It is theoretically impossible to accelerate matter to the speed of light (and therefore impossible to accelerate to a speed faster than light) in normal space. As Christine mentioned, time slows as one approaches the speed of light. And the curve on which it slows is asymptotic (in other words, as you get closer to lightspeed, the factor by which time is slowed increases exponentially.) And the mass of any matter being accelerated also increases along a similar curve.

For any sort of drive on board the ship, the slowing of time is the limiting factor. From your point of view, your acceleration would be constant, but from the point of view of the rest of the universe, your acceleration would decrease. Outside observers would never see you reach lightspeed, even though you've been traveling for billions of years, trillions of years, and any number beyond that.

From your point of view, you are a fraction of a second from reaching the speed of light. You never are aware that the whole universe has passed away around you, and that you never actually finish that final fraction of a second.

For an acceleration force being applied from outside the ship's relativistic frame of reference, mass is the limiting factor. As the ship gets closer to the speed of light, its mass gets larger, which means it requires more energy to maintain the same acceleration. As the ship approaches the speed of light, its mass approaches infinity, and the energy needed to accelerate it also approaches infinity.

1. Warp drive
2. Wormhole
3. Hyperspace

Warp drive involves altering the local spacetime continuum so that the ship does not travel faster than the sped of light locally, even if it appears to do so to an outside observer. Despite the fact that it sounds like it came out of Star Trek, this form of travel is theoretically possible, but involves manipulating exotic forms of matter and energy.

Wormhole travel would involve creating or finding a wormhole, expanding its entrance using exotic matter and energy, and probably moving one end of the wormhole to a desired location (which could take a very long time, as it would have to be done at sub-light speed.) Once it was set up, travel through the wormhole would be very quick no matter what the distance. Again, this is theoretically possible, but requires manipulation of exotic matter and energy.

Hyperspace travel involves leaving our normal universe, either to a parallel universe where the laws of physics are different, or to additional dimensions of our universe. After traveling in hyperspace for a while, the ship re-enters normal space near is destination. I don't know what current theory has to say about this possibility, but if it's theoretically possible, it probably involves manipulating exotic matter and energy.

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Catherine Asaro's faster-than-light (FTL) space drive really works -- at least on paper.

The physicist and science fiction writer has based the "inversion engine" of her Skolian Empire space opera series on her own thought experiments about new forms of space travel.

Besides using it to get her characters from place to place, she first wrote about the mathematics of the FTL drive in an April 1996 paper in The American Journal of Physics.

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For full article see http://www.space.com/sciencefiction/books/asaro_000204.html

Also, it would take materials that haven't been invented yet to withstand the heat and pressure. The person inside the vessel may just crystalize with that kind of force.

The space shuttle is barely able to withstand re-entry, and FTL travel would be alot faster than that. It doesn't take a rocket surgeon to figure that out.

Of course, mathmatically this has some of the same implications as the 'imaginary velocity" Asaro is using, though in this case it is the mass/energy of the ship that becomes more or less 'imaginary'

The shrinking effect means that you can also use naturally occuring wormholes which have become associated with the event horizons of small singularities (you do still need a stasis field, but since I'm already shrinking ships and putting them inside of tiny particles with imaginary mass) as transit points to travel intersteller distances (it isn't safe to go interstellar distances entachyated, since if you hit something that collapses the particle...well, it is bad--and this limits the safe speed of travel).

So in some sense, I'm using all three ideas, plus some complex number geometry. I used to play with an idea that was more hyperspacy, now I've got a mechanism that's a bit more warp speedy combined with wormholes...sometimes (when intership combat isn't involved) the mechanism is pretty much just wormholes.

I would tend to class Asaro's drive as a folded space type because it relies on higher dimension spatial manipulation (though these are implied rather than literal higher dimensions--as though that makes a difference ). Folded space types can be thought of as either hyper-space or warp-space models, depending.

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It doesn't take a rocket surgeon to figure that out.

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Survivor, Is your theory comparable to a "Portable Hole" in Fantasy (D&D) terms. Man, I love those magic items!

