According to Suketu Bhavsar, twentieth century physics rests on two pillars: general relativity (the science of the very large) and quantum mechanics (the science of the vanishingly small), which are two empirically developed, testable and provable concepts that as of right now don't work so well together. While science works on reconciling these two domains, I'll stick briefly to two simpler illustrations brought by Bhavsar to the IdeaFestival today.
Taking a "model of the universe" out of his pants pocket, Bhavsar blows up a party balloon to illustrate how the galaxies are moving away from us, which is, in fact, what they are doing - and at colossal speeds thanks to the 73 percent of the universe that we can't see but, through its interaction with the observable universe, know exists - dark matter. Given sufficient time, an observer on the "surface" of the universe would see the other galaxies disappear over the horizon. Moreover, by walking this surface he or she would never reach an end, but would nonetheless be in a finite and circumscribed space.
It's an apt metaphor.
He says that string theory might one day unite the physics behind the quantum world and the vast mechanics of the universal bodies. But with ten dimensions or more predicted by string theory, where would those extra dimensions be? Using a two dimensional shape that can be found in popular physics books from authors like Brian Greene, Bhavsar uses the following illustration. Image you are standing a hundred years from a telephone line and you spy a squirrel scampering along its length. From that distance, the line would appear as a single dimension, a line in the sky. But move closer and the diameter of the wire becomes apparent. It has a second dimension that wraps around the line.
When it comes to quantum mechanics, we are hampered by our terminology.