Welcome to the Saturday edition of The Conversation U.S.’s Daily newsletter.

As another weekend starts, you might find yourself thinking the week flew by, or perhaps it felt like a slow slog. Physicists and philosophers from the ancient Greeks to Isaac Newton have imagined time in different ways, and often as a flow. But as Adrian Bardon, a professor of philosophy at Wake Forest University, asks – a flow of what? Time isn’t something physical you can see and touch.

Bardon describes how the modern conception of time came to be and how science, including from Albert Einstein, has helped advance our understanding of it. As an eternalist, he takes the view that all time is happening at once, but as you move through the world, and events happen in series, you imagine time as flowing forward. In that way, he argues, time is a psychological projection in your mind. Imagining a flow of time helps us make sense of the world around us.

“Change just means that the situation is different at different times,” Bardon writes. “At any moment, I remember certain things. At later moments, I remember more. That’s all there is to the passage of time.”

This week we also liked stories on why people have baby and adult teeth, advances in lithium-sulfur batteries, and what Maine’s U.S. Senate race says about the Democratic party’s challenges in rural America.

One last note: If you find our work valuable, please support us. We’re giving all our donors a free e-book of our recent series looking at bold solutions to the affordable housing crisis.