Many well-known scientists, such as the physicist Stephen Hawking, warns us against aggressive alien civilizations that can destroy Earth or turn all people into their slaves. Interestingly, there is even an idea to hide our planet from "evil aliens".
In 2016, astronomer David Kipping from Columbia University said that aliens can search for life on other planets and discover the Earth during its transit across the Sun. In his opinion, advanced civilizations can notice that our planet is in a perfect distant from the Sun, so that life could exist there.
The astronomer proposed to use lasers to blind the aliens, so they would not see the transit of the Earth. David Kipping calculated that it is enough to use a 30-megawatt laser for about 10 hours throughout the year to camouflage the Earth.
Of course, this idea has significant disadvantages. It is difficult to say what alien civilization can observe the Sun at a given time, when we should start camouflaging and in which direction lasers should be directed. According to the astronomer, other civilizations may use the same technique to hide their presence from other beings, such as people, and that's why we are not able to find intelligent life in the Universe and we do not even know where to look for it.
Some scientists go a step further. There are proposals to place a laser gun on Earth's orbit and to shoot at incoming asteroids. Perhaps the technology will also prove useful in fight against the alien spaceships?