From: mk_thisisit
Event Horizon
Black holes are defined as regions in space-time [00:53]. These regions are limited on one side by a membrane known as the event horizon [01:02].
The fundamental properties of the event horizon are that everything inside it, including light, can only fall in [01:10]. Conversely, nothing, not even light or information, can fall out of the event horizon [01:17]. An observer situated outside this membrane has no insight into what is happening inside and never will [01:20].
Information Paradox
Initially, studies suggested that whatever enters a black hole is not only completely mixed but also erased [00:00], [01:31]. However, the current scientific consensus is that information eventually emerges from the black hole in a very mixed form, recorded within the radiation [01:42]. The principle of nature suggests that information is conserved and cannot be destroyed [03:48]. This means, theoretically, if one were to burn a book, all emitted light, heat, atoms, photons, and smoke particles could be measured to rebuild the book perfectly [03:57]. This concept clashes with the idea of information being lost within a black hole. The crucial question then becomes: if something enters a black hole and the black hole later disappears, and all radiation comes from the event horizon and the vacuum of space, how is the fallen-in information finally recorded in that radiation [03:01]?
Singularities and the Cosmic Censor Hypothesis
The collapse of material, like a cloud of dust, into what is now called a black hole, leads to the formation of a singularity [08:30]. A singularity is a point of infinite density, as described by Oppenheimer and Snyder in their work on dust collapse [09:03].
A hypothesis known as the Cosmic Censor Hypothesis proposes that all singularities must be hidden inside the event horizon [13:53]. This “cosmic censor” prevents us from gaining direct insight into the nature of these singularities [00:31], [14:08]. However, whether there must always be a horizon surrounding a singularity remains an open and mathematically interesting problem [14:14].
Understanding black holes and their event horizons is expected to result in a quantum leap in the understanding of theoretical physics [00:42], [14:34].
Hawking Radiation
Black holes are described in Einstein’s theory as pure space-time – simply the geometry of space-time [02:33]. Radiation, known as Hawking radiation, emanates from the event horizon of a black hole [00:33], [02:43].
This radiation is thought to originate from the vacuum of space itself, not from matter that has fallen into the black hole [02:54]. It is almost as if the black hole vibrates or tears this radiation from the vacuum [02:51].
Discovery and Mechanism
Stephen Hawking discovered that black holes have their own lifespan and will eventually evaporate through a process called Hawking radiation [04:17], [04:23], [06:49]. He made an attempt to reconcile quantum mechanics with the theory of gravity, despite the lack of a quantum theory of gravity [07:10].
His calculation involved quantum mechanical particles near the event horizon of the black hole [07:27]. The method Hawking used was related to pair creation [07:38]. Quantum theory dictates that at sufficiently high energies, a particle and its antiparticle can be created simultaneously [07:44]. If this occurs near the event horizon, it’s possible that the antiparticle falls into the black hole while the particle escapes and moves towards infinity [07:58]. This process of particle emission is what constitutes Hawking radiation.
Implications
The existence of Hawking radiation implies that black holes, despite their immense mass, will eventually evaporate [04:20]. This process is exceedingly slow for typical black holes, taking approximately 10^100 (one with a hundred zeros) years for them to finally evaporate [06:36].
During the evaporation process, a critical question arises: what happens to the information, energy, and matter that fell into the black hole [04:51]? Stephen Hawking’s initial calculations denied that information could exit from the other side of a black hole [00:16], [02:10], suggesting there might have been inaccuracies in those early calculations [02:15].
Connection to Galaxy Collisions
When galaxies collide, such as the predicted collision between the Andromeda Galaxy and our Milky Way, their central black holes will eventually merge [00:18], [05:09], [05:16]. Andromeda’s central black hole is much larger and will eventually absorb our galaxy’s black hole [05:37], [05:44], [05:54]. This new, larger supermassive black hole will then begin absorbing the entire galactic cluster, which can contain millions of galaxies [06:00], [06:14]. Even these massive black holes will eventually evaporate through the Hawking evaporation phenomenon [06:44].
Wormholes and Event Horizons
Speculative interpretations of complex mathematics suggest the existence of wormholes that could open from the inside of a black hole to the outside, potentially allowing information to escape [09:47], [09:59]. However, there is currently no evidence for this, and it remains a highly speculative idea [10:02].
The concept of wormholes, specifically the Einstein-Rosen bridge, arises from the work of Einstein and Rosen in the mid-1930s [11:07], [11:13]. This is a property of spacetime discovered in 1916 within the context of “eternal black holes” – theoretical black holes that have always existed [11:20], [11:29]. A formal mathematical solution for such a black hole includes a black hole, a white hole, and a space-time tunnel connecting them [11:37].
However, these theoretical wormholes are generally believed to be unstable and impassable due to their internal time and space distortions [11:46], [13:16]. To construct a stable space-time tunnel through which one could travel, forms of energy or matter currently unknown in the universe would be required [11:59]. While theoretically possible, traversable wormholes likely do not exist [13:05]. When two black holes merge to form a space-time tunnel, it implies they must be completely entangled [12:42].