Exactly 40 years after famed theoretical physicist Stephen Hawking brought event horizons and black holes into the public eye, he is now claiming that black holes don’t actually exist. Instead of all-consuming event horizons and black holes which nothing can escape from, Hawking now proposes that there are “apparent horizons” which suck in matter and energy — but only temporarily, before eventually releasing them again.
To be clear, Hawking isn’t proposing that black holes don’t exist — just that black holes, as we’ve understood them for the last 40 years or so (thanks to work done by Hawking and others), don’t exist. The current understanding is that black holes are surrounded by an event horizon — a boundary in spacetime which only allow matter and energy to pass through one way, towards the black hole. It is, in other words, the point of no return. This is why black holes appear black — energy can’t escape, and so they produce no light and no heat. In thermodynamics terms, a black hole is a perfect black body — an object that absorbs all energy and radiation.
The problem with this theory, though, is that it’s based on general relativity. In recent years, as our understanding of quantum theory has improved, numerous conflicts have arisen, especially in places where both theories apply — such as black holes and event horizons. Basically, quantum mechanics has a big issue with the idea that event horizons completely and utterly destroy information — a big no-no in the world of quantum. Hawking’s new proposal tries to ameliorate this conflict between the two theories.
The Event Horizon’s “gravity drive.” I wonder if the
film will have to be renamed Apparent Horizon…
In a short research paper (arXiv:1401.5761) called “Information Preservation and Weather Forecasting for Black Holes,” Hawking proposes that black holes are instead enveloped by an apparent horizon. Basically, instead of an event horizon that blocks everything absolutely, an apparent horizon suspends matter and energy from trying to escape — and when it does escape, due to the wild fluctuations within a black hole and its apparent horizon, the energy would be released in a garbled form. Hawking likens these fluctuations to weather on Earth: “It will be like weather forecasting on Earth. That is unitary, but chaotic, so there is e ffective information loss. One can’t predict the weather more than a few days in advance.” (Unitarity is the part of quantum theory that strongly disapproves of event horizons being a point of no return.)
The research paper concludes: “The absence of event horizons mean that there are no black holes — in the sense of regimes from which light can’t escape to infi nity. There are however apparent horizons which persist for a period of time.”
It’s worth noting that Hawking’s new paper is just two pages long, contains no calculations, and hasn’t yet passed peer review. It does seem to do what it set out to achieve, though. Complex problems don’t necessarily have complex solutions. Speaking to Nature, Hawking had a little more to say about the matter, too: “There is no escape from a black hole in classical theory,” Hawking said. “[Quantum theory, however] enables energy and information to escape from a black hole.” To fully explain the process, though, the theoretical physicist admits that we’re still looking for a theory that ties up gravity with the other universal constants — a theory that , Hawking says, “remains a mystery.”