Scientists struggle to find signals in the noise

Each time I open my e-mail, I scan a long list of subject lines to find the messages that have something important to tell me. Occasionally, I’ll miss one and have to go back later to find it. Sometimes I make a different kind of mistake, opening a missive of no consequence. The point is that, even in a simple system like my in-box (OK, not that simple — the current count shows 19,004 unopened messages), detecting the signal from the noise is not always easy.

That theme is at the heart of both feature articles in this issue. In certain women, finding signs of a tumor using mammography can be akin to “finding a polar bear in a snowstorm,” readers learn in Laura Beil’s “To Screen or Not to Screen.” Normal, healthy breast tissue sometimes looks similar to a nascent cancer. This, as Beil details, leads to a huge number of false-positive mammograms, in turn causing unnecessary stress and further testing. Perhaps worth it, if mammography screening saves many lives. But the latest number crunching suggests that, especially for average middle-aged women, mammograms save far fewer lives than we have been led to believe.

As hard as it is to spy tiny tumors reliably, detecting primordial gravitational waves has seemed nearly impossible. But in March scientists with the BICEP2 telescope excitedly announced finding a surprisingly strong signal, apparently the imprints of those gravitational waves, in ancient light known as the cosmic microwave background (SN: 4/5/14, p. 6). These waves, it had long been theorized, would have been created in the wake of inflation immediately after the Big Bang. The discovery represented a glimpse of the very beginning of the universe, helping astronomers explore that long lost cosmic history. But now, as Christopher Crockett reports in “Dazzle or Dust,” scientists are raising doubts about the true source of the signal. Dust from the Milky Way may be what the scientists are really seeing, not gravitational waves at all.

The answer is still up in the air, literally. Many are counting on the Planck spacecraft to help reveal whether researchers have found a meaningful signal or just very loud noise. Either way the potential value of the gravitational wave signal for understanding the universe is worth the effort, and validates the debate.

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