From: mk_thisisit
Black holes are regions in spacetime [00:57:57]. They are limited on one side by a membrane called the event horizon [01:07:08]. The properties of this membrane dictate that while everything inside can fall in, including light, nothing, not even light or information, can fall out [01:10:10]. An observer outside the event horizon has no insight into what is happening inside and never will [01:21:22].
The Information Problem
Initially, studies suggested that what enters a black hole is not only completely mixed but also erased [00:00:00], [01:31:31]. This implies that a given object would be torn apart in the center of the black hole [00:07:07].
However, a fundamental principle of nature is that information is conserved, meaning it cannot be destroyed [03:48:48]. For example, if a book is set on fire, all its components (light, heat, atoms, photons, smoke) can theoretically be perfectly measured to rebuild the book [03:57:57]. This contradicts the idea of information being erased by a black hole, leading to the information paradox.
The central question is: What happens to the information (energy, matter) that falls into a black hole during its evaporation [04:51:51]?
Hawking Radiation and its Implications
Black holes have their own lifespan and will eventually evaporate [04:18:18], [04:20:20]. This process is due to Steven Hawking’s discovery called Hawking radiation [04:23:23], [06:47:47].
Hawking radiation comes from the event horizon of a black hole, which is described as pure spacetime – simply the geometry of spacetime [02:33:33], [02:43:43]. It is almost as if the black hole vibrates or tears this radiation from the vacuum of space [02:51:51]. Since the radiation comes from the vacuum and not from the matter that fell in, the problem arises: how is it possible that what fell in is finally recorded in the radiation [02:57:57], [03:11:11], [03:16:16]?
Reconciling the Paradox
Information Exit
The current opinion is that information does come out again, albeit in a very mixed way, recorded in the radiation [01:42:42], [01:47:47]. However, Steven Hawking’s initial calculations denied this [00:16:16], [02:10:10], suggesting there might have been something wrong with those calculations [02:15:15].
Hawking’s Quantum Mechanics Attempt
In the 1970s, Steven Hawking attempted to reconcile quantum mechanics with the theory of gravity, despite the lack of a quantum theory of gravity [07:10:10], [07:14:14]. He made calculations involving quantum mechanical particles on and near the event horizon of the black hole [07:27:27].
Hawking’s method was related to “pair creation” [07:41:41]. Quantum theory suggests that at sufficiently high energies, a particle and its antiparticle can be created simultaneously [07:44:44]. If this occurs near the black hole’s event horizon, it’s possible that the antiparticle falls into the black hole while the particle escapes to infinity [07:56:56].
Wormholes
A very speculative interpretation involves a kind of wormholes [09:47:48], different from those Einstein talked about [09:51:51]. These hypothetical wormholes could open from the inside of the black hole to the outside, allowing information to exit [09:55:55].
The idea of the Einstein-Rosen bridge and wormhole comes from Einstein and Rosen’s work in the mid-1930s [11:07:07]. This is a property of spacetime in mathematical solutions describing “eternal black holes” (a black hole that has always existed) [11:29:29]. These solutions include a black hole, a white hole, and a spacetime tunnel connecting them [11:38:38].
However, it’s not possible to pass through these wormholes because of how they develop [11:46:46]. Constructing a stable spacetime tunnel through which one could travel would require forms of energy or matter that, according to current knowledge, do not exist in the universe [12:00:00].
Some physicists agree that two documents published by Einstein (one known as the Einstein-Podolsky document, the other as IP) describe the same phenomenon: a spacetime tunnel created by the merging of two completely entangled black holes [12:24:24], [12:31:31], [12:42:42]. While theoretically they can exist, stable traversable tunnels probably do not [13:05:05], [13:10:10]. It’s difficult to maintain the stability of such a tunnel to allow for exit on the other side [13:37:37].
Singularities and the Cosmic Censor
The collapse of matter into a black hole is described by the concept of “dust collapse,” where material without pressure collapses [08:30:30], [08:39:39]. If this collapse is perfectly spherically symmetrical, everything falls towards the center, creating a singularity of infinite density [08:47:47], [09:03:03].
This leads to the “Cosmic Censor Hypothesis,” which posits that all singularities must be hidden inside the event horizon [13:53:53]. This means a “cosmic censor” forbids insight into the nature of singularities [00:27:27], [14:08:08]. However, whether there must always be a horizon surrounding a singularity is an open and mathematically interesting problem [14:15:15].
Significance of Understanding Black Holes
Understanding black holes is crucial for making a “quantum leap” in understanding science [00:44:44], particularly theoretical physics [14:34:34]. The existence of black holes also proves that the general theory of relativity itself breaks down at certain points [03:23:23].