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Eugenio Bianchi, Marios Christodoulou, Fabio D’Ambrosio | Classical and Quantum Gravity | (2018)
Primary Link Archive DOI Openalex Full text (OA)

Key Takeaways

Plain English Takeaway

Black holes might not just disappear—they could turn into white holes that slowly release what was inside, helping solve the mystery of where all the information goes.

Study Aim

The paper aims to propose and analyze a new scenario for the end of a black hole's life. The authors investigate whether a black hole can quantum tunnel into a white hole (an object that expels matter and energy), forming a long-lived remnant. They explore if this process could resolve the black hole information paradox, which questions whether information is lost when black holes evaporate. Simply put: The study asks if black holes can turn into white holes at the end of their lives, and if this could explain what happens to everything that falls in.

Study Design

The authors use theoretical analysis grounded in established physics and non-perturbative quantum gravity (a way to study gravity at very small scales without using approximations). They examine the properties of white holes with small masses but large interiors, and analyze the quantum tunneling process from black holes to white holes. The paper also addresses common objections to the existence and stability of such remnants, and discusses how entropy (a measure of disorder or information) is involved in this scenario. Simply put: The researchers use math and physics theories to see if black holes can change into white holes, and check if this idea makes sense with what we know.

Findings

The study reveals that white holes with small masses and large interiors already fit within known physics, and that quantum gravity suggests black holes can tunnel into these white holes as they finish evaporating. The authors argue that these white-hole remnants could be stable and long-lived, avoiding previous arguments against their existence. They show that the process of black hole formation, evaporation, tunneling, and slow decay can be a single, information-preserving (unitary) process. This scenario offers a possible solution to the information paradox without breaking any known laws of physics. Simply put: The paper finds that black holes could become white holes that slowly let out what was inside, meaning nothing is truly lost.

Abstract

Abstract Quantum tunneling of a black hole into a white hole provides a model for the full life cycle of a black hole. The white hole acts as a long-lived remnant, providing a possible resolution to the information paradox. The remnant solution of the paradox has long been viewed with suspicion, mostly because remnants seemed to be such exotic objects. We point out that (i) established physics includes objects with precisely the required properties for remnants: white holes with small masses but large finite interiors; (ii) non-perturbative quantum gravity indicates that a black hole tunnels precisely into such a white hole, at the end of its evaporation. We address the objections to the existence of white-hole remnants, discuss their stability, and show how the notions of entropy relevant in this context allow them to evade several no-go arguments. A black hole’s formation, evaporation, tunneling to a white hole, and final slow decay, form a unitary process that does not violate any known physics.

Referenced In

StarTalk

Season 17, Episode 30: What is a White Hole?

Hey StarTalkians! Season 17, episode 30 was a Cosmic Queries edition with Neil and Paul, with a grab-bag of questions on all things cosmic. Early in the show, they tackled a question about the difference between a black hole and a wormhole, which veered into some interesting territory:

Cosmic Queries – Scars in Spacetime - StarTalk Radio

(from 5:45)

A white hole is something you may not have heard of – outside of creative sci-fi like the excellent game Outer Wilds – and Neil’s description covered the basics. But would such a thing really exist? Could it exist based on known physics?

The White Hole as the Opposite of a Black Hole

The easiest way to understand what a white hole is follows Neil’s explanation: it’s the opposite of a black hole.

Theoretical physics often deals with symmetries in nature. You don’t need to tell me if you’re in Chicago or Rome for me to calculate the gravity acting on you, because gravity is symmetric.

One such symmetry is time-reversal symmetry. As an analogy, if I drop a ball and it bounces back to my hand, playing a video of this backwards would make the original “drop” look like the “catch” and vice-versa, but it would still make sense. The video would have time reversal symmetry.

This symmetry applies to general relativity, so what would a time-reversed black hole look like? It would be something which lets matter out but which nothing ever entered. This is a white hole, and ultimately the idea comes from pure theory – we’ve never found one.

Modern White Hole Theory

There are also more modern formulations of the idea. The simplest way to conceptualize these is to think of the white hole as a kind of “exit” to the black hole . This would basically be a solution to the black hole information paradox.  

This kind of works like it does in Outer Wilds (just on a much smaller scale), where falling in the black hole sends you flying out of the white hole, way across the solar system.

youtu.be

A particularly compelling formulation sees white holes as “remnants” of black holes. The black hole doesn’t simply vanish, it quantum mechanically tunnels through into a white hole. This gets more likely the smaller the black hole is, so the resulting white hole would be low mass, and long-lasting.

This formulation appears consistent with modern theories of quantum gravity, so they could exist. But they still probably don’t.  

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May 27, 2026 11:36 AM

Read the tldr-summary of the Bianchi paper. Cool idea (though I don't quite understand fully!). Did a bit more digging and learnt the "mainstream" theory of the conservation of energy in black holes. I guess most people think the information is released as part as (?) Hawking Radiation?