A way to go Faster than Light???

YO-Blah,

Under my understanding of the Theory of Relativity, as the speed of a body (ie a starship) approaches C (the speed of light) the energy required to accelerate it any more approaches infinity. Also the mass of the starship approaches infinity. If this is the case, wouldn’t the starship create its own Gravity Well??? (Mass is related to Gravity, right??) If that is the case, is the reason the energy required to accelerate it any more increases because of its own personally created gravity well? (SOMEWHAT similar to the pressure of air in front of a sonic plane increases, ie the Sonic Barrier–except of course that its the curve of space thats being effected…)

If THAT is the case, then wouldn’t antigravity or some other way to deflect the personal gravity well (for example, the ‘Exotic Matter’ of the Worm Hole Theorists) make FTL travel possible (ignoring, of course, the Hawking Time-Causality Protection Law…)???

I am a SciFi Writer hobbyist, and I try to use the most current Theoretical Physics Ideology as accuratly as possible…PLEASE HELP ME…

Right now the FA\TL (Fast As Light/Faster Than Light) ships in my story can travel instantaniously to anywhere in the Known Unniverse (IE for every 1 LightYear they travel they’re ‘allowed’ to travel 1 year back in time…ie INSTANT TRAVEL), but if the starships’ NavComps plot a course that will have them arrive even a NanoSecond ahead of the time they left (IE ANY amount of time before they left), the ship will Mysteriously Disappear…Perhaps they move into a different, parallel Heisenburgh Time-Stream, or just wink out of existense, it’s Unkown…One other thing, I know the Theory Of Relativity obolishes any type of Unniversal time…Im DESPERATLY trying to fit that into the model of my unniverse…

HELP ME PLEASE!!!

-Blah

+“Everything that has happened, Is Happening, Or Will Happen has ALREADY HAPPENED…there is NO WAY to change it…” – me with strong influences of S. Hawking, David Deutcsh, and Machio Kaku…

Unfortunately, your starship would also shrink to zero size and time would stop. Also, remember that in their frame of reference their mass is still the same, so an anti-gravity engine in the ships frame would have nothing to do.

My relativity class was a long time ago, so I suspect that there are even better arguments why this doesn’t work.

Why don’t you just use another universe in the manifold where the speed of light is higer. That’s what I’m doing in my book, and I have superficially plausible arguments why causality is not violated.

Nope. The gravity well is just a byproduct. The faster you go, the greater your mass becomes, and the greater your mass is, the more energy is required to accelerate.

Well, the higher the body’s mass becomes, the more anti-gravity you’d have to exert. Theoretically, this anti-gravity would require energy. So you still need to ultimately spend an infinite amount of energy to get your body up to the speed of light.

However, since the real problem is mass and not gravity (although the two are directly connected), what you’d REALLY want to do is devise some sort of mass-lightening system. Star Trek already does this… for ST ships to get up to warp (and even to use their STL impulse engines), they shunt some good chunks of the ship’s mass into subspace, where the laws of physics aren’t as limited.

How about an Alcubierre Drive (do a Google on Miguel Alcubierre)?

You basically create a spacetime curvature that destroys space on one side and expands it on the other. Of course, this would take humongous (scientific term ;)) amounts of energy, not to mention some exotic matter with a negative energy density in order to eat up space in the first place.

Several things of note. Mass does not increase as you go faster in any meaningful way. There are interpretations of special relativity that say that it does, but they’re generally considered not to be a terribly useful interpretation. Mass means rest mass in modern day physics.

Note: Special relativity. In other words, completely unrelated to gravity.

As to trying to fit relativity into this scheme? It can’t happen:

Relativity
Faster than light travel
No time travel

Pick two, and only two. If you have two of them then you neccesarily can’t have the third.

What I reccomend? Don’t bother trying. Say “relativity is wrong” and don’t try to explain it. You’ll end up confusing and/or irritating your readers, without adding much to the story. And, umm. no offence intended but if your post is typical of your science I reccomend doing that for anything that involves scientific knowledge. Understand physics, or gloss over it. Don’t try to explain things without understanding at least the basics of modern physics.

Oh, and this shouldn’t be in GD.

Aren’t there subatomic particles, like positrons that have been experimentally observed traveling faster than light speed, and going back in time? How does this fit in with theoretical FTL travel?

Gene Wolfe, former ChemE and sci-fi author extraordinaire presented an intruiging FTL travel system based on perfect mirrors and the propagation of light, in <i>Shadow and Claw</i>.
How feasible is this? I’ve only begun my exploration of Wolfe’s works, but so far I’m quite impressed with his knowledge of science and his skills in literary narrative.

