On Mar 11, 6:52*pm, "
wrote:
On Mar 12, 12:20*am, "Dirk Van de moortel" dirkvandemoor...@ThankS-NO-



SperM.hotmail.com wrote:
wrote in message

*

On Mar 11, 9:08 pm, "
wrote:
Hello again,

Assume I take a spaceship to Alpha Centauri, which is 4 light years
away. And the ship goes so fast, that the travel time seems to me to
be one hour. Will it not seem to me that Alpha Centauri made a journey
that started at x=4[ly] and ended at x=0, during a time of one hour,
and therefore its speed was much faster than lightspeed? Where is my
mistake?

Ram.

Is there anyone interested in answering my question?

Like David said, you divide a distance as measured in the
Earth system (4ly) by the time measured on your lock (1 hour),
but speed is defined as the ratio of distance to time both measured
in the same frame. To you the distance looks shorter and to the
Earth the time looks longer in such a way that both measure the
same value for the speed.

Dirk Vdm

I did not change frames.

You are using numbers from two different frames.

We are talking about the frame of the
spaceship.

The travel distance is not 4 light years in that
frame.

The ship was first at rest on earth, and then it
accelerated towards Centauri.

When it is moving at the very high gamma you
proposed, the distance to Centauri is a small fraction
of 4 light years in that frame.

It is not inertial, true: Does that mean that objects can go faster
than light in a non-inertial frame?

Huh?

- Randy