So many galaxies, so many planets out there in the universe circling so many stars... it just feels like there's a very good chance that there is another Earth-like planet out there that is able to support some kind of life similar to what we're familiar with.

Einstein's theory of relativity does a fantastic job for explaining big things. Quantum mechanics is fantastic for the other end of the spectrum - for small things.

How can a speck of a universe be physically identical to the great expanse we view in the heavens above?

There's a picture of my dorm room in the college yearbook as the most messy, most disgusting room on the Harvard campus, where I was an undergraduate.

Exploring the unknown requires tolerating uncertainty.

In quantum mechanics there is A causing B. The equations do not stand outside that usual paradigm of physics. The real issue is that the kinds of things you predict in quantum mechanics are different from the kinds of things you predict using general relativity. Quantum mechanics, that big, new, spectacular remarkable idea is that you only predict probabilities, the likelihood of one outcome or another. That's the new idea.

General relativity is in the old Newtonian framework where you predict what will happen, not the probability of what will happen. And putting together the probabilities of quantum mechanics with the certainty of general relativity, that's been the big challenge and that's why we have been excited about string theory, as it's one of the only approaches that can put it together.