I said type 3 "civilizaton" without explaining myself.
Type 0 - Us. Simple cavemen compared to the potential. We are still struggling with old, inefficient forms of energy.
Type 1 - Capable of harnessing the energy in their home planet with supreme efficiency.
Type 2 - Capable of harnessing the energy of an entire star, and even manipulating the body itself.
Type 3 - Capable of harnessing the energy of whole galaxies. They would be so advanced to us that we would barely be able to comunicate with them.
For an "Alien" civilization to visit Earth, they would probably have to be type 3 in order to have the energy required to manipulate time/space.
As far as we understand, for such an advanced civilization, there would be nothing for them here on Earth that they could benefit from.
Had some tragic events not ocurred, like the burning of the Library of Alexandria, the dark ages, and the Church's complete grip on advancement for a long time, we could well be into Type 1 territory.
Sadly and ironically, the only thing that pushes us forward into that territory, is war itself. With the discoveries we make in the research for better ways to kill each other, we end up pushing our technology further, so war itself is what may put us as a contender in the intergalactic race, IF we dont kill each other first.
We dont have to fear the aliens. They have to fear us
