dystopic dystopic

bussard ramjets, cryonic stasis, and exoplanetary colonization

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bussard ramjets, cryonic stasis, and exoplanetary colonization

what will it take?

from GalCiv2 Forums
hello everyone,

i'm a bit of a writer, and i can't help but feel drawn to science fiction. that shouldn't be surprising.

lately i've been reading up a great deal on theoretical physics, exobiological speculation, and all that. i was dismayed at first to learn that the chances of faster-than-light travel being physically possible are slim. it was also pretty discouraging when i sat down and looked at the actual speeds that'd be required to traverse sizable parts of the galaxy in a single conscious lifetime. it was a kick when i was down to learn about how difficult terraforming probably would be. but the more i've been learning, the more i've been excited about telling a different kind of science fiction story.

to draw an analogue to our world, the thing that made both the european colonial age and the modern process of globalization have been technology. it's not that we couldn't go to various places around the world before, it just cost too damn much to make anything worth it. i got my BA in sociology, and these sorts of things interest me.

if FTL travel isn't possible, then more than likely it'll be too damn costly to ever colonize beyond our own solar system as the way it's been envisioned in most of the celebrated scifi universes. But there are examples such as Arthur C. Clarke's Songs of a Distant Earth or Sid Meier's Alpha Centauri where humans colonize to escape destruction on earth.

recently i had the chance to meet both Kim Stanley Robinson and Geoff Ryman. Robinson is a hard scifi writer after my own heart; the Mars Trilogy is a really interesting look at our first attempts to colonize within our own star system. Ryman was actually more interesting to talk to, though. maybe because few people have ever heard of him (i was only there because i work at UCSD where he was being hosted). but i actually got to talk to him. he said he thinks we probably won't ever leave our galactic neighborhood.

i'm interested in writing a hard scifi story (or series) myself. i'm interested from a sociological point of view: what would drive us to colonize space? from a writer's point of view, i want to keep the earth around, so i'm not interested in a flight from disaster. what would societies be like after colonies were established? trade would be difficult, but not impossible. same goes for war.

while i'm certainly interested in contributions along those lines, i'm also interested in learning more about the hard science and engineering behind interstellar travel. i've got a lot of questions i haven't been able to answer through wikipedia and google alone. but i'm not about to list them all here.

it seems like a discussion about real ("real") colonization and space travel could use a place on these boards.

i'll kick it off. i've been reading up on propultion especially, and bussard ramjets seem like the most economically feasible option since they gather their fuel as they go - perhaps especially if it could be hybridized with another form such as antimatter-catalyzed fusion. the wikipedia article on bussard ramjets describe that they'd probably need what is essentially a magnetic funnel or ramscoop to gather interstellar hydrogen as propellant.

The mass of the ion ram scoop must be minimized on an interstellar ramjet. The size of the scoop is large enough that the scoop cannot be solid. This is best accomplished by using an electromagnetic field, or alternatively using an electrostatic field to build the ion ram scoop. Such an ion scoop will use electromagnetic funnels, or electrostatic fields to collect ionized hydrogen gas from space for use as propellant by ramjet propulsion systems (since much of the hydrogen is not ionized, some versions of a scoop propose ionizing the hydrogen, perhaps with a laser, ahead of the ship.) An electric field can electrostatically attract the positive ions, and thus draw them inside a ramjet engine. The electromagnetic funnel would bend the ions into helical spirals around the magnetic field lines to scoop up the ions via the starship's motion through space. Ionized particles moving in spirals produce an energy loss, and hence drag; the scoop must be designed to both minimize the circular motion of the particles and simultaneously maximize the collection. Likewise, if the hydrogen is heated during collection, thermal radiation will represent an energy loss, and hence also drag; so an effective scoop must collect and compress the hydrogen without significant heating.


talk about kick-butt imagery! spirals of heated gas careening towards a ship only to be fused and expelled in a jet plume? sweet.

anyway, i've written enough, and i hope it hasn't put anyone off. some of the the community here has proven to be very well read with regard to these kinds of science, so i thought it'd make a great topic for discussion: all things related to space exploration and colonization with reasonable extrapolations of current technology.

