Facts about blackhole12/15/2023 Hawking radiation evaporates the black hole. Here is the black hole information paradox, a paradox that has bedeviled theoretical physics for over half a century, a paradox whose resolution lays in the unknown lands of quantum gravity, a resolution that promises to give rise to a new understanding of physics: information goes into a black hole. You can sit in front of your homemade black hole and register the energies and momenta of every single emitted particle of Hawking radiation until it collapses in on itself in 10 100 years and you will learn absolutely nothing other than the dumb fact that the black hole is, indeed, evaporating at a particular temperature. In physics jargon we say that the emission is thermal, which is another way of saying that it contains no unique information. Eventually, if you wait long enough, the black hole will evaporate completely, disappearing in a poof of energetic emission. With every emission, the black hole loses a little bit of mass (after all, there's no such thing as a free lunch, and somebody has to foot the energetic bill for this newfound radiation in the cosmos). The black hole duly emits Hawking radiation, spitting out one photon at a time. You then isolate a black hole away from any source of growth: no matter, no radiation, no energy for it to feast upon. Constructing that black hole consumed an enormous amount of information about all the particles that once enjoyed freedom, and all that information is now safely tucked away behind the event horizon. Let's pretend that you build yourself a black hole, compressing a sufficient amount of matter into a sufficiently small volume that one appears before you. Here's how this radiation, now known as Hawking radiation in Stephen's honor, throws a monkey wrench in the pristine picture of black holes painted by general relativity and the no-hair theorem. And while that program has yet to realize its full potential, Hawking did discover something utterly extraordinary about black holes, as if they weren't extraordinary enough already. Hawking, among others, embarked on a program in the 1970's to use black hole event horizons to poke and prod at the combined nature of gravity and quantum mechanics in extreme conditions, hoping to tease out some clue to their union. Something must marry gravity and quantum mechanics, some trick of mathematics or feat of physical insight, and whatever accomplishes the task does so here at the event horizon of every black hole in the universe. While our mathematics blow up, black holes most certainly do not. And because the event horizons are mathematical constructs, not actual surfaces with finite extent, to truly understand them we must examine them microscopically, which plants them firmly in the realm of the quantum. But here we are at the boundaries of black holes, which by definition are places of strong gravity. Anytime gravity became strong at small scales, our equations diverged to infinity and gave useless non-results. What prevented their unification was a proliferation of infinities in the mathematics. The quest to unify quantum mechanics and gravity stretches back over a century, soon after the development of those two great domains of physics. It turns out that these dark beasts were not as simple as we had been led to believe, and that the event horizons of black holes are one of the few places in the entire cosmos where gravity meets quantum mechanics in a manifest way. This was fine, until the 1970s when Stephen Hawking discovered the secret complexities of the event horizon.
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