Something really important happened in Massachusetts today — something that has nothing to do with the final throes of the Brown-Warren Senate race.

Massachusetts passed a law months ago that put a global cap on how much its state would spend on health care — not just Medicaid, but all spending on doctors and hospitals by all patients. That law takes effect today. That makes Massachusetts the only state in the country that, as of this morning, limits how much its residents will pay on medical services.

The goal of the Massachusetts law is to get health-care costs to grow no faster than the rest of the economy, between 2013 and 2017. After that, the law dictates that health care spending will grow 0.5 percent slower than the rest of the economy. This is after years of health spending outpacing the rest of Massachusetts’ economy.

The big, looming question is: How do you get there? How do you limit health-care spending in a way that doesn’t hurt patients, but does root out unnecessary or expensive care?

To answer that question, the state of Massachusetts has turned to Stuart Altman, a Brandeis professor who has spent decades working on controlling health-care costs. Massachusetts Gov. Deval Patrick recently appointed Altman the chair of the Health Policy Commission Board, which will oversee the cost containment work.