uwot wrote:Noax wrote:In Oscar's frame:
After 194 minutes, Oscar has gone nowhere, but his clock reads 194, and event Q happens, which is when Oscar and Irving meet. Irving at that time sets his clock to 194. Meanwhile, Edgar is 168 light minutes to the left of event Q, and his clock reads 97 at the same time as event Q since at the speed he's moving, his clock runs at half normal pace.
Well, if his clock reads 97, then it is Edgar that is moving.
Quite right. The paragraph is preceded by "In Oscar's frame". In anybody's frame, the others are moving. Those headers above each paragraph identifying the frame of the paragraph is very important. Nobody is objectively stationary, a concept with no meaning in SR.
Noax wrote:If Oscar tries to read Edgar's clock from event Q, he might see a figure near 35 I think since the light reaching him now came from when the clock said that. That's the only figure with complicated math, and that one is unimportant.
If Oscar sees a figure of 35, then it confirms that it is Edgar who is moving.
No, it is the fact that the paragraph was described in Oscar's frame that confirms it is Edgar who is moving (relative to that frame). In relativity, you can't say somebody is moving. It is always "moving relative to frame X". There is no objective moving (motion not relative to anything).
Noax wrote:In Edgar's frame:
After 388 minutes, Edgar has gone nowhere...
Only from his point of view.
By definition. Edgar's frame is, by definition, the frame in which Edgar is stationary. Same for the others.
Noax wrote:...but his clock reads 388...
How did it jump from 97 to 388?
In Edgar's frame, event Q (Edgar is not present there, it is some distance away) is simultaneous with the event of Edgar's clock reading 388. Simultanaity is completely frame dependent, and the figure of 97 was worked out in Oscar's frame, not Edgars. So in Oscar's frame, it only takes 194 minutes for Q to happen, and since Edgar's clock is the one moving, it ticks off only half that, so 97. In Edgar's frame, 388 go by, and Oscar's clock is moving at half speed, so it reads 194 at event Q. Notice that in the frame of either, the clock of the other runs half as fast. I chose the speed to get that factor of 2, to help keep the math simple.
Noax wrote:...and event Q happens 336 light-minutes to the right, which is Oscar and Irving meeting. Oscar's clock is running at half-speed, so it reads only 194.
Now it's Oscar moving. The speed of 0.866c is relative to Edgar; they can't both be going that fast.
It said "In Edgar's frame" above this part. Edgar is stationary here.
Noax wrote:In Irving's frame:
Irving is moving at .866c to the left in Edgar's frame, so Edgar is moving .866c to the right in Irving's frame. Irving's clock reads 194 because he is just now at event Q syncing his clock to Oscar's. At event Q, Edgar's clock reads 679 minutes.
Note that simultaneous with the same event Q, Edgar's clock reads 97 in Oscar's frame...
That's in Edgar's frame, if indeed he is the one moving. In Oscar's frame, Edgar's clock reads 35 according to you.
Nobody is "indeed the one moving". This is relativity, which has no such concept. In Oscar's frame at event Q, Edgar's clock reads 97. I said that at the top in the part labeled "Oscar's frame". If Oscar looks at Edgar's clock from that distance, he would not see 97 because Edgar is 168 light-minutes away, so the ~35 value is just what he sees, not what it is now. I told you the 35 figure is unimportant, and also not accurate, but it is somewhere around there.
Noax wrote:Still in Irving's frame, between events Q and R:
After 194 minutes, Irving has gone nowhere, but his clock reads 388, and event R happens, which is when Irving and Edgar meet.
In order that Irving and Edgar meet, they will have to be travelling at different speeds, relative to Oscar.
Yes, that is described at the top. From Edgar's frame, Oscar is moving to the right, and Irving to the left, both .866c. That means in Irving's frame or Oscar's, the other is moving more like .989c with a dilation factor of 7, but those two don't care about each other's clocks, so I didn't ever describe things between those two.
I dunno; this is doing my head in. Get back to me if I misunderstand and we'll take it from there, but I think this illustrates the problem of mistaking what you see for what there is.
Forget what anybody sees, since they see only the past if they're looking at something not in their own presence. Clocks are synchronized/compared only when they're in each other's presence, such as each of the 3 events. If something is in your presence, that is what is. If something is distant, then what you see is the past, not what is. The whole description I gave (except for the 35 thing) is about what is, not what is seen. Drop the preconception that there is "indeed the one moving or stationary" and it is not too hard to understand.