The most likely solution to the Fermi paradox is that being intelligent isn’t a particularly successful evolutionary strategy. Our level of smarts took a long time to evolve on Earth and it only happened once, a few thousand years ago. This strongly suggests that the evolution of intelligence isn’t particularly easy or likely. The Great Filter is behind us.
I don’t find the solution for the Fermi paradox favored by Casey Handmer on his blog convincing. He argues that if aliens travel close to the speed of light, only a short while would pass between us observing their spaceship and them arriving on Earth.
This would only be an solution for the Fermi Paradox if there were only one alien species. This is unlikely if intelligence evolves easily. If it doesn’t, my favored solution of the Great Filter being behind us is more likely.
A more subtle point is that with respect to the Fermi Paradox, it doesn’t matter how fast the aliens travel, assuming that they’re detectable at all. If they traveled slowly, we’d see their ships in our telescopes and the paradox would be resolved. If they traveled fast, we probably wouldn’t see them until shortly before they arrived here, but again, the paradox would be resolved. If they were already here, there wouldn’t be a paradox in the first place.
Nehaveigur 