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Also, it would take materials that haven't been invented yet to withstand the heat and pressure. The person inside the vessel may just crystalize with that kind of force.

The space shuttle is barely able to withstand re-entry, and FTL travel would be alot faster than that.

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As for pressure, I suppose you mean the force on the body due to high acceleration. As already mentioned, it's impossible to accelerate to the speed of light, so FTL travel would make use of other methods to have the apparent effect of exceeding the speed of light. Wormhole travel, for example, is like taking a shortcut through the universe, so it would probably not require high velocities.

However, travel through hyperspace or through warped space might still require acceleration to a high fraction of the speed of light.

With a constant acceleration of one gravity (the same amount of force you feel pulling you to earth right now), you could accelerate to any fraction of lightspeed in less than a year of subjective time. (Due to relativistic effects, it could take more than a year from the point of view of an outside observer.

However, a year of speeding up and a year of slowing down at the other end doesn't make for nice, efficient interstellar travel for story-telling purposes.

And if it hit anything, that was fine. It just stopped.

OK, so I can see the theoretical problems with this kind of drive, but hey, it _was_ funny.

Alas, after running into relativity a zillion times in my reading, something clicked inside my head and I finally understood why nothing can acellerate faster than light. It's nothing I can put into words quickly and easily, and certainly I'd be no better than Carl Sagan or Stephen Hawkings in attempting to describe it. Still, it's pretty obvious to me now that we don't live in the same universe where "Star Trek" takes place.

For a long time, I tried to adjust my writing accordingly--writing only SF tales set within the solar system, which is probably as far as mankind has any real hope of going for the next 10,000 years or so. Eventually, I think interstellar travel is possible, but only after the human life span has been stretched to virtual immortality (a possibility that seems more likely than finding a loophole in the speed of light). One day a thousand year trip among the stars will me no more of an investment of time as a percentage of life than the long journeys sailors used to make to come to America.

Fortunately, as I've grown older I've found myself more open to fairy tales. I'm finally able to believe seven impossible things before breakfast. Now I don't mind including FTL drives in my stories, and when I stick them in they are explained only with the silliest SF gobbledegook. Fortunately for most SF writers, SF readers want to make the leap of faith and believe in FTL drive, and will probably go along with it, even if you have only the flimsiest explanation. And sometimes these flimsy explanations are the best part of the story. Cordwainer Smith's "Game of Rat and Dragon" has a terrific line about ships travelling _under_ space, and finding strange beasties there. The human mind percieves theses beasts as dragons, and die from terror, but cats aboard ship see the beasts as rats, and kill them. It's an utterly bizarre premise to build a story on, but it worked, at least for me.

I don't have the exact quote, but I know that OSC once said that most Science Fiction is really only fantasy that uses "science" as magic.

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Still, it's pretty obvious to me now that we don't live in the same universe where "Star Trek" takes place.

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Fortunately, as I've grown older I've found myself more open to fairy tales. I'm finally able to believe seven impossible things before breakfast. Now I don't mind including FTL drives in my stories, and when I stick them in they are explained only with the silliest SF gobbledegook.

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Sorry James, this isn’t meant to be a troll or an attack, but with respect to science if you can’t explain something, and explain it well and to an interested layman, then you really don’t understand it. (I guess I should come clean and say that I am not actually a writer at this point but rather a scientist who wants to learn to write. This also means that on this point I am biased as hell. )

Any way the thing to remember about all our models of the physical universe is that they are just that; models. These models all rest on the long, long, list of initial conditions and assumptions that we consider to be “reality” or “physical laws”.
When we use math it is just a system of conventions and tools we bent to fit our model of the universe so that we can manipulate it symbolically. You are making a common mistake. You appear to be confusing the validity of the mathematics behind relativity, and its wonderful fit to the macro universe, to mean to mean that the theory of relativity is in fact inviolate. That is both the beauty and the ugly little secret of science; nothing is inviolate.

As we use our observations to continually refine our models our assumptions about the universe and the nature of reality also change and in some cases old heresy becomes the new reality. Our model for that same physical universe is actually pretty poor when you start talking about applying energy on the scale found only in unstable atomic reactions.

