03-12-2011, 08:42 PM | #11 | |
Join Date: Aug 2010
Location: The Land of Enchantment
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Re: Alcubierre warp drive
Huh. The Alcubierre thing is sounding much different than I had thought it was. I had heard stuff along the lines of it working like whatever drive Star Trek uses, in that you can still interact with the universe, but move at arbitrary pseudovelocities. I guess that's yet another example of why one shouldn't listen to the press, even the science press...
Frankly, the whole thing sounds more like what GURPS calls a Jump drive rather than a Warp drive. Quote:
I think this sounds the most workable, eh? You'd have defined "routes", which means that you have a reason to have a starmap rather than just a chart of the locations of starts (which is rather, er, unromantic..). I actually really like the idea of tramlines, from a campaign viewpoint, because it allows for strategic systems where multiple tramlines converge. But I couldn't come up with decent technobabble to explain them, so I was pursuing the Alcubierre thing. But you're saying that a ship couldn't carry it's own drive? In essence, there must be a "stargate" or "jump-station" or whatever? In which case, would you need a jump station at both termini, or only one? Or would you just set up this curved path once, then it just sits there and anyone can fly into it, working more like a stable wormhole than a jump-station? If so, could you "build" a pathway from one terminus, or would you need to send a ship in real space (sublight) to the other terminus? Would the termini orbit? Or would they just sit there, ignoring the gravitational gradients around them? If the latter then the delta-v to get to them would be inconveniently high, right? (If there is a station involved then I suppose it must orbit, but what if there is no station?) I'm ruminating on a campaign that is very hard science fiction except of course for the existence of a means of FTL travel. Sort of in the same vein as 2300AD. Last edited by acrosome; 03-12-2011 at 09:07 PM. |
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03-12-2011, 08:46 PM | #12 | |
Join Date: Aug 2010
Location: The Land of Enchantment
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Re: Alcubierre warp drive
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03-12-2011, 08:49 PM | #13 | |
Join Date: Aug 2010
Location: The Land of Enchantment
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Re: Alcubierre warp drive
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Oddly enough, I think I get the negative energy concept. And I got the joke. Very droll. :o) Last edited by acrosome; 03-12-2011 at 08:59 PM. |
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03-12-2011, 09:06 PM | #14 | |||
Join Date: Nov 2004
Location: The plutonium rich regions of Washington State
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Re: Alcubierre warp drive
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Luke |
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03-12-2011, 09:47 PM | #15 | |
Join Date: Nov 2004
Location: The plutonium rich regions of Washington State
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Re: Alcubierre warp drive
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Now assume that we can change our velocity in essentially zero time. I will use primes (') to denote the coordinates measured in the reference frame with a changed velocity. This gives us x1' = 0 t1' = 0 and x0' = cosh(eta) x0 - sinh(eta) t0 t0' = cosh(eta) t0 - sinh(eta) x0 The parameter eta is called the rapidity, and corresponds to a speed v = tanh(eta) * c. The function cosh is the hyperbolic cosine cosh(x) = (exp(x)+exp(-x))/2 sinh is the hyperbolic sine sinh(x) = (exp(x)-exp(-x))/2 and tanh is the hyperbolic tangent tanh(x) = sinh(x)/cosh(x) exp(x) means raise the base of the natural logarithm (often denoted e) to the power x (or e^x). Since I don't feel like doing algebra right now, I wrote a quick program in c++ to run the calculations. For a speed of 0.0009999997 c (eta = 0.001, v ~ 300 km/s) I find that x0' = -100.00004 ly and t0' = 0.09000001 y. Since it still takes pretty near 0.01 year to get back, we would arrive at a time coordinate of t2'=0.01 y (and, of course, a space coordinate of x2' = x0' to a very good approximation, although to be rigorous we would include the change in position due to our relative motion). This is 0.08 y before we left, or about a month. So in this example you get back a month before you left (rigorously, we would transform from x2',t2' coordinates back to x2,t2 coordinates if you wanted to find out how long you had been waiting for your former self to jump in the frame of reference of the earlier you, but for these small velocities it doesn't make much of a difference, you still get back a month before you left in both reference frames). In fact, in this example a change in velocity of little more than 60 km/s gets you back just before you left. Luke Last edited by lwcamp; 03-12-2011 at 11:31 PM. |
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03-13-2011, 08:22 AM | #16 | |
Join Date: Aug 2010
Location: The Land of Enchantment
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Re: Alcubierre warp drive
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If I'm willing to assume that the exotic matter problem has somehow been solved I assume that stable wormholes are also possible. And after all, I'd have to assume that for the Alcubierre drive, anyway. So, how would they differ, in practice? I'll have to google Krasnikov tubes... EDIT- I looked up Krasnikov tubes. Both they and wormholes seem to have immense potential for screwing with causality, don't they? The Alcubierre drive as you explained it, assuming that I understand it correctly, seems to be a bit more difficult to (mis)use in that manner. Last edited by acrosome; 03-13-2011 at 08:40 AM. |
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03-13-2011, 08:39 AM | #17 | |
Join Date: Aug 2010
Location: The Land of Enchantment
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Re: Alcubierre warp drive
