A theoretical investigation into Loop Quantum Gravity would be the key to understanding singularities
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In April 2019, the world marveled at the first image of a black hole. Captured by the Event Horizon Telescope (EHT), the photograph showed a luminous ring surrounding a dark shadowthe heart of what seemed to be an unfathomable mystery. However, beyond the visual impact, that image raised fundamental questions: What happens inside a black hole? Are singularities really the end of the laws of physics? These questions have been a source of fascination and bewilderment for scientists around the world.
In a recent study, a group of researchers has explored how the Loop Quantum Gravity (LQG)an advanced theory of quantum physics, could offer a new way to understand black holes. This work, focused on the properties of rotating or Kerr black holes, proposes that the concepts of the LQG could solve the problem of singularitiesin addition to providing new clues about the shadows of black holes observed by the EHT.
What are black holes and why do they intrigue us?
Black holes are regions of space where gravity is so intense that nothing, not even light, can escape. They form when massive stars collapse at the end of their lives, creating a singularity, a point where the density and curvature of space-time become infinite. Although the equations of the Einstein’s general relativity predict the existence of singularities, they also indicate that in that place the laws of physics as we know them are no longer valid. This paradox has led scientists to search for theories that can reconcile general relativity with quantum mechanics.
What makes black holes especially fascinating is their ability to challenge the limits of human knowledge. They are true natural laboratories where extreme gravitational forces can test our physical theories. But what really happens inside them? The answers could be hidden in quantum physics, and more specifically, in theories such as Loop Quantum Gravitywhich rethinks the very nature of space and time.
Loop Quantum Gravity: a look at the basics
Loop Quantum Gravity (LQG) is a theory that seeks to unify general relativity and quantum mechanics. Unlike other proposals, such as string theory, the LQG does not introduce additional dimensions or hypothetical particles. Instead, suggests that space-time is not continuousbut is made up of small “blocks” or discrete loops of energy.
According to the LQG, these loops form a three-dimensional network called spin network (spin network). This quantum fabric of space-time has a granular structurewhere areas and volumes are quantified. This means that There are minimum limits for the measurements of these magnitudesthus eliminating the possibility of a singularity with infinite density. In this case, what appears is a region where space-time behaves in a completely new way, allowing “quantum bounces” instead of infinite collapses.
But this theory also has an advantage: it is independent of the background, that is, it does not assume a pre-existing space-time. Instead, space emerges as a property of the quantum system itself. This radical approach transforms the way physicists understand extreme gravitational interactions and opens the door to new ways of analyzing phenomena like black holes.
Black holes according to the LQG: the study model
The recent study applies the principles of LQG to the Kerr black holesa type of black hole that spin quickly. The researchers introduced quantum corrections to the classical Kerr metrics, modifying key aspects such as the size of the event horizon and the internal structure of the black hole. The results were revealing: quantum metrics predicted black holes with smaller event horizons and a reduced overall size compared to classic models.
One of the most fascinating implications is the elimination of singularities. Instead of a point of infinite density, the LQG suggests the existence of a region where space-time “bounces” due to quantum effects. This idea not only solves one of the most important problems in general relativity, but also proposes a model more consistent with the laws of quantum mechanics.
On the other hand, the researchers also analyzed the rotational behavior of these black holes. According to the study, the maximum spin speed (or extreme rotation parameter) is limited by quantum corrections. This limit is smaller than that predicted by classical relativity, indicating that quantum black holes would be less extremes in his behavior.
The shadows of black holes: what do they tell us?
The “shadows” of black holes are the dark areas that appear when light is trapped near the event horizon. These shadows are crucial because they allow astronomers to indirectly observe black holes using telescopes like the EHT. However, the recent study suggests that quantum black holes have smaller and slightly distorted shadows compared to classical models.
In particular, the researchers used EHT data on two supermassive black holes: M87* and Sgr A*. While the quantum predictions do not fit the observations of M87* well, they do fit the characteristics of Sgr A* much better. This could be because quantum corrections are more evident in lower mass black holes, such as Sgr A*.
Differences in shadows are a window into the quantum properties of space-time. If future observations confirm these distortions, it would be a direct indication that the Loop Quantum Gravity is on the right track to describe the fundamental reality.
The future of Loop Quantum Gravity and black holes
Despite the advances this study offers, Loop Quantum Gravity still faces significant challenges. One of the main limitations is lack of direct observational evidence. Although the shadows of black holes are a good starting point, More precise instruments and new techniques will be needed to confirm quantum predictions.
But there is an important point to keep in mind, and that is that the LQG It is not the only theory that attempts to unify general relativity and quantum mechanics. Other proposals, such as string theory, also offer alternative explanations for black holes and singularities. However, the simplicity and direct approach of LQG, focusing on the discrete nature of space-time, make it one of the most promising theories.
Ultimately, this study not only sheds light on black holes, but also highlights the importance of collaboration between advanced theories and astrophysical observations. By combining theoretical ideas with empirical data, Physicists are closer than ever to solving one of the universe’s greatest mysteries.
References
- Muhammad Ali Raza, M. Zubair, Farruh Atamurotov, Ahmadjon Abdujabbarov. Probing Loop Quantum Gravity via Kerr Black Hole and EHT Results. arXiv (preprint): 2501.01308.
