Ask Ethan: Do white holes actually exist as the opposite of black holes?

American astrophysicist Ethan Siegel explores the theoretical possibility of white holes in his column. While Einstein's general theory of relativity mathematically allows for objects that are time-reversed versions of black holes, their existence in physical reality remains uncertain. Unlike black holes, which were predicted mathematically and later confirmed by observations, white holes remain purely hypothetical. Siegel examines why mathematical models do not always correspond to the physical universe and explains the thermodynamic and cosmological barriers to their existence. He emphasizes that despite their popularity in science fiction, there is currently no observational evidence for white holes. The article provides a deep look at the boundaries of modern theoretical physics and how scientists distinguish between mathematical abstractions and real astrophysical phenomena.