Mimsofthedawg said:
Well, I recently read up on a guy's work. He basically said that Earth is the only planet capable of life. His reasoning is basically like this: mathematically, each universe (he has mathematically proven the possibility of other universes outside of our own - completely unconnected to ours existing in a field of limitless energy)has a set of physics. Each universe would have completely different mathematical laws governing it. One universe could be completely devoid of gravity. Another could be completely devoid of mass. Still another may have gravity and mass in such abundance, that they hardly meet our concepts of what gravity and mass are. Essentially, at the creation of this universe, the "mathematical dials" of the basic laws of physics were turned in such a way that it ensured ONLY earth could have life on it. In otherwords, you can mathematically fix the position in each universe and find where life would exist in that universe. In ours, earth is the only possible solution - because there is only one solution to this equation. In others, there may or may not be a solution. This guy said that the possibility of life on another "planet" isn't on a solar system by solar system basis, or even on a galaxy by galaxy basis. It's on a universe by universe basis. Assuming that other universes are created along this field of energy, he calculated that only 1 in every 13 trillion would have life. He also calculated that there could be an exact duplicate of earth and even our timeline in another universe. But that chance was such a big number, I can't remember what it was... but it had a LOT of zeros after it.
I'd like to see this theory, because the last I heard (studying Astrophysics at university a few years ago) there is no way of proving the existence of other universes. There are lots of mathematical and logical theories that, if they are right, prove their existence, but we currently have no way of proving if they are right. Ditto for the laws of physics in other universes, we have no way of knowing or proving if they would be the same or different.
Back OT:
There almost certainly are other civilisations out there somewhere, but I'm afraid the 'conservative' estimates mentioned earlier don't get nearly conservative enough. There are so many factors involved in solar and planetary formation: to have 1 million civilisations in the Milky Way, you need 1 civilisation for every 100,000 - 400,000 stars. Half of those will be in multiple-star systems, so there is 1 civ per 100,000. 76% of those stars are too cold to support habitable planets, and 1% too hot, so now it's 1 civ per 23,000. 10-20% of these stars are estimated to have planets - roughly 1 per 3500.
It is believed that we need both a very large moon around the planet AND a very large gas giant to even allow life to form without being shelled by asteroids every few centuries. I believe the current rate of either of these happening is less than 1%, based on our observations of several hundred extra-solar planetary systems, although this could change with more observation. This puts us at 1/3 of a civ per star, or to put it better, there are roughly at most 300,000 inhabitable planets in the Milky Way, and that's before you consider ecology and biology in the equation (don't worry, I'm not a biologist as well, I'm almost done).
Finally, I will also add that there is about one fifth of the galaxy we cannot see because of the galactic core blocking all signals from it, so any civs there will be almost permanently uncontactable, and that any signals from other galaxies will be so weak when they arrive that we will not be able to detect them above the cosmic background radiation.
TLDR: There are probably fewer than 1000 or even 100 civilisations in the Milky Way, and other galaxies are so far away as to be completely irrelevant.
EDIT: Forgot to put my actual opinion in here: I believe that it is almost certain that life exists somewhere, just not that we are likely to ever encounter it.
