Black holes and wormholes have long become a familiar attribute of many science fiction films and TV series, in which space travelers use them to instantly travel across the Universe. What are black holes and wormholes, how plausible is travel through time and space? What incredible truth is shown in science fiction films? This was told by Russian physicists from the universities of the "Project 5-100".
What is a black hole?
Physicists call a black hole a region of space-time with such a strong gravity that no matter, energy or information (including light) can leave this region once it gets into it. A black hole is bounded in space by an event horizon: the boundary of a black hole, beyond which no object or radiation can escape. Thus, observers outside the black hole cannot get any information about what is going on inside it.
According to general relativity, the geometry of black holes is described by Einstein's equations, linking the metric of curved space-time with the properties of the matter filling it, and gravity is a manifestation of the curvature of space-time, said a professor at the Educational and Scientific Institute of Gravity and Cosmology at the Peoples' Friendship University of Russia (RUDN University) Kirill Bronnikov.
“Scientists have theoretically described many varieties of black holes. They differ in the presence or absence of rotation, electric charge, and other possible parameters. It is believed that black holes can arise from the collapse of sufficiently massive stars at the final stage of their evolution or from fluctuations of superdense matter in the early Universe,”he said.
According to him, it is impossible to see a black hole, since an external observer cannot receive any information directly from the event horizon. Therefore, a black hole can manifest itself only indirectly - by the curvature of light rays passing nearby, by electromagnetic radiation from the surrounding matter falling into it, etc.
Scientists still do not understand what the inner regions of black holes, hidden under the event horizon, are. According to most models of black holes in general relativity, they must have "singularities" - points, lines or surfaces with infinitely large values of the curvature of space-time, as well as the density and pressure of matter. However, many researchers believe that in reality this cannot be.
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“Here we are faced with the limit of applicability of our classical ideas about space-time and enter the unknown area of the quantum theory of gravity that has not yet been built,” noted Kirill Bronnikov.
He spoke about the possibility of the existence of another type of black hole - the so-called "black universe". From the outside, it can look like any other black hole. However, an observer who has penetrated into it, crossing the event horizon, falls not into a singularity, but into a new expanding universe.
Looking for black holes
At the beginning of 2019, the observation program of the Radioastron ground-space interferometer was completed, with a resolution several thousand times higher than that of the famous Hubble Space Telescope. "Radioastron" is a few dozen of the most powerful ground-based radio telescopes and a space observatory, connected with the help of special algorithms into a virtual "dish" with a diameter much larger than our planet.
Radioastron allowed Russian astronomers to find clear observational indications of the existence in the center of the galaxy OJ287 in the constellation of Cancer of a pair of supermassive black holes that rotate at a short distance from each other, said the head of the laboratory for fundamental and applied research of relativistic objects in the Universe of the Moscow Institute of Physics and Technology (MIPT) Yuri Kovalev.
“Our observations fit well with the predictions of the OJ287 binary black hole model. In the future, using the Millimetron ground-space interferometer, we plan to study at shorter wavelengths the shadows and the vicinity of black holes in our and other galaxies. It will also help test the theoretical understanding of the existence of other objects - "wormholes", "he said.
Tunnels to other dimensions
"Wormholes" (the English equivalent of the name - wormholes, or wormholes) - the most intriguing objects in the universe, the existence of which scientists argue. These are configurations of space-time in the form of a kind of tunnels between distant regions of our Universe or even between different universes.
“Wormholes are akin to black holes, as they are localized objects with sufficiently strong gravity and curvature of space. But, unlike black holes, they do not have a "trap" - an event horizon, therefore theoretically they allow not only "entry", but also "exit". That is, you can go through them and come back,”said Sergei Rubin, professor at the National Research Nuclear University MEPhI (NRNU MEPhI).
Despite the fact that wormholes do not contradict general relativity and are predicted by some cosmological theories, the real candidates for the role of such objects are still unknown. In addition, wormholes imply a very atypical space-time geometry, which requires matter with exotic properties (for example, with negative energy density) to maintain.
“The discovery of wormholes in nature or their creation in the laboratory would mean a real revolution in the physics of space-time,” the scientist stressed.
Sergei Rubin does not share the confidence of astronomer Heino Falke that recent images of the black hole in the center of the M87 galaxy, obtained in the Event Horizons Telescope project, can confirm the existence of tunnels in the structure of space-time. For final conclusions, there is not enough measurement accuracy.
At the same time, theoretical ideas about these objects help scientists to better understand the nature of space-time and gravity.
How to get into a wormhole?
Not all science fiction films about tunnels to other dimensions are far from modern scientific theories, says Professor of the Immanuel Kant Baltic Federal University (IKBFU) Artem Yurov.
“In the film Interstellar, the information about black holes and additional spaces is in line with scientific ideas. This is not surprising, since the film's scientific advisor was the Nobel Prize-winning black hole physicist Kip Thorne. It was he who breathed new life into the idea of the existence of wormholes,”he said.
According to Artem Yurov, although wormholes are allowed by the laws of physics, they cannot arise on their own. However, they could be built by a civilization that is extremely developed in technical and scientific terms.
“This should not be surprising, after all, a Toyota car also cannot appear spontaneously, even if you wait tens of billions of years - it must be made,” he said.
Today physicists are thinking about the possibility of forming wormholes that do not disintegrate quickly, as well as how to make them large enough so that even molecules can fit and not collapse there.
“It is hypothetically possible to send the human genome through a wormhole. According to calculations, there are also funnels in additional dimensions, but they are still quite small, 10 to minus 31 degrees of centimeters,”said Sergei Rubin.
According to the scientist, through a wormhole it is hypothetically possible in the future to send humanity from a dying universe to another, just beginning to live. To do this, it is not necessary to send a person there physically - you can send information there, on the basis of which our civilization will be restored independently in the new Universe.
