They could be defined as the opposite of black holes: while these are true greers that do not let anything escape (not even light), white holes would be a colossal eruption of matter and energy. It is a hypothetical phenomenon, not observed, but which can be deduced from Einstein's theory of general relativity.
The origin of these cosmic flashes would be, as with black holes, a singularity, that is, a point where the gravitational field is infinite. In the unlikely event that a ship approached one, its occupants would not live to tell the tale. And if, let us continue to imagine, the vehicle were fully shielded against the emission of radiation, the astronauts would experience a progressive deceleration, as if they were trying to ascend a steep mountain until they were frozen in space-time .
Candidates for white holes include gamma-ray bursts, pulsars (neutron stars that periodically emit intense radiation), or dying black holes. Even the big bang itself that gave rise to the universe could be considered a white hole.
However, many scientists reject the possibility that these phenomena really exist. The main argument against them is that they violate the laws of thermodynamics, which postulate that entropy or molecular disorder must always increase in the universe ; white holes, colossal explosions that seem to come out of nowhere, would be exceptions to this inexorable increase.
