We have been aware of the need for dark matter since the 1930s. Without this stuff, we can't make sense of the rotation of galactic clusters, or how galaxies formed in the first place. And yet, to date, we have found nothing. Even CERN's Large Hadron Collider, our best and by far most expensive tool for finding it, has so far drawn a blank. How much longer can we keep looking?

Dark matter is posited as the resolution to several obstinate anomalies – as Isaac Asimov put it, things that make you exclaim not "Eureka!" but "that's funny..." Such anomalies are often the key to scientific progress. But dark matter, and our efforts to pin it down, have been around long enough for doubts to creep in.

Perhaps we have simply been looking for the wrong thing. Perhaps dark matter particles are very massive, rather than fairly light, as many assume. The first experiments are now under way to detect any such "superheavy" dark matter that might have been created when the universe was just getting started (see "WIMPZILLAs: Monster particles from the dawn of time").

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