Twin paradox: the real explanation

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Recommends user218113 · 2018-04 · Physics Stack Exchange · on “What if two twins flew off in opposite directions and were reunited in a perfectly symmetric way, would they have aged same?”

Thanks, just one more clarification, the above space time diagram is from the reference of Earth, but if we use the reference of a twin, we will get the space time diagram of the classical twin paradox which predicts time disagreement between the twins. So my question is this how is this different from the classical twin paradox? (I know acceleration is not the key, thanks to [this video] ), and if not for acceleration the classical twin paradox and this are essentially the same thing

Recommends Mauro Giliberti · 2020-10 · Physics Stack Exchange · on “Does changing direction change the frame?”

There is no "turns back instantly" in relativity. He needs to decelerate, stop, turn, and accelerate again. Acceleration (for special relativity) is a change in frame of reference (so yeah, a person orbiting a planet is constantly changing frames. This is explored in GR). There is a way to go past this problem and study the real core of the twin paradox (I think this is what you were referring to): in the "modified twin paradox" one person stays on earth (1), one leaves (2), and one comes from far away (3). When (2) and (3) meet they exchange data on distance and time, and then compare them with the ones for (1). You still need three frames of reference but there is no acceleration involved:

Recommends Roger Wood · 2020-12 · Physics Stack Exchange · on “Time dilation due to acceleration - four simple situations to try to clarify”

I see some relatively comprehensive answers here [LINK] but then I listen to this Don Lincoln presentation on the twin paradox [this video] which seems to be saying that the resolution to the paradox is more fundamentally due to the change in inertial reference frame, not the acceleration implicitly involved. To try to clarify, let me pose that there are four observers in four distinct situations. At a particular instant in time, the four observers determine that they will all be stationary with respect to each other. The differences lie only in their accelerations and gravitational fields. The four situations are: A) Zero velocity, zero acceleration, gravitational field and potential = 0 B) Zero

Recommends mmesser314 · 2021-02 · Physics Stack Exchange · on “How could we determine how much time have passed without an artificial reference frame?”

There really is no one answer to this. There is no such thing as absolute time. There is only time difference between the start and end. So you have to keep track of how far you have come in time in some way. It is sort of like seeing how far you have travelled on a featureless plain. You have no way of knowing where you are. But you can put an X where you started, and measure how far from the X you are. You can keep track of time by wearing a watch that you keep with you. Or by setting up a clock and reading the time from where ever you are. But time doesn't travel at the same rate for everyone. You can different answers, depending on the route you take. In special relativity, you always se

Cites user218113 · 2018-04 · Physics Stack Exchange · on “What if two twins flew off in opposite directions and were reunited in a perfectly symmetric way, would they have aged same?”

Thanks for the answer, this means a lot to me, just one more clarification, the above space time diagram is from the reference of M, but if we use the reference of P'', we will get the space time diagram of the classical twin paradox which predicts time disagreement between the twins. So what my question is this how is this different from the classical twin paradox? (I know acceleration is not the key, thanks to [this video] ), and if not for acceleration the classical twin paradox and this are essentially the same thing

Cites user218113 · 2018-04 · Physics Stack Exchange · on “Does two people heading towards each other see each other's clock getting faster?”

But the symmetry is only because of the acceleration, and acceleration can be completely removed from the argument [this video] if we assume instant acceleration, then the space time diagram looks the same

Critical Jacques Le Normand · 2022-05 · Physics Stack Exchange · on “Simple resolution to the twin paradox?”

There's also this video that claims that the "real explanation" is not acceleration (from a very good source: Fermilab): [this video]