wrote:
Dirk Van de moortel wrote:
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.

I did not change frames. We are talking about the frame of the
spaceship. The ship was first at rest on earth, and then it
accelerated towards Centauri.
It is not inertial, true: Does that mean that objects can go faster
than light in a non-inertial frame?

What you did not account for is that at your ship's "so fast"
speed, the distance between Earth and Alpha Centauri is much
less than 4ly.


--
--Bryan