Pyrotex Posted April 27, 2006 Report Share Posted April 27, 2006 Except that it wouldn't last long.True. But maybe long enough, if we are to believe Robert Forward, PhD.{yes, I threw that degree in there just to intimidate you! :surprise: } If memory serves me {and it rarely does} the outer, total size of the light sail was 20 km in diameter. The inner sail was just 2 km in diameter. The inner sail, with its cargo pod released from the outer sail, backed away, and reversed position. The outer sail reconfigured to be concave, with focal point at the lesser sail. Comes the laser light from our Solar System, some tens of light-years away. Fortunately, it is "focused" by a lensing system near the orbit of Neptune, and so is able to focus the light to a beam only a few hundred km wide at the distant star. All the light that hits the outer sail is reflected onto the inner sail. Since the inner sail also carries a cargo pod, let's assume that inner sail and pod have the same mass as the outer sail alone. Therefore, the outer sail accelerates at A m/sec/sec, and the inner sail and pod decelerates at -A m/sec/sec. As the distance between the two sails increases by 2A, the outer sail continuously reconfigures for a larger focal length. This can be continued until the distance between them is many million miles. But at some point, the efficiency will fall off, and the light hitting the front side of the lesser sail will equal the light hitting the back side, and that will be the end of that. Maybe a year. The question is, can you decelerate from .5 c to 30 micro-c in one year using the low forces inherent in light sails? Inquiring minds want to know. ;) PS: the answer is NO, but there's another trick up Forward's sleeve! Care to figure out what it is??? Quote Link to comment Share on other sites More sharing options...
Qfwfq Posted April 28, 2006 Report Share Posted April 28, 2006 {yes, I threw that degree in there just to intimidate you! :evil: }:lol:Two of the courses I chose were actually PhD ones! So there! :hyper: PS: the answer is NO, but there's another trick up Forward's sleeve! Care to figure out what it is???Goodness, :eek: I left my sliderule at home! I'll have to think about it tomorrow! Quote Link to comment Share on other sites More sharing options...
cwes99_03 Posted April 28, 2006 Report Share Posted April 28, 2006 I'll take a stab. Could it be that wherever we decide to travel to there will be a large body of light to use as well for braking? Maybe he also has calculated that with this large body and a small booster rocket one can jetison enough matter (including that outer sail which we have agreed to call 1/2 the total mass of the initial ship) to slow the momentum of the remaining ship to 30 micro c? Quote Link to comment Share on other sites More sharing options...
TheFaithfulStone Posted June 20, 2006 Author Report Share Posted June 20, 2006 By the dark powers of Hypography, I resurrect thee, FTL thread! [crackles of lighting, a sound of thunder] Muhahahahaha! Okay, so I was reading "The Mote in Gods Eye" the other day and I realized just how freakin' sneaky the Alderson Drive is. Basically, you jump between two "Alderson Points" where the travel is instantaneous, and it occured to me that this actually DOES get around the time travel paradox in a pretty clever way. Basically, you can only go FTL from Alderson point to Alderson point along the "tram lines" In order to make an Alderson Jump you have to go to the point, match speeds and location with it, and engage your drive - you then appear, with matched speeds and location at the other jump point. Basically, it's a restricted reference frame scheme. FTL is only available if your reference frame matches that of the Alderson Point, and when you get to the other one, your reference frame still matches that of the Alderson Point - thus avoiding any nasty FTL time travel paradoxes. Clever Jerry Pournelle! Clever Larry Niven! Just thought I'd share. TFS Quote Link to comment Share on other sites More sharing options...
Pyrotex Posted June 20, 2006 Report Share Posted June 20, 2006 I'll take a stab. Could it be that wherever we decide to travel to there will be a large body of light to use as well for braking?...Yes, of course! Give that dude a cigar. It is assumed that the vehicle is going to a planet around another star, so terminal braking is done by diving into the star and using its light. By tacking at the right time, the vehicle may achieve any desired orbit. Quote Link to comment Share on other sites More sharing options...
Pyrotex Posted June 20, 2006 Report Share Posted June 20, 2006 ...Okay, so I was reading "The Mote in Gods Eye" the other day and I realized just how freakin' sneaky the Alderson Drive is....TMIGE !! One of the best ten science fiction novels ever written! Quote Link to comment Share on other sites More sharing options...
TheFaithfulStone Posted June 20, 2006 Author Report Share Posted June 20, 2006 Isn't it though? It's one of my favs. Right up there with Foundation and Dune. TFS Quote Link to comment Share on other sites More sharing options...
Pyrotex Posted June 20, 2006 Report Share Posted June 20, 2006 Isn't it though? It's one of my favs. Right up there with Foundation and Dune.I think I will start a new thread... The best SF novels ever! :) Quote Link to comment Share on other sites More sharing options...
EWright Posted June 20, 2006 Report Share Posted June 20, 2006 To really consider methods of FTL achievability, science is going to need a better understanding of why light is limited to speed that it is and why matter is limited to slower than this speed. I don't believe the current understanding is correct. Quote Link to comment Share on other sites More sharing options...
