Physics

The Oh-My-God Particle Was An Appropriately Named Physics Anomaly

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On October 15, 1991, astronomers detected a particle going faster than anyone thought was possible. "Nobody ever thought you could concentrate so much energy into a single particle before," said David Kieda, an astrophysicist at the University of Utah. Enter the Oh-My-God particle—not to be confused with the God particle—the mysterious little cosmic ray that could. Probably.

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Photograph showing the detector modules at Little Granite Mountain oriented for data-taking.

No Cosmic Speed Limits Here

When this little particle racing at nearly the speed of light was detected in 1991, it took about a year for scientists to believe what they had observed. It was spotted in the sky above Utah by the crude Fly's Eye telescope array, and the signal appeared to break a cosmic speed limit. Quanta magazine puts that in perspective: "[The Oh-My-God particle] possessed 320 exa-electron volts (EeV) of energy, millions of times more than particles attain at the Large Hadron Collider, the most powerful accelerator ever built by humans. The particle was going so fast that in a yearlong race with light, it would have lost by mere thousandths of a hair. Its energy equaled that of a bowling ball dropped on a toe."

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Scientists didn't think particles could go this fast based off something called the GZK cutoff. This "speed limit" says that cosmic rays going faster than 60 EeV will be slowed down by background radiation. That wasn't the case with the hair-splitting OMG, which is why a few eyebrows went up.

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It's A Bird! It's A Plane! It's... OMG

Because background radiation didn't drag the Oh-My-God particle down to a slower speed, it must have come from nearby. This little guy inspired a desire in scientists to unwrap the mysteries of ultrahigh-energy cosmic rays, "particles accelerated by the most powerful forces in the universe," as Quanta explains. Since that fateful day in 1991, scientists have built more and more powerful instruments in hopes of solving the mystery of ultrahigh-energy cosmic rays.

Because we have yet to detect another particle that even comes close to the EeV range of the OMG, could it have been a fluke? "The flux of particles at energies that high must be so low that it would have been an incredible fluke that the Fly's Eye detected one," Paul Sommers, a semiretired astrophysicist at Pennsylvania State University who specializes in ultrahigh-energy cosmic rays, told Quanta. The origin of the Oh-My-God particle, not to mention how—or even if—it existed is still a mystery. But these unknowns are still pushing physics forward two decades later.

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Key Facts In This Video

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  2. The universe is expanding faster than what the laws of gravity can predict. 03:33

  3. Visible matter only makes up approximately 5 percent of the universe. 04:01

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