a_vesper%Shasta@sarah.UUCP (02/29/84)
My first reaction to Steven Maurer's letter (SFL v 9 # 36) was to send a brief note with my own comments on possibility/impossiblity of FTL travel to the SFL newsletter. My second reaction was a feeling that the subject has been discussed enough for this year. I eventually decided to go through some previous SFL issues (volume 9 only 'cause that's what was on-line) and point out all discussions of FTL, give a (very) brief summary and add my comments after each. I searched for "FTL" so if there was any discussion that did not use that abbreviation I did not pick it up. Mon, 16 Jan, # 12 : Ken Varnum <decvax!dartvax!kenv @ ucb-vax> Does time slow down as you approach the speed of light (c) and go backwards if you go faster than light? The answer to the first half of the question is very well explained in the next citation. The second half cannot be answered at this time -- we just don't know because we don't any experimental data. Mon, 16 Jan, # 13 : Bruce Giles <decvax!duke!ucf-cs!giles @ ucb-vax> An excellent discussion of special relativity, length contraction and time dilation, but longer than I want to include here. Wed, 18 Jan, # 15 : Joe Buck <buck@nrl-css> "Special relativity shows that if FTL travel is possible, time travel (and causality violation) must occur as well." "Actually, relativity doesn't explicitly prohibit FTL travel. It just shows that an object with mass can't be accelerated continuously from a velocity below c to one above c." I believe that special (and general) relativity simply don't say anything about FTL travel, but only STL travel. The definitions that Einstein came up with for 'time' and 'simultaneity' are paired directly with relativity and the STL universe. A new theory showing how FTL travel is possible would have to redefine those terms, and probably 'cause' and 'effect' as well. Einstein also showed that it takes more and more energy to accelerate a body (with mass) closer and closer to c and that it would take infinite energy to accelerate a body TO c. Assuming that you must accelerate from below c THROUGH c to above c gives you the impossibility of FTL travel. (There is a discussion of Tachyons later in this note.) As an aside, bodies without mass (e.g. photons) always travel at c in a vacuum. Sun, 22 Jan, # 17 : Jeff Duntemann <duntemann.wbst @ PARC-MAXC.ARPA> Postulates a starship drive which accelerates all particles within a given volume equally. "This violates no physical laws that I know of." With 2000 or 3000 G acceleration a trip to the nearer stars becomes a matter of weeks or months rather than centuries. (Personal time rather than universe time.) I don't have my copy of *Have Space Suit, Will Travel* by Robert A. Heinlein with me, but in that novel RAH shows that a constant acceleration of less than 10 G is sufficient to get to the nearer stars in a matter of 'weeks or months'. 2000 or 3000 G would probably get you there within seconds. I can't do that kind of math in my head so I'll leave it as an exercise for the reader. Tue, 24 Jan, # 18 : Eric G. Stern <hplabs!hao!seismo!philabs!sbcs!bnl!stern @ Ucb-Vax> Eric comments that the starship drive which accelerates all particles within a given volume equally requires communicating a change in velocity instantly over a non-zero distance, which is prohibited by special relativity. Oh well. TANSTAAFL. Thu, 23 Feb, # 36 : Steven Maurer <sun!qubix!steven @ Ucb-Vax> "Thus, though it is possible for "Psychism" to exist, even "magic" (as long as it is in another universe), FTL cannot." "Period." Bunk. Why can't FTL exist in another universe? Call it "magic" if you want. Why can't FTL exist in our universe? It might, but we don't know how yet. Personally I don't expect to see it possible in my lifetime, and maybe never (although 'never' is a very strong word). Hard science fiction often takes a theory just past where it breaks down (such as relativity and 'c') and declares that reality works differently from there. FTL is prime science fiction material in this light. Tue, 28 Feb, # 38 : Mike Gannis <offnet at LOGICON> Mike compares Einsteinian relativity to Newtonian physics: "Would you class as fantasy all stories involving sub-c time dilation effects simply because they aren't predicted by Newtonian physics?" I agree. Newtonian physics cannot handle time dilation. Einsteinian relativity cannot handle FTL. Both are 'true' in that they are useful descriptions of the 'world' with certain limitations. I have not seen any mention of Tachyons in the recent past, so I will bring up the subject myself. If you take Einstein's theories and turn them around slightly, you have a universe where all massive objects travel faster than c, it takes energy to slow them down towards c and infinite energy to slow them down to c. This universe is called a Tachyon universe and the particles in it are Tachyons. This gives rise to the following FTL drive principle: change matter into tachyons going in the right direction, travel the distance then change back into normal matter. In order to do this, you need (1) the normal universe, (2) the tachyon universe, (3) some way to convert between normal matter and tachyons and (4) someplace to stand while doing the conversion. (4) implies that the normal 'universe' and the tachyon 'universe' are only subspaces of the 'real universe'. The normal 'universe' would then not have to obey conservation laws, which are tricky things to get around when all that normal matter/energy disappears (and reappears somewhere else -- presumably with different potential energy). Wormholes in space are also convenient FTL 'drives'. Unfortunately, this also implies a space larger than the 'universe' within which the 'universe' is folded. And you still have to do something about conservation. (Simply saying that conservation doesn't hold is tacky and doesn't help much anyway.) Sorry for running on to such a length, but I hope I cleared up some of the misconceptions. I will close with my recollection of an old limerick: There once was a woman named Bright, Whose speed was far faster than light, She set out one day, In a relative way, And came back the previous night.