NASA image of a black hole

Black holes might be portals to alternate universes

Contributed by
Feb 27, 2018, 11:49 AM EST

Black holes are called “black holes” for a reason. No one knows what lies beyond that impenetrable darkness, and there is no spacecraft in existence (and obviously no human) that could possibly make it past an event horizon and withstand the crushing gravity. But are there exceptions?

Imagine a black hole you could look into without getting shredded down to your last atom. An almost sci-fi study published in Physical Review Letters by UC Berkeley postdoctoral fellow Peter Hintz and colleagues could mean that there are black holes out there that would be more like portals than gaping mouths of destruction — if you didn’t mind your entire past being erased and entering into infinite futures.

Physicists are constantly debating the nature of these collapsed stars. Physics is deterministic, meaning that knowing exactly what happened in the past, such as the origins of the universe, determines just one future. This would have to mean that Einstein’s theory of general relativity predicted singularities. The only issue is that they are invisible to us. Most argue that there is no possible way we could ever see beyond the event horizon and into the naked singularity deep within a black hole, because that would basically upset physics as we know it.

“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,” Hintz said. “This is a question one can really only study mathematically, but it has physical, almost philosophical implications, which makes it very cool.”

Enter cosmic censorship. The weak cosmic censorship hypothesis insists that there are no naked singularities in the universe except the one that arose in the wake of the Big Bang, and that the event horizons of black holes must obscure their singularities. It’s believable. It’s uncomplicated. It lets you sleep at night.

Now, this is where things get weird and insomnia could set in. The strong cosmic censorship hypothesis limits how far a universe governed by the determinism of physics extends. After you pass a strange and intangible boundary within the event horizon of a (smooth, non-rotating, highly electrically charged) black hole, known as the Cauchy horizon, bizarre things start to happen. Hintz thinks it is actually possible to cross over to where determinism starts to break down and actually live to tell about it. The only problem is that no one will know what you saw, because you’ll never return.

Scientists who argue against this theory believe that gravity would slow down time as you approached the Cauchy horizon, and all the energy that the black hole has ever seen since the universe began will fall in with you and obliterate you right there.

While Hintz can’t see into an infinite future, he does acknowledge that no one may be able to in a constantly expanding universe, though he also suggests an alternate situation in which the expansion of the universe would cancel the time dilation of a black hole that has the prerequisites mentioned before, allowing you to make it past the Cauchy horizon in one piece and live in ... we have no idea. Nothing is certain in the vast expanse of theoretical physics.

“There are some exact solutions of Einstein’s equations that are perfectly smooth, with no kinks, no tidal forces going to infinity, where everything is perfectly well behaved up to this Cauchy horizon and beyond,” said Hintz. “After that, all bets are off.”

(via UC Berkeley)