Saving the world! One crazy plan at a time.
Time being the key word there. It's the one variable that shows up in almost every set of equations in physics. Why, you ask? BECAUSE IT'S IMPORTANT! If we have the time to see the gigantic asteroid hurtling at earth that wants to just annihilate humanity as we know it, why rush? Let's take our time and let physics do all the work.
I present to you: THE SPACE TRACTOR!
So as an easy example, lets look at running and walking. You run the same distance as you walk, but why does it make you so much more tired to run? Because time! The more time you take, the less energy is required. Falling from a bridge to the ground would kill you, right? But because of the water, it lowers your impulse.
So what does that have to do with saving the world? Well, the space tractor is a plan to launch up a probe to the asteroid before it hits us and position it so that it's gravitational force slowly, over the span of a lot of time, pulls the asteroid out of the path of earth and into deep space. We don't need a great amount of force because we're not doing it over a small amount of time. But of course, this plan only works if we have some warning beforehand. I think the best part about this is that it's been tested already, since Nasa has sent several probes into deep space to slowly circle the massive space rock, Vesta.
So this plan isn't fast or flashy, we don't need Bruce Willis to save us, all wee need is a little tiny probe and some time.