Black hole with recurrence?

Stephen Hawking contradicts conventional theory on the event horizon of black holes

Black Hole: Is there the event horizon or not? © NASA
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So far, the thing was clear: A black hole escapes nothing, not even the light. Now cosmologist Stephen Hawking explains that perhaps the event horizon does not exist, the magic limit of no return. Instead, an apparent horizon ensures that light and matter are held fast, but the information about it can very well escape in a very different form.

According to current doctrine, black holes are singularities - places of infinite density at the center of which the laws of general relativity no longer apply. The tremendous gravity of these singularities ensures that matter and even light is attracted and can not escape - at least as soon as they cross the event horizon. It marks virtually the border to the area without recurrence.

Imperceptible border or wall of fire?

According to Einstein's theory, an astronaut who accidentally passes through the event horizon would not notice it at first. Because this is invisible and differs purely outside in nothing from the surrounding space. Quantum mechanics, however, sees it differently: According to its basic principles, the event horizon would more closely resemble a wall of fire, an extremely high-energy region. A passing astronaut would immediately burn to ashes according to this theory. Both views were incompatible side by side.

But now the British physicist Stephen Hawking presents a third solution that would satisfy both Einstein's laws and quantum theory: In his article "Information Preservation and Weather for a Black Hole, " he postulates that there is no event horizon at all. Because the space-time structure in the vicinity of the black hole fluctuates too much to be able to form a clear boundary, so the researchers.

The cosmologist Stephen Hawking during a lecture at NASA © NASA / Paul Alers

But not a final end for matter?

"The absence of an event horizon, however, means that there are no black holes - at least in the sense of places that the light can never escape, " explains Hawking. "But there are apparent horizons that exist for a certain period of time." Behind these, the black holes only temporarily hold matter. In Hawking's view, black holes should therefore be considered "metastable boundary states of the gravitational field." Display

But this means that the information about the trapped matter is not lost completely, as common theories state. It is only extremely changed and distorted and then radiated again as the so-called Hawking radiation. This radiation, postulated by Hawking in 1975, develops when matter particles near the black hole. For a short time, virtual pairs of these particles and their antiparticles form. If only one of the two sinks into the black hole, the energy of the remnant is released as radiation.

Hawking radiation as a remnant

This radiation is all the stronger, the smaller and the poorer the black hole. In the case of microscopic holes, this radiation even causes them to shrink over time and then dissipate almost completely into radiation. By contrast, the massive black holes, which arise from star explosions or sit in the heart of galaxies, emit only little of it.

Now Hawking has broadened his theory that this Hawking radiation could still contain information about what once fell into the black hole. This contradicts the concept of the event horizon, which leaves everything behind. Because the information about the sucked matter would be released in an extremely transformed form again. However, reading this information would be almost impossible. Hawking compares it to trying to accurately forecast weather over the long term: that is feasible in theory, but almost impossible in reality, at least so far.

Reactions skeptical to careful

Whether Hawking is right with his latest litter remains to be seen. The echo among his fellow physicists has been divided until cautious. Some consider it quite possible that there could be black holes without an event horizon. Others are rather skeptical, because the spacetime fluctuations that are supposed to cancel out the event horizon have so far not been proven, at least for the black holes in our environment.

And also Raphael Bousso from the University of California at Berkeley, a former Hawking student, is rather cautious in "Nature News": "The idea that there is no point in a black hole There is no return from this, is even more radical and problematic than the existence of the event horizon as a wall of fire, "said the physicist. (High Energy Physics Theory, 2014; arXiv: 1401.5761)

Video: Stephen Hawking explains his theory at a lecture in Cambridge

(Nature News, 29.01.2014 - NPO)