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Old 05-03-2013, 06:32 AM
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CalMeacham is offline
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The current issues of Skeptical Inquirer has a good article on this. I thoughht this was what might have set the OP off, in fact, but he doesn't seem to give any indication that he read it. The SI article, in tyuirn, cites in large part an appendix to a 1960s article by Edward Purcell* that considers practical near-lightspeed travel in some detail and shows that it wouldn't be practical.


Occasionally SF writers will point out how extremely hard and unlikely the realities of near-luminal speeds are, but this makes for short, depressing, and often dull stories, so they take really high speed trabvel as a "given" asnd see wghere that gets them. It's really no different from Jules Verne making the assumption that firing his heroes out of a cannon (in From the Earth to the Moon) wouldn't simply smash them to pulp, sop that he really could proceed to the interesting stuff.


And occasionally someone will suggest a workaround. Physicist and Robert L. Forward wrote a book entitled Indistinguishable from Magic, in which he alternates essays about seemingly improbable high-tech possibilities with stories that use them. One of his favorites is near-luminal travel, and he devoted considerable time and effort to the topic, coming up with his "Starwisp" concept of laser-light-pressure-driven ultralight craft. For this, both the effective "engine" and the effective "reaction mass" don't have to be carried aboard and accelerated along with your payload, so you can avoid the absurdly higfh mass-to-payload ratios even matter-antimatter engines would, by Purcell's calculations, require**. But it's still a helluva huge effort and expenditure. Neverheless, his concept has been published in respectable journals, and I heard him lecture about it at a meeting of the American Institute of Astronautrcs and Aeronautics.








*Physicist and nobel prize-weinner. And author of my first college text in Electricity and Magnetism.


** Purcell came to the conclusion that using matter-antimatter you could accelerate to relativistic speeds with a ship-to-payload mass ratio that's about a single order of magnitude (a factor of teon or so). But if you actually wanted to slow down and stop, it required a couple of orders of magnitude. For even perfect fusion-fueled accerelation the ratios were completely absurd.

Last edited by CalMeacham; 05-03-2013 at 06:33 AM.