To put it another way, a thing or person is often seen as having a "defining essence" or a "core identity" that is unchanging, and describes what the thing or person really is. In this way of thinking, things and people are seen as fundamentally the same through time, with any changes being qualitative and secondary to their core identity (e.g. "Mark's hair has turned gray as he has gotten older, but he is still the same person"). But in Whitehead's cosmology, the only fundamentally existent things are discrete "occasions of experience" that overlap one another in time and space, and jointly make up the enduring person or thing. On the other hand, what ordinary thinking often regards as "the essence of a thing" or "the identity/core of a person" is an abstract generalization of what is regarded as that person or thing's most important or salient features across time. Identities do not define people, people define identities. Everything changes from moment to moment, and to think of anything as having an "enduring essence" misses the fact that "all things flow", though it is often a useful way of speaking.
In Whitehead's cosmology, what are the only things that fundamentally exist?
occasions of experience

Before World War II, Guam and three other territories American Samoa, Hawaii, and the Philippines were the only American jurisdictions in the Pacific Ocean. On December 7, 1941, hours after the attack on Pearl Harbor, Guam was captured by the Japanese, and was occupied for thirty months. During the occupation, Guamanians were subjected to culture alignment, forced labor, beheadings, rape, and torture. Guam endured hostilities when American forces recaptured the island on July 21, 1944; Liberation Day commemorates the victory. Since the 1960s, the economy is supported by two industries: tourism and the United States Armed Forces.
What was the date on the attack of Pearl Harbor?
December 7, 1941

Vacuum is useful in a variety of processes and devices. Its first widespread use was in the incandescent light bulb to protect the filament from chemical degradation. The chemical inertness produced by a vacuum is also useful for electron beam welding, cold welding, vacuum packing and vacuum frying. Ultra-high vacuum is used in the study of atomically clean substrates, as only a very good vacuum preserves atomic-scale clean surfaces for a reasonably long time (on the order of minutes to days). High to ultra-high vacuum removes the obstruction of air, allowing particle beams to deposit or remove materials without contamination. This is the principle behind chemical vapor deposition, physical vapor deposition, and dry etching which are essential to the fabrication of semiconductors and optical coatings, and to surface science. The reduction of convection provides the thermal insulation of thermos bottles. Deep vacuum lowers the boiling point of liquids and promotes low temperature outgassing which is used in freeze drying, adhesive preparation, distillation, metallurgy, and process purging. The electrical properties of vacuum make electron microscopes and vacuum tubes possible, including cathode ray tubes. The elimination of air friction is useful for flywheel energy storage and ultracentrifuges.
What are two things made possible by the electrical properties of vacuum?
electron microscopes and vacuum tubes