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A "tramline" gets made, and is a permanent structure. (I'm still interested if this would most likely be a "jump-point" or if it would require a "jump-station." I'd prefer the former, but I would want it to orbit and can't think of a reason why they would. And if they don't orbit, what reference frame are they attached to?!? Would a given solar system drift away from them? And I suppose that it would be too much to ask for if these could be naturally-occurring structures. If they are man made, presumably at great expense and over the course of centuries as sublight ships make that first run, this leads to tramlines radiating out from Sol like spokes with no cross-links and precluding strategic systems (other than Sol) which is boring.) The Alcubierre drive puts the ship into a pocket universe which is connected to our universe by a proton-sized "mouth", akin to a wormhole. Presumably, this is done by temporarily dilating this mouth open via some mechanism. It is this mouth that gets transported along the tramline at ludicrous speed, and when it arrives at the destination the mouth is again dilated and the ship emerges. Thus unlike a wormhole the transit time is something greater than zero. Is this making "sense"? EDIT- If the tramline termini are natural structures and they orbit a star, this is sounding oddly similar to the Ten Worlds setting: http://www.adastragames.com/universe.html But you'll have to dig around quite a bit to find the info on the setting- it is ratehr scattered at the moment. You might have better luck searching for the game, Attack Vector: Tactical. It's the most "realistic" space combat game I know of, and the Atomic Rockets website agrees. Last edited by acrosome; 03-13-2011 at 08:55 AM. Reason: add comment |
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03-13-2011, 11:05 AM | #18 | |||
Join Date: Nov 2004
Location: The plutonium rich regions of Washington State
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Re: Alcubierre warp drive
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You can always say that the same thing that prevents wormholes from forming time machines works for warping as well - as soon as you are in a configuration in which a time machine is just barely possible, you get a sort of perfect resonator for quantum fluctuations that follow the time travel path and meet themselves to build up and amplify themselves to destructive levels. This not only prevents time machines but discourages people from trying. Quote:
Also, think about the implications of a spacecraft being able to bottle itself up in a basement universe, connected to this universe only via an umbilicus the diameter of a proton. It would seem to be a near-perfect defense, for example. You could save a lot of propellant by not decelerating at your destination planet - just turtle up and plow into it, then dig yourself out (although at proton size you are likely to zip through the entire planet, so maybe this isn't the best example). Warp tramlines likely operate on schedules - to get around the issues of information not being able to propagate from the inside of the warp bubble to the space-time in front of it (resulting in a metric pileup and singular surface, which gives you the nasty radiation problems) what you do is have the equipment on the tramline synchronized to pulse at the right time to give the effect of a superluminal disturbance traveling down the line without actually having to transmit the information superluminally. So if you have arranged for this to happen once per day, for example, you can only take the warp line once per day. With a wormhole you can go through any old time. When forging new routes to distant unexplored stars, wormholes can potentially lead to wait times much shorter than what you would expect from the difference in coordinate time of sending a light speed signal and the signal arriving at the new star (you do this by exploiting the time dilation of the projected end of the wormhole, and the fact that the other end, the end left at home, is at rest with respect to the projected end when viewed through the wormhole). If you can do the same trick with a warp tramline, it is not so obvious. Quote:
As an aside, I am getting a significant amount of deja vu from this discussion - Rick Robinson't Rocketpunk Manifesto blog recently features an entry on the limits of realistic FTL and I participated in the extensive discussion in the comment section. You might find reading through the comments interesting - we cover a lot of the ground you have been asking about, and you might get additional insights into how to structure your setting http://www.rocketpunk-manifesto.com/...est-cheat.html You might want to just skip through the parts where people digress to talking about the metaphysics of duplication, Herbert's kludge of shields in Dune, and other side-tracks, of which there are many. For example, you could start at this comment http://www.rocketpunk-manifesto.com/...13686130748261 and not miss much. Luke |
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03-13-2011, 11:36 AM | #19 | ||||||
Join Date: Nov 2004
Location: The plutonium rich regions of Washington State
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Re: Alcubierre warp drive
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The stuff that makes up the physical structure of the tramway will be following its normal geodesic path through spacetime (neglecting the forces that the stuff exerts on itself - if you need self forces to keep the tramway intact the tension built up over light years would break it). These geodesic paths are called orbits when the occur around stars, planets, and other things that can be approximated as a localized bit of mass. However, the tramway itself might be very massive - we already assume that it has a significant effect on space-time locally - which could affect the paths of things around it. A massive tramline of this sort might need to be located very far away from a star to keep from messing up the planetary system. Of course, you would also need to find enough mass to make the tramline in the first place. Maybe it is best to assume the tramlines are not that massive. Quote:
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Luke |
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03-14-2018, 08:47 PM | #20 |
Join Date: May 2009
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Re: Alcubierre warp drive
How could a spaceship go through a Wormhole smaller than the width of a proton without being destroyed? I don't get it. It doesn't make sense. The link above doesn't work anymore.
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