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Black Holes and Wormholes: Tunneling Our Way into Another Universe?

August 2, 2019

Black holes and wormholes have long become a fixture in sci-fi films where space travelers use them to hop about the universe. But what are these holes, and how feasible is travel through spacetime? What incredible truth lurks behind science fiction? We put these questions to physicists from Russian universities that participate in Project 5-100, a government-funded initiative aimed at making Russian institutions of higher learning more competitive globally.

What’s a Black Hole When It’s at Home?

Physics defines a black hole as a spacetime region with so strong a gravitational pull that no matter, energy or information, once inside, can leave it anymore. Since no object or radiation, including light, can breach the event horizon which bounds the black hole, the outside observer can never learn what is going on at its core.

In terms of the theory of general relativity, the geometry of black holes is described by the Einstein field equations that relate the spacetime curvature metric to the distribution of the matter filling it, with gravity being an effect of this curvature, says Kirill Bronnikov, a professor with the Institute of Gravitation and Cosmology at RUDN University.

Scientists have theoretically described several types of black holes, he continues: rotating and non-rotating, charged and non-charged, etc. Black holes are believed to have formed through the gravitational collapse of massive stars in the terminal stages of their evolution or as a result of perturbations of superdense matter in the primordial universe.

Black holes, Kirill Bronnkov stresses, cannot be seen, as no information from the event horizon reaches the outside observer. Therefore, they can only be detected indirectly by their effects such as the bending of light paths in their vicinity, the electromagnetic radiation emitted by the matter falling into them, etc.

Scientists are still struggling to form an idea of what the regions inside the event horizon may look like. Here, the general relativity theory posits singularities, with infinitely large spacetime curvatures, densities and pressures. However, many argue that this is impossible.

Kirill Bronnikov is cautious. This is the lim it beyond which our classical concepts of spacetime do not go, the uncharted waters of a quantum theory of gravity which is yet to be propounded, says he.

There may exist, he says, yet another type of black hole, the so-called black universe. It would look like an ordinary black hole from the outside, but an observer crossing the event horizon into the black hole would encounter a new expanding universe rather than a singularity.

How to Find a Black Hole

Early 2019 saw the completion of an observation mission by the RadioAstron interferometer project. RadioAstron uses algorithms to link together dozens of extremely powerful ground-based telescopes and a space-based observatory to produce a virtual dish larger than Earth in diameter, which provides a resolution several thousand times higher than does the famed Hubble telescope.

According to Yury Kovalev who leads the Laboratory of Fundamental and Applied Research of Relativistic Objects of the Universe at the Moscow Institute of Physics and Technology (MIPT), RadioAstron has allowed astronomers to discover binary supermassive black holes in close orbit around each other at the center of OJ287, a galaxy in the constellation of Cancer.

He adds that the observations made by the project team were fully consistent with the predictions of theory. Russian researchers now plan to use ground and space-based interferometers in the Millimetron project to explore the neighborhood of black holes in our galaxy and beyond at shorter wavelengths, which should help validate the theory of other remarkable astronomical objects, wormholes.

Peeping down Tunnels to Other Dimensions

Wormholes are spacetime configurations that resemble tunnels between disparate locations in our universe or between universes. These are arguably the most intriguing structures out there, and their existence is still a matter of debate.

As localized objects with a strong force of gravity and space curvature, wormholes are akin to black holes. Unlike them, however, they do not have an event horizon to trap matter and energy which therefore can, theoretically, get both in and out, making wormholes traversable, says Sergey Rubin of National Research Nuclear University MEPhI.

While wormholes are not inconsistent with the theory of general relativity and are in fact predicted by some cosmological theories, no likely candidates have yet been identified. Besides, to support wormholes’ highly unorthodox spacetime geometry, one has to postulate the existence of matter with exotic properties such as negative energy density.

Sergey Rubin points out that, should a natural wormhole be discovered or an artificial one created in a lab, this would revolutionize the physics of spacetime.

He does not share the confidence of Heino Falcke, a leader of the Event Horizons Telescope collaboration, that the recent images of the ‘shadow’ of the black hole at the heart of the galaxy M87 confirm the existence of spacetime tunnels. No definitive conclusion can yet be drawn due to insufficient measurement accuracy, he warns.

That said, theorizing about these objects gives scientists a deeper insight into the nature of spacetime and gravity.

Wriggling Down a Wormhole

Artem Yurov of Immanuel Kant Baltic Federal University (IKBFU) admits that not all sci-fi movies that feature tunnels to other dimensions are parsecs away from current theory.

For instance, what Interstellar has to say about black holes and extra dimensions is good modern science, which is hardly surprising, given that the film drew on the expertise of Nobel Prize winner Kip Thorne, a top authority on black holes. It was Kip Thorne who breathed new life into the idea that wormholes do exist, says Artem Yurov.

He believes that, while wormholes are allowed by the laws of physics, they cannot appear spontaneously, any more than a Toyota car can. However, they could be built by a highly scientifically and technologically advanced civilization.

Physicists are now looking at the possibility of creating wormholes that would not collapse too quickly and that would be large enough to hold at least molecules.

In theory, human genetic material could be dispatched through a wormhole. Calculations suggest that there are vortices to other dimensions, too, but they are as yet tiny, ten to the power of minus 31 centimeters in size.

The scientist believes that it might eventually be possible to whisk humanity out of its dying universe into a young one down a wormhole. This does not mean packing off human beings, body and all, but transmitting the information that would allow our civilization to rebuild itself in its new home.