CNN  —  Whenever you type a search into Apple’s Safari browser — say, on an iPhone — chances are it’s Google that returns the results. You can tell Safari to pick another search engine, but in practice most people tend to stick with Google by default. You might know that Google pays Apple enormous sums of money every year for that prime placement. What you might not know is just how much. By May 2021, Google was paying Apple more than $1 billion a month, according to the US government, and as much as $20 billion in total in 2022 — just for the privilege of being Apple’s primary search engine. Those eye-popping figures, newly unsealed this week, come from a blockbuster antitrust lawsuit against Google that’s just entered its closing stages. They highlight the enormous stakes of a case that could revolutionize how millions of Americans search for information online and, according to some, reshape the high-stakes battle for dominance in artificial intelligence. On Thursday, the Justice Department launched its final assault on Google’s search engine dominance, wrapping up a case that began during the Trump administration and trying to persuade a federal judge that Google illegally monopolized the online search industry through payments like the kind it’s made to Apple. Closing arguments in the case will continue through Friday, and District Judge Amit Mehta is expected to issue a decision later this year after sitting through a grueling 10-week trial last fall that was largely shut to the public. The outcome could have far-reaching effects on the tech industry, serving as a bellwether not just for the billions Google pays to Apple, wireless carriers and other device makers but for a veritable pipeline of tech antitrust cases moving through the courts. Government attorneys in the case argue that Google maintained an illegal monopoly through a web of contracts that made its search engine the default on millions of devices and browsers around the globe. Those contracts, the DOJ has alleged, allowed Google to build an unassailable search business that hoovered up ever more data revealing what users were looking for — creating a feedback loop that allowed Google to further fine-tune its product at the expense of fair competition. At trial, Microsoft told the court that Google is trying to turn that search data advantage into an artificial intelligence advantage by training its models on large volumes of search queries that nobody else has access to. Google has argued that consumers choose its search engine because it is simply the best, not because of anticompetitive behavior, and that Google’s search helps support its Android operating system, which competes against Apple. Nothing prevented Apple from choosing a different default search partner, Google contends. But DOJ attorneys have questioned the logic of Google’s payments and contracts. If Google’s product is truly better than the competition, they have asked, and if it is as easy to switch search engines as Google claims, then why spend tens of billions of dollars a year to be the default search provider everywhere? ‘Microsoft couldn’t do it’ Throughout the proceedings, Mehta has kept his own cards close to the vest. At the end of the trial last fall, he told the two parties that he was truly undecided. “I can tell you, as I sit here today, I have no idea what I’m going to do,” Mehta said last November. Mehta kept up that routine on Thursday, asking tough questions of both sides at the first day of closing arguments. At one point, Mehta pointed out to Google attorney John Schmidtlein that to unseat Google’s dominant position, a hypothetical rival would not only need to invest billions in a viable search engine alternative but also billions to compete with Google’s contracts with Apple and others. “If that’s what it takes for somebody to dislodge Google as the default search engine, wouldn’t the folks who wrote the Sherman Act be concerned about that?” Mehta asked, referring to a key US antitrust law. “I can’t conceive of a world in which some other competitor, particularly a new competitor, could do that. Microsoft couldn’t do it.” Schmidtlein responded that US antitrust law protects the competitive process, not competitors. It is unclear how soon District Judge Amit Mehta could issue a decision after this week’s arguments. But if he sides with the US government and finds fault with Google, it would trigger a separate proceeding to determine what penalties Google may face.