Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ukma!xanth!lll-winken!uunet!portal!cup.portal.com!PLS From: PLS@cup.portal.com (Paul L Schauble) Newsgroups: sci.space Subject: Re: approaching "C" Message-ID: <14544@cup.portal.com> Date: 11 Feb 89 07:50:08 GMT References: <3316@xyzzy.UUCP> Organization: The Portal System (TM) Lines: 41 >From: throopw@xyzzy.UUCP (Wayne A. Throop) >Subject: approaching "C" >Then there are things like "it is impossible to travel FTL", or >"it is impossible to travel in time", or "it is impossible to >extract work from a system in equilibrium", or "it is impossible >to build a perpetual motion machine". These involve models >of the real world. The abstract entities in the model constitute >absolute impossibilities, and the only question is whether the >model accurately describes or resembles reality. >Now it seems to me (and I don't mean to put anyone down here, mind you) >that most people making the argument "well we broke the sound barrier, >so maybe someday we'll break the light barrier" are classing allok >"impossible things" as things of the third kind. It is my belief that >supersonic travel was an "impossibility" of the third kind. After all, >there were known objects that traveled supersonically, and (as far as >I know) there was no well-checked model of supersonic airflow which >disallowed it. So all that remained was a small matter of engineering. No, supersonic flight was an impossible of the second kind. Aerodynamic theory, as it was then understood, predicted several effects that were thought to make controlled flight impossible. As I recall, one of the effects was that the air pressure at the leading edge of the wing would become infinite, thus requiring infinite power. It wasn't until some WW II fighter planes were OBSERVED to exceed the speed of sound in a dive that the theories were revised. The current theories regarding FTL flight (I think. I'm sure someone will correct me if I'm wrong.) are similar. FTL is forbidded in two ways. First, you can't accelerate continuously through the speed of light. Second, FTL in any form either provides time travel or violates conventional causality. I'm not sure how strong this second point is. Physicists are very attached to causality, and so assume FTL impossible.But there are known effects that call conventional causality into question. ++PLS