Invisible <voi### [at] devnull> wrote:
> >> My understanding of general relativity is limited, but I was under the
> >> impression that "first" is not a meaningful concept at relativistic
> >> velocities.
> >
> >    That would be paradoxical.

> Yes. It's general relativity. It bemuses everybody.

  General relativity does not introduce paradoxes.

> >    Assume that intelligent life evolves in planet A, and it starts sending
> > radio signals to outer space. These radio signals eventually reach planet B.
> >
> >    Some time later life

> Your language is still assuming that "earlier" and "later" are valid terms.

  Clearly if B receives a radio signal from A, the radio signal was sent
before it was received. The signal being received before it had been sent
would be paradoxical (it would mean that the signal travels back in time,
which would require FTL travel, and as we know, radio signals don't).

  If we define the concept of "intelligent life" at "capable of sending
and receiving radio signals to/from space", clearly intelligent life
developed in A before it developed in B.

  I'm not saying there aren't situations where whether A evolves before B
or the other way around depends on the frame of reference. What I am saying
is that when A's light cone (which started when intelligent life appeared
on A) reaches B (before intelligent life appears on B), it becomes
unambiguous. An ambiguous situation in this case would require FTL (and
hence time) travel.

  Hence you can unambiguously state that intelligent life developed in A
before it developed in B.

-- 
                                                          - Warp

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