Defining Antimatter
Antimatter is a substance composed of antiparticles, which have the same mass as ordinary particles but opposite electrical charge and other quantum numbers. For example, the antiparticle of an electron (which has a negative charge) is a positron (which has a positive charge), and the antiparticle of a proton is an antiproton.
Annihilation: The Key Interaction
When a particle meets its antiparticle, they annihilate each other, converting their entire mass into energy, typically in the form of high-energy photons (gamma rays). This process is highly efficient, demonstrating Einstein's famous mass-energy equivalence, E=mc², on a fundamental level. This annihilation is a defining characteristic of antimatter.
Practical Application: PET Scans
Antimatter has real-world medical applications, such as in Positron Emission Tomography (PET) scans. In a PET scan, a radioactive tracer that emits positrons is introduced into the body. These positrons quickly encounter electrons, leading to annihilation events that produce gamma rays. Detectors then capture these gamma rays to create detailed images of organs and tissues, aiding in disease diagnosis.
Significance in Physics and the Universe
The existence of antimatter is crucial for our understanding of the universe. According to current cosmological models, the Big Bang should have produced equal amounts of matter and antimatter. However, the observable universe is overwhelmingly composed of matter. This cosmic imbalance, known as the baryon asymmetry problem, is one of the biggest unsolved mysteries in physics, driving research in particle accelerators and astrophysics.