The Earth is a little blue marble floating on the space, with very favorable conditions for life: water, atmosphere, magnetic field, oxygen... Out of here, life seems impossible: extrem hot over 5000º, or extrem cold ( - 273º); solar storms, radiation... Very hard conditions indeed. However, we do not know if there is (or not) life out of our plantet. Let's see some arguments in favor and against the existence of aliens:
In favor: Universe is very wide, even vast. So big that cannot be conceived by our human minds. Billions of galaxyies with billions of stars, many of them surrounded by dozens of planets... Why not possible that in one of those plantes life could arise?
Against: If there is life out of the Earth, How is that no Alien has come to say hello?
In favor: They haven't say hello because we are not enough important for them. If you meet an ant, "would you try to communicate with it?"
Against: Life, as we know it, is a complex thing which needs a lot of requirements for arising: water, carbon, oxygen... It is not very common to find all these elements together in a planet.
 |
| Gliese 667cc, a possibly habitable planet |
In favor: As said before, the universe is very very vast. NASA is constantly finding planets defined as "habitable": this means that in those planets there is water, athmosphere with oxygen, etc.
Against: Let's assume that there is intelligent life out of the Earth. Here comes the problem of distance. The closet star to our Solar System is Alpha Centauri, which is 415.900.000.000.000 km far. And this is the closest one. Imagine the distance which an alien had to cover from remote areas of Universe. It would take hundred of years to travel from one to other habitable planet.
In favor: Alien's technology could be more advance than ours. Maybe they have found a way for travelling great distances very fast; for example, curving the space - time line.
The discussion could be eternal. What do you think? In favor or aganist the existence of aliens?
