@S1-A.ARPA,@MIT-MC:TENCATI@JPL-VLSI.ARPA (05/13/85)
From: Ron Tencati <TENCATI@JPL-VLSI.ARPA> I know this is impossible, but what would happen if... A ship could exceed the speed of light? When the space shuttle crosses the sound barrier, there is a sonic boom. If it were possible to cross the "light barrier", what phenomenon would result? Ron Tencati JPL-VLSI ------
jim@randvax.UUCP (Jim Gillogly) (05/15/85)
In article <1776@mordor.UUCP> @S1-A.ARPA,@MIT-MC:TENCATI@JPL-VLSI.ARPA writes: > >I know this is impossible, but what would happen if... >A ship could exceed the speed of light? When the space shuttle crosses the >sound barrier, there is a sonic boom. If it were possible to cross the >"light barrier", what phenomenon would result? As the ship approaches the speed of light its mass approaches infinity. So as it crosses the speed of light I would expect an infinitely strong (if momentary) gravity wave across all of space ... and don't expect it to attenuate by the time it gets here, since the cube root of infinity is going to be pretty big :-) . Perhaps the Tralfamadorians in _Slaughterhouse Five_ did exactly this when they ended the universe -- I seem to remember that it was caused by experiments with a new rocket propulsion system. I'd recommend that you find a way to skip directly from our tardyon universe into the tachyon universe without going across the speed of light. -- Jim Gillogly {decvax, vortex}!randvax!jim jim@rand-unix.arpa
darrelj@sdcrdcf.UUCP (Darrel VanBuer) (05/16/85)
Cherenkov radiation results (i.e. light) when anything goes faster than the
speed of light in a medium. Of course this only happens when the medium is
"slower" than a vacuum (e.g. water at 75% of c) since the particle still
limited by c.
Darrel J. Van Buer, PhD
System Development Corp.
2500 Colorado Ave
Santa Monica, CA 90406
(213)820-4111 x5449
...{allegra,burdvax,cbosgd,hplabs,ihnp4,orstcs,sdcsvax,ucla-cs,akgua}
!sdcrdcf!darrelj
VANBUER@USC-ECL.ARPA
--
Darrel J. Van Buer, PhD
System Development Corp.
2500 Colorado Ave
Santa Monica, CA 90406
(213)820-4111 x5449
...{allegra,burdvax,cbosgd,hplabs,ihnp4,orstcs,sdcsvax,ucla-cs,akgua}
!sdcrdcf!darrelj
VANBUER@USC-ECL.ARPAhenry@utzoo.UUCP (Henry Spencer) (05/16/85)
> I know this is impossible, but what would happen if... > > A ship could exceed the speed of light? When the space shuttle crosses the > sound barrier, there is a sonic boom. If it were possible to cross the > "light barrier", what phenomenon would result? A lot of heart attacks in the physics community, for one. :-) More seriously, as I recall it, the basic answer to this from relativity (if we ignore tachyons, which are a messy case) is "does not compute". Faster-than-light speeds involve logical contradictions (notably, loss of the normal cause-and-effect relationship) according to special relativity. This being the case, the theory basically cannot give coherent predictions about such a situation. I'd be very interested to hear this contradicted by somebody who knows more about the subject... -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,linus,decvax}!utzoo!henry
gv@hou2e.UUCP (A.VANNUCCI) (05/17/85)
> I know this is impossible, but what would happen if... > > A ship could exceed the speed of light? When the space shuttle crosses the > sound barrier, there is a sonic boom. If it were possible to cross the > "light barrier", what phenomenon would result? > > Ron Tencati > JPL-VLSI It *is* possible. A particle can move through a medium faster than the speed of light in that medium. It emits Cherenkov radiation, which is the electromagnetic wave analog of a sonic boom. This phenomenon is commonly used by particle physicist to detect the presence of particles. Giovanni Vannucci AT&T Bell Laboratories HOH R-207 Holmdel, NJ 07733 hou2e!gv
ran@ho95b.UUCP (RANeinast) (05/17/85)
>> I know this is impossible, but what would happen if... >> >> A ship could exceed the speed of light? When the space shuttle crosses the >> sound barrier, there is a sonic boom. If it were possible to cross the >> "light barrier", what phenomenon would result? > >A lot of heart attacks in the physics community, for one. :-) >More seriously, as I recall it, the basic answer to this from relativity >(if we ignore tachyons, which are a messy case) is "does not compute". >Faster-than-light speeds involve logical contradictions (notably, loss of >the normal cause-and-effect relationship) according to special relativity. >This being the case, the theory basically cannot give coherent predictions >about such a situation. > >I'd be very interested to hear this contradicted by somebody who knows >more about the subject... It's known as Cerenkov radiation. It turns out that the speed of light depends upon the medium through which it travels (the speed in vacuo is the ultimate limit), so you can have particles going very near the speed of light in a vacuum enter water (where the speed of light is much slower) and create a "sonic boom", except, of course, it is light that is emitted. This slows the particle rather quickly. Regarding tachyons, the idea first came up about 15 years ago when it was noticed that the relativity equations had no problems with faster- than-light if an object ALWAYS went faster then light, so tachyons were proposed. Despite possible mechanisms for how a tachyon might be observed, there is at present NO experimental evidence for their existence. Quantum field theory also has a few problems if tachyons exist, since the mass (imaginary for tachyons) of the particle defines an integration path in complex space for the calculation of certain measureable quantities. I realize the last sentence is not real clear, but I'm afraid I can't explain it much better. -- ". . . and shun the frumious Bandersnatch." Robert Neinast (ihnp4!ho95b!ran) AT&T-Bell Labs
larryk@tektronix.UUCP (Larry Kohn) (05/18/85)
In article <1776@mordor.UUCP> @S1-A.ARPA,@MIT-MC:TENCATI@JPL-VLSI.ARPA writes: > > If it were possible to cross the >"light barrier", what phenomenon would result? An image, resembling a subliminal flash, produced when an improbability wave formed by a spacecraft travelling at superlight speed traverses another dimension. Call it an Optic Flooey.
