From History of the Universe’s YouTube channel, this video – appropriately entitled “What Is The Universe Expanding Into?” (loaded on Feb. 15, 2025, and already over 190,000 views!) – is a superb introduction to central concepts in the field of cosmology, particularly focusing on theories concerning the “shape” of the universe. This is presented to the viewer upon a historical backdrop of discoveries and theories by central figures in the realms of mathematics, geometry, and physics. Truly well written; truly well and subtly animated; truly well narrated.