When accelerated particles hit other particles such as atoms, smaller pieces come out. This helps people see particles smaller than an atom. Normally those particles cannot be seen, but they can in the particle accelerator. This is because in some ways energy and matter are the same thing. At the high speed created in these machines, some of the movement energy is changed into matter. It is the opposite process that nuclear weapons use; nuclear weapons turn matter into energy. Small amounts of antimatter are also created during the process.