If for example I creatively dump a tera-joule into a volume of say a cubic micro meter, or apply a couple of tera-eV across the same space. Are you so sure you could tell me what would happen to matter passing through that region of space-time? We already know that aspects of relativity break down. Better yet lets say I found a way to convert energy directly into angular momentum? In that case relativity goes the way of Kepler’s approximations; gorgeous but suddenly an echo simplifying reality for the humble minds of man rather then defining it.

You little monkeys are staying right here till the bitter end, and I mean bitter. And end...don't forget that part

Relativity isn't that hard to understand...I think that most people just get told they can't understand it so often they start to believe it and don't bother trying.

Simply and easily, take a system where light signels are emitted from a device at the middle of your ship, and those signals bounce off mirrors at the prow and stern (or whatever you want to call the front and back of your ship), reflect back to a detector at the middle (right below the emitter, say).

As you speed up the ship to a relativistic velocity, the round trip for light bouncing off either mirror gets longer and longer...eventually, when you reach lightspeed, the round trip takes forever. The speed of light in your FOR has reached zero.

But the speed of light is the speed of electro-magnetic propagation...and all our physical processes depend on electro-magnetic forces. Freeze those, and everything else freezes too. Or if you like, think of the lamp and mirrors being replaced by a vibrating cesium atom (or whatever kind of atom). The electrical forces that allow it to vibrate at a given frequency slow down and eventually stop as it gets closer to lightspeed. Theoretically all atoms do this, we've only bothered to check with atoms embedded in the middle of an atomic clock so far.

If you do the math behind this, it turns out that the ship also gets shorter, and looking at it from the side it appears rotated, and fatter, and all kinds of strange stuff. But the basic concept is simple and doesn't require a lot of mathyness.

We currently have a few experiments in the works to verify that the other forces have the same speed as the EM force...observations tend to fit this idea so far, but it doesn't hurt to double check.

The thing is, this applies to a highly specific method of traveling through space (taken here as meaning space-time). The simple fact that this is the method with which we have the most practical experience doesn't change the fact that there are other means of 'travel' through space...some of which are unaffected by the theory of relativity (some of which we only know about because we see things travelling faster than light...which they can't be doing in the 'normal' way under relativity).

So, here's a new and related question. If I go to FairyTale land where I've got an FTL ship, would anyone like to make a guess on how long the subjective time of a 200-light year journey would be to the people on board the ship?

If you were dealing with relativity, then you'd need to know what percent of lightspeed you were going at to figure this out.

However, with FTL relativity doesn't apply. So you can pretty much make up whatever subjective elapsed time you want, and no one can argue with you. (My daughter adds: "At least not if you don't explain how it works.") You could even have the subjective time take longer than the actual time, e.g., the ship makes the 200 light-year trip in 2 years, but when it gets there, all the people on board are 10 years older than when they left.

Sincerely,
Mr. Fisher

But the warp drive brought up is really interesting. The "first working model" I guess you could say, was given by Miguel Alcubierre. THIS website can explain it much better, but the jist of it is that by contracting spacetime ahead of the vehicle, and expanding the spacetime behind the vehicle, the ship starts to ride the "wave" in a "bubble," where the ship would achieve FTL travel. I wonder what would happen if you put an engine on that ship though... acceleration inside the bubble? What would happen?

Einstein used a lot of constants in his equations that were based on givens (very strong guesses.) Ultimately he demonstrated mathematically that mass increases to infinity as velocity approaches the speed of light.

Mass seems to be constant under all conditions until you reach relativistic speeds, then it starts gaining a phantom multiplier that quickly slams on the brakes. I don't know how this could actually be tested, so I find it dubious.

Here's a link to confuse the issue further:
http://www.newton.dep.anl.gov/askasci/phy99/phy99186.htm

Personally, I believe we'll overcome the problem someday by finding there's just an error in one of our suppositions or discovering some unknown factor. (This is where Survivor steps in and corrects me. Please do.)

