The universe began as an incredibly hot and dense point approximately 13.8 billion years ago, according to the 36 . 37. are regions of space where gravity is so strong that nothing, not even light, can escape. The discovery of potentially habitable exoplanets has intensified the search for 38. . Edwin Hubble's observation that galaxies are moving away from us suggests that the universe was once concentrated in a single 39. . Dark matter, which makes up about 27% of the universe's mass-energy content, does not emit, absorb, or reflect 40.F.