NEWS
Black Holes might not be dead-ends after all
2016 June 06

Diego Rubiera-Garcia

A physical body might be able to cross a wormhole1, in spite of the extreme tidal forces, suggests a new study2 by Rubiera-Garcia, of Instituto de Astrofísica e Ciências do Espaço (IA3), and his team. This result, published on April 28 in the journal Classical and Quantum Gravity, is supported by the fact that the interactions between the different parts of the body, which hold it together, are preserved. The team was invited by the journal editors to write an insight article4 that was published online today.

In their previous work5, the authors arrived at theoretical descriptions of black holes without a singularity, that bizarre and infinitesimally small point where space and time ends abruptly. What they found at the centre of a black hole, and without actually being in search of one, was a spherical and finite size wormhole structure.

Diego Rubiera-Garcia, of IA and Faculdade de Ciências da Universidade de Lisboa, commented on how the team solved the singularity problem: “What we did was to reconsider a fundamental question on the relation between the gravity and the underlying structure of space-time. In practical terms, we dropped one assumption that holds in general relativity, but there is no a priori reason for it to hold in extensions of this theory.

Presented with this wormhole structure of finite size, where space and time continue past and beyond the black hole and into another part of the Universe, the authors then inquired about the fate of a physical object venturing into it. They asked if a chair, a scientist, or a spacecraft, would withstand the intense gravitational field and retain its unity as a body through the journey, and also to what extent would be the damage.

In their study, a physical body approaching a black hole is analysed as an aggregation of points interconnected by physical or chemical interactions holding it together.

Each particle of the observer follows a geodesic line6 determined by the gravitational field. Each geodesic feels a slightly different gravitational force, but the interactions among the constituents of the body could nonetheless sustain the body,” Rubiera-Garcia said.

General relativity theory predicts that a body approaching a black hole will be crushed along one direction and stretched along another. As the wormhole radius is finite, the authors demonstrate that the body will be crushed just as much as the size of the wormhole. Instead of converging to an infinitesimal separation, the so called singularity, geodesic lines will still be apart by a distance greater than zero.

In their work, the authors show that the time spent by a light ray in a round trip between two parts of the body is always finite. Thus, different parts of the body will still establish physical or chemical interactions and, consequently, cause and effect still apply all the way across the throat of the wormhole.

We can then imagine that finite forces, no matter how strong they would have to be, could compensate for the impact of the gravitational field near and inside the wormhole on a physical body traversing it. At least, according to these study, there isn't anything beyond all hopes, and the passage to another region of the Universe might be feasible.

Francisco Lobo, of IA and Faculdade de Ciências da Universidade de Lisboa, leader of the Cosmology group at IA, said: “The authors' insights into the concepts of space-time singularities and curvature divergences are representative of the fundamental theoretical research carried out at the IA, going beyond Einstein's General Relativity. This research will also probably be important to understand these difficult concepts for the fate of the Universe, in a plethora of cosmological models.

Notes:
  1. A wormhole, also known as Einstein-Rosen bridge and first proposed in 1935, is a hypothetical shortcut connecting two far away places in space-time.
  2. The article “Impact of curvature divergences on physical observers in a wormhole space–time with horizons”, by G. J. Olmo, D. Rubiera-Garcia and A. Sanchez-Puente, was published on April 28, 2016, in the journal Classical and Quantum Gravity, Volume 33, Number 11, available at http://iopscience.iop.org/article/10.1088/0264-9381/33/11/115007
  3. The Institute of Astrophysics and Space Sciences (IA) is the largest national research unit in the field of Space Sciences in Portugal, encompassing most of the field’s national scientific output. It was evaluated as "Excellent" by the European Science Foundation (ESF) in the latest assessment requested by Fundação para a Ciência e Tecnologia (FCT).
  4. The insight article “Wormholes can fix black holes” was published today on CQG+ website at https://cqgplus.com/2016/06/08/insight-wormholes-can-fix-black-holes/
  5. See for example “Geodesic completeness in a wormhole spacetime with horizons”, by G. J. Olmo, D. Rubiera-Garcia, and A. Sanchez-Puente, published on August 26, 2015, in the journal Physical Review D, Volume 92, Issue 4, available at http://journals.aps.org/prd/abstract/10.1103/PhysRevD.92.044047
  6. A geodesic line in space-time is the path in space and story in time followed by a freely falling particle.
Contacts

Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa Fundação para a Ciência e a Tecnologia