Time is a contentious topic in physics. Some physicists, such as Julian Barbour, argue that it doesn’t even exist. Others, such as Carlo Rovelli, hold that it arises as a secondary effect of deeper quantum processes. Yet others, such as Lee Smolin, maintain that time is the sole fundamental dimension of nature. And because the laws of physics are time-symmetrical, much debate has gone into figuring out why we seem unable to travel back in time.

All this theorizing is motivated by—and attempts to make sense of—our subjective experience of the forward flow of time. Indeed, our reliance on what we think we experience as the flow of time goes so deep that some philosophers take it for a self-evident axiom. For instance, writing for this magazine, Susan Schneider claimed that the flow of time is inherent to experience—so much so that, according to her, “timeless experience is an oxymoron.”

But do we actually experience the flow of time? We certainly experience something that looks like it. But if we introspect carefully into this experience, is what we find accurately describable as “flow”?

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