It used to be said that Nature abhors a vacuum. I think nowadays it can be said that Nature abhors anything that would make faster than light travel possible. :wink:

Read up a bit on Relativity. One of the strange facts of relativity is that there is no absolute time frame, just as there is no absolute rest velocity. Two events which seem simultaneous to an observer in one framework may seem nonsimultaneous to an observer in another framework - and there is no way of choosing one preferred framework over the other. So if a ship seems to have “instantaneously” moved from spot A to spot B, there exists an framework from which the ship will appear before it disappears. Basically, under relativity, travel faster than the speed of light is mathematically equivalent to travelling back in time.

Short answer: No.

Slightly longer answer: No. There are certain models of physics where it is useful to think of a positron as an electron temporarily moving backwards in time. When it ‘changes direction’ in time you are either having an anti-particle pair being created or destroyed. It is not possible to use this to send information back in time, nor is it possible to use this to send objects back in time (ref: uncertainty principle).

Umm. Without knowing more about the proposed system, I can’t destroy it in detail. However the first thing that comes to mind is that perfect mirrors are physically impossible (unless you can come up with some magical forcefield to do it). The second is that I can’t even begin to think of a mechanism within modern physics that even suggests a shred of plausibility to that. However, my knowledge of physics is admittedly far less than complete. I could be wrong. I suspect I’m not 'though.

Yo,

kitarak: Thank you for the usual scathing Straight Dope Forums Welcome. (and theres no sarcsm in that remark, I really do thank you for showing me the error of my ways…) (and theres no sarcasm in that remark either) Also, if I know anything about the Straight Dope forums, almost everything will turn into a GD. Especially since I intend to argue what I dont agree with…Umm I said Relativity, not Special Relativity…I already came up with that ‘Einstein was Wrong’ thing, but it seems too contrived…As for talking about my understanding of science…TRUE I read Einsteins books on Special Relativity and General Relativity many, many years ago, way back in 7th grade (wow…has it already been at least 10 years??? WOW) and I dont remember very much of them and TRUE I really only have an understanding of those theories from TLC and The Discovery Channel, but you could have been a little more…diplomatic… about how you said it…Umm, one more thing, please tell me how my science is wrong, and please give me your interpretations of the Relativity Theories…t/y…Finally, since my first post ive read ‘A Brief History of Time’ and ‘Black Holes and Baby Universes’ by S. Hawking and im 1/2 way through ‘Hyperspace’ by Michio Kaku (I respect him much more than the Hawk King) so my science is a little more improved…

Voyager: I think the other universe idea is a great idea except 1. Its been done before, and 2. Thats not much better than taking a shortcut through ‘Hyperspace’ (which has been done OVER AND OVER again). I read somewhere a story that used the alt unniverse idea, and it was very good, it may have been yours. Do you post to the Critters Workshop? I used to be a part of that, maybe thats where I read it. My ship wil shrink to 0 relative a stationary viewer, as well as the mass wont increase according to the people on the ship…hmmm…good point…thinking…still thinking…ill have to think about this more…

BlahMan: WTF were you thinking??? The mass relative a ‘stationary’ observer would increase, as well as relative time slowing down. AGrav would not help much, if at all, b/c the mass is only relative to a ‘stationary’ observer. What may help is the Star Trek ‘Enertial Dampers’ (which pretty much shunts away the ships mass and in my mind has something to do with antigrav…). Too bad thats been done many times before…You need to come up with a unique way of FTL space travel. Good luck. The HyperSpace, Wormhole and Warp ideas have been used to pieces…The alternate unniverse idea is good, but still not unique…Like I said, GOOD LUCK!!!
Speaking of which: Even if a ship could travel somewhere instantly you still have to figure in the Relativistic movements of the stars around the Galaxy, ie if you go instantly to another star system that is moving relative to the former one at near C(speed o light) speeds, time would travel differently there. ie one moving away from the sol system at close to C, time would be moving much slower…this raises alot of fun literary situations :slight_smile: (What!!! You’re back already? You just left yesterday! Wow you look older…[sic])

Does anyone know the ‘Whys’ of Relativity? From what I remember Einstein said something about rulers shrinking, but why? No matter how fast you go, you’ll still see light speeding ahead of you (but at different frequencies…) therefore your ‘ruler’ would shrink…hmmm…

-Blah

I believe that’s called the Picard Maneuver :wink:

Also it would not have a problem w/ it’s own gravity because the well would move with the ship.

