From: throopw@sheol.org (Wayne Throop) Newsgroups: sci.physics.relativity Subject: Re: A Rebuttal of the Relativity of Simultaneity Distribution: world Organization: sheol Message-ID: <859392610@sheol.org> Date: Wed, 26 Mar 1997 16:10:10 GMT References: <5f30od$k9c@usenet81.supernews.com> <01bc251e$52d57a20$2b90b8cd@bjon.ix.net.com> <5f7iem$f6b@usenet81.supernews.com> <01bc2735$93442d40$6490b8cd@bjon.ix.net.com> <5h1gtj$fgn@usenet81.supernews.com> <859073016@sheol.org> <5h1rid$ke5@usenet81.supernews.com> <859083331@sheol.org> <5h2bik$qp8@usenet81.supernews.com> <859123668@sheol.org> <5h3li9$cik@usenet81.supernews.com> <859148693@sheol.org> <5h4ro6$sbv@usenet81.supernews.com> <859212927@sheol.org> <5h6dum$it5@usenet81.supernews.com> <859317265@sheol.org> <5hb5kg$m3p@usenet81.supernews.com> ( Discussing the train gedanken in chapter 9 of Einstein's "Relativity", where a train moves WRT a track, points A and B are struck by lightning, and reach the midpoint M between A and B on the track simutaneously; but the light doesn't reach the midpoint M' on the train simultaneously. Since (by postulate) light travels at c, that means that the lightning strokes are simultaneous in track coordinates, but not simultaneous in train coordinates. Hence, the relativity of simultaneity. C.J. Luke insists that Einstein's conclusion is flawed, and there is a conflict between calculating where light strikes M' using track coordinates, and the postulate that light has velocity = c in train coordinates. Let's join in the conversation already in progress: ) : cj@totcon.com (C.J. Luke) : Did you have a difficult time with reading comprehension in school Wayne? Nope. No trouble at all. Tested in the top coupla percentile or so. My parents were so proud. : I have already made it as simple as it gets. Your problem is you keep : insisting that the lightning strikes happen at two different times and : as a consequence of that, M' observes it as two events. That's not a "problem". That's just a fact. The lightning *does* have two different time coordinates in the train coordinate system. For one example of a consistent assignment of coordinates, we have [1] below. : The problem with your argument is that you can't show how the : lightning happens at two different times for M'. Of course I can. I already laid out the steps of the proof [2]. I already gave specific numbers [1]. I already drew diagrams of it [1a], so I can't even say "what, you want me to draw you a picture?". It is, in fact, difficult to propose how I can possibly have "shown" it any more thoroughly. : There is a way, Wayne...if the light from the flashes at A and B have : different velocities WRT M'. There is another way. If the light from the flashes at A and B started out at different times in train coordinates. : Of course that is why I started this post, and what you have been : arguing against ineffectually, but you do have one more option...the : events were simultaneous for M'. But they weren't. Why should one count as an "option" something that contradicts the givens of the gedanken? : So here are your choices: : 1) Events were not simultaneous for M'. : LPL in trouble. : 2) Events were simultaneous for M'. : SRT in trouble. Sorry, no, I'll choose 3) "The events were not simultaneous for M', LPL is just fine". Absolutely nothing cj has said has in the teeniest, tiniest way shown any conflict whatsoever between the POR+LPL and the non-simultaneity for M'. -- Let me ask a simple question in analytic geometry. By "analytic geometry" I mean the simple stuff that was covered in jr high school (in USA public school terminology). We have M and M' located at the midpoint between A and B. M and M' both have a coordinate system with the y axis aligned in the direction they are facing, but they are facing slightly different directions. Now, we are given that the y coordinates of the points A and B are the same in M coordinates. Can we prove that the y coordinates in M' coordinates are the same, or can we prove they are different? Remember! M and M' are both at the midpoint between those selfsame points A and B. The points A and B are the same points in both coordinates, and M and M' are both at the midpoint! To be consistent with our positions in the train gedanken, cj would have to conclude the M' y coordinates for A and B must be identical. I say they must differ. In other words, cj is persisting in making a mistake so elementary that 9th grade geometry students would flunk for it. Sorry to say it, but it's true. That is all I have to say about that. -- Wayne Throop throopw@sheol.org http://sheol.org/throopw throopw@cisco.com -- [1] +-------------- coordinates WRT ------------------+ event track (v=-.8 wrt train) train (v=.8 wrt track) ----- ----------------------- ---------------------- A (t=0,x=-4) (t=5.33,x=-6.67) B (t=0,x=4) (t=-5.33,x=6.67) M x M' (t=0,x=0) (t=0,x=0) A->M,B->M (t=4,x=0) (t=6.67,x=-5.33) A->M' (t=20,x=16) (t=12,x=0) B->M' (t=2.222,x=1.778) (t=1.33,x=0) [1a] The same point is made diagramatically in the gif at http://sheol.org/throopw/train-gedanken-diagrams.gif Interpretation of spacetime diagrams such as in that gif at http://sheol.org/throopw/sr-ticks-n-bricks.html -- [2] An informal proof, broken into small statements, with the justification for each statement annotated to the right. Near as I can tell, cj's objection is that (6) conflicts in some way with the POR+LPL. In fact, it does not. And cj has not pointed out any valid flaw in the reasoning sketched out here, contenting himself with merely asserting (without any justificaiton I can detect) that a flaw exists. 1) M has velocity 0 in the track frame (given) 2) M' has velocity v in the track frame (given) 3) M' has velocity 0 in the train frame (given) 4) light has velocity c in the track frame (POR+LPL) 5) light has velocity c in the train frame (POR+LPL) 6) light and M' close at rate (c-v) or (c+v) in the track frame ((4)+(2)) 7) M and M' are both at the midpoint (given) between two events (flashes) 8) the flashes are simultaneous in the track frame (given) 9) the flashes reach M at the same time (((8)+(7)+(4)+(1)) 10) the flashes do not reach M' at the same time ((7)+(6)) therefore, the flashes are not simultaneous in the train frame ((10)+(4)+(2))