Plate Nº 67 · recorded October 10, 2026
PhysicsReported finding
ETH Zurich Builds 'Atomic Cannon' to Test Gravity on Exotic Matter
ETH Zurich and PSI built a controlled muonium beam, described in Nature Physics, removing a key obstacle for testing how antimatter-containing atoms respond to gravity.
By Elena Vasquez3 min read544 words
In brief
- ETH Zurich and the Paul Scherrer Institute in Villigen, Switzerland, produced a tightly controlled beam of muonium.
- Muonium is made of an electron bound to an antimuon and lives about 2.2 microseconds before decaying.
- The advance is described in a paper published in Nature Physics.
- The work clears a major technical obstacle for future antimatter-gravity experiments.
- No gravitational acceleration for muonium has been measured yet; the published result is enabling technology, not a verdict on Einstein.
ETH Zurich and the Paul Scherrer Institute (PSI) in Villigen, Switzerland, have produced a tightly controlled beam of muonium, an exotic atom made of an electron bound to an antimuon. The advance, described in Nature Physics, clears a major technical obstacle for future experiments that ask whether antimatter-containing matter falls the way Einstein's general relativity predicts.
What is muonium?
Muonium is a hydrogen-like atom, but with the proton replaced by an antimuon — the antiparticle of the muon, a heavier, unstable cousin of the electron. The atom lives about 2.2 microseconds before the antimuon decays.
Because it contains only leptons, muonium carries no quarks and no nuclear complications. That makes it one of the simplest exotic atoms physicists can produce.
Why call it an "atomic cannon"?
The ETH/PSI setup fires muonium atoms as a narrow, directed beam at controlled velocities. Researchers nicknamed the device the "atomic cannon" because the beam behaves like a stream of tiny projectiles — only the projectiles are individual atoms.
The setup uses a beamline tied to PSI's proton accelerator, where protons strike a target and produce muons. A fraction of those muons can capture electrons and form muonium before leaving the apparatus.
Why test gravity with muonium?
Most antimatter experiments use charged particles such as antiprotons or positrons. Stray electric and magnetic fields can mimic gravitational effects on those particles, blurring any gravity reading.
Muonium is electrically neutral. In principle, only gravity should act on it, giving researchers a cleaner probe of how antimatter responds to acceleration.
What did the new work actually clear?
Earlier attempts struggled to deliver enough muonium atoms to a target before they decayed. Many atoms were lost inside the apparatus itself.
The new result demonstrates a denser, slower, well-collimated beam — a configuration that lets enough atoms survive the trip to a downstream experiment.
What's the next step?
The team now has the hardware needed for a free-fall or interferometry test. In such a test, physicists would release muonium atoms and measure their acceleration directly.
Any deviation from 9.81 m/s², or from the more precise predictions of general relativity, would hint that antimatter couples to gravity differently from ordinary matter.
How should the result be read?
The Nature Physics paper documents the beam, not a gravity measurement. It is enabling technology rather than a verdict on Einstein.
Reviewers caution that statistical noise and systematic effects will dominate early data. Years of refinement may separate today's proof of concept from a measurement sharp enough to challenge existing theory.
Why a slow beam matters
A slow muonium beam buys physicists two things at once:
- Longer flight time before the antimuon disintegrates
- More time to register a gravitational deflection
Both matter, because the antimuon's 2.2-microsecond lifetime sets a hard upper bound on how far any experiment can push the measurement.
Why this matters for fundamental physics
General relativity has survived more than a century of tests. Nearly all of those tests, however, involve ordinary matter.
Antimatter gravity remains poorly measured, and small asymmetries between matter and antimatter would point to physics beyond Einstein. If the muonium beam delivers a clean gravitational signal, it gives physicists one of the first neutral test particles for that question.
via google.com (Original)
More from Elena Vasquez
Nearby plates
- CERN's Super Proton Synchrotron Marks 50 Years of Particle Physics Firsts
- Physicists Create Mini 'Big Bang' Using Surprisingly Small Atoms
- Two Unexpected Exotic Particle Structures Appear at Jefferson Lab
- Trapped-ion quantum device simulates matter popping into existence
- Caltech Team Directly Measures Quantum Energy Ladder Predicted for 40 Years