HAYHURS@IUBACS.BITNET (01/31/89)
Distribution-File:
SPACE@ANDREW.CMU.EDU
SPACE Digest Volume 9 : Issue 212
Today's Topics:
Approaching c
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Date: Tue, 24 Jan 89 09:28 EDT
From: "That's not lake Minnetonka..." <CALVIN%JHUIGF.BITNET@VMA.CC.CMU.EDU>
Subject: Approaching c
> An object becomes more massive the faster it travels.
> Since F=ma (Newton), an accelerating body requires more and more
> force to keep accelerating it
> At (near?) c, this force would become infinite, and thus, acceleration
> past c is impossible
> THEREFORE, c is the highest attainable speed by an accelerating body.
>
>Ok. One thing screams out to me, though. c is a finite number, being 3x10^8 m/s
>which all of you know. Then, why would the force required to accelerate a
>body past c be infinite if c isn't infinite? How can it be assumed that a
>body will become infinitely massive at c if c itself is not infinite, UNLESS
>one assumes, subtlely, that c already is the fastest attainable speed (that
>is, c is in effect, infinite).
>
>Thanks for your time, and again, I apologize if this question is either very
>simple, or has been beat to death in the past. I'ma new subscriber to this
>list.
>
>
>Damian Hammontree
>System Programmer
>Johns Hopkins School of Medicine, Baltimore, MD (301) 327-2959
>DAMIAN@JHUIGF.BITNET
>CALVIN@JHUIGF.BITNET
>
------------------------------
Based on Damian's question, and being even "dumber" (or more ignorant on
the subject), I'll propose something even more radical, but a notion that
might be supported by his idea concerning "C"...
If ou follow the course of development, the speed of sound was a barrier
for a very long time; now we have broken the speed of sound. A lot of
questions about doing that involed the effects of approaching that mark.
The spped of sound was a barrier - you could fly up to it, break it, &
cross over BUT NOT FLY AT IT. Who says that the speed of light is not
similar?
Okay, you Physicists, you can eat me alive on this one. +:') (i even put
the crosshairs on my forehead for you.)
- Steve Hayhurst, HAYHURS@IUBACS
_________________________________________________________________________
| : Steve Hayhurst, Indiana Univ. :
: "ET TU NVIRII?" said the MacIntosh : HAYHURS@IUBACS BITNET ADDRESS :
: as it collasped into an endless loop :"I sent it, I guess that means :
: : I have to take the blame." :
:______________________________________:________________________________:rg20+@andrew.cmu.edu (Rick Francis Golembiewski) (02/02/89)
Here's a question I've alaways wondered about relativity: Suppose there are two space ships, one going at .6 C (an attainable theoretical velocity) and one going .6 in the opposite direction, what would observers inside each see? // Rick Golembiewski rg20+@andrew.cmu.edu \\ \\ #include stddisclaimer.h // \\ "I never respected a man who could spell" // \\ -M. Twain //
ethan@ut-emx.UUCP (Ethan Tecumseh Vishniac) (02/02/89)
In article <EXtpzNy00WB9E0jnx8@andrew.cmu.edu>, rg20+@andrew.cmu.edu (Rick Francis Golembiewski) writes: > Here's a question I've alaways wondered about relativity: > Suppose there are two space ships, one going at .6 C (an attainable > theoretical velocity) and one going .6 in the opposite direction, > what would observers inside each see? Each one would see the other receding at a velocity of 1.2/1.36 times c. Velocities do not add in the simple way you are used to. The correct formula to apply involves dividing the sum by one plus the product of the velocities (as fractions of c). -- I'm not afraid of dying Ethan Vishniac, Dept of Astronomy, Univ. of Texas I just don't want to be {charm,ut-sally,ut-emx,noao}!utastro!ethan there when it happens. (arpanet) ethan@astro.AS.UTEXAS.EDU - Woody Allen (bitnet) ethan%astro.as.utexas.edu@CUNYVM.CUNY.EDU These must be my opinions. Who else would bother?
