It’s Sunday afternoon. I’m cutting down some ivy in my garden which is growing up a neighbour’s wall. I’m listening to a podcast: BBC’s World Book Club – the host is interviewing Carlo Rovelli, a professor of physics and author of some of my favourite popular physics books. It’s a phone in and Dan from Canada is asking a question:
Dan: “Hi, Carlo, very nice to meet you. First, I’d just like to start by saying I’m a huge fan of yours. Your books speak to me like no other in your field. I find myself on the edge of my seat as a chapter builds, even though there’s no hero or villain or love affair, yet I’m totally enthralled. You speak so eloquently to our current understanding of time.
Quote: “we must not think of time as if there were a great cosmic clock that marks the life of the universe. We have known for more than a century that we must think of time instead as a localized phenomenon. Every object in the universe has its own time running at a pace determined by the local gravitational field.”
“We all also accept that the universe is approximately 13.8 billion years old. So my question is, how can there be no universal time and yet the universe itself have an age?
Carlo Rovelli: Great question, wonderful. Thank you very much Dan. We are fellow Canadians. I spent most of my last four years in Canada. Yeah, it’s a great question and people often get confused about that. The answer is that what we call the age of the universe, it’s sort of an average and let me put it precisely, we live on Earth in the solar system and our sun is part of a galaxy, our own galaxy, right, the Milky Way and if we look around outside the galaxy, there’s a nearby galaxy which is Andromeda and the astronomers have seen very well that Andromeda and our galaxy are moving toward one another so they’re going to meet in the future. We’re talking about 100 million years, maybe, long time, but not tomorrow. But they’re definitely going to meet.
And here’s the point. When they are going to meet, the age of one since the Big Bang and the age of the other since the Big Bang are going to be different. So one is older since the Big Bang and one is younger. There isn’t a age since the Big Bang. They’re different, depending on how you’ve been moving since then, have you been, how much mass was around you, and so on. So the notion that the universe is 13.8 billion years old, I’m not sure this is the right number, but whatever it is, it’s not a very correct notion. It is the age for us, or it’s an average age from our galaxy, right? But precisely in the same manner in which if here on Earth you spend time in the mountain or you spend time by the sea, you have less time by the sea and more time in the mountain. Similarly in the universe as a whole there are some galaxies where there’s more time and some where there’s less time because there is more mass, because they’re moving differently, and when we meet the age of the universe is different.”
BBC World Book Club: Carlo Rovelli: Seven Brief Lessons on Physics
Does Dan comprehend Carlo’s answer. One one level I think he probably does. Carlo has taken his mental model, which is physics professor level, selected the minimum needed to answer the question and converted it into words for Dan.
Dan has two sources of information to build his own mental model: Carlo’s words and his own background knowledge. He builds his own mental model. Is it the same as Carlo’s?
Unless Dan is a sneaky physics professor phoning in, his mental model isn’t even close to Carlo’s, but it might be similar to the simplified model Carlo attempts to communicate.
Did you read Carlo’s words and build your own mental model? Is it the same as Dan’s? I think it isn’t. You received the same words, but you don’t have the same background knowledge. You weren’t in Dan’s class at school. You haven’t been out stargazing on the same night looking at the Milky Way and trying to find Andromeda with binoculars. You didn’t watch the same sci-fi as a kid.
Maybe you only skimmed Carlo’s response. You haven’t built much of a model. You haven’t examined the words against your own background knowledge to build something richer than you had before. I understand – that process is hard work.
That’s why you need a teacher to support you. Ideally you’d have Carlo in the room asking you questions, checking your understanding; helping you recall the relevant background knowledge. And you’d be able to ask him questions too. Together you’d be able to build a more accurate mental model. That’s how comprehension happens.
Thanks for reading,
Ben
p.s. I’ve been reading around comprehension all summer. Christian More-Anderson’s new book: Difference Maker (chapter 1) has a nice explanation of conversation theory.
Reading for Learning 
1 Comment