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In a shaft at the Large Hadron Collider, scientists want to suspend atoms and let them fall to hear the whisper of dark matter.
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In the shaft leading to the Large Hadron Collider, an unusual tenant may soon move in: a hundred-meter vertical tube where clouds of strontium atoms will be dropped. Each cloud is cooled to near absolute zero, so the atoms move slowly and in sync, like dancers in slow motion. Then they are released into free fall, and their matter waves are made to overlap — creating an atom interferometer.
This device acts like an incredibly sensitive scale: it registers the slightest jolts and changes in gravity. If an ultra-light dark matter particle passes through the tube, it will slightly alter the atoms' fall, and the interferometer will catch it. Scientists call these particles ultra-light dark matter. Their mass could be billions of times smaller than the electron's, which is why ordinary detectors simply miss them.
A hundred-meter tube is roughly the height of the Statue of Liberty from the ground to the torch. The longer the fall, the more noticeable the effect of even the tiniest forces.
The project is named AICE. Its creators have already surveyed the PX46 shaft and confirmed it's ready — no technical obstacles. Construction could begin during a planned pause in collider operations, without disturbing physicists. Beyond dark matter, the device could hunt for gravitational waves at frequencies current detectors can't hear, and test whether different atoms fall identically — a question at the very heart of gravity.
Someday, such tubes could grow hundreds of times longer, giving humanity a new way to study the universe — not through light, but through the very act of matter falling.
The strontium atoms in this experiment will fall from a height of one hundred meters, and during the fall, about four and a half seconds, they will 'feel' even the gravitational pull of a person walking nearby.
In Greg Egan's novel 'Schild's Ladder,' physicists build giant detectors to catch elusive particles that alter the laws of physics — AICE looks like a first step toward such a 'ladder.'