Black and White Holes

The Privilege of Rebirth

Black holes are strange enough on their own — objects so dense, so curved in spacetime, that nothing, not even light, can escape once it crosses the event horizon. But what if a black hole isn’t the end of a process, but only half of one?

What if some black holes are paired with white holes — hypothetical objects that do the exact opposite: spewing matter and energy and refusing to let anything enter?

What exactly is a white hole?

Both black holes and white holes are solutions to Einstein’s equations — specifically, the maximally extended Schwarzschild solution (Misner, Thorne & Wheeler). The maximally extended Schwarzschild solution contains not just a black hole region, but also a white hole region and two asymptotically flat universes connected by a wormhole-like geometry. In that context, a white hole appears as a region of spacetime from which particles and light can only emerge, never enter. It’s not just opposite in behavior; it’s opposite in causal structure (Penrose, _The Road to Reality_).

This isn’t just poetic symmetry or science fiction. Theoretical white holes emerge directly from the mathematics of general relativity. The Schwarzschild solution, which describes a non-rotating, uncharged black hole, is time-symmetric — implying a mirror structure in reverse: a white hole. But what does it mean for an object to be a time-reversed twin of another? If white holes are mathematically valid, why haven’t we observed any in the universe?

Would We Recognize a White Hole If We Saw One?

Theoretically, a white hole might appear as a sudden, bright and intense burst of energy, with no observable cause — an eruption of matter from an otherwise empty region of space.

What a white hole might look like:

• A bright, energetic object, possibly ejecting high-energy particles, light and radiation.
• Seemingly violating causality, because it would be spewing out stuff without any apparent source or mechanism.
• Something you cannot approach — nothing can enter a white hole, only escape from it. Its event horizon works in reverse.

That raises the question: Have we already seen something like this?

Some researchers have speculated that gamma-ray bursts (GRBs), fast radio bursts (FRBs) or even quasars could resemble white hole events. These phenomena exhibit characteristics consistent with sudden energy outflows and seem to arise from nowhere. But we also have standard explanations for them — neutron star collisions, magnetar flares, accreting black holes — so if a white hole does exist among them, it would have to defy those models in very specific ways.

In all these cases, we observe high-energy outflows, but we can usually trace them to known causes. A true white hole would need to be:

• Not powered by anything observable — just seemingly appearing and ejecting matter without consuming anything.
• Short-lived, because they are theorized to be unstable in most scenarios.
• Exotic in signature, with a spectrum or radiation pattern we can’t explain with standard astrophysics.

Could a white hole be distinguishable by the fact that it is inaccessible — nothing can fall into it — and that its energy release is causally disconnected from anything in the observable past?

Is a White Hole a Physical Object or an Event?

Perhaps our model of white holes as continuous physical objects is the problem. What if a white hole is not a stable object like a star or black hole, but a spacetime event? A momentary, one-time expulsion of matter and energy? A cosmic rebirth?

Theoretically, Can We "See" a White Hole?

Some speculative models suggest that white holes could appear as low-entropy objects with time-reversed thermodynamic behavior, but it’s unclear how such a signature could be differentiated from natural cosmic variability.

If a white hole is time-reversed from a black hole, it would “explode” into our universe in a way that seems to come from nothing, ejecting its contents in a single, possibly instantaneous burst.

In that sense:

• You might see the aftereffects, but not the white hole itself.
• The white hole might not even be a persistent object — it could just be a spacetime event, a momentary window ejecting something into the universe and vanishing.

And here’s the more poetic layer: if white holes are extremely rare or only appear under unique cosmological conditions (say, near the end of a black hole’s evaporation), we may never get close enough or observe them directly. We’d have to infer them.

If this is the case, then perhaps not every black hole is paired with a white hole, at least not in the way we imagine. Most black holes may never produce a white hole at all. Instead, only under extraordinary conditions — say, at a certain mass threshold or after surviving long enough for quantum effects to dominate — might a black hole undergo a bounce.

This leads naturally into Loop Quantum Gravity (LQG), which predicts that the singularity at a black hole’s core may be avoided through quantum geometry. Instead of collapsing to a point of infinite density, a black hole might experience a quantum bounce and become a white hole, ejecting information and energy at a later time (Ashtekar et al., 2006).

In Loop Quantum Gravity, space itself is quantized. When a collapsing star reaches Planck-scale densities, quantum geometry may resist further compression. Instead of a singularity, the theory predicts a bounce — a reversal in spacetime curvature that would manifest as a white hole, possibly after billions of years of black hole aging from an external perspective.

Could a Black Hole Become a White Hole?

