Black holes are difficult enough to understand, but it gets much worse: also known as an “impossible possibility”, a white hole is a hypothetical, celestial body that emits energy—in the manner of a time-reversed black hole. In simpler language, a white hole is the opposite of a black hole. While a black hole sucks in all matter that crosses its event horizon, a white hole explosively pours out all the matter that was initially lost in the black hole.
This is a hypothetical concept, and can be quite difficult to wrap our heads around. But hopefully, by the end of this list, we’d have learnt a lot more about this fascinating phenomenon.
10. The Opposite of a Black Hole
A black hole is a region in space-time with such high density and gravitational pull that nothing, not even light, can escape from it. Once an object crosses its event horizon, it undergoes a gruesome-sounding process called spaghettification, and is lost into oblivion. For example, if a light-emitting particle crosses a black hole’s event horizon, its light wavelength will grow longer and longer, and will lose energy until it’s no longer detectable. Moreover, the powerful gravitational forces in a black hole would make time appear to go slower, to a distant observer—such that it would appear to take infinite time to even reach the event horizon.
Hence, if a black hole resembles a one-way portal to oblivion, would there be any way to enter that portal from the other end, and travel in the opposite direction? Theoretically, this thought should make perfect sense—since General Relativity and Newtonian physics are time-symmetric concepts. And this opposing gateway is a theoretical concept, known as a white hole. White holes may be considered the time-reversed equivalent of a black hole.
Due to their elusive nature, white holes are described as “mathematical oddities”, and are generally considered as fictional and fantastical as dragons and krakens. In fact, white holes have even been regarded as “cosmic creatures that straddle the line between tall tale and reality”.
9. The Concept of a White Hole
In the words of Caltech physicist Sean Carroll, “A black hole is a place where you can go in but you can never escape; a white hole is a place where you can leave but you can never go back”.
So, white holes are also one-way passages—except that it means entrance, as opposed to exit, is impossible. However, both structures possess the same mathematical and geometrical features—since they are theoretically just opposites of each other. Their geometry essentially consists of a singularity (a one-dimensional point which contains a huge mass in an infinitely small space) and an event horizon (a notional boundary).>
While there is a plethora of evidence to back up the existence of black holes, there is very little when it comes to their opposite. Moreover, even though white holes are solutions to General Relativity’s equations, “they’re not realistic,” says Andrew Hamilton, an astrophysicist. Indeed, right now, discussions of white holes revolve around the words “unrealistic”, “hypothetical”, and “imagination”.
8. The Creation of a White Hole
Most black holes are formed when stars collapse in a supernova explosion. However, it has been suggested that black holes end their lives by transforming into white holes—which explosively pour out the information that had been swallowed by the black hole. According to this model (developed by Carlo Rovelli and Hal Haggard from Aix-Marseille University), the transition of a black hole to a white hole would occur right after the formation of the former.
As a black hole is formed, it is shielded by its event horizon (beyond which nothing can escape); however, at one point, the star that is collapsing under its own gravity will reach a point beyond which it cannot shrink any further. At this moment, it experiences an outward pressure called a quantum bounce—which transforms a black hole into a white hole. As concluded by the calculations of the team, the transformation should be instantaneous. However, it would seem like black holes exist for billions of years due to their intense gravitational pull, which makes time appear to go slower to an observer.
As written by Nature, “If black holes turn into white holes and release all of their innards out again, it could provide a solution to one of the most troublesome questions of fundamental physics” (more specifically, the information paradox). However, in this sentence, the word “if” is crucial—for it reminds us that white holes are still largely hypothetical concepts, and that this proposal is only a theory.
7. Depictions of White Holes in Popular Culture
Yes, these phenomena have triggered the vibrant imaginations of writers and filmmakers. In The Hitch Hiker’s Guide to the Galaxy (by Douglas Adams), there is a planet inhabited by a group of aliens—which created worlds using the matter and information ejected from white holes! And in the novel The Children Star by Joan Slonczewski, an organization plans to use a white hole to annihilate the existing life on a planet, so that they may earth-shape the planet to suit the needs of human colonists.
Moreover, in a Transformers episode (“The Killing Jar”), a few characters are transported through a black hole—where they find themselves locked in a negative universe composed of anti-matter. They then escape this universe by travelling through a white hole, which ejects them back to their own universe. And in the film The Black Hole (1979), a spacecraft is swallowed by a black hole, and is then spit out by a white hole—where they consequently find themselves in an entirely different part of the universe!
These are some intriguing depictions, and mirror a few of the scientific speculations so accurately. And somehow, even though these are all fictional portrayals, they make the concept of a white hole seem more real to us… Because if black holes have been proven to exist, why not white holes?
6. The Second Law of Thermodynamics
According to the Second Law of Thermodynamics, the entropy (lack of order or predictability) of the universe is always increasing. It is this universal law that threw the possibility of a white hole existing into disorder. Because if white holes do exist, they would violate the second law of thermodynamics. To repeat, this law states that the state of entropy of the entire universe, as an isolated system, will always increase over time.
Black holes are cosmic bodies that beautifully work with this law—for black holes can swallow celestial objects over long periods of time, thereby spreading their matter across a larger space, and adding to the chaos of their surroundings. But white holes, on the other hand, would theoretically do exactly the opposite—they would bring objects or scattered materials into arrangement or order, which would go against the second law. Naturally, any phenomenon that violates such a universal law would certainly be extremely unstable, and would therefore be unlikely to exist for over a few seconds. So… how can the possibility of a white hole exist?
