Antihydrogen (H) is the antimatter counterpart of hydrogen. Whereas the common hydrogen atom is composed of an electron and proton, the antihydrogen atom is made up of a positron and antiproton. Scientists hope studying antihydrogen may shed light on the question of why there is more matter than antimatter in the universe, known as the baryon asymmetry problem.
- Antihydrogen is produced artificially in particle accelerators. In 1999, NASA gave a cost estimate of $62.5 trillion per gram of antihydrogen, making it the most expensive material to produce.
- This is due to the extremely low yield per experiment, and high opportunity cost of using a particle accelerator.