One of the most puzzling mysteries in modern astrophysics is the “black hole information loss paradox.” It pits the concepts of quantum mechanics against the theory of general relativity. Fundamentally, this paradox deals with whether or not information that has fallen into a black hole is completely lost or not.

Black holes are regions in space where gravity is so immense that even light cannot escape their pull. They are formed when a massive star nears the end of its life and collapses. The result is a singularity: a point at the center of the black hole that is characterized by its infinite density. Around the singularity, an event horizon forms; this is the point at which no information can escape the influence of the singularity and the black hole. 

For many years, this definition of a black hole—outlined in Einstein’s theory of general relativity—was widely accepted and did not change. However, in 1974,  Stephen Hawking theorized that black holes actually were not actually “black.” He discovered that black holes actually emit radiation which he later named “Hawking radiation.” This meant that black holes would lose their mass over time and evaporate.

Hawking’s theory sparked a huge debate over black holes and started the information loss paradox. A fundamental principle of quantum mechanics is that information can never be destroyed. At a moment, given the state of something physical, one is able to calculate its past and future states since its information should always be present. Hawking’s radiation carries no information about the materials that were the basis of the black hole’s formation since they are just electromagnetic waves traveling through space. Therefore, if a black hole eventually evaporates, where would the information about its contents go? Does it violate the basis of quantum mechanics and just disappear? The information loss paradox is based on this conflict between quantum mechanics and general relativity. 

Since the start of this paradox, physicists around the world have proposed numerous solutions to this paradox, but none have been proven. One such solution is that a “firewall” forms around the event horizon of the black hole which destroys any information that comes out of the black hole and passes it. However, this challenges another fundamental principle of general relativity which states that crossing the event horizon should feel no different than moving through space. Another theorized solution is that Hawking radiation actually contains information from the black hole, but the information is encoded into the radiation in a very subtle form that we cannot detect. However, this solution has not been proved. Lastly, physicists theorized that black holes do not completely evaporate, but rather leave behind a remnant which consists of all the information that fell into the black hole. Again, this solution also hasn’t been proved by physicists. 

The debate behind the truth of the black hole information loss paradox still continues today. Across the world, physicists are continuing to explore more ideas in order to hopefully solve this troubling anomaly in astrophysics. Resolving this paradox would grant us a deeper understanding of quantum mechanics and relativity. As research continues, this paradox reminds us that the universe still holds many tantalizing mysteries that we have yet to figure out.