The observed Universe is about  90.000.000.000 light years long. There are billions of galaxies each one with billions of stars. The Universe should be full of amazing spaceships.But it is not! The Fermi Paradox offers some ideas to explain, but no one knows why… We need to stick to the Milky way because even if we add light-travelling space ships it would still take billions of years to reach other galaxies that are not in our Local Group.

Here are some ideas:

1. We are still undetectable to aliens because we have not learned to communicate the right way
2. Mostly all species go extinct so maybe, since we only had good science knowledge for about the last 200 years , we missed all those alien civilizations
3. We still aren’t sure how life begun, and our galaxy could have been too hostile in the past for life to evolve, so, perhaps we were the first civilisation to exist and maybe we are the only ones.

There are more ideas but I tried to keep It has short has possible or you would not have the patience to read this. If you want to know more just ask or check out this link

https://www.youtube.com/watchannotation_id=annotation_2848678835&feature=iv&src_vid=1fQkVqno-uI&v=sNhhvQGsMEc