What Is a White Hole? Does the Cosmic Phenomenon Exist?

By: Marie Look  | 
As currently theorized, a white hole would be like a time-reversed black hole, from which light and matter emerge (instead of getting sucked in) and in which time flows backward. Nicole Antonio/DALL-E

Black holes have long held the spotlight as celestial objects from which nothing, not even light, can escape. However, theoretical physicists propose a less understood but equally fascinating counterpart: the white hole.

Unlike black holes, which attract matter, white holes would repel it.


What Are White Holes?

In astrophysics, a white hole represents a theoretical phenomenon where matter and light would emerge from, rather than be pulled into, a certain area in space. It's the exact opposite of a black hole.

You may already know that a black hole is an area in space where gravity is so strong that escape velocity surpasses the speed of light, making it impossible for light to escape.


Escape velocity refers to the speed a thing would have to travel to be able to escape the gravitational field of a planet, such as Earth, and instead travel outward into space.

The Theoretical Basis of White Holes

The idea of a white hole is rooted in the Schwarzschild black hole solution, named after the German physicist and astronomer Karl Schwarzschild, who formulated it in response to Einstein's general theory of relativity.

When Schwarzschild was formulating equations that described black holes, he found that white holes could exist under the same laws of physics that govern black holes.


Extending his black hole solutions through a time reversal invariant transformed the black hole singularity into a white hole singularity — an area that would eject matter rather than draw it in.

In the context of physics, time reversal means imagining a scenario where time flows backward, reversing the sequence of events.

Schwarzschild's solution to Einstein's equations describes a point singularity surrounded by an event horizon.

Einstein's General Theory of Relativity

Einstein's general theory of relativity is a theory about gravity, describing it not as a force between objects, like Newton's theory, but as a curvature of space and time that mass and energy cause.

According to this theory of general relativity, planets, stars and other massive objects bend the space around them, and this bending of space is what we perceive as gravity.

Essentially, objects move along these bends in space, which is why, for example, the Earth orbits the sun.

What's a Point Singularity?

A point singularity is a location in space where certain quantities (like density or gravity) become infinitely large.

In simpler terms, it's like a point where everything we can conceive of in the entire universe — including the laws of physics themselves — breaks down because everything is crushed into an unimaginably tiny space.

Physicists often use this concept to describe the core of a black hole, where all its mass is concentrated at a single point.

What's an Event Horizon?

An event horizon is essentially a boundary around a black hole beyond which nothing can escape — not even light.

Think of it like a point of no return; once anything crosses this boundary, it's pulled into the black hole with no chance of getting out. This makes the event horizon the outermost layer of a black hole, defining the limit where its gravitational pull becomes too strong for anything to escape.

As Schwarzschild theorized, in the curious case of time reversal, such as in a white hole, this event horizon becomes a boundary from which matter and light can only escape, not be absorbed.


Quantum Considerations of White Holes

When you consider white holes as concepts in the realms of classical and quantum gravity, these ideas expand even further.

Quantum mechanics, alongside theories of quantum gravity, predicts phenomena like Hawking radiation, where black holes emit radiation due to quantum effects near the event horizon.


By applying time reversal to these processes, some scientists speculate that white holes could similarly emit matter and light as a physical process mirroring Hawking radiation.

Do White Holes Exist?

The question of whether white holes exist is fraught with challenges. No observational evidence directly supports the existence of such objects in the observable universe.

However, theoretical physics offers scenarios where white holes could theoretically appear. One possibility is during cosmic inflation, or a "big bang," in the early universe, where extreme expansion might have stretched regions of space-time to create white holes.


Another intriguing idea is the big bounce theory, which suggests our universe began as a white hole formed from the remnants of a collapsing parent universe.

Loop Quantum Gravity Theory

Andrew Hamilton, an astrophysicist, proposes that if white holes exist, they could be remnants of supermassive black holes that underwent a quantum gravitational transformation, reversing their roles from absorbing to expelling mass and energy. This theory is called loop quantum gravity.

This transformation could potentially occur under the influence of dark energy or dark matter, which are known to affect the universe. However, physicists still don't have a clear understanding of how dark matter interacts with fundamental particles.


Connections to Other Theoretical Frameworks

Exploring the concept of white holes touches on several other areas of physics. For instance, gravitational lensing — a phenomenon where light bends around massive objects like black holes — might similarly apply to white holes, altering our perception of space behind them.

Furthermore, the idea of a baby universe, potentially born from the outer layers of a parent universe through a white hole, connects deeply with the multiverse theory, suggesting that our universe could be just one of many.


White holes also challenge our understanding of thermal equilibrium in the universe.

Since they emit rather than absorb energy and matter, they could theoretically serve as cosmic seeds, dispersing energy density and fundamental particles across the universe, thereby influencing the formation and evolution of galaxies in ways fundamentally different from black holes.

We created this article in conjunction with AI technology, then made sure it was fact-checked and edited by a HowStuffWorks editor.