Silverberg's second novel, a "juvenile."
There is some interesting social extrapolation in this book. Earth of the 37th century is a heavily populated place where employment is difficult to come by and virtually all jobs are taken by the members of hereditary guilds. This is combined with a kind of enforced consumerism: it is considered improper to save money; in order to preserve the jobs of others, everyone must buy, buy, buy. Interstellar travel is possible but expensive, so few can escape the crowding or relentless economic pace by moving offworld. The only legal profession open to the non-guilded is gambling (which of course does a very good job of keeping currency circulating).
It's hard to imagine this book being reprinted today. Although the story is engaging, combining realistic science with fairly well-drawn characters, there are a number of features that take it far enough out of "political correctness" to make it anathema to publishers. Primary among these failings is the fact that Alan, once on Earth, supports himself as a gambler. In the context of the book, this is a perfectly logical choice, but it's certainly not something you'd see today. So Our Hero finds himself in a world of smoky game parlors, casual drinking and drugs, and criminal activities. As a side note, there is no mention of sex or prostitution in any of this. In fact, aside from one annoying teenage girl with a crush on Alan, there are no female characters in the story at all. (This is probably as much a reflection of the market for which Silverberg wrote it as anything else.)
Putting the social issues aside, the science in the book is good. Silverberg takes the famous Twin Paradox of relativity and puts it into a book intended for young readers. The fact of time dilation is the central problem of the plot, though I noticed not a single mention of Albert Einstein by name.
Now for a spoiler-containig observation... When Alan gets started building the hyperdrive which will end the necessity of time dilation for space travelers, he doesn't do it all himself, like you might expect in a Tom Swift type adventure. He hires mathematicians and other experts to help him. That is a nice touch that departs from the long-accepted tandards of the genre.