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From: ram@zedat.fu-berlin.de (Stefan Ram)
Newsgroups: sci.physics.relativity
Subject: Re: Langevin's paradox again
Date: 11 Jul 2024 14:09:32 GMT
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"Paul.B.Andersen" <relativity@paulba.no> wrote or quoted:
>But what happens when twin B is accelerating makes all the difference.

  From the perspective of the twin chilling back on Earth, the
  traveling twin is getting the time dilation treatment the whole time,
  so he ages way less. That part's a no-brainer. But now let's flip
  the script and look at it /from the traveling twin's point of view/:

  When the traveling twin bounces from Earth (I'm assuming
  constant velocity for simplicity), time on Earth starts slowing
  down for them. Not like, looking through a telescope slow,
  but like, the time between two moments on Earth that line up
  with a single second on the spaceship is actually less than a
  second. Trippy, right? 

  Then when the traveling twin boomerangs back to Earth, time is
  still dragging for them. That's the time dilation working its
  magic - independent of the direction of the movement.

  So the traveling twin should be thinking his Earth-bound bro is
  aging slower. But somehow, it's the opposite - the Earth twin is
  looking way more mature. What gives? Could it have something to do
  with that quick boost in the middle to flip the script and head back?

  This is the question that's been stumping everyone, but get
  this - I found the answer last year in some old Einstein text. 
  Here's how it breaks down:

  The traveler thinks of himself as stationary and unaccelerated. But
  how does he keep that mindset when the engines are blasting during
  the turnaround? It's like there's a uniform gravitational field
  filling the whole space - the engines are just keeping the ship from
  falling in it, so it stays at rest! 

  So if the traveler sees himself as at rest during that acceleration,
  a uniform gravitational field is filling the whole space for him.

  In this field, the traveler and Earth twin are at totally different
  potentials (and the farther apart, the bigger the difference).
  This potential gap makes time on Earth zoom by so fast, it more
  than makes up for the slowdown on the outbound and return legs!

  And that's why, /also from the traveler's point of view/, more time
  has passed on Earth than on their ship by the end of the trip!

                              ~~

  BTW: I just read the name "Langevin" in some book:

|In 1924, Prince Louis de Broglie of France proposed in his
|doctoral dissertation that the electron, evidently a discrete
|point particle, might actually be a wave. De Broglie's thesis
|advisor, Paul Langevin, did what befuddled senior professors
|are wont to do: defer to a higher authority. He sent the
|dissertation to Einstein, who recognized its importance
|immediately. On Einstein's say-so, Langevin gave de Broglie
|his degree.

  .