White Hole - Contrasting Twin Version of a Black Hole

The existence of white holes, the giant cosmic structure that repels all approaching objects, is still controversial and is considered to be "ghosts" born from the mathematics of general relativity.

The Event Horizon Telescope imaged the supermassive black hole at the center of galaxy M87. Photo: EHT Collaboration

Black holes are regions of complete gravitational collapse, where gravity overwhelms all other forces in the universe and compresses a mass of matter down to an infinitely small point called a singularity. Surrounding the singularity is the event horizon, not a solid physical boundary but just a border around the singularity, where gravity is so strong that nothing, not even light, escapes. Okay.

When a massive star dies, its massive weight presses on the core, leading to the formation of a black hole. Any matter or radiation that gets too close to the black hole is captured by strong gravity and pulled below the event horizon, leading to extinction.

Experts understand this black hole formation process and how the black hole interacts with the environment through Einstein's theory of general relativity. General relativity is not concerned with the flow of time. The equations are time symmetric, which means they still work well mathematically whether moving forward or backward in time.

If we filmed the formation of a black hole and rewinded it, we would see an object emitting radiation and particles. Eventually, it will explode, leaving behind a massive star. That is the white hole, and according to general relativity, this scenario is entirely possible.

A white hole is a theoretical cosmic structure that works in the opposite way of a black hole.  Photo: Future/Adam Smith
A white hole is a theoretical cosmic structure that works in the opposite way of a black hole. Photo: Future/Adam Smith

White holes are even more exotic than black holes. They will still have the singularity at the center and the event horizon at the outer edges. They are still massive objects, with strong gravity. But any matter that approaches the white hole will be immediately ejected at a speed faster than light, causing the white hole to shine brightly. Everything outside the white hole will not be able to get in, because they need to travel faster than light to get through the event horizon.

However, the existence of white holes is still controversial because general relativity is not the only theory in the universe. There are other branches of physics that explain how the universe works, such as the theories of electromagnetism and thermodynamics.

In thermodynamics there is the concept of entropy, which is simply a measure of the chaos in a system. The second law of thermodynamics states that the entropy of closed systems cannot decrease.

For example, if you throw a piano into a wood chipper, the output will be a bunch of debris. The chaos in the system increases, satisfying the second law of thermodynamics. But if random shards were thrown into this same wood chipper, the output would not be a complete piano as that would reduce the chaos. Accordingly, it is not possible to simply reverse the process of black hole formation to obtain a white hole, because this reduces entropy, stars cannot form from a violent explosion.

As such, the only way for a white hole to form is by some strange process going on in the early universe, avoiding the trouble with reducing entropy. They simply existed from the very beginning of the universe.

However, the white hole will still be very unstable. They pull matter toward them, but nothing can cross the event horizon. Anything, even a photon (particle of light) will be annihilated as soon as it approaches the white hole. The particle will not be able to cross the event horizon, causing the system's energy to skyrocket. Eventually, the particle had so much energy that the white hole collapsed into a black hole, ending its existence. So, while interesting, white holes do not appear to be a structure in the real universe but just "ghosts" born out of the mathematics of general relativity.

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