[ExI] End of Story? Re: QT and SR

[Lee Corbin]

Serafino writes

>> > It is not safe to use a single looong spaceship, because
>> > the front and the back like to accelerate differently and
>> > ... people who take seats in front age differently from
>> > the people who are on the back.
>
> Lee:
>
>> But that's only true if the engines are separate and spread
>> throughout the length of the spaceship.
>
> It is the relativistic (single engine) rocket, in uniform
> acceleration.

Oh!  Of course. You're right. *This* effect occurs
according to the Equivalence Principle also if one
had a very tall building in a hypothetically greatly
extended uniform gravitational field. The Mössbauer
effect

Yes, and it's not acceleration that causes time-retardation
(a misunderstanding under which I labored for twenty
years) but being that deep in a gravitational field.

> http://math.ucr.edu/home/baez/physics/Relativity/SR/rocket.html
>
> From what I remember, the front and the back of the
> (single engine) rocket, accelerating uniformly, have
> different worldlines and they have different accelerations.

Well, let's see. Although we've drifted into GR from SR,
yes, clearly the two trajectories must be different as
seen on a spacetime diagram, since the loooong ship
does become shorter. So it would also follow that
they'd have different accelerations too.

Lee

> It follows that clocks run at different rates through
> the rocket, and travelers age differently. Of course
> since the length of the rocket is small, these time effects
> (and the possible stress due to the differential acceleration)
> are relevant only in theory.