jim@nih-csl.UUCP (jim sullivan) (02/04/89)
In article <10116@ut-emx.UUCP> ethan@ut-emx.UUCP (Ethan Tecumseh Vishniac) writes: >In article <EXtpzNy00WB9E0jnx8@andrew.cmu.edu>, rg20+@andrew.cmu.edu (Rick Francis Golembiewski) writes: >> Here's a question I've alaways wondered about relativity: >> Suppose there are two space ships, one going at .6 C (an attainable >> theoretical velocity) and one going .6 in the opposite direction, >> what would observers inside each see? > >Each one would see the other receding at a velocity of 1.2/1.36 times >c. Velocities do not add in the simple way you are used to. The >correct formula to apply involves dividing the sum by one plus the >product of the velocities (as fractions of c). > Last night I was reading Calder's book "Einstein's Universe" which I've said in past postings (maybe too many times) is a good laymans book on this subject. It gave an example which I must share: If you are stationary and ship A is moving at .75*c away from you and ship B is doing the same but in the opposite direction, you would think that ship A would see ship B moving at 1.5*c. But you can communicate with both ship A and ship B. Therefore, both ships should be able to communicate with one another and they can because as shown in the previous posting, each ship's relative speed to the other would be (1.5/(1+(.75*.75)))*c = (1.5/1.56)*c = ~.96*c Just had to share this... Jim jim@alw.nih.gov
throopw@xyzzy.UUCP (Wayne A. Throop) (02/08/89)
> HAYHURS@IUBACS.BITNET > If ou follow the course of development, the speed of sound was a barrier > for a very long time; now we have broken the speed of sound. A lot of > questions about doing that involed the effects of approaching that mark. > The spped of sound was a barrier - you could fly up to it, break it, & > cross over BUT NOT FLY AT IT. Who says that the speed of light is not > similar? Well, there are several meanings of "impossible"... at least three. One might mean something like "it is impossible to trisect the angle", or "it is impossible to square the circle", or "it is impossible to completely solve the halting problem". These are absolutely impossible. They involve abstract entities, the definition of which make it completely certain beyond rational question that they cannot be done. 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. Finally, there are things like "it is impossible to make a heavier than air flying machine", or "it is impossible to travel faster than 10mph by rail", or other examples. These merely involve things that haven't been done yet. There is no particular well-founded model of the situation that forbids the situation. 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 all "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. But impossibilities of the second kind, FTL for example, are NOT a small matter of engineering. Finding them "possible" will require building a new basic model of reality, and one just about as radical as one which would allow a perpetual motion machine. In the Navy, the difficult is one immediately and the impossible takes a little longer. But I note that even the Navy hasn't tackled impossibilities of the first or second kinds, only the third kind. So, to answer the question posed, *I* say they are not similar. FTL and FTS are not really remotely in the same class of "difficulty". ( Note well, I am NOT, repeat, NOT saying that FTL is absolutely impossible. After all, conservation of matter was once thought to be pretty secure until it became conservation of mass-energy. It's just that the analogy of FTL to FTS is flawed. ) ( Somebody else mentioned that aerodynamic equations of some sort predicted infinite stresses at SoS, "just like" special relativity predicts infinite mass at SoL. But the two are NOT "just alike". The aerodynamic equations were engineering equations that were developed to model subsonic airflow, and were tested against reality for only fairly narrow ranges of conditions. Special relativity, on the other hand, is intended to model velocities and interactions of all kinds, and has been tested very thoroughly indeed, very close to lightspeed indeed. ) -- All things dull and gargully, All creatures short and squat, All thngs rude and nasty, The Lord God made the lot. --- Monty Python -- Wayne Throop <the-known-world>!mcnc!rti!xyzzy!throopw
dietz@cs.rochester.edu (Paul Dietz) (02/09/89)
Just an aside: Robert Forward mentioned in a talk he gave here that he is now looking at tachyons. Antimatter is old hat, I guess! I can see it now: the Air Force, surveying Soviet research, announces the existence of a Tachyon Gap. SDI begins studying tachyon guns for shooting backwards in time for pre-boost phase defense. :-) Paul F. Dietz dietz@cs.rochester.edu
regnery@wpi.wpi.edu (George Regnery) (02/10/89)
In article <3316@xyzzy.UUCP>, throopw@xyzzy.UUCP (Wayne A. Throop) writes: > > Finally, there are things like "it is impossible to make a heavier > than air flying machine", or "it is impossible to travel faster than > 10mph by rail", or other examples. These merely involve things that > haven't been done yet. There is no particular well-founded model of > the situation that forbids the situation. Haven't been done yet? Where do you live? Seriously, the above statements are just a misuse of the word impossible. Impossiblility, to most people, denotes something that can not ever be done under any circumstances. There are some things that can't be done now, yet aren't impossible (such as space travel to Mars or Jupiter). Then there are things that are just impossible now, and always will be, like the things you mentioned such as squaring a circle. Impossible is defined as something that will never be able to be done under any circumstances. What if you said the circumstances were a situation where only impossible things sould be done? I think the book Godel, Escher, Bach talks about impossibility, but i'm not sure... It is an interesting book though. . ----George Regnery -- George M. Regnery ! Worcester ! Albedo 0.39 ! Going on means regnery@wpi.wpi.edu OR ! Polytechnic ! --Vangelis ! going far. Going regnery@wpi.bitnet ! Institute ! (a good album) ! far means returning. CompuServe: 73300,3655 ! (Worc, Mass.) ! =-=-=-=-=-=-=-=! --Tao Te Ching
