Antimatter Physics
The universe's rarest substance — produced one atom at a time, stored in magnetic traps, measured to 12 significant figures. From Dirac's prediction to the 2023 ALPHA-g gravity result, antimatter sits at the frontier of CPT symmetry, baryogenesis, and the most energy-dense reactions in nature.
e⁺e⁻ Annihilation — Live
A positron (e⁺) meets an electron (e⁻). Both particles cease to exist; 100% of their rest-mass energy — exactly 1.022 MeV — becomes two back-to-back 511 keV gamma-ray photons. This is E = mc² made literal.
Energy Density Comparison
Antimatter annihilation converts mass with 100% efficiency via E = mc² — yielding c² ≈ 9×10¹⁶ J per kilogram. That is ~2 billion times the energy density of gasoline and ~250× better than fusion.
Note: Antimatter production today costs far more energy than it releases. CERN produces ~1–2 ng/year. Practical antimatter power remains a long-term research goal.
Active Experiments
Trap antihydrogen, measure 1S–2S spectrum, Lyman-α, and (ALPHA-g) gravitational free-fall. 2023: first gravity measurement on antimatter.
Measure antiproton and proton magnetic moments to parts-per-billion precision for CPT tests.
Measure gravitational acceleration of antihydrogen using Moiré deflectometry.
Precision spectroscopy of trapped antihydrogen; CPT tests via 1S-2S and hyperfine transitions.
CP violation in B-meson system at the Tevatron p-p̄ collider.
Search for antinuclei (anti-helium-3, anti-helium-4) in Au-Au collisions.
Does Antimatter Fall Down?
For decades physicists wondered: does antihydrogen fall upward (anti-gravity)? In 2023, the ALPHA-g experiment at CERN gave the first direct answer. They released trapped antihydrogen inside a vertical magnetic trap and observed which end it escaped from.
The result rules out antigravity (−g) at >99% confidence and is consistent with the Einstein Equivalence Principle. Improving precision to 0.1% level is the next goal — that would be sensitive to quantum gravity corrections.
Nature 621, 699 (2023) →Data & Literature Explorer
Search live databases: arXiv preprints, INSPIRE-HEP citations, and HEPData experimental tables from ALPHA, BASE, AEgIS, and other antimatter experiments.
Landmark Papers in Antimatter History
From Dirac's 1928 prediction to the 2023 ALPHA-g gravity result — the key papers that built the field.
Observation of the Effect of Gravity on the Motion of Antimatter
The ALPHA-g experiment released trapped antihydrogen in a vertical trap and measured how it fell. The result: antihydrogen falls downward — just like regular matter — with gravitational acceleration g̃ = (0.75 ± 0.13⁺⁰·¹⁶₋₀.₁₇) × g. This rules out 'antigravity' at the 1% level for the first time. The measurement settles decades of speculation: antimatter gravitates the same way as matter, consistent with the Equivalence Principle.
DOI: 10.1038/s41586-023-06527-1 →Open Questions in Antimatter Physics
Why is there more matter than antimatter?
The Big Bang should have produced equal amounts. The known CP violation (CKM matrix) is 10 billion times too small to explain the observed asymmetry. New sources of CP violation — possibly in the neutrino sector or BSM physics — are actively searched for.
Does antimatter experience the same gravity?
ALPHA-g (2023) confirmed antimatter falls at ≈g. But the measurement uncertainty is still ±20%. The next generation aims for 0.1% precision, sensitive to quantum gravity effects and violations of the Weak Equivalence Principle at a new level.
Can we build an antimatter engine?
In principle, 1 gram of antimatter releases 1.8×10¹⁴ J — enough for a Mars mission. The catch: CERN produces ~1 ng/year; 1 gram would take 10⁹ years at current rates. The energy cost to produce 1 g antihydrogen exceeds current world energy production by a factor of billions.
Are CPT symmetry violations observable?
CPT symmetry (the combination of charge conjugation, parity, and time reversal) is believed to be exact in any local Lorentz-invariant quantum field theory. Tests comparing particle and antiparticle masses, charges, and magnetic moments constrain CPT violation to 1 part in 10⁹. BASE aims for 10⁻¹².
Can antihydrogen exist as bulk antimatter?
ALPHA has trapped hundreds of antihydrogen atoms simultaneously for minutes. Producing anti-molecules, anti-helium, and eventually macroscopic quantities requires containment without annihilation with ordinary matter — requiring ultra-high vacuum and magnetic confinement indefinitely.
What is the 1S–2P transition of antihydrogen?
The 1S–2S transition of antihydrogen now matches hydrogen to 2 parts per trillion. The next target is the 1S–2P (Lyman-α) transition, which is extremely challenging because the lifetime is ~2 ns. ALPHA-LASER is working on this measurement.