Should we launch into a serious attempt to protect ourselves from dangerous aliens, whether hostile or non-hostile (prohibition of gigantically powerful broadcasts, global camouflage, hugely improved military technology, space-war games, or so on)?

No. Simply because of distance.

All of this alien nonsense does not take into account that the nearest star is four light years away. It is such a great distance that traveling at the fastest speed possible it would take at least 150 years each way to traverse. Other stars are many, many more light years. 40 light years would take 1,500 years to traverse, that is where the Trappist-1 system is which is the next best candidate for “Earth-size” planets to exist.

Traveling at light speed is impossible, both for us and for aliens. I’m sorry to say, it is unlikely we’ll ever know for sure if intelligent life exists elsewhere, and if it does, it is unlikely they will ever know we exist.

trapist1

Why do aliens always have to look and have similar biology to us?

Exactly! To date, no life has been found on any other planet or meteor. We would really like to find life elsewhere, and the most likely candidates within reach would be the moons of Jupiter and Saturn.

Beyond that you have to go interstellar. Since it would take hundreds or even thousands of years to reach even the nearest stars at the fastest speed we’ve ever achieved in space, interstellar travel is unlikely now or in the future.

Put away Star Trek and Star Wars. Aliens are not visiting us and we are not going to visit them, whatever they may look like.

If 50 years into the future, an alien civilization comes to Earth to invade our planet and only you know about it, what will you do?

Sneeze. That would probably kill them all off since they would not have developed evolutionary immunity to our germs. George Orwell was quite right.