5. The Eternal Black Hole Theory
White holes appear in the theory of eternal black holes. Eternal black holes are interesting concepts, which were brought up by physicist and cosmologist Stephen Hawking. It was widely assumed that matter that enters a black hole is permanently lost, and is completely past the stage of retrieval. However, Hawking predicted that black holes should gradually lose energy by radiation—in accordance with the second law of thermodynamics. Hence, black holes continuously radiate energy beyond their event horizons, ultimately losing all their energy and ceasing to exist.
But could an eternal black hole exist, that would serve as a cosmic lockbox? In simple terms, an eternal black hole is a black hole that can absorb matter—without feeling the need to lose some of it through radiation. Basically, an eternal black hole can continue swallowing information forever. However, this violates the second law of thermodynamics—because it indicates that the entropy of the universe is decreasing.
As written by the New Scientist, “The recipe for this unlikely object [the eternal black hole] was discovered by looking at an even more abstruse entity, the white hole”. Theoretically, an eternal black hole is the opposite of a white hole: for while a white hole spews out matter without letting anything enter, an eternal black hole sucks in matter without letting any information escape. Hence, white holes have theoretical applications when conceptualizing an eternal black hole—which could potentially store extremely sensitive information.
4. White Holes and the Big Bang
Most of us have a rough idea about the Big Bang Theory: approximately 13.7 billion years ago, the matter in the universe was compressed into a single, infinitesimally small point. This point then enlarged in a heated explosion, and is still expanding today. There is a great amount of evidence to buttress this theory, which includes the observation that all the galaxies are moving away from us.
However, an intriguing idea has been suggested by physicists and cosmologists—revolving around the concept of a white hole. It has been suggested that a white hole could be the reason behind the Big Bang—for it would explain how such a gigantic amount of energy and matter just spontaneously appeared. It was even argued in the paper The primordial explosion of a false white hole from a 5D vacuum that the Big Bang was produced by a white hole explosion—which presumably ejected all the matter and information that had been swallowed by a black hole. Of course, we don’t know if this theory is true; but then again, it is fascinating to think that we all emerged from a white hole.
3. Have we detected a White Hole?
White holes ceased to become complete theory after an unforgettable discovery on June 14, 2006. On this day, an extraordinarily powerful gamma-ray burst was sighted by the Swift satellite (of NASA); this phenomenon was called GRB 060614. However, this gamma-ray burst did not fit into the normal category and parameters of these phenomena, since such processes take place in regions of low star formation or are commonly linked with supernovae.
Moreover, whereas typical gamma-ray bursts last for only a few seconds, the one detected in June 2006 had lasted for a remarkable 102 seconds, and was trillions of times more powerful than our own star! And since this sudden, massive burst didn’t originate from a supernova, astronomers and astrophysicists could only conclude that it had emerged from… nowhere, or from an infinitesimally minuscule speck, and had then collapsed upon itself once those 102 seconds were over.
The features of the 2006 gamma-ray burst perfectly matched with the little knowledge humans have about white holes: i.e., the spewing out of a huge amount of matter in a few minutes, before disappearing into oblivion. Certainly, the occurrence of this astonishing phenomenon does not confirm the existence of a white hole… but it does lead to some interesting speculation.
2. Black Holes, White Holes, and Wormholes
Amazingly enough, it has been speculated that there is a white hole at the other end of a black hole: so, the matter and information that have been swallowed by the black hole are ejected by the white hole into an alternative universe. Ludwig Flamm, an Austrian physicist, also suggested that these two regions in space-time could be connected by a space-time conduit, and that the black hole “entrance” and white hole “exit” could be located in two entirely different universes! These speculations were so intriguing that Einstein and Nathan Rosen further built upon these ideas, finally reaching at a solution in 1935 known as the Einstein-Rosen bridge (or a Lorentzian wormhole or Schwarzschild wormhole). A wormhole may be defined as a hypothetical area of warped space-time with enough energy to create tunnels through the fabric of space-time.
So, the complete Schwarzschild geometry comprises of a black hole, a white hole, and two different universes connected at their event horizons by a wormhole; the wormhole is an exact solution to Einstein’s equations. The Schwarzschild metric has two solutions—a positive square root and a negative square root. The latter represents a white hole, which is a black hole going backwards in time.
Honestly, the number of theories and equations that abound in the scientific world is astounding… For who would have ever thought that at the other side of a black hole, in an alternative universe, there would be a white hole spitting out the information that had been lost?
Could the existence and concept of white holes lead to advances in the field of time travel? It has been speculated that in some special cases, a wormhole (or Einstein-Rosen Bridge), rather than connecting two points in space, could connect two points in time. Hence, a body falling into a black hole could travel through a wormhole, be ejected by the white hole, and land up in another region of space or time! However, there are several flaws with this idea: namely, a wormhole is so unstable that is would immediately collapse upon itself, and that any body entering a black hole would be ripped apart by the tremendous gravitational forces.
Another possibility was theorized by Kip Thorne of Caltech, who proposed a wormhole with the following features: one end of the wormhole is on earth, and the other end is located in a spaceship (presently at rest of Earth). Without getting into the technicalities of his proposal, let’s just say that numerous other time-travel situations have since been developed by other cosmologists and physicists… most of which include black holes, wormholes, and white holes. And we never know—maybe in a few hundred years, these three phenomena (two of which are currently hypothetical) may actually allow humans to travel back and forth in time!
Even though white holes only exist “in theory”, that may not be the case for long. After all, they are valid solutions to the equation of General Relativity… and what about the exciting, unforgettable 2006 discovery? And we must not forget: black holes were once theoretical. So many phenomena in the world of astrophysics were once theoretical! White holes may or may not exist, but that doesn’t mean that we stop questioning, wondering, and trying to unravel the mysteries behind them. It is a natural instinct of humanity to never give up once an enigma lies before them… and hopefully we’ll untangle the enigma of the white hole soon.