| Atoms may acquire energy that excites electrons by random thermal collisions, collisions with subatomic particles, or by absorbing a photon. |
| The big bang theory of cosmology asserts that the universe was once a very small and very hot soup of energetic subatomic particles. |
| To study subatomic particles, physicists build giant accelerators that smash the particles together. |
| Neutron stars are the most dense objects of normal matter in the universe, supported against gravitational collapse by subatomic forces. |
| However, as a subatomic particle the electron is also a quantum-mechanical object. |
| This is probably not a serious problem for banana salesmen, but could impact subatomic physicists, for example. |
