Carlo Rovelli opens his book by warning us there is no such thing as time.
“We convetionally think of time as something simple and fundamental that flows uniformly, independently from everything else, from the past to the future, measured by clocks and watches. In the course of time, the events of the universe succeed each other in an orderly way: pasts, presents, futures. The past is fixed, the future open ….. And yet all of this has turned out to be false” [p 2
Most of us have read about aging for the fictional space traveller who comes back to earth after travelling close to the speed of light. The traveller will have aged “naturally” (to him) but everyone he knew will be much older or dead. Rovelli points out that we don’t need to be space travellers to see that effect: a clock on top of a mountain runs faster than a clock at sea level; even a clock on a table runs faster that a clock on the ground. From this we can see that “[t]imes are legion: a different one for every point in space. There is not one single time, there is a vast multitude of them.” [p 16]
And by the time we finish chapter two we learn that “the difference between the past and the future refers only to our own blurred vision of the world.” [p 33] By blurred Rovelli means we don’t (can’t) see the totality of the universe; we abstractions of things. We may see a stone; but that is really made up of the non-pebble like things that make up atoms. We only sense time because of our incomplete, blurred vision.
Time exists like quantum mechanics does for the physical world where we can’t predict where an electron will be at any point in the future.
“It is not possible to think of duration as continuous. We must think of it as discontinuous: not as something that flows uniformly but as something that in a certain sense jumps, kangaroo-like, from one value to another. In other words, a minimum interval of time exists. Below this, the notion of time does not exist – even in its most basic meaning.” [p 84]
Physicists – at least those who study quantum gravity as does Rovelli – can describe our universe with no variable of time. When we enter a universe without time we discover that the world is made of “events, not things.” [p 95] “[E]ven the things [like a rock] that are most ‘thinglike’ are nothing more than long events.” [p 98] But I get hung up on the language here. An event – or at least the word ‘event’ – presupposes time. And event happens over time. Rovelli works through that for us, explaining that the words we use are just references to that “blurred” vision of the universe. In actuality,
“The theory [of quantum gravity] does not describe how things evolve in time. The theory describes how things change one in respect to the others, how things happen in the world in relation to each other.” [p 120]
Okay, but I can’t get my head to unblur the world: “change” holds the concept of before and after.
But what about causes and effect? Cause happens in [what we think of as] the past and the effect is the present/future. Rovelli tells us there is no “magical force of ‘causality’ going from the past to the future.” [p 168] Events occur as we go from a universe that is transforming from low entropy to higher entropy. This “notion of low entropy of the poast renders the notion of cause an effective one.” [p 169]
Time is really just a human invention created because our “brains are made up essentially of memory and foresight.” [p 189]
This book completely boggled my mind when I first read it; I found it helpful to go back through the passages I highlighted after a week or so passed. It was an interesting read that opened my eyes (a little bit) to the world of science today. Although I may now have a slightly better understanding of the issues, I am struck by the fact that the concepts of past and future are tied up in the explanations. Even though there may be no such thing as time, I’m still going to wear a watch.