The back-and-forth came in the federal government’s first monopoly trial since it tried to break up Microsoft more than two decades ago. This case — U.S. et al. v. Google — is set to have profound implications not only for the internet behemoth but for a generation of other large tech companies that have come to influence how people shop, communicate, entertain themselves and work.

Over the next 10 weeks, the government and Google will present arguments and question dozens of witnesses, digging into how the company came to power and whether it broke the law to maintain and magnify its dominance. The final ruling, by Judge Amit P. Mehta of the U.S. District Court of the District of Columbia, could shift the balance of power in the tech industry, which is embroiled in a race over artificial intelligence that could transform and disrupt people’s lives.

A government victory could set limits on Google and change its business practices, sending a humbling message to the other tech giants. If Google wins, it could act as a referendum on increasingly aggressive government regulators, raise questions about the efficacy of century-old antitrust laws and further embolden Silicon Valley.

“It is a test of whether our current antitrust laws — the Sherman Act, written in 1890 — can adapt to markets that are susceptible to monopolization in the 21st century,” said Bill Baer, a former top antitrust official at the Justice Department, adding that Google was “indisputably powerful.”

The case is part of a sweeping effort by the Biden administration and states to rein in the biggest tech companies. The Justice Department has filed a second lawsuit against Google over its advertising technology, which could go to trial as early as next year. The Federal Trade Commission is separately moving toward a trial in an antitrust lawsuit against Meta. Investigations remain open in efforts that could lead to antitrust lawsuits against Amazon and Apple.