Cosmic Inflation
Concept
The mainstream solution to the Horizon Problem, hypothesizing a period of extremely rapid expansion in the early universe that allowed distant regions to be in causal contact.
Mentioned in 2 videos
Videos Mentioning Cosmic Inflation

Avi Loeb: Aliens, Black Holes, and the Mystery of the Oumuamua | Lex Fridman Podcast #154
Lex Fridman
A cosmological model, criticized for being unfalsifiable by its inventor, making progress impossible without empirical tests.

What If The Speed of Light is NOT CONSTANT?
PBS Space Time
The mainstream solution to the Horizon Problem, hypothesizing a period of extremely rapid expansion in the early universe that allowed distant regions to be in causal contact.