In message , Androcles
writes

"Rudolf Drabek" wrote in message
...

"kenseto" schrieb im Newsbeitrag
...

"Rudolf Drabek" wrote in message
...
Indeed its very simple. Look into the FAQ files for the Twin
Paradoxon.
The moving twin coming back e.g. from Sirius needed only e.g. 4 years
on
his
clock.
And the distance is about 8 lys. so 16ly years in 4y shiptime gives
about
avg. 4c.
But observers on earth measure that the ship has never exceeded 1c.
Its a question of where you are.

Ah....but you can't compare the ship's 4 clock years with the earth's
16
clock
years directly. Why? Because the passage of a clock year in the ship is
not
equal to the passage of a clock year on earth. To make the comparison
you
must convert the ship's clock years to the earth's clcok year as
follows:
Converting the ship's time to earth time=gamma*4 ship's clock
years
=16
earth's clcok years.
What this means is that a physical clock is NOT a universal clock. A
clock
second does not contain the same amount of universal time (absolute
time)
in all frames of reference.

Ken Seto

Yes you are right. But I don't know a universal clock.
But the original question was, if its possible to exceed c.
The gamma of 4 is no question and o.k.
The observation of the rocketeer twin after return is that he needed 4y
and
his twin on earth is 16y older.
So the moving twin knows he had a passage of 16ly in 4y shiptime = 16y
earthtime.
speed in the rest frame was nearly c, speed in moving frame was about 4c.
That's all what Androcles wanted to know I think.

Rudi
Not at all.

[Hiyaah!]

I didn't ask the question you attempted to answer.

Well maybe you should have done.

If there were
any such animal as time dilation,

There is no time.

then GPS clocks would slow down, not speed
up.

Androcles, haven't you heard of retro rockets?

They are actual evidence that your conjectures are hopelessly wrong, and
there is nothing (except the practical difficulties of constructing a
fuelling a suitable vehicle) to prevent a velocity exceeding c, except a
religious-like faith in the word of one man that got his math wrong.
Androcles

What a c***!
--
[Hiyaah!]
http://www.earthpoetry.demon.co.uk
RC