Any time you accelerate a mass, you're adding energy to it. Add enough energy, and you start to noticibly increase the mass. When you're accelerating something up to lightspeed, you eventually get to the point where all the energy you add is needed just to get the energy you're adding up to near lightspeed, there isn't much left over for accelerating the thing you're accelerating. And at lightspeed, there is nothing left over, all the energy you add is being used to accelerated it's own mass up to lightspeed.

But as has already been mentioned, there are a lot of unknown factors. Relativity only prohibits a system composed of mass/energy contained in unification force bonds from propogating faster than the rate of propogation of unification forces. Stated this way, we can see that there are a number of ways around this difficulty. But as EJS said before, all of them are, pretty much by definition, somewhat exotic.

Alfred Bester in 'The Stars My Destination' outlined his idea of capability to move via willpower alone. The theoretical basis if I recall is develping the ability to visualize the desired place and one's self in it. Castaneda proposed the same in his Don Juan books. Both of these are arguably SciFi rather than fantasy.

Edgar Rice Burroughs discussed out of body travel in his Mars books. These are much closer to fantasy though I find it interesting that Stanislav Grof has accumulated some experimental evidence for its commonality even though I would argue with its validity.

Too great a tangent, or no greater than the concept of planoforming or warp drive?

Even further afield is wondering what would happen if we tapped the side of a cryocontainer of Bose condensate (with its light speed slowed to about 70 mile per hour) and sent a shock wave through it. Would the shock wave exceed the local speed of light in a normal manner or would it travel in a quantum manner?

[This message has been edited by keldon02 (edited March 06, 2005).]

A beam of energy is sent to a location in distant space. This beam contains a timed decay function which allows it to cease travel at a specific point and disperse over an area, affecting local quanta in such a way as to entangle a small batch of particles with a batch back on Earth. (This is the most theoretical point I think.)

With the entanglement achieved the batch on Earth is manipulated to create a series of nano-bots. Due to the entanglement identical nano-bots are created at the distant location. The bots are also programmed in this manner.

The nano-bots get to work on local matter (possibly having been sent to a cloud or giant where materials would be plentiful compared to open space) to multiply themselves into a number suited to work on larger projects.

At this point the bot-swarm can be programmed by use of the original entangled bots, and can get to work on just about anything including ships, colonies, or even organic matter.

Because entanglement more or less skips over the whole light speed limit, and a large enough swarm of nano-bots could build anything in a remarkably short span of time since they would be building it from the atoms up. Things, and even people, could be sent anywhere that could be reached by the initial energy beam. A system of relays built in this way could allow total population of the universe regardless of distance.

Now this is clearly all just theory and as I said, I am not a scientist. But nothing I’ve read and no one I’ve spoken to is able to disprove the possibility of it given current understanding. One of the first books I read on writing science fiction was titled Space Travel, edited by Ben Bova. It advises that a writer tries to stay as close as possible to the truth, but that it’s okay to be far fetched as long as no one can actually disprove you.

I would cite sources, but frankly it comes from so many bits and pieces of stuff I've read and heard over the years that I wouldn't know where to start.

The problem with relativity is that space travel would resemble a tangent line. As your speed increases time slows. The problem with traveling the speed of light is that the math specifies that the speed of light is an infinite number that is never obtainable. However...what happens if you plot a 1.1 on a tangent curve? You get a legitimate number. So, just because our current knowlege of space is relying on decades old concepts, why would FTL travel be impossible. I bet 5 years ago the concept of stopping and starting light was concidered impossible as well. Now that it has been done, I guess the impossible is only impossible while people believe it cannot happen.

As for exotic materials, what makes them exotic? Becuase they are not common in everyones life? Bah! We are only limited by what we choose to be limited by. I'm still hoping that before I die I'll have a car that runs on some form of fusion power that never has to be replaced.

"You can't travel faster than the speed of sound."

"You can't run a mile in under 4 minutes."

"You can't travel faster than the speed of light."

Can someone explain to me why you can't travel faster than the speed of light? Please don't tell that the human body can't stand it. That's what people said about the 4 minute mile and the speed of sound.

Rux, please read at least the first post in a thread before replying. That can help you avoid totally irrelevant comments.