Particle Physics is the branch of physics that deals with the properties, relationships, and interactions of subatomic particles. Particle physics is a search for the most primitive, primordial, unchanging and indestructible forms of matter and the rules by which they combine to compose all the things of the physical world. It deals with matter, energy, space, and time. It is also called high energy physics, because many elementary particles do not occur under normal circumstances in nature, but can be created and detected during energetic collisions of other particles, as is done in particle accelerators. The objectives of particle physics are to identify the most simple objects out of which all matter is composed and to understand the forces which cause them to interact and combine to make more complex things. Modern particle physics research is focused on subatomic particles, which have less structure than atoms.