From: "Ralf Müller" <r_mueller@...>
Date: 2005-02-09T16:18:18+09:00
Subject: Re: [OT] Physics of black holes (Was: RubyConf '05)

On Wed, 9 Feb 2005 07:18:02 +0900
"Josef 'Jupp' Schugt" <jupp@gmx.de> wrote:

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> Tim Bates wrote:
> | Josef 'Jupp' Schugt wrote:
> |
> |> Superluminal speed ist nothing that requires a hyperspace. The
> |> relative speed of galaxies for example is known to exceed the speed of
> |> light.
> |
> | If you have two galaxies on opposite sides of the universe (call them
> | A and B) with an observer in between (called O) then from O's frame
> | of reference the sum of the speeds of A and B might exceed c (the
> | speed of light), although neither galaxy's individual speed can
> | exceed c, BUT from A's frame of reference B's speed does not exceed c
> | and vice versa.
> 
> Actually it is the distance as a property of space-time that increases
> faster than c. This means that light from B has no chance to reach A. So
> ~ no information from B reaches A and relativity is not violated.
> 
> The problem of frames of reference leeds me to the following question:
> 
> Say object A and B represent two physical objects moving at relativistic
> speed. Should A.speed(B) represent the speed of B in the frame of
> reference of A or the speed of A in the frame of reference of B?
> 
> Josef 'Jupp' Schugt

Isn't this just a question of definition? If A.speed(B) stands for one thing, maybe b.speed(A) should stay for the other, but this is just a language topic. What is intuitive and what is not. 
I think the main thing is, that there are two speeds, both having equal rights.