my biggest point of curiostiy was with respect to ramjets, so i'll take the kickoff: could the spiral motion of the inbound gas somehow be harnessed to artficially generate gravity by rotating the ship, instead of producing drag?

any volunteers?

final words: i hope no one minds my double-motive. i won't try to steer any dicussion, though if things quiet down i might pose more general questions to keep it going; i encourage anyone interested to pose your own!
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Reply #851 from GalCiv2 Forums Top
So this is wrong then or am I just not understanding it...


a little of both. that link you provided is a conspiracy theory website - not the most reliable. i think whoever wrote that quote misunderstood the point. that part that says "cannot claim any unlimited validity" really just means there's no way (we can imagine) to experimentally prove that constancy of the speed of light in all situations. basically it's just Einsteins way of saying, "yes, world, i made an assumption and all my theories rest on it; reject them or deal with it, i don't care."

"the speed of light is constant" <- think of it like this: there is never a situation in which you can observe light in one place to be going slower or faster than light in another place.

However with turned on a flashlight, the speed of the light would we the same, whether its measured by me (I'm moving remember) or by someone who is stationary. That's why its considered a constant.


bingo. there's a thought experiment that goes something like "if i were going at the speed of light and turned on a flashlight, would the light go twice the speed of light, or just accumulate at its source somehow?" it's a fallacious question in the first place, since anything capable of emitting light is incapable of travelling at light speed. that aside, the light would "bunch up" at the bulb's filament (if it were possible), and i'm guessing it might eventually reach a kind of 'critical mass' necessary to convert itself to electrons - but i don't have time to research that any further.

his is the part i disagree with. light may be traveling so fast that you can't see the difference but it is there.


you're of course free to disagree, but just to be clear you're disagreeing with every accepted model of physics.
Reply #852 from GalCiv2 Forums Top
but just to be clear you're disagreeing with every accepted model of physics.


you mean every accepted model of physics that changes every 10 to 20 years
Galactic Civilizations III
Reply #853 from GalCiv2 Forums Top
when you hear someone talking you hear them at a constant speed.


when you are in a plane moving twice the speed of sound and the man next to is talking. you hear him at the same constant speed.
Reply #854 from GalCiv2 Forums Top

So this is wrong then or am I just not understanding it...


a little of both. that link you provided is a conspiracy theory website - not the most reliable. i think whoever wrote that quote misunderstood the point. that part that says "cannot claim any unlimited validity" really just means there's no way (we can imagine) to experimentally prove that constancy of the speed of light in all situations. basically it's just Einsteins way of saying, "yes, world, i made an assumption and all my theories rest on it; reject them or deal with it, i don't care."

yeah I was in a hurry and looked just for some book quotes.. its funny how the weirdo websites come up first
Reply #855 from GalCiv2 Forums Top

when you hear someone talking you hear them at a constant speed.


when you are in a plane moving twice the speed of sound and the man next to is talking. you hear him at the same constant speed.


Basically, your example is based on the word IN. IN a plane.

Your both IN motion. Your both IN the same inertial system. The source of the speech and the receptor are moving at the same speed, plus you're IN an enclosed space, no interference from the unmoving air that would otherwise be between you. (Or rather, it would move at twice the speed of sound, from your perspective. Making conversation pretty much impossible, because the sound waves would be 'carried away' before they make it to your ear.)

You know the sound that formula 1 cars make when they drive by? That's because they're moving and you're not. They still emit sound at a constant speed, but you perceive it as much higher frequency (closing in on you) or much lower frequency (going away from you).

The source is moving, bunching the soundwaves closer together than they would normally be. Or stretching them. Also known as *drumroll* Doppler-Effect.
Reply #856 from GalCiv2 Forums Top
The source is moving, bunching the soundwaves closer together than they would normally be. Or stretching them. Also known as *drumroll* Doppler-Effect.



you have never heard of red shift effect. that is when a star is moving away from it shifts to the red spectrum. because the light waves are getting further apart.


Reply #857 from GalCiv2 Forums Top
Which is exactly what I said...

Speed of sound -> constant -> Doppler Effect.

Speed of light -> constant -> Red-Shift (or Blue-Shift).


