The present is a boundary, not a thing, in physics—it has no duration and no privileged status—yet the present you actually experience is a constructed window a few seconds wide, so "now" is a dimensionless edge in the world and a thick, lived room in the mind.
Physically, the instant has no width. A durationless "now" is a point on the time axis, a boundary between what has happened and what has not, with no thickness for anything to occur within.
Worse for the intuition, relativity denies the present even the status of a global thing: since simultaneity is relative, there is no universal set of events that counts as "happening now" for everyone.
On the block-universe reading, the objective present is not a special moving slice at all—just wherever a given observer is located along time.
Experientially, though, the present is manifestly not a point. Perception has to integrate information over a short span to build a coherent scene—to hear a melody rather than isolated tones, to catch motion, to feel continuity—so the brain constructs a "now" with real duration, the specious present, on the order of a few seconds.
This felt window is stitched from just-past memory and just-ahead anticipation, which is why the present seems to have thickness and flow that the physical instant lacks.
It is a psychological construction, not a physical measurement.
So both answers are true at their level: the present is a boundary in the physics and a room in the experience, and the mismatch is the source of the puzzle.
The practical point is that the thick, constructed present is the only place experience ever happens—past and future are only ever represented, never inhabited—so training the capacity to actually occupy it is not a metaphysical confusion but attention to the sole site of your life. This would need revision only if a physical present with intrinsic duration were established; physics offers none.
Both, at different levels—and the gap between them is the whole interesting part. As a physical fact, the present is a boundary with no width: a knife-edge between past and future, and (per relativity) not even a universal one. But the present you actually live in isn't a knife-edge at all—it's a window a few seconds wide that your brain constructs.
Why the felt "now" has thickness:
Here's why it matters practically: that thick, constructed present is the only place anything is ever experienced. The past is only ever remembered; the future only ever imagined. Every joy, every pain, every actual moment of your life happens in that few-second window and nowhere else.
So the takeaway isn't metaphysical, it's directional: presence—the skill of actually occupying the now instead of living in replay and rehearsal—isn't spiritual decoration. It's attention to the single room your entire life takes place in. The instant is a boundary; the lived present is a room; spend more of your life actually inside it.
The Edge With No Land.
Try to stand on "now" and you find no ground—only an edge, a border with no country, a line between a past that has ceased and a future that has not begun. The present, taken strictly, is where two kinds of nonexistence meet: it has no width for you to set your foot on. And yet here you are, standing somewhere, living in a moment that, examined, dissolves into a boundary too thin to hold you. The most solid-seeming fact of experience—that it is happening now—turns to vapor the instant you grasp for it.
The Thick Now the Mind Builds.
But experience refuses the knife-edge and builds itself a room. To hear music you must hold several notes at once; to catch a thrown ball you must feel the arc, not a frozen point. So the brain fabricates a "now" with real duration—a few seconds wide, memory bleeding in from behind, anticipation reaching from ahead—a specious present thick enough to live in. The physical instant is a razor; the felt present is a raft. We do not experience the boundary at all. We experience the small, warm, constructed room the mind builds around it, and mistake the room for the world.
The Only Place You Have Ever Been.
Here is the vertigo and the gift: you have never once been anywhere but the present. Not for a single instant have you visited the past or the future—they are lands you only ever picture, from here. Every experience you have ever had, every one you ever will, happens in this same moving room and nowhere else. Your whole life is lived at a single address, endlessly renovated, never left. The present is not one place among three. It is the only place, and the past and future are just the pictures on its walls.
The Now the Mystics Called Eternity.
Strangely, the traditions that took the present most seriously ended up calling it not fleeting but eternal. Their claim: the flowing now, if entered fully, opens onto something that does not pass—that the present is not a moment in time but a doorway out of it, the one place where the succession stops and pure being remains. Whether metaphysics or metaphor, the report is consistent across cultures: dive deep enough into the present and its thinness inverts into a strange depth, the boundary revealing itself as the only thing that was ever actually here. Perhaps the present is neither thing nor boundary but aperture—the narrow gap through which a temporal creature touches, for an instant, what has no when.
The present has no physical thickness—strictly it is a boundary between past and future, and relativity denies it even a privileged, universal status—yet the present you actually experience is a constructed window a few seconds wide, built from memory and anticipation. So "now" is a dimensionless edge in the world and a thick, lived room in the mind, and the mismatch is the source of the puzzle. What matters is that this constructed present is the only place experience ever happens—the past is merely remembered and the future merely imagined—so occupying it is attention to the single site of a life.