So far, the U.S. has reported only about 200,000 antigen-test results. But some evidence suggests that these tests are being used on a much wider scale than is understood: Thousands, if not tens of thousands, of antigen tests may already be happening every day without their results appearing in any public data. Just as dark matter can’t be observed directly, even though it makes up much of the universe, this “dark testing” does not show up in the data but may already account for a substantial chunk of the coronavirus testing done in the U.S.

The result of these changes is that some once-trustworthy numbers and measurements—such as the number of tests conducted in each state, and the percentage of tests that come back positive—now seem less reliable. Over the past months, as states have developed their testing systems, the picture of the pandemic clarified, but now it is blurring again.

In the immediate future, antigen tests could roll out nationwide, allowing health-care workers to catch outbreaks before they erupt. Or the national testing system could deteriorate further under White House pressure, meaning that states and cities might realize that an outbreak is growing only when hospitalizations bloom. As we stand at this crossroads, still confirming tens of thousands of cases a day, the shape of the pandemic is going to change again, and we may not have the tools we need to see how.