Matthew Salesses | Longreads | April 2019 | 11 minutes (2,630 words)
I have been reading books about time: theoretical physics, evolution, parallel universes. Recently I realized that I was reading them because I wanted one to tell me how to go back in time — to before my wife died of cancer.
In The Order of Time, physicist Carlo Rovelli challenges our concept of time. Time passes more quickly the closer one is to a gravitational mass (like a planet or a star or a black hole). This fact is popular in science fiction. A space traveler might return to Earth to find that her friends and family have aged more than she has. Even at different altitudes on Earth, time is different. Rovelli writes that if identical twins separate early in life and live one in the mountains and one below sea level, then they will find in old age that the one below sea level has aged more, being closer to the center of the planet.
Time, Rovelli claims, is not linear. It is a gravitational field. If he is right, time is like everything else in the universe and must be made up of extremely tiny particles. There is no past or future; we only experience it this way.
So why, my grief asks, can’t we change times simply by changing our perceptions? Rovelli suggests that our linear experience of time is due to thermodynamics. The second law of thermodynamics dictates that the total amount of entropy in the universe can never decrease, only increase. For us, or at least in our section of the universe, time operates in only one direction.
As consolation, Rovelli offers the mind as a time machine — we travel via memory. This is a disappointing compromise. In mourning, memory is only another cause for mourning. It does not change time, only reminds one that time has passed.