Hi there Jack,
 JS> >  JS> I do not believe we have been visited by aliens from outside our
 JS> >  JS> solar system because of the distances involved. I don't think 
his
 JS> >  JS> will ever happen.
 JS> > This line completely stunned me.   What problem do you see with the
 JS> > 'distances involved'?   Some ship voyages used to take a year or so
 JS> > using the wind and there are about 1000 stars within 50 ly of earth.
 JS> > Nothing impossible about it.  I only feel that it is not a good
 JS> > arguement to hold.
 JS> None of the nearby stars have planets in a configuration that will
 JS> support life as we know it. We cannot see the planets (if any) but we
 JS> can detect a wobble from the star. This is a dead giveaway that one
 JS> or more planets exist in an orbit around the star.  We know of no
 JS> nearby stars that have such a wobble.
Yes, however this method only works when the star is being orbited by a very 
large planet, we can not detect the wobbles of earth sized planets in Earths 
type of orbit. 
 JS> >  JS> I do believe there is a possibility that we will establish 
ontact
 JS> >  JS> via radio some day with at least one other race within the next
 JS> >  JS> thousand years.
 JS> > Exactly the same problem as above, even worst in some respect.
 JS> > Communicating with a star 100 ly away would take 200 years per
 JS> > message. Where as, a trip using relativitic velocities could get real
 JS> > occupants to the other planet in a far shorter time (and not with
 JS> > exceedingly large energies).
 JS> George, there seems to be a little confusion as to how time dilation
 JS> works... Only the clocks aboard the space craft itself are slowed
 JS> down. ...Not those back on earth. If I sent you on a mission to a
 JS> star system 1000 light years away, and you could manage to reach
 JS> relativistic speeds, it would still take you more (considerably
 JS> more) than a thousand years (by earth-time) to reach there. ...And
 JS> the same amount of time to return. I would have aged by more than
 JS> 2000 years, although you may have aged less than 100 years,
 JS> depending on how close to c your ship was able to travel. Time
 JS> dilation only works for the traveler, not the home base of his
 JS> operations, and not for the people at the destination planet.
Exactly, I understand that the people at home do not obtain these benefits, 
but that main purpose was to reduce supplies and increase the interest of the 
crew.  There is no reason why we would not launch such a self-sustained 
mission of colonisation and forget about it.   These arguements strike into 
the heart of the possibility of space travel beyond the solar system.  Do 
some social values make these trips impossible.  I do not think so. 
 JS> You as the traveler have NOT reached the destination star in any kind
 JS> of short time to do us back here on earth any good. ...And you will
 JS> find only your great, great, great grandchildren awaiting your
 JS> return. You would have done well to stay on your giant generations
 JS> ship until you found a suitable planet for your descendants
 JS> to migrate to when the earth is eventually consumed by Sol, in about
 JS> another 5 billion years from now. You do know what a "generations"
 JS> ship is, don't you? It is the only feasible way for man to go to the
 JS> stars. ...Here is one reason why... The closer to c a ship travels,
 JS> the more energy the ship is required to expend. A point is reached
 JS> where it is impossible to expend any more energy to go any faster.
 JS> Even if vast amounts of energy were available, the ship could never
 JS> exceed .9c due to its mass and the energy required to move that mass
 JS> any faster. The fastest speed measurement ever made of an object
 JS> containing mass was that of a receding quasar clocked at .75c. The
 JS> energy source for this feat can be attributed to the energy released
 JS> at the time of the Big Bang itself.
 The energies are not as extreme as some people would like you to think.  The 
reason we can only see a 0.75C quasar is because the particles horizon is 
only about 15 billion ly in radius.  The universe is far far larger with 
higher speeds the further out we go.  Yet the 15 billion year time limit, 
ensures we can only see that far into space.  Anyhow, this was obtained 
through a faster than light expansion of space-time early on and is not very 
relevant.  Since we a discussion expansion through space-time not the 
expansion of spacetime.  I will post up the energy requirement of a trip 
on.
       Regards George
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