Relatively confused

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Relatively confused

Postby ralfcis on October 6th, 2018, 8:52 am 

I'm seeing a lot of confusion about the terms reciprocal time dilation, permanent age difference (as shown in the twin paradox) and doppler shift ratio. If Jorrie could just verify the example and interpretation I give here as correct.

This is the STD of the clock handoff of Alice's clock information speeding away from earth at .6c (in red) to Charlie (in green) speeding toward earth at .5c. The pink signals are light signals Bob receives and the yellow are ones he transmits.

6cab.jpg


As long as constant relative velocity is maintained between participants, their clocks as seen from each others perspective are reciprocally dilating wrt one another but there is no permanent age difference occurring between them; they age at the same rate even though each one swears the other is aging slower than they.

So neither Alice or Charlie will show a permanent age difference with respect to Bob. The reason is Alice never closes her spacetime path with Bob and Charlie never starts it. There are rules in relativity in what constitutes valid starts and ends to spacetime paths. Even though Charlie and Bob co-locate, there is no age difference established between them. Even though Charlie has sync'd his clock to Alice's at the handoff and the reading on his clock says that Alice's clock reading has permanently aged 2 yrs less than Bob's when Charlie and Bob co-locate, Alice herself has not aged 2 yrs less than Bob. No acceleration has been involved in causing the age difference on Charlie's clock once co-located with Bob.

If Alice, Charlie and Bob had televised their entire trip and continually transmitted their tv signals out into space, Alice would see Bob's motion picture going at half speed slow motion. Bob would reciprocally see Alice moving in half speed slow motion. Bob would see Charlie going at 2x fast forward and Charlie would see Bob also moving at 2x fast forward normal rate of time. If c is the normal rate of time flow within a frame, Bob and Charlie would apparently see time flow in the others frame at 2c. This is an appearance as there can be no speed greater than c through either time or space.

This is the doppler shift ratio, not reciprocal time dilation. The reciprocal time dilation is .8 the time of earth's clock for both Charlie and Alice from Bob's perspective and also .8 of Charlie and Alice's clocks for Bob's clock from Charlie and Alice's perspectives.

Please confirm as I myself can't convince anyone of these facts.

P.S. Also a quick side question. Are multiple spacetime paths that feed each other in sequence allowed to be depicted on a single STD. I found when this happens, subsequent spacetime paths can erase a permanent age difference as if it never occurred.
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Re: Relatively confused

Postby davidm on October 6th, 2018, 10:03 am 

Sorry, not wading through all this. You don’t engage with what others tell you anyway, so what’s the point? Just two things, briefly.

As long as constant relative velocity is maintained between participants, their clocks as seen from each others perspective are reciprocally dilating wrt one another but there is no permanent age difference occurring between them; they age at the same rate even though each one swears the other is aging slower than they.


As I explained, you can only tell if there is an objectively agreed-upon age difference if the clocks are brought together again and compared. As to the rest, so what? Yes, each swears the other is aging slower; so what? Since each is an inertial frame, they each consider themselves to be at rest and everything is normal for them. This is all well understood.

There are rules in relativity in what constitutes valid starts and ends to spacetime paths.


Here you go again with your “rules.” I’ve already told you about your alleged “rules,” but you ignored it, as is your wont, which is why I suspect most people are ignoring you: you don’t engage with rebuttals.

What are your “rules” for “starts and ends to spacetime paths”? A spacetime path has a beginning and an end! That’s a “rule” to you? And not just a “rule” — you speak of “rules” plural! Why don’t you name those “rules”?
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Re: Relatively confused

Postby TheVat on October 6th, 2018, 10:24 am 

Please keep chat in the one thread on "ralfativity."
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