What Are Time and Space?

Craig CallenderApril 18, 2022Time and SpacePerSpectives

Artwork by Jessica Denkins, age 14

Perhaps my earliest memory of thinking about time and space is of reading the gentle Super Friends comic book series as a 10-year-old boy.

In issue #8 — which I still have — the Super Friends find themselves in a terrible predicament: the evil Grax has distributed bombs all over the Earth and they have only 26 minutes to stop them. To find so many bombs so quickly, the heroes divide up the task. I guess the Red Tornado drew the short straw, because he is charged with finding a bomb that has fallen into a time shift. The bomb might be in the past, present, or future.

Quickly the Red Tornado goes to New Zealand to enlist the aid of Tuatara, a meta-human with a third eye. Tuatara dramatically introduces himself. He tells us that two eyes let us see in 3D, and then he opens his third eye, informing us that it allows him to see in 4D, where the fourth dimension is time. Using his third eye, he locates Grax’s bomb 120 million years in the past. Red Tornado travels back in time, battles dinosaurs, and disarms the bomb. The Earth is saved.

This idea of seeing the past, present, and future all at once is not new. The so-called Second Buddha, Padmasambhava, aka Guru Rinpoche, is said to have been able to perceive it all, too. Using this ability, legend has it that he sprinkled his teachings in hidden places where they will emerge when they are most needed. He is alleged to have seen times of need like Tuatara could find bombs scattered through time.

Put aside the idea of perceiving all of time at once. That’s kind of silly. However, the thought behind Tuatara’s and Guru Rinpoche’s ability presupposes a way time could be. The philosophical position known as eternalism says that the past, present, and future all exist. According to this view, we can’t see all of time, just as we cannot see all of space, but it nonetheless exists. You may not be in San Diego and so cannot see it. But I’m in it right now and can assure you that it exists. According to eternalism, other times — like that of your birth — likewise exist, even if your current self isn’t there. I didn’t know this view of time when I was 10 years old, but you can still see the idea.

Only later did I learn that one can find this view of time in ancient texts worldwide and even in contemporary science. Many believe that Albert Einstein’s theory of relativity implies that eternalism is true. Relativity doesn’t mention a special present or need to do so. And in fact it allows for the possibility, in some sense, of time travel. So one could tell a story like the Red Tornado’s in a relativistic spacetime.

If eternalism or something like it holds, it challenges the most familiar of all facts — that only the present seems to exist. You reading this is what’s really happening, right? If that familiar fact is wrong, many deep questions follow. Is the flow of time an illusion? Why do we think the present is special if it’s not? If my death “already” exists, do I still have free will? And should I still be afraid of dying if I’m nonetheless going to exist on the “block” of existence anyway? Here we see how a theory of time immediately invites many puzzling important questions.

Saint Augustine of Hippo, 354-430 AD

That’s what I love about studying time and space. They’re in your face in the most familiar and ordinary way. A class in school takes an hour, and the salt on the table is two feet to the left. Yet as soon as you start thinking about them, they become mysterious. Saint Augustine really put his finger on this all the way back in 400 AD when he famously wrote,“What then is time? If no one asks me, I know; if I want to explain it to a questioner, I do not know.” What he is saying is that time is at once the most familiar and yet strange thing. This gulf between the familiar and strange is what attracts me to time. I’m not sure if the Super Friends adventures stayed with me and influenced what I worked on later, but I’ve always been drawn to time.

Yet space, too, is really perplexing. Augustine’s famous quote about time could also have been about space. Space couldn’t be more familiar. To pass the salt at dinner my hand needs to extend across some space. But what does it mean for my hand to extend through space? Here are three famous ideas.

Isaac Newton, the father of classical physics, thought space is a substance, a genuine independently existing entity. We move through it a bit like a fish moves through water. The fish is oblivious to water because water is everywhere for it, just as space is everywhere for us. In this view, space is a little bit like water.

The philosopher Gottfried Leibniz, by contrast, held that space is instead a network of relations amongst physical objects. That sounds complicated, but this picture of space reminds me of another childhood pursuit from back in the 1970s, the game Tinker Toy. Tinker Toys were construction sets where one built structures with wood sticks that fit into circular nodes. In Leibniz's view, the nodes are the objects (like me, you, a computer, a ball) and the network of sticks is space.

Another great philosopher, Immanuel Kant, held that space is constructed by us, that it is a kind of filter we impose on the world to make sense of experience. In the book version of the Wizard of Oz, the Emerald City looks green because everyone is forced to wear glasses with green-tinted lenses. Kant’s view is more complicated than that, of course, but the idea is something like that for space: everything is spatially located because that’s how your mind must process things.

The three views are each counter-intuitive and massively different from one another. In one space is like water, in another it’s like Tinker Toys, and in a third it’s like tinted glasses. If you removed all the objects in the universe, space would still exist, according to Newton. For Leibniz, however, no objects, no space. For Kant, you need creatures with minds. These three views are so different! Yet one of them may be the correct way of understanding the spatial distance through which your hand passes salt to another person.

All of these questions lead to rich research programs in both science and philosophy. Many are exotic and exciting and controversial. And yet it all begins with the most familiar of facts, that we persist through time and extend through space.

Craig Callender is a philosopher of science who has been interested in time and space his whole life. He believes that they are the two greatest mysteries in science. With artist Ralph Edney, he wrote a cartoon book Introducing Time: A Graphic Guide that traces our understanding of time through history. His book What Makes Time Special? tries to reconcile our experience of time with the physics of time. It won the 2018 Lakatos Award and the 2022 Patrick Suppes Prize. Craig works in the Department of Philosophy at the University of California, San Diego, where he is also a Director of the Institute for Practical Ethics. When he is not working, he is often paddling up and down the San Diego coastline looking for interesting marine life.