As a physics (and SF) enthusiast, I've come to realize that we've discovered most of the physics that exists, and all of what we can use. This is disappointing for those who yearn for FTL or teleportation, but it's good news when you consider that it creates an impregnable defense against interstellar invasion. Within the limits of modern physics, there remains a great deal to understand and apply, especially in QM because to quote Feynman "there's plenty of room at the bottom". Biology and nanotechnology can still revolutionize human existence.

The key problem humans must grapple with an solve, if we are to make it long-term, is how to harness greater and greater power without destroying ourselves. Nuclear destruction has been a very real option for 80 years. Biological weapons could do the job, too. And of course, climate change looms. For many years I agreed with the thinkers that wish for a "backup plan" for humanity; however, I don't think Mars will do it simply because its environment is even harsher than a post-nuclear holocaust Earth. The important reality that THIS is our home, and we must protect her even if it's hard. Yearning for advanced physics to solve all our problems has the unfortunate side-effect of undermining motivation to solve the problems we have now with the tech we have now. It underlies an unfortunate "disposable planet" attitude that we'd be better off without.