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10 September 2015updated 01 Jul 2021 11:40am

Stephen Hawking’s black hole poser

A black hole is the ultimate physics laboratory.

By Michael Brooks

It’s been a good week for weird ideas. First, Stephen Hawking announces he has solved a long-standing puzzle about the nature of black holes. A few days later, physicists in the Netherlands prove that space and time are nothing like we imagine. The only problem is, the second result might pull the rug from under the first.

Hawking claims to have solved a problem known as the black hole information paradox. There are three strands to this phenomenon. First, black holes swallow stuff that contains information. Second, thanks to “Hawking radiation”, black holes emit energy and finally evaporate away to nothing. Third, quantum theory tells us that information cannot disappear from the universe. So, if information can’t be destroyed, what happens to the information in a black hole?

It’s not an idle question. A black hole is the ultimate physics laboratory: if we can find ways to describe what happens to information in a black hole, we should find fundamental descriptions of the origins of the universe.

Hawking’s solution is that the information about the swallowed stuff is imprinted on the space and time surrounding the black hole. Specifically, it is written on to the spherical surface known as the event horizon, the boundary beyond which the black hole’s gravity becomes so strong that nothing can escape.

Hawking radiation forms in the vicinity of this event horizon. His idea is that the radiation picks up a hint of the information as it leaves: thus the information is preserved after the black hole is gone.

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Is he right? He can’t be – not exactly. Hawking’s calculations are done within the framework of Einstein’s general theory of relativity. This is built on the idea that the universe is composed of space and time as we observe and understand them (Einstein joined them together as “spacetime”). Unfortunately, the new Dutch experiment gives definitive proof that our conception of spacetime is far from complete.

After more than 50 years of inconclusive observations, the new experiment proves the existence of quantum entanglement, which allows two particles to exert an instantaneous influence on each other’s properties no matter how far apart they are. This is a problem, because we have no idea how this influence travels – there is no known mechanism. It goes deeper than ignorance about a physical mechanism, though. Because entanglement’s influence is instantaneous, it makes a mockery of the notion of distance: a fundamental feature of the geometry of spacetime as found in general relativity.

Einstein refused to believe that entanglement was real, dismissing it as “spooky”. Now we know he was wrong. All the previous experiments contained loopholes that could
have explained away the results, such as low-efficiency particle detectors that captured too few particles for the statistical analysis to be ironclad.

The new experiment closed all loopholes, so we can say for sure that being distant from something doesn’t show you can’t affect it instantaneously in some way. Might that help solve the black hole information paradox? After all, a black hole is made of spacetime, and entanglement might preserve information in various regions of this spacetime in interesting ways. Despite Hawking’s efforts, there is still plenty to learn. 

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This article appears in the 02 Sep 2015 issue of the New Statesman, Pope of the masses