Simplify the following text for a Grade 12 native English-speaking person.
Original: According to this definition and our present understanding , the universe consists of three elements : space and time , collectively known as space-time or the vacuum ; matter and various forms of energy and momentum occupying space-time ; and the physical laws that govern the first two .
Simplified: This definition says that the Universe is made of two elements : space and time , together known as space-time or the vacuum ; and matter and different forms of energy and momentum occupying space-time .