Reality Is Not What It Seems: The Journey to Quantum Gravity

by Carlo Rovelli

The present is like the flatness of Earth: an illusion. We imagined a flat Earth because of the limitations of our senses, because we cannot see much beyond our own noses. Had we lived on an asteroid of a few kilometers in diameter, like Antoine de Saint-Exupéry’s Little Prince, we would have easily realized we were on a sphere. Had our brain and our senses been more precise, had we easily perceived time in nanoseconds, we would never have made up the idea of a “present” extending everywhere. We would have easily recognized the existence of the intermediate zone between past and future. We would have realized that saying “here and now” makes sense, but that saying “now” to designate events “happening now” throughout the universe makes no sense. It is like asking whether our galaxy is “above or below” the galaxy of Andromeda: a question that makes no sense, because “above” or “below” has meaning on the surface of Earth, not in the universe. There isn’t an “up” and a “down” in the universe. Similarly, there isn’t always a “before” and an “after” between two events in the universe. The resulting knitted structure that space and time form together, depicted in figures like 3.2 and 3.3, is what physicists call “spacetime” (figure 3.4). Figure 3.4 What is the world made of?

General relativity