Transcription
Hello Mortals. Have you ever cleaned your house, gently caressing the vacuum cleaner while your mind wanders off to cosmic distances, in the frontier of science and human understanding? Pondering the parallels between the mundane machine in your hand, sucking up dust and the occasional insect, and the cosmic equivalent of it: black holes, devouring interstellar gas and stars in a swirling maelstrom of superheated matter?
Did you look at the vacuum and think, like any normal person would do, "Black holes have dust bags in their centers like vacuum cleaners"? Or is the unsuspecting scientist, peering beyond the event horizon by means of imagination and curiosity, doomed to discover a cosmic abyss of unimaginable horror, a maddening chaos that defies mortal comprehension? But is it even possible to get a glimpse beyond the inescapable veil of darkness, the black shield of the arguably most enigmatic mystery of our time?
Welcome naked singularities and the cosmic censorship hypothesis. Born in the cataclysmic collapse of a colossal star, black holes grow by pulling in interstellar gas and other celestial objects, often forming an accretion disk. As the matter in the accretion disk spirals inward, it experiences intense friction and interactions between particles. This process, known as viscous dissipation, converts gravitational potential energy into heat, raising the temperature of the disc to levels significantly hotter than your average jalapeño pepper and causing it to emit radiation visible to modern telescopes.
Not all black holes possess accretion disks, but every black hole has an event horizon: a mathematical boundary in space-time, which is the threshold that once an object or even light crosses it, it can never escape. Because the escape velocity required to overcome the gravitational pull at the event horizon exceeds the speed of light. Thus, the region inside the event horizon is believed to be causally disconnected from the rest of the universe. This means that nothing that happens inside the event horizon has any effects on the rest of the universe, yet at the same time, that prevents us from observing the interior. Honestly, a great place to hold political elections or to simulate sending risky messages.
According to the no-hair theorem, yes, really, black holes can be completely characterized by only three independent, externally observable parameters: mass, electric charge, and angular momentum. Richard Feynman criticized the name because he thought of it as obscene. I, however, have a different problem with it. It is misleading. Theorems or theories are statements that have been proven to be true based on logical deduction from a set of axioms, fundamental true statements, or previously established theorems, which has not been the case with the no-hair theorem. Therefore, I propose a new name: the hairless hypothesis. I'm sure Feynman would be proud.
Conjectures or hypotheses are statements that are considered to be true or plausible given limited information, but which have not been definitively proven. Let's assume that there is indeed a singularity at the center of black holes and ignore other hypotheses like fuzzballs or quantum gravity dust bags. This singularity is the point where our general relativity breaks down: a point of infinite density and infinitely curved space-time. In the case of rotating black holes, called Kerr black holes, the singularity takes the shape of the "one ring to rule them all," and more exactly, a one-dimensional ring with no thickness. But that's just the singularity. The outside event horizon would still look more or less spherical.
How can we test this hypothesis? Jumping into a black hole would result in certain death and the disappointment of not being able to tell anyone what was actually inside. Luckily, there are better hypothetical ways. Let's consider the three parameters given by the hairless hypothesis. Increasing the mass would just expand the event horizon, so let's try to increase the angular momentum. This results in a rotating or Kerr black hole. As the black hole spins faster, the photons can move closer to the black hole's center while still being able to escape and reach our sensors. That is because space itself gets dragged around with the black hole, thereby giving photons a boost and deforming the event horizon itself.
When the black hole reaches a certain rotational speed, photons could escape from the singularity itself, which means that there is no more event horizon. At this point, the singularity becomes naked, as it is no longer clothed by an event horizon, which is sad, as it was a great choice of fashion: minimalistic but boasting a masterful slimming effect.
Now, what about the charge parameter? Another electrifying idea to create a naked singularity is to add large quantities of electric charge to the black hole, preferably electrons, since they are more common than positrons and do not add as much mass as protons would to the black hole, which then would promptly decide to rename itself to a Reissner-Nordström black hole. Upon adding enough charge, the electric field and gravity should find a balance, and the event horizon should vanish, tantalizingly exposing the singularity to the greedy gaze of astrophysicists and science file fans.
These monstrous possibilities arise from the formulas of the theory of relativity, as it does not prevent the existence of naked singularities. But even well-established theories are often found to be incomplete and erroneous in specific circumstances, and it is well known that the theory of relativity is prone to this, much to the anger of Einstein, as it describes the behavior of objects of vast mass and scale, inevitably breaking down when trying to predict the behavior of small things in the realm of quantum mechanics. Thus, general relativity and quantum mechanics are bound to clash when it comes to singularities. The heavyweights of the quantum scale, resulting in some nasty infinities. When you encounter infinities using physical formulas, usually something went wrong, for example, a wrong transformation, or you're severely limited understanding of what you are doing.
Appalled by the apparent breakdown of causality when approaching a singularity and repulsed by the error-implying infinities elicited from general relativity, Roger Penrose proposed the cosmic censorship hypothesis, which suggests the existence of a cosmic censor that prevents the formation of naked singularities. This cosmic censor is some not-yet-understood physical principle that discreetly covers naked singularities, ensuring they remain shrouded behind the cosmic curtains, or at least get pixelated there.
