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What If A Black Hole And White Hole Collided? | Unveiled

VOICE OVER: Noah Baum WRITTEN BY: Dylan Musselman
What if a black hole went head-to-head with its hypothetical opposite? In this video, Unveiled asks the extraordinary question: What if a black hole collided with a white hole? Causing cosmological chaos across all of space and time, this monumental event would shake the universe to its core... and could even kick-start a new reality altogether!
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What If a Black Hole and White Hole Collided?


Black holes can become some of the most massive objects in the universe. A collision between two of them can cause waves to form in the fabric of spacetime itself. Theoretically speaking, though, black holes have an opposite; white holes. So, what would happen if these two structures were to meet?

This is Unveiled and today we’re answering the extraordinary question; What if a black hole and a white hole collided?

White holes are a currently hypothetical structure, but they’re thought to work like an inverted twin to Black Holes; to be their exact opposite in nature. A black hole attracts and devours matter; a white hole repels and regurgitates it. Nothing can escape a black hole, but nothing can enter a white hole. White holes essentially act as a black hole would if video footage of it was played in reverse, with matter being expelled from the centre at the speed of light. Despite their opposite nature, though, it’s thought that white holes would look very much like black holes from a distance - if we ever were to observe one!

Although they are theoretically possible, scientists don’t know how white holes would form - if indeed they do. We have a little bit more of an idea for black holes, which often form when a massive enough star loses enough of its fuel and explodes into a supernova. That event leaves an extremely dense core behind… which assumes new shape as a kind of tunnel in spacetime; a black hole. White holes can’t form in the same way, though, because their core has zero mass - so they can’t exist with actual matter at their centre. In theory, if just one atom of hydrogen somehow managed to enter a white hole’s singularity, it would collapse. Because they’re so unusual, some researchers even believe that white holes could be the key to understanding other mysteries like dark matter; with one theory being that dark matter is formed from microscopic white holes ejecting it.

Despite the fact that white holes cannot have mass in their singularity and constantly repel matter from their core, however, it’s thought they would have gravity… which means they could attract objects from a distance. So, if we assume for the purposes of the question that white holes do exist, then a collision between one and a black hole is possible.

If anything else - something less massive - approached a white hole, like a planet or a spaceship, then there’d really be no contest. The route toward the white hole would be extremely dangerous. The matter being expelled from it is traveling at the speed of light, meaning any object that got close enough would be relentlessly bombarded with incredible amounts of energy probably in the form of gamma rays. These would tear most objects apart, or at least make it physically impossible to travel any further. Since no matter can reach the centre of a white hole, there’d be a kind of cosmic cut-off point where any object that tried would be held at a distance by the repelling forces at work… and would still be getting blasted with wave upon wave of destructive energy.

The situation changes, though, when that object is a black hole. Now we have the ultimate example of two opposites attracting and an extreme case of energy transference. Since the white hole is constantly ejecting matter and the black hole is constantly causing matter to fall into it, the white hole would end up feeding the black hole like water down a drain. It’d be one-way traffic, but accelerated to unimaginable speeds.

A black hole that’s endlessly “fed” in this way could well grow larger and larger, to eventually form an exceptionally massive supermassive structure. It would be a battle which could rage for thousands of years, with both objects promising an infinite resource… but given what we know about black holes and what we don’t know about white holes, in time the black hole could become massive enough to engulf even its bottomless provider of matter to consume. It’s possible that it would outlast the white hole, and the white hole would disappear. If this were to happen, it’s truly unknown what would happen next. We’re still not exactly sure where non-theoretical, conventional matter goes when it enters a black hole… so predicting the ultimate fate of a hypothetical construct is even harder still.

Due to Hawking Radiation, the black hole should eventually shrink and eject the matter from natural decay, but some scientists think that there’s more to it than that. It’s argued by some that matter entering a black hole is totally isolated and altogether disappears from the universe. It’s actually because of this that some theories suggest that black holes are already connected to white holes in other universes by a tunnel they form between each other in spacetime. When a black hole devours matter in one universe, that matter could be ejected out into another via a white hole - meaning infinite matter goes in, and infinite matter comes out. To make that particular idea just a little stranger, some even theorize that white holes are actually older than our universe, and that the connections between multiple universes via black and white holes could explain the beginning of our own reality.

But the encounter doesn’t (or needn’t) end there. In a different scenario, the black hole could in theory expire through Hawking radiation before consuming the white hole. In this way, the white hole will have trumped its counterpart by effectively “overfilling” it. Equally, though, even were the black hole to win in the initial collision, then time could eventually tell a different story.

Theoretical physicist Carlo Rovelli proposes that when black holes decay and ultimately die, they create white holes in their wake. When black holes lose enough mass via Hawking Radiation, they’re more traditionally thought to shrink until they vanish. But that’s a problem in some models of the universe because there should be an “other side”. For Rovelli, then, a black hole wouldn’t simply evaporate into nothing, but would instead rebound when it becomes too small - and that rebound produces a white hole.

Rovelli also suggests that this would be an exceptionally slow process - potentially taking millions of times more than the age of our universe to complete, were the original black hole to be about the mass of the sun. The also currently hypothetical primordial black holes, though, are much smaller… so Rovelli also notes how it could be that the primordial black holes theoretically created at the beginning of the Big Bang have already been able to die and form white holes since the start of the universe.

If that’s true, then we’re suddenly contemplating much more than one isolated cosmic collision. Even were the black hole to overcome its opponent in that particular event, achieving an incredible size in doing so, it could still be survived by the very structure it had just consumed. And, over time, more and more of the universe’s black holes would go through a similar transformation, leaving the cosmos littered with multiple, unknowable, enigmatic points all ejecting matter back out into it. Space would then be shaped by white holes.

All of that said, it pays to keep in mind that this particular hypothetical comes with a sizeable caveat; that the basic existence of white holes is still very much up for debate. Our current understanding of the universe means they’re possible, but plenty of physicists still argue that they’re unlikely to form in nature… On the one hand, weird and wonderful features of the universe like gamma ray bursts could actually be white holes (we just don’t know it yet). On the other, we could simply be pondering a plain impossibility. But that’s what would happen if a black hole and a white hole collided.
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