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Sunday, June 22, 2008

Earth Will Survive After All, Physicists Say

That black hole that was going to eat the Earth? Forget about it, and keep making the mortgage payments — those of you who still have them.

A new particle accelerator, the Large Hadron Collider scheduled to go into operation this fall outside Geneva, is no threat to the Earth or the universe, according to a new safety review approved Friday by the governing council of the European Organization for Nuclear Research, or Cern, which is building the collider.

“There is no basis for any concerns about the consequences of new particles or forms of matter that could possibly be produced by the LHC,” five physicists who comprised the safety assessment group wrote in their report. Whatever the collider will do, they said, Nature has already done many times over.

The report is available at

The physicists, who labored anonymously for the last year and a half, are John Ellis, Michelangelo Mangano, Gian Giudice and Urs Wiedemann, of Cern, and Igor Tkachev, of the Institute for Nuclear Research in Moscow. In a press release, Cern’s director general Robert Aymar said, “With this report, the Laboratory has fulfilled every safety and environmental evaluation necessary to ensure safe operation of this exciting new research facility.”

It is full speed ahead, they say, on the new machine, which is designed to accelerate protons, the building blocks of ordinary matter, to energies of 7 trillion electron volts and then bang them together to produce tiny primordial fireballs, miniature versions of the Big Bang. Physicists will comb the detritus from those fireballs in search of forces and particles and even new laws of nature that might have prevailed during the first trillionth of a second of time.

Some critics have argued, however, that Cern has ignored or downplayed the risk that the collider could produce a black hole that would swallow the Earth, or that it could create some other dangerous particle.

The safety group, however, pointed out that cosmic rays have produced equivalently energetic collisions with the Earth and other objects in the cosmos over and over again. “This means that Nature has already completed about 1031 LHC experimental programs since the beginning of the Universe,” they write. But the stars and galaxies endure.

The new report, which is an update and expansion of a previous 2003 report, pays particular attention to the issue of black holes, which could be produced according to some speculative variations of the already speculative string theory. Could one eat the Earth? These same theories predict that the black holes would immediately disintegrate, the authors say. But if stable black holes could somehow be produced, they would also have been produced by cosmic ray collisions.

The report draws heavily on a dense 96-page analysis by Steven B. Giddings of the University of California, Santa Barbara, and Dr. Mangano, which will be available on the physics archive on Monday. In that paper, Dr. Giddings and Dr. Mangano conclude, “Indeed, conservative arguments based on detailed observations and the best-available scientific knowledge, including solid astronomical data, conclude, from multiple perspectives, that there is no risk of any significance whatsoever from such black holes.”

The difference between these two ways of making black holes is that the ones from cosmic rays would be going near the speed of light and would shoot through the Earth with no effect, while collider black holes would be at rest relative to the Earth and could be captured. But if such black holes from cosmic rays existed, the physicists concluded, dense cinders like neutron stars or white dwarfs would capture them and get eaten. But that doesn’t happen; such objects continue to exist.

The safety report was itself reviewed and approved by another panel of scientists outside Cern. And so, after 14 years and $8 billion, the future of physics is almost here.

Cern’s engineers are in the process of cooling the superconducting magnets that power the protons around their 17-mile racetrack down to within 3 degrees Fahrenheit of absolute zero. They are on track, they say to begin circulating protons in the machine in August and to begin colliding them a couple of months later.

Because the engineers have not yet finished “training” the magnets to carry the currents necessary to propel the protons to full energy, the plan is for the colliding protons to have 5 trillion electron volts apiece initially, still five times more energetic than physicists have achieved before.

In the winter, when Cern traditionally shuts down for a period, the magnets will be trained for the full energy. In the spring the collider will start up again with 14-trillion volt collisions. And physicists can finally stop holding their breaths.

An earlier version of this article misstated the number of authors of the report. There are five, not four. Gian Giudice of Cern is also an author.

Original here

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