What would happen if a Independence Day movie-like alien invasion happened today?
There are not many things to find on our planet that cannot be found elsewhere. Both water and oxygen can be found on other planets.
The one thing our planet has that the others do not is a biosphere. But this is only really interesting if the aliens have a compatible biology, meaning DNA based. That may well be the case if the panspermia theory is right - and it does look to be the case.
So, aliens could be interested in colonizing our planet if it is sufficiently close in composition to theirs. I talk about the air here. So, if they also need around 21% of oxygen and nitrogen isn't toxic for them and that our bacteria aren't too much of a problem for them and they really want to settle here, then they'll probably either create some new disease that wipes out humanity in a few weeks or months or send some nanometer sized robots that can kill discriminatingly (only humans) in which case the "war" would be over in a few hours at most.
I doubt there would be single gunshot (or laser or whatever) exchanged between our species. Humanity would just cease to exist.
Using big blazing guns when you want to take over the place is stupid.
What could present say humanity do to fight of an alien invasion, like the one from Independence Day.
So far the only time a technologically inferior force beat a technology superior force was when the Afaganastan mujahideen were able to slowly wear down both the Anerican and Soviet forces and forced them to retreat. We would try and make it a war not worth fighting for the aliens.
We would have to wear down the alien invaders, not fight them head on. We would destroy the satilites in orbit so there would be lots of tiny pieces of space junk going tens of thousands of kilometres an hour, this would prove a difficult challange to the alien invaders as they would most likely have space ships damaged and destroyed from the debri.
If this doesnt work and the aliens make it to earth, we would nuke ourselves so the earth wouldn't be valuable enough for the aliens.
All of this would hopefully drive the aliens into just giving up on their campaign to invade earth.