A Dark Matter Breakthrough?

New evidence of the invisible matter that could make up 90% of the universe.

In early December, the Cold Dark Matter Search (CDMS) experiment located in the deep Soudan Mine in northern Minnesota leaked a tantalizing hint that they may have discovered something remarkable. The experiment is designed to directly detect new elementary particles that might make up the dark matter known to dominate our own Milky Way galaxy, all galaxies, and indeed all mass in the universe—so news of a possible breakthrough was thrilling.

The actual result? Two pulses were detected over the course of almost a year that might have been due to dark matter, CDMS announced on Dec. 17. However, there is a 25% chance that the pulses were actually caused by background radioactivity in and around the detector.

Physicists remain fascinated by the possibility that the events at CDMS, reported on the back pages of the world’s newspapers, might nevertheless be real. If they are, they will represent the culmination of one of the most incredible detective stories in the history of science.

Beginning in the 1970s, evidence began to accumulate that there was much more mass out there than meets the eye. Scientists, mostly by observing the speed of rotation of our galaxy, estimated that there was perhaps 10 times as much dark matter as visible material.

At around the same time, independent computer calculations following the possible gravitational formation of galaxies supported this idea. The calculations suggested that only some new type of material that didn’t interact as normal matter does could account for the structures we see.

Meanwhile, in the completely separate field of elementary particle physics, my colleagues and I had concluded that in order to understand what we see, it is quite likely that a host of new elementary particles may exist at a scale beyond what accelerators at the time could detect. This is one of the reasons there is such excitement about the new Large Hadron Collider in Geneva, Switzerland. Last month, it finally began to produce collisions, and it might eventually directly produce these new particles.

Theorists who had proposed the existence of such particles realized that they could have been produced during the earliest moments of the fiery Big Bang in numbers that could account for the inferred abundance of dark matter today. Moreover, these new particles would have exactly the properties needed for such material. They would interact so weakly with normal matter that they could go through the Earth without a single interaction.

Emboldened by all of these arguments, a brave set of experimentalists began to devise techniques by which they might observe such particles. This required building detectors deep underground, far from the reach of most cosmic rays that would overwhelm any sensitive detector, and in clean rooms with no radioactivity that could produce a false signal.

So when the physics community heard rumors that one of these experiments had detected something, we all waited with eager anticipation. A convincing observation would vindicate almost half a century of carefully developed, if fragile, arguments suggesting a whole new invisible world waiting to be discovered.

For the theorist working at his desk alone at night, it seems almost unfathomable that nature might actually obey the delicate theories you develop on pieces of paper. This is especially true when the theories involve ideas from so many different areas of science and require leaps of imagination.

Alas, to celebrate would be premature: The reported results are intriguing, but less than convincing. Yet if the two pulses observed last week in Minnesota are followed by more signals as bigger detectors turn on in the coming year or two, it will provide serious vindication of the power of human imagination. Combined with rigorous logical inference and technological wizardry—all the things that make science worth celebrating—scientists’ creativity will have uncovered hidden worlds that a century ago could not have been conceived.

If, on the other hand, the events turn out to have been mere background radioactivity, physicists will not give up. It will only force us to be more clever and more energetic as we try to unravel nature’s mysteries.

Mr. Krauss is director of the Origins Institute at Arizona State University, and a theoretical physicist who has been involved in the search for dark matter for 30 years. His newest book, “Quantum Man,” will appear in 2010.


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