Black holes are one of the strangest objects in our universe and have captured the attention of scientists and space enthusiasts since their discovery. However, despite many decades of research into these mysterious black voids, some questions remain unanswered. The most famous of these mysteries is the black hole paradox.
The black hole paradox, sometimes called the black hole information paradox, is a puzzle that arose from contradictions in our understanding of how the universe works. First, let's have a quick recap on what a black hole is. A black hole is a region of space where the gravitational field is so intense that nothing, not even light, can escape from it.
One of the essential principles of our universe is the idea that no information can be created or destroyed. In other words, the universe is a self-contained system where information (atoms, particles, waves, and other matter) simply shift around. For example, if you grow a tree from an acorn, while it might appear that the tree has grown in mass from seemingly nothing, this isn't the case. The tree has taken information (nutrients, water, etc.) from the Earth. No matter how many trees you grow, the mass of the Earth remains the same. A similar principle exists in quantum physics, describing that the information of a system must be conserved. On a quantum level, information means the position, spin, and velocity of an atom. The idea here is that if you have this information, you can rebuild any object.
Black holes violate these rules because the information that enters them is destroyed forever, and no encoded information remains. But is this true? In the 1970s, Physicist Stephen Hawking proved that black holes emit radiation very slowly, suggesting that information does escape a black hole. However, it's believed that this radiation, called Hawking radiation, is random (the encoded information wasn't preserved). So next, scientists supposed that the information of objects inside a black hole must be encoded onto the surface of the black hole, called the event horizon. But still, that idea doesn't entirely work. Black holes decay, so what happens to that information when the black hole has completely evaporated?
Scientists aren't just sitting around scratching their heads in confusion but constantly trying to solve the black hole information paradox. However, so far, no one explanation fits all of the facts, although it does appear that we're getting closer.
Some scientists argue that we must be missing the last piece of the puzzle, and when we find it, everything will come together. This idea stems from the fact that black holes operate based on general relativity principles (the study of very large objects and their behavior) and quantum mechanics (the study of tiny objects like atoms). These two theories are critical to our understanding of the universe, but they don't match up. Thus, some scientists argue that the black hole paradox and other mysteries will be solved when we find a unified Theory of Everything.
Still, some rather wacky solutions to the paradox exist. Let's look at one of these unusual explanations; the holographic principle. The holographic principle expands on the concept of the 2D surface of a black hole's event horizon. The principle argues that perhaps the entire universe is encased in a 2D boundary encoded with information. If this is true, it means that everything we know to be real, like you and me, and the cereal you ate for breakfast, is actually just a holographic projection of the encoded information.
Excitingly, in 2020, new papers did shed some light on the paradox. Scientists studying "very old black holes" found that black holes not only start to dissipate matter as they age but start spewing it out. You can think of a black hole like a box that you overstuff with objects. Eventually, items will begin to spew out of it. These new studies don't explain how black holes empty themselves or whether this information is genuinely conserved, but it's a step towards answering the mystery for good.