henry@utzoo.UUCP (Henry Spencer) (05/19/85)
> >I'd be very interested to hear this contradicted by somebody who knows > >more about the subject... > > It's known as Cerenkov radiation. It turns out that the speed of light > depends upon the medium through which it travels (the speed in vacuo > is the ultimate limit), so you can have particles going very near the speed > of light in a vacuum enter water (where the speed of light is much slower) > and create a "sonic boom", except, of course, it is light that is emitted. > This slows the particle rather quickly. Sigh, I knew about Cerenkov radiation, and if I thought people would be this picky [I know, I know, I've done it myself sometimes...] I would have qualified all references to "speed of light" with "in a vacuum". I thought it was reasonably clear from the original posting that the question referred to spaceships, i.e. operations in a vacuum. Now, if somebody can tell me whether an FTL starship would emit Cerenkov radiation in a vacuum, *that* would be interesting. -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,linus,decvax}!utzoo!henry
rl@ucsfcgl.UUCP (Robert Langridge%CGL) (05/20/85)
In article <1776@mordor.UUCP> @S1-A.ARPA,@MIT-MC:TENCATI@JPL-VLSI.ARPA writes: >I know this is impossible, but what would happen if... >A ship could exceed the speed of light? When the space shuttle crosses the >sound barrier, there is a sonic boom. If it were possible to cross the >"light barrier", what phenomenon would result? There is an equivalent to the "sonic boom" which occurs when the speed of a particle entering a transparent medium (i.e. water) exceeds the group velocity of light in that medium. It is known as Cerenkov radiation and is in fact used in some modes of particle detection. Bob Langridge (rl@ucsfcgl.UUCP) Computer Graphics Laboratory 926 Medical Sciences (rl@ucsfcgl.ARPA) University of California San Francisco CA 94143 (Phone: +1 415 666 2630)
throopw@rtp47.UUCP (Wayne Throop) (05/20/85)
In <1982@sdcrdcf.UUCP> Darrel VanBuer says > Cherenkov radiation results (i.e. light) when anything goes faster than the > speed of light in a medium. Of course this only happens when the medium is > "slower" than a vacuum (e.g. water at 75% of c) since the particle still > limited by c. > Darrel J. Van Buer, PhD I was under the impression that the "anything" had to be charged, IE, an FTL neutron would not produce Cherenkov radiation. If I'm wrong, can someone more up on particle physics mail me a contradiction? In <5608@utzoo.UUCP> Henry Spencer says > Sigh, I knew about Cerenkov radiation, and if I thought people would be > this picky [I know, I know, I've done it myself sometimes...] I would > have qualified all references to "speed of light" with "in a vacuum". > I thought it was reasonably clear from the original posting that the > question referred to spaceships, i.e. operations in a vacuum. Now, if > somebody can tell me whether an FTL starship would emit Cerenkov radiation > in a vacuum, *that* would be interesting. > Henry Spencer @ U of Toronto Zoology Now *there's* a more difficult question. Since a spaceship presumably contains some charged particles, if it went FTL (thru water for example) I expect it *would* emit Cherenkov radiation. This probably would be pretty hard to detect amidst the vaporization of the spaceship. :-) On the other hand, just how is the ship supposed to acheive FTL status (in a vacuum)? If it is "hyperspace" or "wormholes" or whatnot, I'd expect no FTL shockwave, since these ideas generally have to do with remaining STL with respect to some "higher space" and sidestepping the issue. If it uses the "correspondence tachyon" method (where every particle of the spaceship is replaced by a corresponding tachyon), I expect it *would* emit Cherenkov radiation, assuming that tachyons have charge. Isn't one of the methods used to search for tachyons to look for the Cherenkov radiation? Interestingly enough, assuming that a tachyon emits Cherenkov radiation, it would naturally decay to lower energy (that is, higher speed) states, accelerating to "infinite" speed. A convenient way to get your spaceship to hurry up. In any event, I'm performing the "public service" of adding net.physics to the newsgroups of this line of discussion. It seems more relevant to particle physics than orbital mechanics or near term space engineering. -- Wayne Throop at Data General, RTP, NC <the-known-world>!mcnc!rti-sel!rtp47!throopw
freeman@spar.UUCP (Jay Freeman) (05/20/85)
