A new mathematical solution shows that the past of an object inside certain black holes can be erased and that this does not determine its future. So the saying that you can learn from your past and change the future is not exactly universal.
The study, published in Physical Review Letters, focused on electrically charged black holes and what happens to objects crossing their event horizon – the surface from which nothing can escape. Charged black holes are a possible type of black hole from relativity, but they are not actually expected to form in nature.
The paper shows a violation of a well-established idea about the nature of general relativity: the strong cosmic censorship conjecture. Relativity is a deterministic theory. If you knew the position and velocity of every object at one moment in time, you would know the past and could predict the future. But the singularity within black holes messes with this deterministic idea.
So the conjecture enshrines this determinism. The singularity is hidden by an event horizon from the rest of the universe, and if you enter the event horizon, there is a second surface called the Cauchy horizon that still prohibits seeing the singularity. And you would spend all eternity slowly getting closer to that surface.
What Hintz and his colleagues realized was that for a charged black hole in an expanding universe like ours, this hypothesis is not valid. It is possible to cross the Cauchy horizon and get into a world where the past doesn’t influence the present and the future anymore.
“No physicist is going to travel into a black hole and measure it. This is a math question. But from that point of view, this makes Einstein’s equations mathematically more interesting,” co-author Dr Peter Hints of UC Berkley said in a statement. “This is a question one can really only study mathematically, but it has physical, almost philosophical implications, which makes it very cool.”
Several papers have already been produced in reply to this work that argue that the strong censorship could still apply to our universe since there shouldn’t be any charged black holes out there. But Hintz highlights that there is still much work to do to understand black holes.
“People had been complacent for some 20 years, since the mid-’90s, that strong cosmological censorship is always verified,” Hintz added. “We challenge that point of view.”
The theory of General Relativity continues to be the best way to explain the vast universe, but maybe this will be its undoing.