Some Emerging Possibilities For Space Propulsion

http://www.nasa.gov/centers/glenn/technology/warp/possible.html

by mike_esspe • 12 years ago

53 57 12 years ago

nasa.gov

thearn4• 12 years ago

NASA used to have a small program to evaluate concepts for breakthrough propulsion, which ended around 2002.

http://www.grc.nasa.gov/WWW/bpp/

chroem• 12 years ago

Why not a fission fragment rocket? We could send a probe to the centauri system with current technology.

https://en.wikipedia.org/wiki/Fission-fragment_rocket

Steuard6• 12 years ago

Speaking 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 gravity theories are still up for debate." That's perhaps generous: quantum gravity isn't far from my field, and I've never heard of this take on the origin of gravity and inertia.

I'm also rather puzzled by the quote "Although gravity’s effects on electromagnetism and spacetime have been observed, the reverse possibility, of using electromagnetism to affect gravity, inertia, or spacetime is unknown." That's really not at all true. Our models of gravity all include very well-defined effects of electromagnetism on spacetime: the energy density in those fields causes space to curve, just like any other form of mass or energy. Hypothesizing anything else would require fundamental changes to the theory. That's entirely possible! But it's misleading to characterize the current state of affairs as having an unfilled gap like this.

So yeah. I'd love a good spacedrive as much as the next guy. But this article doesn't do much to make me optimistic about it.

mrfusion4• 12 years ago

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?

TheLoneWolfling3• 12 years ago

http://arxiv.org/abs/1005.1614

tinco• 12 years ago

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.)

Steuard6• 12 years ago

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.

logfromblammo4• 12 years ago

I have a hypothesis, unsupported of course, that everything has a fixed spacetime velocity. As beings with mass, we perceive the universe as having three spatial dimensions and one temporal dimension. We move relatively slowly in the spatial dimensions, and we find it easy to change direction. As a result, we are hurtling incredibly fast in the temporal dimension.

A photon, on the other hand, moves incredibly fast in the spatial dimensions, and finds it difficult to change directions in them. From its perspective, the spatial dimensions might as well be one dimension, represented by its vector of movement in space. It moves relatively slowly in our temporal dimension, however. And that leads to the question.

What if we only perceive time as a single temporal dimension because we are moving so fast through time that we have so far been unable to perceive any other temporal dimensions or change temporal direction?

It may be that if a human were to accelerate close to the speed of light in the known spatial dimensions (thus decelerating in the temporal dimension) it would become possible to perceive additional temporal dimensions, and maybe alter one's course through time. Our current understanding of causality assumes that one's movement through time does not change direction.

If time does have additional dimensions, a massless particle could execute a u-turn in the temporal dimensions, and it would appear to us as though it turned itself into its antiparticle. If the u-turn was in any way imperfect, the particle probably could never intersect any point in spacetime that it has ever previously passed through and interact with itself in a way that could create a paradox. Or maybe all electrons and positrons really are the same particle, endlessly interacting with itself as it bounces around in spacetime, and all paradoxes become self correcting, since causality flows in multiple directions.

TL;DR: Our assumptions about causality may be wrong.

pdonis3• 12 years ago

People always use causality to argue against FTL, but then readily acknowledge that wormholes or Albicurie might allow it

Wormholes and Alcubierre drives do lead to causality violations. That's why most physicists view them as not physically possible. They're just mathematical solutions to the Einstein Field Equations that can't be physically realized. There are plenty of other such solutions; nobody has ever claimed that every mathematical solution of the equations has to correspond to something that's physically possible.

trhway3• 12 years ago

People always use causality to argue against FTL,

for some definitions of causality. Anyway, far-far galaxies are running away from us FTL using part of the same machinery as Albicurie drive - ie. space expansion and no causality violation so far.

Anyway before FTL, we need to get basic aneutronic fusion drive working - emitting 0.05c alphas - so that we can comfortably travel inside Solar system and send first near-by star systems probes. Unfortunately continuing work on non-starter schemas like Tokamak or laser-driven (better than Tokamak, yet laser driver is the worst one) neutronic fusion wastes so many resources and creates public distrust to the fusion as a technology.

mrfusion4• 12 years ago

Have you heard of the idea of running a current through a long wire to propel a spacecraft against the earth's magnetic field?

I remember reading about it somewhere, but I can never find it again.

TheLoneWolfling3• 12 years ago

Yep. It's called an electrodynamic tether. Proposed for stationkeeping for everything from space stations to skyhooks, among other things.

yxhuvud• 12 years ago

Awefully light on recent information as well. The last experiment they refer to was 20 years ago!

bsilvereagle• 12 years ago

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/2011002...

That's meatier but I thought it was still light on information.

pdonis3• 12 years ago

quantum gravity isn't far from my field, and I've never heard of this take on the origin of gravity and inertia

That's probably because nobody in the field pays any attention to Haisch, Puthoff, and Rueda, who have been publishing papers on "zero point energy" and how they claim it causes gravity and inertia for a couple of decades now.

