Intergalactic Expansion
With all of the resources in our own solar system, we could engineer 3,000 Earth-like planets. Think about that simple fact for a minute. Yes, we want to leave our solar system, and yes that would be damn interesting. But there is a very interesting logic to staying right here. You have 4 billion years or so left on our very friendly (according to Clark Kent anyway) yellow sun. Let's use it. The engineering challenge is simply that: a matter of time, money, and technology. Why would we really have to go anywhere? You you want to be careful with planetary engineering yes - but the concept that we are going to destroy the Earth is stupid. Why not replicated it? Why not make other planets for us to live on? Dyson sphere my butt.. you don't need that (though again - cool concept). You just need to tug planetary bodies into the habitable zone and terraform. Hell, you could even use one of them to build the all-time best interplanetary traveler - a planetoid with a fully und...