Additionally the ship would alwasy be moving at 0 speed relative to the ship and wouldnot have the increased mass but that dust partical that is moving at several times the speed of light would.

LOL, the Picard Maneuver aside…

I tend to hear people speculate about FTL travel as if there’s something we just “haven’t learned yet” that will enable it. To me, this sounds like wishful thinking. All the theories that people propose would, even if they worked, require so much energy as to be impracticable. There’s no new technology we’ll ever learn that will alter the hard cap on how much energy can be harvested from a certain amount of physical mass, and there’s certainly not enough mass in the depths of space to just refuel as you go.

You wanna travel to other solar systems, let the science-fiction writers take you there in your mind. You wanna go there physically, you’re outta luck. You could build a colony ship and accept the fact that you’ll probably have to go about .02c the whole way, and maybe you’re descendants would live to reach a local star. There wouldn’t be any planets or aliens in it, just a star, but if that’s what floats your boat…

So anyway, these speculations might be theoretically interesting, but don’t offer much in the way of practical realizations.

Yes there is - and it is exactly ftl that will allow this. One of the biggest problem with space travel is the fastest we can throw fuel out the back of our ship is the SOL which limites our thrust. If we can throw fuel at a multiple of c then our fuel requirments would go down.

You’re right, I could have been a little more diplomatic about that. I apologise for that. I tend to be overly critical of bad science due to some experience (not here on the SDMB) arguing about it with people who wouldn’t know a clue if I came over to them and repeatedly beat them around the head with it. I know this from experimental verification. :slight_smile: I’ll try not to let it happen again. FTR, this isn’t a typical SDMB welcome. They’re usually nicer than I am.

I’m sorry that you had to suffer through a brief history of time. Did it hurt much? Hawking’s writing style is truly painful. He’s a great physicist, but I wish he’d stick to writing technical papers…

Ok, where your physics is wrong. First of all, there’s the whole issue of increased gravity/mass/whatever, but that’s been dealt with. The second problem is the idea of accelerating to the speed of light (or past it) simply doesn’t work. There’s a fundamental difference between travelling at the speed of light and travelling arbitrarily close to it - In the second there is an inertial frame in which you are at rest, in the first there isn’t. No massive object can travel at the speed of light as it would have infinite energy (as you said), but of course this is intrinsic to the mass and has nothing to do with gravity (as it’s part of special relativity, which says nothing about gravity). If you were to somehow decrease the mass to 0 you still wouldn’t get a smooth acceleration up to the speed of light - At one moment it would be moving at less than the speed of light, then it’s speed would ‘jump’ and it would be travelling at light-speed.

Incidentally, massless objects do not travel faster than light. They will always travel at exactly the speed of light - no more, no less. This is because at any speed other than c they will have no momentum or energy.

I know you were talking about relativity in general (which isn’t the same as general relativity), but that means that it must take into account special relativity. And to an observer sufficiently far removed from the point the ship leaves from and arrives at special relativity will apply to a very good approximation. This means that, by fiddling the observers relative velocity, you can get the ship to seem to appear before it departs (after the time delay for light propagation is taken into account). There is no way to get around this and retain relativity.

I won’t go into my interpretation of SR, as it’s rather abstract and mathematical. At the moment I’m more of a mathematician than a physicist. It involve isometry groups of minkowski space-times. I have yet to fully get my head around GR, so I don’t have an interpretation of that to give you.

Incidentally, you don’t have to come up with a new way of faster than light travel. Technology does not define a story - the people in the story do that. The science and technology is secondary, otherwise we’d be reading technical manuals.

And yes, there are very good reasons for relativity. SR follows from the principle of relativity - the laws of physics are the same in all inertial frames - and that the speed of light is the same in all inertial frames.

An alternate way of looking at it is that by making some basic assumptions about the transformation between co-ordinate systems you can show that the only possibilities are the lorentz and the gallilean transformations. I forget exactly what the assumptions are, but most of them are rather basic. Things like the transformations being linear, that they depend continuously on your velocity, if a reference frame S’ has a positive velocity with respect to S then S has a negative velocity with respect to S’, etc. All rather basic stuff. You then check that the galilean transformations don’t work, so the lorentz ones must be the correct transformation laws. Then observe that the speed of light is constant in all frames, et voila. That way requires a lot of maths 'though.

k2dave: I think the idea of the picard maneuver was that you outrun the light from your ship rather than to do with relativity of simultaneity. That would have been far too scientific for star trek. :slight_smile:

k2dave: No, that’s wrong. The maximum amount of energy you can get from mass is m c^2. There is no way around that, any attempt to do so contradicts conservation of energy. Whether or not you can get a higher momentum transfer with FTL exhaust velocity is another question, but the energy still has to come from somewhere.