Steuard6• 12 years ago

I know nothing about their theories, clearly. But if I had a nickel for every suggestion I've heard for somehow extracting energy or momentum or something useful from quantum vacuum energy, I'd have, well, a couple bucks.

The thing is, we've already got some awfully good theories about gravity and inertia, and a lot of their predictions are very well tested. Just as one example, if these folks think that what they've been working on is "a possible alternative to the Higgs" (a quote by Haisch himself in 2006 on the Talk page for his own Wikipedia entry), doesn't that mean that the actual recent discovery of the Higgs (and its good agreement with mainstream theory) strongly disfavors their alternative explanation for inertia?

There are too many fringe theories like this for any working physicist to have time to refute them all in detail. (I did my time years ago, trying to refute the nonsense of "Heim Theory" that had a crowd of Wikipedia proponents and a few overly credible mentions in the popular press.) At some point, when people start talking about replacing the foundations of modern physics you have to be skeptical, and raise the bar quite high before they merit serious attention.

eudox• 12 years ago

I honestly can't imagine why NASA even acknowledges the idea of FTL travel - Is there some kind of propeller beanie PAC forcing their hand?

They should just have a page that says: "FTL is impossible, but that's fine, once you get used to the way things are."

ceejayoz3• 12 years ago

Scientists, rightly so, are a little leery of stating "we know everything". There's no guarantees our current theories are perfect - in fact, it's extraordinarily unlikely that they are.

Also of note: https://en.wikipedia.org/wiki/Alcubierre_drive

jp5552• 12 years ago

I consider how we understand that at the speed of light, all distances are zero. So even if you can somehow travel at C, there would be nowhere to go, because you're already everywhere. Given this, travelling faster than C can be seen as travelling a distance of less than zero... which makes no sense.

fooqux• 12 years ago

They should just have a page that says: "FTL is impossible, but that's fine, once you get used to the way things are."

No offense intended to you, but I feel this is a disastrously negative attitude to have. Except where morals dictate otherwise (which are outside the scope of science anyway) nothing is banned from exploration. Suggesting otherwise implies that we know all there is to know about a subject; to me, this is analogous to willful ignorance. Science is dedicated to removing ignorance, not enforcing it.

crusso2• 12 years ago

nothing is banned from exploration

Nothing is banned, per se... but there's just too much search space to sift through to not be smart about where you look.

logfromblammo4• 12 years ago

I would amend that to "FTL is economically impossible", rather than an unqualified impossible. It may be allowed by physics, but if we have to effectively bankrupt a whole galaxy just to move quickly from one star to the next, humans simply won't ever do it.

As it is now, with our current level of understanding, the best way to move around in space is by throwing tiny things very fast in one direction, to make a big thing move in the opposite direction, then wait a few thousand years for that big thing to get somewhere.

Given that we sometimes have difficulty being alive after waiting a few thousand years, it is understandable that some people have a problem with this, and want to explore other options.

madaxe_again3• 12 years ago

The sun orbits the Earth, but that's fine, once you get used to the way things are.

mcguire• 12 years ago

NASA is made up of the same Science Fiction-obsessed, excessively optimistic people who also probably make up most of the employees of wherever most of us work. Some of them, I understand, even go to 'cons and such. I suspect it's based on disappointment over not being capable of actually launching anything. In any case, they're regrettably not all hard-headed realists like you and me.

ctdonath• 12 years ago

I've long observed there's a small but profitable industry in proposing & researching megaprojects: suggest doing something so intriguing and outlandish and expensive that somebody will figure it's worth coughing up a minuscule percentage of the ginormous price tag to fund at least an amusing cursory overview, at a price sufficient to employ a small team for several years. Space elevators, floating (ocean) cities, bridging the Strait Of Gibraltar, world-spanning freeway, FTL interstellar travel, mile-high buildings, etc all are engaging concepts that people with deep pockets are willing to toss some "pocket change" at, giving a group a tidy sum to live on for a while doing something amusing.

sdegutis• 12 years ago

"Theory for a faster-than-light "warp drive" consistent with general relativity."

For real?

madaxe_again3• 12 years ago

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

crusso2• 12 years ago

The only bright spot in that article is that the math doesn't contradict general relativity. Everything else points to its being a curiosity that would disappear if GR were more integral with Quantum Mechanics.

sehugg• 12 years ago

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#....

madaxe_again3• 12 years ago

Here's an interesting Wired interview with Podkletnov on his anti-gravity work from '97 : http://archive.wired.com/wired/archive/6.03/antigravity.html...

jcfrei• 12 years ago

I would be much more excited if NASA resumed the research on NERVA (http://en.wikipedia.org/wiki/NERVA). 50 years later a nuclear propulsion drive still seems like the most promising and cost-efficient way to explore our solar system.

misterfusion• 12 years ago

A real-life warp drive can be practically possible by employing phased standing waves. http://www.youtube.com/watch?v=6zh9abFF3ZE

throwwit• 12 years ago

The submitter should have tacked on (2007).

Some Emerging Possibilities For Space Propulsion

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