We're not going to travel beyond the solar system, according to Leonard Susskind. And neither are aliens, coming to visit us. We may not be alone, but we are stuck here for, essentially forever. 1. The nearest star is 4.24 light years away. The fastest spacecraft ever built would require 6,600 years to get there. 2. Surely we can just build faster spacecraft. The problem is to get to anywhere close to the speed of light, we need exponentially more energy. 3. Chemical rockets will just not work. Even fusion rockets won't work. Even 10% of the speed of light is not achievable. The Tsiolkovsky Rocket Equation prevents it. 4. Interstellar dust becomes hand grenades when traveling anywhere close to the speed of light. Ships break. 5. Space radiation will kill us over the time need to travel interstellar distances. Impossible to protect without massive shields, which require massive energy to accelerate and de-accelerate.