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Relative reference is an illusion that appears
We are told that there is no absolute reference, so pretending to run is as good as actually doing it
The beaker that is not moving, if it had consciousness and an imagination, can pretend to be the moving reference,
Bored_Chemist, this seems like it may just be "fighting talk" and yo mama jokes but be careful not to drive people away from taking an interest in science, please.
Each relative reference may see the other reference appear contracted in space and time. However, if you include mass, as a stand alone variable, one has a way to determine absolute reference priority.
It's like another paradox to be resolved.
I was going to mention the bug - rivet paradox which was discussed back in my day.
those two events are outside each other's causal light cones
I wish they'd stop calling things paradoxical that are not.
An interesting observation about relativity is connected to clock experiments where clocks will permanently gain or lose time. Paradoxically, although time will change in a permanent way clock distance/size changes due to relativity are fully reversible.
Let's say that initially both twins are separated from each other, while having the same age
and one of them is moving at a constant velocity towards the second one.
But when at some point those twins will meet in space, one of them will be older than the other - how can it be, if in the rest frames of each twin it was the other twin, that was moving?
Problem is, that in SRT the twin paradox can be explained only in the case of two-directional motion, where one twin is traveling to a distant destination and comes back to the second twin.
Quote from: CrazyScientist on 20/05/2021 08:34:20Let's say that initially both twins are separated from each other, while having the same ageThat can only happen if they both accelerated and decelerated at exactly the same rate.
Quote from: CrazyScientistand one of them is moving at a constant velocity towards the second one.That means the moving twin must have accelerated to the constant velocity.
But The twin that accelerated will be the one that is younger when he decelerates to the other twins frame, just as SR predicts.
A one way trip will still result in the traveling twin being younger. Say you fly to a planet at relativistic speeds that is 10 ly away. When he lands on the planet (let's assume the 2 planets are relatively stationary with each other) he will be younger than the stay at home twin.
No, that can only happen relative to a few very specific frames and not relative to most others. The comment by CS is making the very same mistake as the OP: Assuming an absolute ordering of events, such that the comment has meaning without a frame reference.
The question was about twins separated by space but both having the same age.
My thought was this could be accomplished by...
Quote from: CrazyScientist on 20/05/2021 08:34:20Let's say that initially both twins are separated from each other, while having the same ageThat can only happen if they both accelerated and decelerated at exactly the same rate.Quote from: CrazyScientist on 20/05/2021 08:34:20and one of them is moving at a constant velocity towards the second one.That means the moving twin must have accelerated to the constant velocity.Quote from: CrazyScientist on 20/05/2021 08:34:20But when at some point those twins will meet in space, one of them will be older than the other - how can it be, if in the rest frames of each twin it was the other twin, that was moving?The twin that accelerated will be the one that is younger when he decelerates to the other twins frame, just as SR predicts.Quote from: CrazyScientist on 20/05/2021 08:34:20Problem is, that in SRT the twin paradox can be explained only in the case of two-directional motion, where one twin is traveling to a distant destination and comes back to the second twin.A one way trip will still result in the traveling twin being younger. Say you fly to a planet at relativistic speeds that is 10 ly away. When he lands on the planet (let's assume the 2 planets are relatively stationary with each other) he will be younger than the stay at home twin.
Quote from: Origin on 21/05/2021 12:04:34The question was about twins separated by space but both having the same age.That part is ambiguous, as I have explained. CrazyS also stipulated that they're moving towards each other, not reflected in your example which has them moving apart.QuoteMy thought was this could be accomplished by...It can be accomplished in any number of ways, including one of them being inertial the whole time. Each 'twin' represents a worldline, and them being age X (unspecified) defines a pair of events, one each on their respective worldlines. Events are frame independent facts. There are two possibilities regarding the relationship between the two events: Either they are outside each other's light cones or they are not. In the latter case, one twin is objectively older than the other, so this is inapplicable. In the former case, the ordering of the two events is frame dependent, so saying they're the same age is the same as saying the two events are simultaneous, which they are only relative so some very specific frames. Relative to most frames, one of the events occurs before the other. This is straight up relativity of simultaneity. Saying they're the same age without a frame reference is the same as saying two spatially separated events are simultaneous without a frame reference. It's not even wrong.In your scenario, due to symmetry, they're the same age relative to the Earth frame, but if they're moving apart at over .88c relative to each other as you have them, then in their respective frames, each will say that the other ages ~1.88 years after those 4 years. So different answers depending on the frame used.Similarly, one could stay home and the other zooms to a star 10 LY away, turns around and starts the journey home. This actually corresponds to the scenario CS mentioned where they're moving towards each other. In that scenario, there are frames in which either is older than the other, and some where they are the same age. It all depends on your arbitrary choice of frame.