As for the forces, electromagnetism and gravity we experience in everyday life. But the weak and strong forces are beyond our ordinary experience. So in physics, lots of the basic building blocks take 20th- or perhaps 21st-century equipment to explore.
Edward WittenI have a much easier time imagining how we would understand the big bang, even though we can't do it yet, than I can imagine understanding consciousness.
Edward WittenThere was a long history of speculation that in quantum gravity, unlike Einstein's classical theory, it might be possible for the topology of spacetime to change.
Edward Witten