Antihydrogen

Antihydrogen is the neutral antimatter counterpart of hydrogen, consisting of an antiproton bound to a positron. Its atomic spectrum and gravitational behavior can test whether antimatter follows the same laws as ordinary matter.

Antiproton: An antiproton is the negatively charged antiparticle of the proton. It supplies antihydrogen’s nucleus and must be combined with a positron.
CPT symmetry: CPT symmetry states that physical laws remain invariant under combined charge conjugation, parity inversion, and time reversal. Comparing hydrogen and antihydrogen spectra tests this fundamental symmetry.
Paul Dirac: Paul Dirac was a British theoretical physicist whose relativistic quantum equation implied the existence of antimatter. His theory predicted the positron, one of antihydrogen’s two constituents.
Hydrogen: Hydrogen is the simplest chemical element, with one proton and one electron in its neutral atom. It is antihydrogen’s ordinary-matter counterpart and the reference for precision comparisons.
Positron: A positron is the positively charged antiparticle of the electron. It binds to an antiproton to form a neutral antihydrogen atom.
Hydrogen spectroscopy: Hydrogen spectroscopy measures the frequencies of light absorbed or emitted by hydrogen atoms. Its exceptionally precise measurements provide the benchmark for antihydrogen comparisons.
Carl Anderson: Carl Anderson was an American physicist who discovered the positron in 1932. The positron’s discovery established the first ingredient needed to make antihydrogen.
Positronium: Positronium is a short-lived bound state of an electron and a positron. Unlike antihydrogen, it contains no antiproton and consists entirely of leptons.
Antimatter trapping: Antimatter trapping confines charged antiparticles or neutral antiatoms using electromagnetic or magnetic fields. Charged ingredients are trapped before antihydrogen forms; neutral atoms require magnetic confinement.
Antihydrogen laser physics apparatus: ALPHA is a CERN experiment that traps antihydrogen and measures its properties. ALPHA has measured antihydrogen’s spectrum and its response to gravity.

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