I just watched a very interesting documentary on black holes that proposed a fascinating theory as to why we haven't been visited by alien life forms yet.
If we take into account the scales of the galaxy and the number of planets there ought to be at least some alien civilisations. And these would most likely be millions if not billions of years ahead of us in terms of technological development. And on that time scale they should have been able to develop some sort of faster than light travel. (and even if they didn't...just by jumping from one star to the next slower then light one could colonize the entire galaxy in a few million years). So why haven't we seen any evidence of aliens comming to visit?
Well recent calculations on the development of black holes have revealed that just before their formation as the star starts to collapse into themselves a HUGE SCHOCKWAVE or Gamma radiation is shot out into space. And the intestity of this radiation is such that it equals 10^9*10ˇ9*10^9 = 10^27 the ammount released in the most powerful hydrogen bomb we have.
So these guys went on to calculate that if such a black hole were to appear up to several hundred light years away from our solar system it would practicaly STERILISE all advanced life on our planet. (perhaps those bacteria deep inside the earth mantle would survive). quote: "It would be the equivalent of Hiroshima type bombs going off all over the planet."
As they can track these Gamma ray "explosions" via a sattelite in orbit (only with a delay of the time it takes for the light to come to us) they began to calculate the probability of something like this happening in our "backyard".
And the recent results (not very accurate yet) say that is possible that these events are frequent enough to sterilise entire regions of the galaxy in short enough time scales to really make it improbable for advanced lifeforms to develop often. ... so I guess we're pretty lucky
[ January 06, 2004, 11:20: Message edited by: JurijD ]