(Constant in a given transporting medium, that is. Or vacuum in the case of light.)
Reply #858 from GalCiv2 Forums Top
Speed of sound -> constant -> Doppler Effect.

Speed of light -> constant -> Red-Shift (or Blue-Shift).


your constant is dependent on the environment.


see you keep saying that light can not be effected by gravity. but we know it can be effected by water.
Reply #859 from GalCiv2 Forums Top
Please read again what I said.

Constant in a given transporting medium


And please don't randomly switch subjects. You were saying (torch example) that you don't believe the SPEED of light to be a constant. You contradicted yourself by bringing forth the red-shift example (which in fact only supported my initial post).

That gravity alters the DIRECTION of light, or that water changes the REFRACTION of light has nothing to do at all with the SPEED of light.
Reply #860 from GalCiv2 Forums Top
You contradicted yourself by bringing forth the red-shift example


no i didnt


sound is not constant.


light also changes speed in space. but this wouldn't do away the red shift just modify it.
Reply #861 from GalCiv2 Forums Top
The speed of light when it passes through a transparent or translucent material medium, like glass or air, is slower than its speed in a vacuum. The ratio of c to the observed phase velocity is called the refractive index of the medium. General relativity explains how a gravitational potential can affect the apparent speed of distant light in a vacuum, but locally light in a vacuum always passes an observer at a rate of c.


but space is not a vacuum. and intersteller space is full
Reply #862 from GalCiv2 Forums Top
sound is not constant.


In a given medium, it is.
More to the point, you brought in the airplane example stating sound is constant. Please, make up your mind.


light also changes speed in space.


Where?

And we are not talking about changing the transmitting medium.

We are not talking about light being 'slowed down'. We are (Remember our torch?) talking about light exceeding the speed of light. Which it can't.

Reply #863 from GalCiv2 Forums Top
ok here is a question for you


if nothing can travel faster than the speed of light.


then how come just after the big bang the universe started expanding faster than the speed of light.

source science channel this weekend i believe the show was, how it all began.
Reply #864 from GalCiv2 Forums Top
pndrev, don't get overly worked up on the subject. i've explained twice that the speed of light in a vacuum is constant and equal to c, and that the only reason light travels more slowly through media is due to quantum absorption and re-emission, which isn't a change in speed, but a change in state (in other words, in the nanometric spaces between molecules, photons absoluteley do travel at speed c, and they momentarily cease to exist as photons when they colide when electron clouds, resulting in a lower net propogation speed).

the significance of this seems lost on some: in either regard, the fact that light travels more slowly through media absolutely does not refute relativity, since relativity is based on the speed of light in a vacuum.

quote:
The light does not actually travel more slowly when in material. The light
travels from atom to atom. An atom absorbs the light for a short time and
then releases it. These short delays are what cause the apparent slowing.
When a lens is viewed as billions of atoms, light travels at the speed of
light as it moves from atom to atom. When viewed as one lens, the light
seems to just move at a slower speed.


source: Ask A Scientist physics archive


then how come just after the big bang the universe started expanding faster than the speed of light.


this is a mis-quote/misunderstanding. spacetime expanded faster than light speed; that doesn't mean anything in spacetime went faster than light.
Reply #865 from GalCiv2 Forums Top

pndrev, don't get overly worked up on the subject. i've explained twice that the speed of light in a vacuum is constant and equal to c, [...]


Don't worry, it takes more to get me worked up. Mostly I was bored, so I thought I'd have a go as well. I'm just a bit irritated about the constant switching of subjects mid-argument...
Reply #866 from GalCiv2 Forums Top
i have an argument now against light not slowing down between atoms.


if i am running down a street at 5 miles an hour no matter what gets in my way. and ever 5 feet i enter water up to my knees. i am still running at 5 miles an hour when i leave the water. am i not slowing down because of the interaction between me and the water.


you stated that light keeps moving at c but when it encounters an atom it appears to slow down.

in the above example i would appear to be slowing down because i am. it doesn't matter that the light is be refracted or reflected it is still slowing down to the observer.
Reply #868 from GalCiv2 Forums Top
this is a mis-quote/misunderstanding. spacetime expanded faster than light speed; that doesn't mean anything in spacetime went faster than light.



also at this point in time there wasn't anything in it.
Reply #869 from GalCiv2 Forums Top
ok here is a question for you

if nothing can travel faster than the speed of light.

then how come just after the big bang the universe started expanding faster than the speed of light.

source science channel this weekend i believe the show was, how it all began.


