From: mk_thisisit
Sir Roger Penrose, a brilliant British mathematician and physicist, was awarded the Nobel Prize in Physics on October 6, 2020, for explaining how the existence of black holes results from Albert Einstein’s theory of relativity [00:04:30].
Understanding Black Holes
Despite the popular perception, Maciej Dunajski, a mathematician at the University of Cambridge and a student of Roger Penrose, does not consider black holes to be a deep mystery [00:05:37]. He explains that scientists have a very good understanding of them [00:05:33]:
- We know about the initial solution, which is the Oppenheimer Sider model [00:05:00].
- We know what black holes look like when they rotate, known as the Kera solution [00:05:07].
- Numerous computational algorithms have been developed to observe how black holes collide and the gravitational waves they produce as they spiral into each other [00:05:13].
- Observations from the Ligo gravitational wave detector have further enhanced this understanding [00:05:27].
The existence of black holes has been directly confirmed by various telescopes in recent years [00:05:51].
The Problem of Singularity
Penrose feels like an “outsider” among cosmologists due to his concept introduced around 2004, which he developed to solve problems in cosmology [00:06:19]. The core problem lies with the concept of singularity [00:06:44].
Definition: Singularity
A singularity is a region in space-time where curvature is often large [00:06:52]. Another characteristic is that geodesics (preferred curved lines in the universe) have a beginning but no end, terminating at a point that does not belong to space-time. This implies that physics as we know it ends in such singularities [00:07:03].
Penrose gave a lecture on this topic in 1964 at King’s College in London, which Stephen Hawking, though not present, later learned about through Denis Sciama [00:07:22]. Penrose repeated the lecture in Cambridge, where Hawking was present and engaged in a detailed private discussion with Penrose and George Ellis [00:07:48]. Hawking quickly grasped the solution and applied it in a cosmic context, incorporating it into his doctoral thesis [00:08:11]. Penrose developed the singularity theorem for black holes [00:09:03], and later collaborated with Hawking on a paper that summarized their results [00:09:12].
Mathematics and Physics in Black Holes
The research of Penrose and Hawking suggests that the mathematics we know “breaks down” in black holes, specifically at the point of singularity [00:11:46]. This breakdown implies that our current understanding of physics is inadequate to describe phenomena within black holes [00:12:02].
The challenge lies in the fact that Einstein’s general theory of relativity, which describes the physical theory, becomes inadequate at the point of singularity [00:12:12]. To accurately describe the evolution of what happens inside a black hole, a theory connected to quantum mechanics—known as quantum gravity—is needed [00:12:30]. Currently, a good theory of quantum gravity is unknown, and Penrose expresses skepticism towards string theory’s claims in this regard [00:12:54].
The Cyclic Universe Theory
Penrose’s groundbreaking work includes his concept of a cyclic universe [00:36:55]. This idea emerged from his contemplation of Fred Hoyle’s lecture on the theory of the universe, specifically the expansion of galaxies moving away from each other until they reach the speed of light and disappear [00:36:37]. Penrose found this notion problematic and developed his own model [00:36:50].
His theory posits that we do not need inflation in cosmology [00:37:17]. Instead, the exponential expansion observed in our current eon is self-similar and completely consistent with observations [00:38:07]. Penrose explains that he changed his mind about the cosmological constant, realizing his previous assumptions were incorrect, and now believes in a positive cosmological constant that leads to exponential expansion [00:38:24].
In his book Cycles of Time, Penrose suggests that the universe is cyclical, with the Big Bang being the final phase of a previous universe [00:40:03]. He describes a mathematical “trick” where an enormously expanded “boring era” of a previous universe, containing only specific types of particles like photons, can be mathematically equivalent to a new Big Bang when “squeezed” [00:40:12].
The Boring Era and Hawking Evaporation
According to Penrose’s cyclic universe concept, our current epoch is part of a “boring era” [00:40:58].
- Galaxies like the Milky Way and Andromeda are on a collision course, and astronomers predict they will eventually merge into a larger galaxy [00:41:10].
- The supermassive black hole at Andromeda’s center, being much larger, will absorb our galaxy’s black hole and eventually the entire cluster of galaxies [00:41:41].
- This leads to a prolonged “boring era,” lasting approximately 10^100 years, during which this massive black hole gradually evaporates via the phenomenon of Hawking evaporation [00:42:35].
- The energy released from this evaporation then contributes to the creation of the next eon, appearing as a point in the sky for future observers [00:43:00].
Penrose claims that observational evidence supporting this cyclic model, specifically points in the cosmic microwave background radiation, has been published in collaboration with Krzysztof Meisner, Paweł Nurowski (Polish scientists), a South Korean scientist, and himself [00:43:58]. The theory of a cyclic universe suggests there is no absolute beginning or end [00:39:48].