If a white hole is not the opposite of a black hole in space, but in time, then could a black hole eventually transform — become - a white hole?

The idea isn’t merely speculative — it’s mathematically and physically motivated. According to Loop Quantum Gravity, when matter inside a black hole compresses to Planck-scale densities, quantum spacetime resists further collapse. Instead of terminating in a singularity, the geometry may “bounce,” reversing its curvature and initiating expansion. In this view, the black hole does not end, but transitions into a white hole over time (Planck Stars).

But time for whom?

From the outside, a black hole appears frozen at the event horizon due to gravitational time dilation. From the inside, the collapse continues. If a bounce happens internally, it may occur rapidly from the in-faller’s frame — but appear to take trillions of years to manifest externally. This decoupling of timescales is not just a curiosity — it may be the very reason we’ve never seen such a transition. We’re simply not waiting long enough.

And what triggers the bounce? Is it purely mass? Or is there an informational threshold — a tipping point in entropy, density or quantum coherence that flips the internal geometry?

Could the end state of black holes — traditionally considered "information sinks" — be reinterpreted as information recyclers, re-expelling encoded structure back into spacetime?

If so, the white hole is not a reversal of a black hole’s behavior, but a completion of its arc — a transformation across scales and timeframes. This raises deep questions:

• If black holes emit Hawking radiation slowly over time (Hawking, 1975), is the final burst a white hole event?
• Could that final act be a rebirth not just of matter, but of order — restoring quantum information that seemed lost?
• Do all black holes eventually undergo this bounce only those isolated long enough from external interference?
• Is there a cosmological analog — where entire universes undergo this transformation cycle?

A black hole that becomes a white hole isn’t just a theoretical curiosity — it’s a bridge. Not between two places in space, but between two regimes of physics. Between collapse and expansion. Between past and future.

Maybe this is the true cosmic symmetry: not black and white as opposites, but as consequences.

Was the Big Bang a White Hole?

This opens the door to one of the most profound and unresolved questions in cosmology: Was the Big Bang itself a white hole event?

If the Big Bang is a white hole, this might offer an alternative framing to the inflationary model — explaining the uniformity of the early universe as a product of causal coherence within a single ejected structure.

From our perspective, the Big Bang was the spontaneous appearance of space, time, matter and energy, with no known prior cause. This maps eerily well onto what a white hole might look like — an irreversible, one-way explosion of contents, unapproachable and unobservable from the outside.

Recap:

• There was no “before,” from our perspective.
• All the mass-energy appears suddenly.
• It behaves like a one - way boundary in time.

Could the Big Bang be the internal experience of a white hole, born from a black hole in another universe?

If so, then not every black hole is granted this fate. Only the most massive or complex ones — those that reach a certain information density, entropy or gravitational threshold — might trigger this universe-seeding transformation. In this model, white holes become rare and privileged rebirths, not inevitable counterparts.

The Evolutionary Implications

This idea is further explored in Cosmological Natural Selection, a theory proposed by Lee Smolin (The Life of the Cosmos). In it, black holes become portals to new universes, each slightly different from their parent. Universes that are good at producing black holes generate more offspring and over time, natural selection acts on the constants of physics themselves.

In Smolin’s view, each new universe could have slightly different values for physical constants — like gravity, charge or the strength of fundamental forces. Those changes affect star formation, which affects black hole formation. Universes that “inherit” good black hole - making parameters proliferate, leading to a kind of Darwinian landscape of cosmoses.

In this model, universes evolve like organisms. The capacity to produce black holes — especially ones that can bounce — might be an adaptive trait. Could our universe be particularly well-tuned to generate black holes because it descends from one?

And if so, does that mean our cosmos is optimized not for life, but for black hole fecundity?

Are We Inside a White Hole?

This brings us full circle to a haunting possibility: if white holes are real — but only visible from the inside, as expanding universes — then perhaps we live inside one right now.

Could our observable universe be the internal horizon of a white hole, the aftermath of a cosmic bounce that we interpret as a beginning?

And if that’s true, maybe the real question isn’t whether black holes lead to white holes... but whether we ever really left one.

Some cosmologists have explored models where the cosmic microwave background acts as a thermal echo of such an event horizon — a kind of Hawking radiation seen from within.

Further Questions

• Can the transition from black hole to white hole be simulated or is it forever behind a cosmic horizon?
• Do black holes in our universe already contain the seeds of future Big Bangs?
• Would it be possible for information emitted by a white hole to be detectable across universes?
• Is there a conserved quantity across black-to-white transitions that preserves causality?