scotth@harlie.SGI.COM (Scott Henry) (02/10/89)
> Well, there are several meanings of "impossible"... at least three. > ... > So, to answer the question posed, *I* say they are not similar. > FTL and FTS are not really remotely in the same class of "difficulty". > ... > -- > Wayne Throop <the-known-world>!mcnc!rti!xyzzy!throopw I am reminded that many people do not understand the distinction between "natural" law and "man-made" law (a very unfortunate overloading of terminology! I wonder if this problem exists in non-english speaking societies?). It is similar to the (lack of) distinction between your types 2 and 3 impossibles. -- --------------------- Scott Henry <scotth@sgi.com> #include <std_disclaimer.h>
PLS@cup.portal.com (Paul L Schauble) (02/11/89)
>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
sl161022@silver.bacs.indiana.edu (02/12/89)
>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. Like the entire discipline of Quantum Mechanics, for example, some followers of which would tell you that we can never know everything about an electron, not just because our instruments interfere with it, but because the electron ITSELF doesn't even know precisely where it is or where it is going. How the electron knows what the hell to do next is an unresolved question. The complaint about breaking the speed of light barrier is usually that it would violate our notion of causality, that it would require overthrowing modern-day physics. I would propose that our notion of causality is a fuzzy one at best, and for physicists to chain themselves to the word "causality" while embracing Heisenberg's view of QM is the pinnacle of Orwell's double-think, intentional or not. (I, by the way, am in astrophysics, of which physics is just a special case :-) This does not mean I think breaking C is possible, or even probable. I do believe, however, that if we are unable to break the speed of light barrier, then we are forever confined to this solar system. It would be a tragic limitation on our travels, but it is there nonetheless. I would even go further and say that given the nature of humans and the governments they create, we are probably also condemned to this planet for the rest of our species' existence, despite the occasional Mars or lunar expedition. But I hope I'm wrong on both counts. __________________________________________________________________ "May the forces of evil become confused on the way to your house." Sincerely, -- George Carlin Phaedrus (aka Colin Klipsch) sl161022@silver.bacs.indiana.edu Indiana University at Bloomington
128a-3cl@e260-1f.berkeley.edu (Cimarron D. Taylor </>) (02/13/89)
I feel constrained to add a comment to this perennial discussion. The transmission of matter or energy faster than the speed of light would not require an overthrow of current theory. Relativity, which introduced this limit, was more a broadening of theory than a revolution. To suggest that relativity is, in turn, just a special case of some larger model is not absurd. All one can say about FTL transmission is that it is not predicted in the models that best fit physical observations. --MYC
throopw@xyzzy.UUCP (Wayne A. Throop) (02/14/89)
> regnery@wpi.wpi.edu (George Regnery) >> throopw@xyzzy.UUCP (Wayne A. Throop) >> [...] "it is impossible to travel faster than >> 10mph by rail", or other examples. These merely involve things that >> haven't been done yet. > Haven't been done yet? Where do you live? Just in case this was not clear, "done yet" at the time of the pronouncement of "impossibility". > Seriously, the above statements are just a misuse of the word impossible. > Impossiblility, to most people, denotes something that can not ever be done > under any circumstances. True, it *is* a sort of "misuse". But I didn't intend to judge whether people are using the term "impossible" correctly or not. I was merely pointing three common ways in which the term is actually used (this being one of the three). To reconcile it with George's definition, read an implied "impossible (for current technology)" or some such into this usage. -- The seeds of crime bear bitter fruit. --- Dick Tracy -- Wayne Throop <the-known-world>!mcnc!rti!xyzzy!throopw
myers@hpfcdj.HP.COM (Bob Myers) (02/14/89)
>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. I do not believe that there were any instances of a WWII fighter definitely exceeding Mach 1; some may have come somewhat close, and experienced problems with their controls in so doing, but there was still some who believed in a "sound barrier" right up to Yeager's flight in the X-1. Certainly, the counter-examples of bullets, etc., were known, but it was still believed by some that *controlled* flight in excess of the speed of sound was impossible. The X-1 was a very "brute force" approach at proving this to be incorrect. Bob Myers KC0EW HP Graphics Tech. Div.| Opinions expressed here are not Ft. Collins, Colorado | those of my employer or any other {the known universe}!hplabs!hpfcla!myers | sentient life-form on this planet.
markh@csd4.milw.wisc.edu (Mark William Hopkins) (02/14/89)
In article <EXtpzNy00WB9E0jnx8@andrew.cmu.edu> rg20+@andrew.cmu.edu (Rick Francis Golembiewski) writes: >Here's a question I've alaways wondered about relativity: >Suppose there are two space ships, one going at .6 C (an attainable >theoretical velocity) and one going .6 in the opposite direction, >what would observers inside each see? Each would "see" the other going at 1.2/(1 + .36) C. See is a word to be taken lightly, because you can't see what's going on instantaneously. For example as you look up into the sky at the sun, it may have already gone nova up to 8 minutes ago. ON APPROACHING C: Relativity says you can't pass beyond C, because no matter how close you get to it, the difference between your speed and C is still C. In relativity, the "difference" between two speeds, v1 and v2, is: (v1 - v2)/(1 - v1*v2) expressed as a ratio in terms of C. When v1 is 1C, the difference becomes 1C.