There are two interpretations of the cosmic censorship hypothesis. The weak cosmic censorship hypothesis proposes that singularities formed by the gravitational collapse of an object are always hidden behind event horizons. While the strong cosmic censorship hypothesis claims that general relativity is deterministic. If you drop a cow from space, you can calculate its future with 100% certainty, assuming you have a perfect understanding of the initial values that could influence its trajectory, such as the cow's aerodynamics, atmospheric turbulences, etc. Around a naked singularity, such predictions become impossible because the formulas break down when trying to describe the future of an object interacting with the singularity, as weird events like future instances of said object influencing itself may occur, thus rendering general relativity non-deterministic. Therefore, the strong cosmic censorship hypothesis asserts that naked singularities without event horizons cannot be observed in our universe, except for the Big Bang, which technically is a singularity itself.
The main takeaway is that both cosmic censorship hypotheses dictate that naked singularities do not exist. So, how about spinning and charged black holes, as discussed before? Well, reality is often disappointing. Let's assume we have an extremely quickly spinning Kerr black hole so that theoretically, if its angular momentum were just a little higher, a naked singularity would form. But how could we increase its spin? It's not like you could just give it a slap. The space around this black hole gets dragged around with it, giving objects in the vicinity a significant boost in velocity, or in the case of light, in energy. Therefore, to avoid being flung away by the centrifugal force, objects approaching the event horizon first have to lose their kinetic energy before being able to fall in. That way, they don't increase the angular momentum of the black hole whatsoever. No matter which angle or how fast you drop something into the hole, it seems impossible to add angular momentum.
A smart person came up with the idea of trying to add angular momentum by dropping something that is already rotating and has intrinsic angular momentum into the black hole. Unfortunately, this won't work either, as any object with angular momentum is required to have non-zero spatial dimensions. Let's drop a rotating chicken into the black hole. Such a dropped object would have to rotate in the same direction as the black hole, because the space nearer to the black hole gets dragged faster than the space farther away. Acceleration forces will act more strongly on the side of the chicken that is currently nearer to the black hole than on the one farther from it. This slows down its rotation while giving it a boost in velocity, thus deflecting it away from its path in the black hole's direction, perhaps even flinging it away with more velocity than it arrived with, rendering it unable to approach it any further while retaining its angular momentum, destroying its dreams to achieve what no chicken has achieved before: the creation of a naked singularity. Not to mention that the chicken would have to be magically indestructible, as otherwise, it would be spaghettified near the event horizon, turning into chicken alfredo pasta. Important to note: to slow down the chicken's rotation and to move it closer to the black hole, its angular momentum and gravitational potential energy have to be converted into another form of energy, such as heat. Hence, if we can deorbit a rapidly spinning chicken around a Kerr black hole, it may be possible to cook it using gravitational forces: the pinnacle of the art of rotisserie chicken.
For charged black holes, the situation is less complex, as Einstein's most famous formula, E=mc², can be applied. If you plug the black hole into a cosmic outlet to pump it up with electrons, it becomes harder and harder to add more, as the electric field gains more and more energy. Since, according to Einstein, mass and energy are equivalent, the climbing energy level of the electric field causes the black hole's mass to grow, increasing gravity and preventing the event horizon from vanishing.
Currently, there is no known way to create a naked singularity, except in imaginary special situations, usually with physically impossible initial conditions that would never occur in our universe, which is why the cosmic censorship hypothesis has gained additional requirements over the years, such as to address and exclude those special cases. But let's hypothesize what would happen if it were possible. What if naked singularities existed? First of all, Stephen Hawking would rise from the dead and give John Preskill and Kip Thorne, to whom he just lost a bet, clothing to cover their nakedness. But would we get anything useful from a naked singularity? Perhaps it would be possible to extract enormous amounts of energy, boosting humanity on the Kardashev scale.
The extreme gravitational effects near naked singularities might create conditions conducive to the formation of closed time-like curves or other phenomena associated with time travel. If one could navigate or control these temporal pathways, it could potentially open doors to explore the past, future, or alternate timelines. But alas, no one has come back yet to save Harambe, so the hope that this would work is low. Naked singularities could potentially resolve the black hole information paradox, which is the conflict between the principles of quantum mechanics and the notion that information is lost in a black hole. Naked singularities do not Hawking radiate away since they have no event horizon and would therefore probably last forever, or at least until the end of the universe, just like the great Skynet empire.
Built upon the possibilities that arise from the zero-dimensional dots of madness, though speculations sure are fun, but given our current understanding, naked gravitational singularities probably belong to the realm of unicorns and honest politicians: beautiful concepts, but very likely fiction. The cosmic censorship hypothesis cannot be rejected yet, and theoretical physicists will likely never behold a naked object of great attraction outside of simulations. And yet, with each rejected hypothesis, we inch closer to understanding the true face of reality, with all its monsters hidden behind event horizons and flesh bodies, just like we've deconstructed the fascinating phenomena of naked singularities.
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