Are black holes prevalent in our Universe and how does matter fall onto them? What kind of electromagnetic radiation and sources are associated with cosmic gravitational-wave events, and where and how are they both produced? When and where did the first generation of stars form and how did they re-ionize the dark early Universe? What happens at the very first instance when a star explodes and generates a supernova? EP will try to address these questions by capturing faint flashes of X-ray radiation produced by energetic events within a cosmic horizon far beyond the reach of any current and previous missions. Its primary scientific objectives are: 

1. Discover and characterize cosmic X-ray transients, to reveal their properties and gain insight into their nature and underlying physics.

2. Discover and characterize X-ray outbursts from normally quiescent black holes, for better understanding of the demography of black holes and their origin and evolution, as well as accretion physics.

3. Search for X-ray sources associated with gravitational-wave events and precisely locate them.