White holes

White holes are theoretical opposites of black holes – they are places in space which cannot be physically entered by any object or matter in the universe, though energy, matter, light, and information can all escape it. They are a part of many theories, one of which is the theory of eternal black holes. The theory states that in a place where a white hole was in the past, there is a black hole in the future, though this is not true for black holes which have formed through gravitational collapse. Another theory states that white holes may be so-called “exits” of black holes, since any free-falling particle should be able to be falling infinitely, and this theory becomes untrue if the theoretical particle entered the singularity in a black hole, being infinitely compressed and unable to continue its movement. It is also theorized that each time a white hole eventually transforms into a black hole, a “Big Bang” occurs at the singularity, and a new, expanding universe is formed. Some scientists’ explanation as to why no white hole was yet discovered is because that its energy is only detectable during the emergence of white hole, called a “Small Bang”.

Links: https://en.wikipedia.org/wiki/White_hole

Sorry for using Wikipedia, but it was only website I could find with such extensive information on the topic. I also compared information available in other sources with the one available on Wikipedia, and it seemed consistent enough for me to use Wikipedia as a somewhat reliable source.