Philosophy
The Metaphysics of Persistence: Endurantism vs. Perdurantism
Quick fact
Endurantism and perdurantism offer two radically different answers to the question of how objects persist: endurantists say objects are wholly present at each moment, while perdurantists say objects have temporal parts, so the 'whole' object is spread across time.
Why this is interesting
You look at the same coffee mug you used this morning — it's the same object, right? But what if everything in it — every atom — has been replaced since you bought it? How can something change yet remain the same?