In his new book What We Owe the Future, William MacAskill outlines the case for what he calls “longtermism.” That’s not just another word for long-term thinking. It’s an ideology and movement founded on some highly controversial ideas in ethics.

Longtermism calls for policies that most people, including those who advocate for long-term thinking, would find implausible or even repugnant. For example, longtermists like MacAskill argue that the more “happy people” who exist in the universe, the better the universe will become. “Bigger is better,” as MacAskill puts it in his book. Longtermism suggests we should not only have more children right now to improve the world, but ultimately colonize the accessible universe, even creating planet-size computers in space in which astronomically large populations of digital people live in virtual-reality simulations.

Backed by an enormous promotional budget of roughly $10 million that helped make What We Owe the Future a bestseller, MacAskill’s book aims to make the case for longtermism.