This week, the U.S. Department of Justice sued Apple, saying the company holds a monopoly over the smartphone market. We break down the lawsuit and ask whether it will be a major turning point in Apple’s dominance. Then, Jonathan Haidt, a social psychologist, argues that smartphones and social media are the cause of widespread increases in mental health issues among young people. He tells us his four potential solutions to the problem. And finally, Reddit’s market capitalization hit $9.2 billion when it debuted on the New York Stock Exchange this week, but the company still isn’t making money. We talk about the challenges Reddit faces as it goes public, and how the site may change as a result.Today’s guest:Jonathan Haidt, author of “The Anxious Generation”Additional Reading:U.S. Sues Apple, Accusing It of Maintaining an iPhone MonopolyEnd the Phone-Based Childhood NowReddit’s I.P.O. Is a Content Moderation Success StoryWe want to hear from you. Email us at hardfork@nytimes.com. Find “Hard Fork” on YouTube and TikTok.