Pyrotex Posted June 20, 2006 Report Share Posted June 20, 2006 To really consider methods of FTL achievability, science is going to need a better understanding of why light is limited to speed that it is and why matter is limited to slower than this speed. I don't believe the current understanding is correct.I can't explain everything about the speed of light, but many of its affects, like Special Relativity are explainable with ordinary geometry. All you have to assume is that whatever a photon is, it can travel only one discrete distance unit in one discrete time unit. It is much easier to understand if you think of light as having a top speed of say 10 MPH. That's just 14.6 feet per second, about the speed of a ping-pong ball. In fact, think of photons as ping-pong balls. To "see" anything, a photon from that event must enter your eye. If you travel at 9 MPH, only those photons that travel odd paths that you can intercept properly will enter your eye. So those are the ones that govern what you "see". Thus the distortions in length and shape. With this thought experiment, there would be no such thing as knowing where things REALLY were, with knowing what was REALLY happening. It becomes obvious that "seeing" (and "knowing") are governed by the geometry of which photons you can intercept ("see") and which ones you cannot. IDMclean 1 Quote Link to comment Share on other sites More sharing options...
EWright Posted June 20, 2006 Report Share Posted June 20, 2006 I can't explain everything about the speed of light, but many of its affects, like Special Relativity are explainable with ordinary geometry. All you have to assume is that whatever a photon is, it can travel only one discrete distance unit in one discrete time unit. It is much easier to understand if you think of light as having a top speed of say 10 MPH. That's just 14.6 feet per second, about the speed of a ping-pong ball. In fact, think of photons as ping-pong balls. To "see" anything, a photon from that event must enter your eye. If you travel at 9 MPH, only those photons that travel odd paths that you can intercept properly will enter your eye. So those are the ones that govern what you "see". Thus the distortions in length and shape. With this thought experiment, there would be no such thing as knowing where things REALLY were, with knowing what was REALLY happening. It becomes obvious that "seeing" (and "knowing") are governed by the geometry of which photons you can intercept ("see") and which ones you cannot. I'm sorry, it seems you misunderstood. I wasn't asking for an explanation of how photons work. I'm saying that I don't believe physics currently explains the proper reason that they are limited to the speed that they are. The discussion is of FTL capabilities. The laws of physics limit matter to sub-c speeds. This fascinating limitation does exist, along with the observations we associate due to perceptions of special relativity, but the reason for these effects have nothing to do with some mystical powers of light. Light does not reach out and dialate time or contract lengths. Quote Link to comment Share on other sites More sharing options...
TheFaithfulStone Posted June 20, 2006 Author Report Share Posted June 20, 2006 ]It's not a mystical property of light that causes relativistic effects and time travel paradoxes, it's a fundamental property of the universe. Massless particles move at c in a vacuum. Why is that? Because they do. But it's a fundamental physical principle, and the fact that it should be true in all reference frames is what leads to relativity and all manner of "light speed" weirdness. It really has nothing to do with light at all. Quote Link to comment Share on other sites More sharing options...
EWright Posted June 20, 2006 Report Share Posted June 20, 2006 ]It's not a mystical property of light that causes relativistic effects and time travel paradoxes, it's a fundamental property of the universe. Massless particles move at c in a vacuum. Why is that? Because they do. But it's a fundamental physical principle, and the fact that it should be true in all reference frames is what leads to relativity and all manner of "light speed" weirdness. It really has nothing to do with light at all. I'm glad you agree, it does have nothing to do with light at all. Most people can't see that. But to say "because they do" is saddly lacking of a more thorough reason as to why they do. How 'bout we just stop asking any scientific questions and explain everything with "because that's the way it is?" Quote Link to comment Share on other sites More sharing options...
Erasmus00 Posted June 20, 2006 Report Share Posted June 20, 2006 To really consider methods of FTL achievability, science is going to need a better understanding of why light is limited to speed that it is and why matter is limited to slower than this speed. I don't believe the current understanding is correct. Then by all means explain where we have gone wrong. -Will Quote Link to comment Share on other sites More sharing options...
TheFaithfulStone Posted June 21, 2006 Author Report Share Posted June 21, 2006 I have to tell you, I don't think there is a "reason" why c is what it is. Why is lambda what it is? Why is the fine structure constant or the gravitational constant what it is? If you take c out of arbitrary human units it's equal to 1. Q explained to me why that was, and Q is much smarter than I am, so maybe you should ask him. TFS Quote Link to comment Share on other sites More sharing options...
IDMclean Posted June 21, 2006 Report Share Posted June 21, 2006 TFS, brilliant. Sometimes it is not quite understood that somethings, simply reduce down to, because they are that way. Quote Link to comment Share on other sites More sharing options...
EWright Posted June 21, 2006 Report Share Posted June 21, 2006 TFS, brilliant. Sometimes it is not quite understood that somethings, simply reduce down to, because they are that way. I think not. Quote Link to comment Share on other sites More sharing options...
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