Part 6/13:
In 1983, the concept of brane cosmology was introduced, and in 1999, physicists Lisa Randall and Raman Sundrum proposed the most influential model. Brane cosmology, also known as the "Brane world" theory, suggests the existence of at least a fourth spatial dimension, and possibly even more. The theory boldly suggests that our universe is confined within a membrane—hence the term "brane"—while most of what exists, known as "the bulk," lies in a higher-dimensional space outside this membrane.