I shouldn't jump into this right at the end, but it's a huge thread, and I'll read the rest later. Answering this specific question (or at least pointing the way to more info):

The current standard model of cosmology includes something called "inflation" which occurred shortly after the big bang. There is no conflict with speed of light, because speed of light is referenced to a static frame of space, and space itself massively exploded and stretched during inflation.

That's a hard concept to get your head around, but it's also the reason why on the outer fringes of the expanding universe (what we can see of it, at least), objects can be red-shifted into invisibility because space itself is expanding. It's all about local reference frames. On the local reference frame, our galaxy will eventually collide with the Andromeda Galaxy, because on the local frame, gravity is the dominant force. On larger scales, expansion of space is the dominant force driving everything apart.

Yeah, it's weird, but the natural world isn't obligated to be easily understood by human brains, and I'm constantly amazed that we've gotten this far, as a species, in figuring some of this out. Here's more info on inflation, for anyone interested:

http://en.wikipedia.org/wiki/Cosmic_inflation
Reply #870 from GalCiv2 Forums Top
Light is affected by gravity, I don't know where you got that, it's not from any where I know.
Reply #871 from GalCiv2 Forums Top
Abstract. Standard experimental techniques exist to determine the propagation speed of forces. When we apply these techniques to gravity, they all yield propagation speeds too great to measure, substantially faster than lightspeed. This is because gravity, in contrast to light, has no detectable aberration or propagation delay for its action, even for cases (such as binary pulsars) where sources of gravity accelerate significantly during the light time from source to target. By contrast, the finite propagation speed of light causes radiation pressure forces to have a non-radial component causing orbits to decay (the “Poynting-Robertson effect”); but gravity has no counterpart force proportional to to first order. General relativity (GR) explains these features by suggesting that gravitation (unlike electromagnetic forces) is a pure geometric effect of curved space-time, not a force of nature that propagates. Gravitational radiation, which surely does propagate at lightspeed but is a fifth order effect in , is too small to play a role in explaining this difference in behavior between gravity and ordinary forces of nature. Problems with the causality principle also exist for GR in this connection, such as explaining how the external fields between binary black holes manage to continually update without benefit of communication with the masses hidden behind event horizons. These causality problems would be solved without any change to the mathematical formalism of GR, but only to its interpretation, if gravity is once again taken to be a propagating force of nature in flat space-time with the propagation speed indicated by observational evidence and experiments: not less than 2x1010 c. Such a change of perspective requires no change in the assumed character of gravitational radiation or its lightspeed propagation. Although faster-than-light force propagation speeds do violate Einstein special relativity (SR), they are in accord with Lorentzian relativity, which has never been experimentally distinguished from SR—at least, not in favor of SR. Indeed, far from upsetting much of current physics, the main changes induced by this new perspective are beneficial to areas where physics has been struggling, such as explaining experimental evidence for non-locality in quantum physics, the dark matter issue in cosmology, and the possible unification of forces. Recognition of a faster-than-lightspeed propagation of gravity, as indicated by all existing experimental evidence, may be the key to taking conventional physics to the next plateau.



this is still about nothing being faster than light.

WWW Link
Reply #872 from GalCiv2 Forums Top
i hope you guys understand the math on that link it is above me.
Reply #873 from GalCiv2 Forums Top
2x1010 c


Did you mean 2020 c, or 2^1010 c, a number with an absurd amount of digits?

Reply #874 from GalCiv2 Forums Top
Did you mean 2020 c, or 2^1010 c, a number with an absurd amount of digits?



i didn't write the article. i found it. the person who wrote it was a physicist i think
Reply #875 from GalCiv2 Forums Top
I don't make assumptions. Don't be fooled by my age. I'm well read.   
Btw, dystopic, Stephen Hawkings was from where I made my "assumptions".