I believe the very idea that life cannot exist on other planets is ludicrous. With the tens of billions of stars in every galaxy, hundreds of millions of galaxies currently visible in the universe and the percentage of stars that have orbiting planets, the chances for life occurring on some other ones is relatively high. This assumes that everything in the universe is visible to us--which may or may not be the case. The universe could be a million times larger than its perceived diameter, and we would never know, since light has only been able to travel for 13.7 billion years, and the rest would be invisible to us.
However, the chances of such life visiting earth are profoundly low, given our current knowledge of physics. If intelligent, space-faring life is to be found out in the universe, it cannot be able to travel faster than the speed of light (again, according to current theoretical physics). This puts the ability of anything to travel to Earth at practically zero, given the enormous distances between the stars and the time it would take to travel even at light speed.
Secondly, Einstein's theory of relativity actually works against light speed travel, much less superluminal speeds. A spacecraft would need an infinite amount of energy to accelerate to light speed, because its mass would increase the closer it came to the speed of light. Our particle accelerators can get electrons and protons to 99% the speed of light, but these are subatomic particles and the mass is tiny, though the gain in mass at these speeds is measurable and significant.
The evidence cited by pro-UFO and pro-alien camps is flimsy at best. Most UFOs end up being weather phenomenon, aircraft, stars, or balloons. The best explanations for the unexplainable saucers is that Area 51 is a test site for advanced Air Force craft, run by humans, since the secret government technologies tend to be 20-30 years ahead of our current knowledge of them. Alien encounters themselves only seem to be experienced by rednecks, which greatly decreases the likelihood of truth.
However, the chances of such life visiting earth are profoundly low, given our current knowledge of physics. If intelligent, space-faring life is to be found out in the universe, it cannot be able to travel faster than the speed of light (again, according to current theoretical physics). This puts the ability of anything to travel to Earth at practically zero, given the enormous distances between the stars and the time it would take to travel even at light speed.
Secondly, Einstein's theory of relativity actually works against light speed travel, much less superluminal speeds. A spacecraft would need an infinite amount of energy to accelerate to light speed, because its mass would increase the closer it came to the speed of light. Our particle accelerators can get electrons and protons to 99% the speed of light, but these are subatomic particles and the mass is tiny, though the gain in mass at these speeds is measurable and significant.
The evidence cited by pro-UFO and pro-alien camps is flimsy at best. Most UFOs end up being weather phenomenon, aircraft, stars, or balloons. The best explanations for the unexplainable saucers is that Area 51 is a test site for advanced Air Force craft, run by humans, since the secret government technologies tend to be 20-30 years ahead of our current knowledge of them. Alien encounters themselves only seem to be experienced by rednecks, which greatly decreases the likelihood of truth.