Good point kitarak

IAMAP but, uh, how about dropping it on a lot of antimatter?

kitarak:

Thank you for the description of Relativity, it was a breath of fresh air, especially after reading the S.Hawking books. One thing I hate about his books is that he usually doesnt go into the whys very much, except very generally, and if you paraphrase the whys it usually comes out like ‘Im Stephen Hawking and thats the way I say it is’. Ive also caught him in a couple of mistakes, for example he said electricity can be turned into heat, but heat cannot be turned into electricity. I know of 2 ways to turn heat into electricity, directly by using thermocouples, or indirectly using steam turbines.

Please go see my other thread: http://boards.straightdope.com/sdmb/showthread.php?s=&threadid=131293
I wrote something there disagreeing with hawking radiation and the Heisenburgh uncertainty principle. Check out my physics please and add your comments. One more thing, how did you come up with your name?
Here’s another idea for a STL drive, it should be pretty efficient and ‘cheap’. I call it a ‘caterpillar’ drive after the Hunt For the Red October (the movie) drive.

You have a very long and thinish ship. Along the entire center of the ship is a huge, powerfull and efficient particle accelerator. In the front is a huge, powerfull and efficient fusion reactor. Toward the back is all the crew quarters, bridge, living areas, etc. Along the rest of the ship, outside of the Accelerator is thousands of Hydrogen storage tanks. Waste Helium from the reactor is accelerated down the length of the ship to near C speeds. As the relative velocity of the He to the ship approaches C its mass approaches infinity. When that happens, the Particle Accelerator pushing against the mass of the He should be great enough to accelerate the ship to near C speeds, cheaply. Not only that, but since the mass of the near C He is so great it shouldn’t take very many He molecules at a time for powerful thrust. At the end of the ship the He would be pushed out the back for a little more thrust. Plus the particle accelerator could also be used as a formidable weapon by using ions or protons, neutrons, etc and accelerating them out the front or back of the ship. (That would also add some cool plot elements, near C space battles, the slower ship has a faster ticking ‘clock’ so it has an advantage, plus any weapon beams shot would be bent, although im sure not by much) Also by cranking up the power of the fusion reacter and ‘burning’ waste helium, other heavier elements could be synthesised such as Iron, lithium and Uranium which can than be captured and used for repairs, etc. Or do you think a hybrid Hydrogen/Helium reactor be more powerful/efficient with the accelerator accelerating waste iron molecules instead of He?

I also have an idea for starting the fusion reactor (because the hard part is starting it, once its started it should produce enough heat/power to run itself). A smallish Uranium reactor is set to full power to power the startup. In the fusion reactor, a large quantity of Hydrogen is squashed down really small using massive electromagnets (or similar). ‘Waste’ heat from the Uranium reactor is added to help out. Finally, to trigger the fusion reaction, some H2 molecules are accelerated up the P. Accl to very fast speeds, focused into the Fusion reactor and collides with the compressed Hydrogen. This should make enough heat/pressure to start the reaction and then the Uranium reactor can be shut down until its needed again. If the reactor is a hybrid H/He reactor, the ‘waste’ He is not extracted, its left in and only the heavier elements are removed and stored. I imagine the waste elements would be extracted in a way similar to the way U238 (or whatever) was seperated from the rest of the uranium toward the end of WW2. Hows all that sound?

I think a hybrid H/He reactor would make more power, although it would need more pressure than a pure H reactor.
To all of you who have said that a SF story should not really focus on ‘realistic’ science, I have to disagree. I personally dont like SF that has alot of contrived elements and scientific work-arounds. One of my favorite SF writers of all time, R.H. Heinlen (sp?) stayed as close to the scientific knowlege of his time, even going as far as describing the ships ‘computer’ which was huge and made out of vacuum tubes. (although he usually conviently forgot that the ship would need massive storage of hydrogen fuel)
-BM

Actually, Hawking is correct on this one. You can convert a heat difference into electricity - by having a hot and a cold side to your thermocouple or other energy-conversion device. A heat source with no heat sink cannot be turned into electricity or any other useful form of energy.

Blah–

Okay, I think you are getting on track. Maybe a bit ahead of yourself in some areas. I can try to give you my understanding of where this weirdness we call relativity comes from.

