propulsion
#15Earlier quoted context omitted.
How do these "legitimate" ideas for FTL deal with causality? I've always wondered that. People always use causality to argue against FTL, but then readily acknowledge that wormholes or Albicurie might allow it. I'm not getting that disconnect?
I think, definitely not an expert, that when thinking about ways to travel faster than light would not actually involve an object moving through space in the classical sense. You could look instead of at the means (i.e. moving through space) at the goal: Mass first being somewhere, and then being somewhere else in a relatively short amount of time. So the solution would be to cross distance at a low velocity, so you…
Whether or not you drift there or instantaneously teleport there, there are still causality issues. You can make it into your own past by jumping once, changing your speed to tilt the frame of reference you're moving "instantaneously" in, then jumping again.
Re: Some Emerging Possibilities For Space Propulsion
#16Earlier quoted context omitted.
How do these "legitimate" ideas for FTL deal with causality? I've always wondered that. People always use causality to argue against FTL, but then readily acknowledge that wormholes or Albicurie might allow it. I'm not getting that disconnect?
http://arxiv.org/abs/1005.1614
That was an interesting paper, but I'm having trouble with the concluding paragraphs. Is the argument against the grandfather paradox essentially "You can set up the mechanism to create the grandfather paradox, but it won't actually work the way you think it will?"
Re: Some Emerging Possibilities For Space Propulsion
#17Speaking as a professional physicist, this page feels awfully light on actual information. And as far as I can tell, that's merited: there's not a lot of solid science discussed on this page, or even especially tantalizing ideas for what might come next. They spend a lot of time discussing quantum vacuum energy, but the one short note about its "propulsion implications" includes the comment that "Those particular gra…
Awefully light on recent information as well. The last experiment they refer to was 20 years ago!
Re: Some Emerging Possibilities For Space Propulsion
#18[deleted]
Re: Some Emerging Possibilities For Space Propulsion
#19Speaking as a professional physicist, this page feels awfully light on actual information. And as far as I can tell, that's merited: there's not a lot of solid science discussed on this page, or even especially tantalizing ideas for what might come next. They spend a lot of time discussing quantum vacuum energy, but the one short note about its "propulsion implications" includes the comment that "Those particular gra…
How do these "legitimate" ideas for FTL deal with causality? I've always wondered that. People always use causality to argue against FTL, but then readily acknowledge that wormholes or Albicurie might allow it. I'm not getting that disconnect?
Here's a link to a good discussion of some related issues by cosmologist Sean Carroll:
http://www.preposterousuniverse.com/blog/2011/09/24/can-neut...
(It's in the context of that mistaken "neutrinos move faster than light" claim from a few years back, but the arguments are general. Bob Geroch's article mentioned near the end is pretty much the gold standard for dealing with these issues as far as I know.)
I really need to sit down at some point and figure out how Alcubierre "warp" spacetimes would relate to causality. It may be a moot point: I've heard people claim that one feature of Alcubierre's solutions in General Relativity is that they are "eternal", in the sense that there's no obvious way to "turn on" a warp bubble around some given region or to "turn off" the warp once you reach some destination. If that's true, it wouldn't be useful for sending information, which might be all that's needed to preserve causality.
As for wormholes or similarly strange spacetime topologies, those really do open a can of worms for causality. There's some interesting physics/philosophy involved, and I'm not sure that we've got any solid answers. (I have my own strong suspicions about what the answer looks like, but I won't try to explain them here.) But that may also be moot: every known wormhole solution in relativity requires matter with properties entirely different than anything ever observed in the universe, so we won't be testing it out any time soon.
Re: Some Emerging Possibilities For Space Propulsion
#20[deleted]
And you will need earth sized spaceship to survive crashes even with hydrogen atoms. Unless there is something that I don't understand.
You just cannot travel with that kind of speeds in normal space IMO.