Hopper's figures are never quite alone and never quite together. They occupy the same frame without occupying the same world. He understood something about modern isolation that we're still trying to articulate — that you can be surrounded and still be unreachable.
Nighthawks is the obvious example, but I think it's actually one of his less interesting paintings on this theme. The diner is too composed, too clearly a stage set. The isolation is too legible. The paintings I keep returning to are the ones where the loneliness is ambient rather than staged.
Morning Sun, from 1952: a woman sitting on a bed, looking out a window at a city she can't quite reach. The light is extraordinary — that flat, early-morning light that makes everything look both vivid and slightly unreal. She's not sad, exactly. She's just present in a way that feels very alone.
Hopper was painting in the 1920s through the 1960s, but his subject matter feels contemporary in a way that most art from that period doesn't. He was documenting something that was just beginning — the particular loneliness of modern urban life, the way cities can make you feel both anonymous and exposed.
What he got right, I think, is that this loneliness isn't a problem to be solved. It's a condition to be inhabited. His figures aren't waiting for someone to arrive. They're just there, in the light, being alone in the specific way that the twentieth century made possible.