A laser beam is only visible in two situations - if you're directly in it's path, or if the light from the beam is scattered out of the beam. Even in air, they're usually invisible to the unaided eye.
Somebody already raised the point, though - in science fiction, ray guns need not be lasers. The weapons in Star Trek use a few different mechanisms, but they're all based on some type of charged particle, not coherent light.
About the brain sucking aliens, though? There's actually a few pretty good examples here on earth of parasites that radically alter the behavior of their hosts, and most of them can infect different species with similar results. A fungus that infects a specific species of ant and causes them to climb to high places and release their spores has been shown to work on almost any ant species. A parasite that causes rodents to seek out predators has been linked to behavioral changes in multiple species it has never evolved to infect.
All this is based on the similar chemistry accross life, but a few scientists are finally starting to fight back against the growing trend that alien life must be so radically different to our own. No example of a viable silicon organic compound has ever been found or created, it's still purely theoretical if it's even possible. Carbon organic molecules follow pretty predictable forms - we've found the simplest ones all over in space already, up to and including amino acids. There's growing evidence that, while alien life will be radically different to us physically, if it's carbon based, there will likely be a great deal of chemical similarities.
A laser beam is only visible in two situations - if you're directly in it's path, or if the light from the beam is scattered out of the beam. Even in air, they're usually invisible to the unaided eye.
Somebody already raised the point, though - in science fiction, ray guns need not be lasers. The weapons in Star Trek use a few different mechanisms, but they're all based on some type of charged particle, not coherent light.
About the brain sucking aliens, though? There's actually a few pretty good examples here on earth of parasites that radically alter the behavior of their hosts, and most of them can infect different species with similar results. A fungus that infects a specific species of ant and causes them to climb to high places and release their spores has been shown to work on almost any ant species. A parasite that causes rodents to seek out predators has been linked to behavioral changes in multiple species it has never evolved to infect.
All this is based on the similar chemistry accross life, but a few scientists are finally starting to fight back against the growing trend that alien life must be so radically different to our own. No example of a viable silicon organic compound has ever been found or created, it's still purely theoretical if it's even possible. Carbon organic molecules follow pretty predictable forms - we've found the simplest ones all over in space already, up to and including amino acids. There's growing evidence that, while alien life will be radically different to us physically, if it's carbon based, there will likely be a great deal of chemical similarities.