In Joshua Cohen’s powerfully strange short story “Emission,” which originally appeared in The Paris Review, a drug dealer has chest hair that sprouts “in spirals like @ signs.” This isn’t an important detail. It’s merely a typically alive and telling one.

Mr. Cohen’s stories are about a lot of things: sex, family, disappointment, literary frustration — the pantry items that stock a young writer’s larder. (Mr. Cohen is all of 31.) But in his new collection, “Four New Messages,” he nestles these subjects inside a more expansive obsession: how the series of tubes we call the Web has recast, often in sick ways, his contemporaries’ sense of who and where and why they are.

In these four stories, as in life, remote software monitors keystrokes; video cameras track nonwired movements. The world has been prechewed by opinionated hordes. Who will ever again visit what Mr. Cohen calls an “undatabased restaurant”? He dilates on what he refers to as “the local errata of burned connections.” His unhappy young people can’t live with technology, except that they can’t live without it.

Mr. Cohen is an especially brooding and lewd observer of how the pervasiveness of Internet pornography is reshaping our moral sense of what sex is. His stories impart an icky feeling that limitless pornography is changing young American men in ways that we may be only beginning to understand. (To learn more, we will have to ask the legions of aghast young women.)