How does Edward Hopper represent loneliness in his paintings?

The images of lone individuals in impersonal spaces, with hollowed and dark eyes gazing from windows or down at their drinks, are combined to remind spectators that the default state of humanity is isolation.  

photography had emerged as an elite art pursued by a few creative individuals for a few wealthy patrons. but now, said bauldelaire, it was succumbing to "the great industrial madness of our times." it was becoming a mass production industry that catered to middle-class tastes, including a taste for gadgetry. the stereoscope, the first 3d imaging system, had turned looking at photographs into parlor entertainment. a "thousand hungry eyes were bending over the peepholes of the stereoscope as though they were the attic-windows of the infinite.