/* libation to line-eater */ In article <5602@utzoo.UUCP> henry@utzoo.UUCP (Henry Spencer) writes: >> I know this is impossible, but what would happen if... >> >> A ship could exceed the speed of light? > >More seriously, as I recall it, the basic answer to this from relativity >(if we ignore tachyons, which are a messy case) is "does not compute". >Faster-than-light speeds involve logical contradictions (notably, loss of >the normal cause-and-effect relationship) according to special relativity. >This being the case, the theory basically cannot give coherent predictions >about such a situation. > >I'd be very interested to hear this contradicted by somebody who knows >more about the subject... I won't claim to know more about it, but that never kept me from contradicting anybody :-) The mathematics of special relativity does not strictly prohibit FTL speeds. That mathematics says, in essence, that objects in the universe can be divided into five classes: (1) Things moving forward in time, slower than light; (2) things moving forward in time, exactly at the speed of light; (3) things moving faster than light (including infinitely fast, and also including both forward and backward in time); (4) things moving backward in time, at the speed of light; and (5) things moving backward in time, slower than light. The mathematics also says that the action of performing a "Lorentz boost" -- the kind of transformation that has all those square roots of (one minus vee square over c square) in it -- can NEVER move an object from one class into another. A Lorentz boost corresponds roughly to applying a classical force to an object for a while -- perhaps more accurately to giving it a classical kick in the pants, so that the physical interpretation of this mathematics is roughly "if it's slower than light now, you can't make it go FTL with classical forces." But there is no objection to objects which are already FTL (though there seems to be no experimental evidence of them, either). And there is no statement, (I think) that such non-classical events such as particle decays cannot produce tachyons. Many particle physicists, incidentally, will claim the "backwards in time" objects are quite real, namely, as antiparticles. It is indeed true that FTL implies breakdown of causality, but it is also true that the mathematics of the Lorentz transformation contains no assumption that causality holds in the first place. This is an ADDITIONAL assumption, which philosphers and physicists may put in or not, as they see fit. It is erroneous to state that "the Lorentz transformations prohibit FTL because causality is then violated"; because the Lorentz transformations do not feature causality as a postulate. Incidentally, an object is moving "infinitely fast" when its world line is (at least temporarily) perpendicular to the observer's time axis. -- -- Jay Reynolds Freeman (Schlumberger Palo Alto Research)
rl@ucsfcgl.UUCP (Robert Langridge%CGL) (05/23/85)
<-- A quick introduction to faster-than-light travel (by charged particles at least), and the use of the resultant electromagnetic equivalent of the sonic boom, is given on pages 58-60 of the June 1985 Scientific American. Bob Langridge rl@ucsfcgl (UUCP and ARPA)
gwyn@brl-tgr.ARPA (Doug Gwyn <gwyn>) (05/23/85)
> Isn't one of the methods used to search for tachyons to look for the > Cherenkov radiation? Yes, and you may notice they haven't found any.
rdp@teddy.UUCP (07/16/85)
In article <5602@utzoo.UUCP> henry@utzoo.UUCP (Henry Spencer) writes: >> I know this is impossible, but what would happen if... >> >> A ship could exceed the speed of light? When the space shuttle crosses the >> sound barrier, there is a sonic boom. If it were possible to cross the >> "light barrier", what phenomenon would result? > >A lot of heart attacks in the physics community, for one. :-) > >More seriously, as I recall it, the basic answer to this from relativity >(if we ignore tachyons, which are a messy case) is "does not compute". >Faster-than-light speeds involve logical contradictions (notably, loss of >the normal cause-and-effect relationship) according to special relativity. >This being the case, the theory basically cannot give coherent predictions >about such a situation. > >I'd be very interested to hear this contradicted by somebody who knows >more about the subject... >-- In fact, under the right conditions, one can achieve "faster than light" travel. While on cannot exceed a certain velocity "c" (2.99 x 10^8 m/s), the velocity of propogation of light through matter is somewhat less than this inviolable "c". For example, (if my memory serves me) light travels about 30% slower in water than it does in a vacuum. Under this circumstance, something which travels faster than that (but still MUST be less than "c") will, in fact, produce the light equivalent of a sonic boom, known as Cerenkov radiation. This is a shock wave which travels outward in a cone (whose included angle is proportional to the ratio of the speed of light in the media to the speed of the particle). Note that no violation of any physical law occurs. Nothing can travel faster than the sacred "Speed of Light" , which is the speed of light absent of any influences (matter).