# Re: Another stab at the universal present moment - a gedanken..

But it does matter how long you coast between accelerating away from Earth and the braking maneuver in which you accelerate back toward Earth. If you don't coast at all there is only a small effect. If you wait a long time, 10yrs, there is a big effect - which is easily seen in terms of the difference in length of the world lines in Minkowski space.
```
Brent```
```
On 1/3/2014 8:13 AM, Edgar L. Owen wrote:
```
```Jason,

```
Come on Jason. Of course not. You have to have EQUAL amounts of acceleration to produce the same effect. But doesn't matter where in space it is.
```
Edgar

On Friday, January 3, 2014 10:24:26 AM UTC-5, Jason wrote:

On Fri, Jan 3, 2014 at 10:19 AM, Edgar L. Owen <edga...@att.net
<javascript:>> wrote:

Jason,

If the acceleration is the same, the slowing of clock time will be the
same...
Doesn't matter where it is. Or equivalently (by the principle of
equivalence) it
could be standing 'still' in a strong gravitational field.

Edgar

Okay but this is certainly not what happens.  If you spent 4 minutes
accelerating
and came back, there would not be a 4 year age difference when Pam returned.

Jason

On Friday, January 3, 2014 10:06:08 AM UTC-5, Jason wrote:

On Fri, Jan 3, 2014 at 9:21 AM, Edgar L. Owen <edga...@att.net>
wrote:

Lliz, Brent and Jason,

Actually Liz is correct here, by GR it is the acceleration.
That is the
physical cause of the clock time differences of the twins.

In my experiment, lets say the acceleration lats for a total of 4
minutes:
one minute to accelerate up to 0.8 c, one minute to slow down at
Proxima
Centauri, one minute to accelerate back up to 0.8 c toward Earth,
and a
final minute to accelerate down to back at Earth.

If the accelerations alone account for the clock discrepancies,
then there
would be no need to go to Proxima Centauri at all.  Pam could spend
4
minutes whizzing around the solar system and get in all the same
accelerations.

Is this what you are saying?

Jason

It is true the effects can also be analyzed just by spacetime
paths as
others have suggested, but it is actually the acceleration (or
equivalent gravitational field which is in effect an
acceleration) which
actually physically produces the clock time differences when
the twins
meet up again.

Edgar

On Friday, January 3, 2014 1:27:55 AM UTC-5, Liz R wrote:

On 3 January 2014 17:30, meekerdb <meek...@verizon.net>
wrote:

On 1/2/2014 8:00 PM, LizR wrote:
```
```                        On 3 January 2014 15:52, Jason Resch
<jason...@gmail.com> wrote:

On Thu, Jan 2, 2014 at 9:31 PM, LizR
<liz...@gmail.com> wrote:

Jason,

You may be missing the fact that the
acceleration of
the space traveller is what causes the twin

I would say it is not so much the acceleration that
explains the paradox, but the fact that no matter
how you
rotate the paths, you always see a kink in the path
Pam takes.

May I venture to suggest this is the same thing :-)
```
```
That's not exactly wrong - but it tends to make it
confusing.
It's like saying a road from A to B is longer than
as-the-crow-flies because of its curves.  Yeah, that's
true; but
if you want to calculate how much longer you see that
the rate
of excess distance is proportional to the first
integral of the
curvature and so the total excess is the second
integral of the
curvature - which is just the distance.  So it boils
down to
unstraight lines are longer than straight lines.  All
the
specific details of acceleration get integrated out so
it's easy
to see that a broken line (infinite accelerations) is
just
longer.  Or in spacetime, unstraight worldlines are
shorter than
straight ones.  To phrase it in terms of acceleration
people into thinking about the stressful effects of
acceleration
and how that could affect a clock,...

the aging
effects of acceleration (as in the Heinlein story where
they have to
fly to Pluto at 3G) but just the fact that the course
changes are
the only way the twin paradox can be enacted - that is to
say, it's
what breaks the symmetry that otherwise exists between one
ref
frame's measurements and another's.

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