I’m watching Falling Skies. Awhile back I saw Independence Day on TV, and I saw Battle: Los Angeles in theaters. They’re all reasonably entertaining (ID4 beats B:LA by a long shot though, jury’s still out on Falling Skies). Still, it’s disappointing that the writers/directors make the aliens so stupid.
Assuming the aliens aren’t in some way handicapped — that their intent is to invade, rather than them being shipwrecked here — they would wipe the Earth clean easily. It wouldn’t even be a contest. The most we could hope to do is be their pets or their food.
How Aliens Would Actually Invade, Scenario 1
Let’s make it hard on the aliens and say they have no more advanced weaponry or technical capabilities than we have, other than the self-evident fact that they are capable of interstellar travel. That still leaves them with an insurmountable advantage: the unassailable high ground of space.
We have no acknowledged offensive capability outside our atmosphere. We certainly have no way to put hardware in space in any quantity, especially beyond low earth orbit — a few hundred miles up. It’s possible we have the ability to point offensive lasers upward, but that’s about it (if we can do that). To ensure we can’t get to them, and to guard against any possible laser attack, the aliens set up shop on the far side of the moon.
To travel between the stars, the aliens must have (at least) the ability to apply a large amount of thrust to things. So once they’re set up 240,000 miles away, they throw rocks, which the moon has plenty of. The rocks might be only about 100 meters in diameter (Meteor Crater meteor). We might be lucky enough to have a few days’ warning, or it could be a complete surprise. Either way, our cities would be gone in a matter of hours. Not just the big ones — there would likely be several thousand rocks (List of urban areas by population). In a day or less, the world would have nothing left but villages, with over half the world either dead or homeless.
Of course, they won’t stop, they’ll keep chucking rocks. They’ll work their way down through every piece of infrastructure we have, systematically destroying everything that supports our current population and technological ability. Within a few months, our level of widespread technology will drop back to the middle ages, with a population to match; without infrastructure, more billions will die.
What happens next depends on how patient they are, and how strong an air and ground force they have. But assume they’re in a hurry, and they have a relatively small/weak force. They’ll take over our orbital space first, destroying everything of ours and putting their own in place. They’ll make sure to destroy every airport on the planet, and establish total air superiority as they move in from orbit. They’ll establish positions on small, relatively uninhabited islands, and start setting up shop.
From this point it’s just further downhill: they set up infrastructure on any island they can clear of humans, while we’re kept primitive because anything we build bigger than a grass hut gets a rock from space. Depending on how fast they breed and how many of them there are to start, we’re totally wiped out in anywhere from two hundred to fifty years or even less.
How Aliens Would Actually Invade, Scenario 2
If the aliens are a little (not much) more technologically advanced than we are, they snatch a few dozen people. They research them, experiment on them, and develop a virus that causes cold-like symptoms at first, but then kills after a few weeks. They drop the virus in a few hundred cities. A month later there are only a few million of us left. Civilization comes to a halt. Then jump to the last two paragraphs of scenario 1 and you’re done.
How Aliens Would Actually Invade, Scario 3
If they aliens are fifty years of development time ahead of us, they send a few billion insect-sized robots down. The robots hunt and poison humans. We’re all gone within a few days or weeks. End of story.
It’s a good thing there aren’t any intelligent aliens looking to take over our planet.