First of all, you had Maxwell who developed a theory of electromagnetism that was uniform (did I say uniform? Yep, uniform!) in all frames of reference. This was a big problem because the consequence of this was that light had to be uniform in all frames. Whether you were travelling at 99.9999999% the speed of light or were sitting still, if you sent off a light beam ahead of you, necessarily you would measure it to be going exactly 3 times 10^5 kilometers every second. Moreoever, ANY lightbeam that happens to cross your path will be measured to be going at that speed regardless of where it was originated from.

This is extremely counterintuitive. When I am going nearly the speed of sound and sitting on the nose of the aircraft, I will likely not hear a sound because it is too hard for any compression wave to reach my ears (I also won’t be able to breathe, but that’s the joys of doing these thought experiments, you don’t actually have to do them to figure out what’s going on). However, if I’m going nearly the speed of light, I can still see photons just fine.

So, Special Relativity was developed to deal with this strange phenomenon. It basically introduces mathematical factors that allow us to modify one of our tried and true beliefs about the universe… namely that an inch is an inch no matter who measures and how everywhere in the universe and a second is a second no matter who measures it and how anywhere in the universe. However, we don’t throw the idea of spatial and temporal absolute away completely. No! We just listen to Mr. Einstein when he tells us that we need to listen to Mr. Newton and Mr. Galileo and interpret a little farther: namely that inertial frames of reference (me sitting on a magic carpet going a particular speed) are indistinguishable. If you build your rulers and clocks on earth, then go sit on the carpet, your rulers and clocks will be fine. And if you land back on earth, your rulers and clocks will be running fine. However, you may notice a difference in the absolute TIME that is on two different clocks that were calibrated simultaneously when we built them.

Why is that? Because relativity says, “Goodbye!” to our concept of simultaneity. We think that if two runners start at a starting block and one runner is faster than the other, they will still measure the same time when they both meet at the finish line. This ain’t true, though. The faster runner’s clock will actually be a bit behind the slower runner’s clock. Likewise, if someone is sitting in the stands and sees the slower runner pass by with a ruler it will look like the ruler is a bit shorter than it should be… and the faster runner’s ruler will be even shorter. However, when they both stop at the end of the race for drinks, all three rulers will be the same size!

Okay, this probably all sounds contrived and made up, but it is exactly what must occur in order for the speed of light to be the speed limit of the universe. And why must the speed of light be the speed limit of the universe? Well, shhh!! I’ll tell you the reason that doesn’t get spoken very often (and I’m not quite sure why this is the case)… it’s because light is a wave that travels through a vacuum.

WHAT? Is JS Princeton off his rocker? What does light travelling through a vacuum have to do with relativity? Well, you may remember Michelson and Morley? They proved once and for all that the speed of light didn’t change no matter what your relative speed was to the background. This trounced the theory of ether. In effect, the nature of light is such that it travels through nothing just like it was travelling through SOMETHING. Maxwell was convinced that the ether existed because he though the electric and magnetic fields were real things. He didn’t figure out that while they were real things they didn’t need a medium through which to travel.

Einstein thought, while on his bicycle to his patent clerk’s job, what it would be like if he could travel the speed of light on this bicycle. Why then, as he was speeding up he’d see all the light ahead of him blueshifted and all the light behind him redshifted. However, once he REACHED the speed of light, there he would be travelling along with these light beams. He could see their crests and their troughs as stationary backdrops alongside of him. Light would be stationary! But that is a contradiction, because the solving of Maxwell’s Field Equations for the vacuum solution (that is LIGHT!) DEMANDS that the light waves travel at the speed of light. They AREN’T ALLOWED TO BE STATIONARY! The math doesn’t allow it.

This is a monumental insight. It’s what prompts the development of Special Relativity by considering the equivalence of reference frames (after all, if light must travel at the speed of light, then in all reference frames light must travel at the speed of light) and E=mc^2 because you can actually see that the energy endemic to matter as it accelerates towards the maximum is equal to that quantity if you carefully look at how much total energy it takes to accelerate a given object. And ulitmately, it leads Einstein to consider how, if space and time are not ultimately absolute, they must look. In effect, this is what leads Einstein to develop General Relativity which incorporates the conservation of energy together with the force of gravity in a thing of mathematical beauty.

If you want to read more about the “practical” effects of relativity, I suggest reading the following two books:

Gott’s Time Travel in Einstein’s Universe

and

Gamow’s
The New World of Mr Tompkins

Hope this helps!