Black holes are 'portals to other universes,' according to new quantum results
It might help to conceptualize exactly what this means if you imagine yourself traveling into a black hole. Under general relativity, falling into a black hole is, in some ways, much like falling into a very deep pit that has a bottom, only instead of hitting the bottom, you get pressed into a single point — a singularity — of infinite density. With both the deep pit and the black hole, there is no "other side." The bottom stops your fall through the pit, and the singularity "stops" your fall through the black hole (or at least, at the singularity it no longer makes sense to say you're "falling").
Your experience would be much different traveling into a black hole according to LQG, however. At first you might not notice the difference: gravity would increase rapidly. But just as you were nearing what ought to be the black hole's core — just as you're expecting to be squashed into the singularity — gravity would instead begin to decrease. It would be as if you were swallowed, only to be spit out on the other side.
In other words, LQG black holes are less like holes and more like tunnels, or passageways. But passageways to where? According to the researchers, they could be shortcuts to other parts of our universe. Or they could be portals to other universes entirely.
Interestingly, this same principle can be applied to the Big Bang. According to conventional theory, the Big Bang started with a singularity. But if time is rewound according to LQG instead, the universe does not begin with a singularity. Rather, it collapses into a sort of tunnel, which leads into another, older universe. This has been used as evidence for one of the Big Bang's competing theories: the Big Bounce.
Scientists don't have enough evidence to decide whether this new theory is actually true, but LQG does have one thing going for it: it's more beautiful. Or rather, it avoids certain paradoxes that conventional theories do not. For instance, it avoids the black hole information paradox. According to relativity, the singularity inside a black hole operates as a sort of firewall, which means that information that gets swallowed by the black hole gets lost forever. Information loss, however, is not possible according to quantum physics.
Since LQG black holes have no singularity, that information need not be lost.