What's your plan in case of an alien invasion??? [...]
Sneeze on them.
Grab a towel and go to the pub for a pint.
Are you sure you wouldn't rather die? I mean, Vogon poetry is supposedly pretty bad.
Anyway, movie/book plots aside, I believe chances are we wouldn't even understand what we were looking at if any alien life were to come this way, let alone have any meaningful chance to fight them. Think of it this way: assuming we don't kill each other or enter another "dark age" before then, what will humans be like in 1000 years? What about 10000 years? Can you imagine all the knowledge we'll possess, and everything we will be able to do? Well, the elements and conditions needed for life as we know it have been around for at least 8 or 9 billion years; life on Earth is at most 4 billion years old. We could potentially be faced with species that have been around billions of years before Earth was even created. Assuming their technological progress was mostly positive, who knows what they would be able to do, or what they could possibly want with Earth for that matter.
Another thing I find interesting is this: even if we were lucky to be visited by a species that were just sufficiently advanced to have practical interstellar capabilities (FTL), but otherwise similar to humans, I'm not sure there would be much reason to assume they came to "invade the planet". I mean, any decent interstellar propulsion system would likely require prodigal amounts of energy to operate; energy which could potentially be redirected to some form of energy-matter conversion technology. Why waste resources on an invasion fleet and on a voyage to risk your hide fighting some weird species, when you could probably use all that energy to just create what it was you were after in the first place?
Too tired to comprehend, but it sounds good
lol also not to mention... considering the time it would take them to get here, they probably wouldn't have known we've evolved into pseudo intelligent beings; earth was probably just a rock. Sure, they could've figured out time travel, but that's just a one way streak and impossible for them to return home. But I guess if they traveled near/at/past the speed of light... wait a sec... they'd be traveling in the future! Traveling the same speed on the way back home will only land them further into the future! off topic