Is the Universe Just One Massive Black Hole?

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“So you have written a book on black holes?”

The stranger sips their cocktail. We are mingling at a gathering, showcasing our conversations. I nodded slightly, mixing my piña colada.

“Well then,” the stranger continues, their gaze fixed intently on me. Is it truly the case that the entire universe resembles a black hole?”

It’s a familiar inquiry. This question often arises when I mention my years spent at observatories, engaging with scientists about our understanding of these cosmic giants.

People are naturally curious. The media frequently reports on distant galaxies coming into view as we gaze out into space. Videos sharing these concepts amass millions of views on platforms like YouTube. Though it seems like fiction, the scientific exploration of this notion began as early as 1972, when physicist Raj Kumar Pathria submitted a letter to Nature titled “The Universe as a Black Hole.” This topic has surfaced repeatedly since then.

So, is it feasible?

How to create a black hole

In simple terms, black holes are regions in space where gravity is so intense that not even light can escape.

These enigmatic entities were first mathematically described by astronomer Karl Schwarzschild during World War I. Amidst the sounds of battle on the Western Front, he was intrigued by how Albert Einstein’s groundbreaking general relativity predicted planetary dynamics and stellar structures.

Schwarzschild derived a formula detailing how space and time behave in ways that defy common experience, creating areas that would be termed black holes.

This discovery provided profound insights into black hole dynamics. It requires a particular mass, like that of a human, planet, or star, compressed within a volume determined by Schwarzschild’s formula, et voilà! A black hole emerges.

The critical volume varies with the object’s mass. For a human being, this volume is minuscule, a hundred times smaller than a proton. For Earth, it’s akin to a golf ball, while for the Sun, the volume resembles the size of downtown Los Angeles (approximately 6 km, or just under 4 miles).

Creating black holes is challenging. Under typical conditions, materials tend not to compress to incredibly high densities. Only extreme cosmic events, like the supernova explosion of a massive star, can compel matter to collapse into a black hole.

Interestingly, the black holes formed from dying stars come from extremely dense matter, whereas the much larger supermassive black holes at the centers of galaxies possess much lower densities. According to Schwarzschild’s equation, bigger black holes actually have less average density than air!

So what about the universe itself? Given that it consists largely of empty space, can such density relate to that of black holes?

Measuring Space

With the help of Schwarzschild’s formula, astronomers can ascertain whether an object is a black hole. First, determine its mass. Next, ascertain the volume. If the object’s mass is contained within a volume smaller than that specified by Schwarzschild’s equation, it qualifies as a black hole.

Now, applying this concept to the entire universe requires knowledge of its mass and volume. However, determining the universe’s total size is impossible, as wandering with a cosmic ruler isn’t feasible. Instead, we can observe light and particles that come to us from the cosmos.

The oldest light we detect originates from the cosmic microwave background, which was produced a mere 380,000 years after the Big Bang. As the universe expands, the origin of this light is now astronomically distant. In fact, the total distance light has traveled since the Big Bang allows us to see an observable universe with a diameter of about 93 billion light years.

Through rigorous measurements over many years, astronomers estimate the mass contained within this volume to be approximately 10⁵⁴ kg (that’s a 1 followed by 54 zeros).

Next, let’s calculate the hypothetical size of a black hole with this mass using Schwarzschild’s formula. After some calculations, it turns out that such a black hole would be roughly three times larger than the observable universe, measuring around 300 billion light years across. Thus, simply from the observed mass and size of the universe, it seems to satisfy the criteria of being a black hole.

“Wow,” exclaimed the curious stranger at the cocktail party, “Does this mean the universe is indeed a black hole?”

“Not so fast, my friend,” I replied. To grasp this question fully, we must delve deeper into the nature of black holes.

Into the Void

Black holes are peculiar. One of their odd characteristics is that while they appear to be fixed sizes externally, they are continuously evolving internally. According to Schwarzschild’s formula, the internal space elongates in one dimension while compressing in the other two simultaneously. (If a black hole spins, its interior behaves differently, but that’s a tale for another time.)

Cosmologists refer to this structure as anisotropy. The term derives from tropos, meaning “direction,” and iso, meaning “equal,” alongside an, denoting negation. The dynamics of anisotropy within a black hole leads to one spatial direction expanding while the other two contract. This phenomenon, along with the infamous spaghettification, relates to the tidal forces experienced by any object drawn in.

In contrast, the universe expands isotropically (uniformly in all directions). Doesn’t that sound akin to the interior of a black hole?

However, this doesn’t eliminate the possibility of a “universe as a black hole.” Both structures share two pivotal features: the event horizon and singularity.

The event horizon marks a boundary beyond which light cannot escape. For a black hole, this signifies a point of no return for anything crossing this threshold. In the universe, space expands so swiftly that light from exceedingly distant galaxies cannot reach us.

The event horizon of our universe can be thought of as an inverted version of a black hole’s event horizon. The former limits our observation from the furthest reaches of space, while the latter confines us from seeing beyond its depths.

This reciprocal relationship is also observable in the singularity—the point where density and curvature of spacetime become infinite. According to Schwarzschild’s formula, the singularity is a destination for unfortunate astronauts crossing a black hole’s event horizon. Conversely, our cosmological models indicate that singularities exist in the past—backtracking the universe’s expansion leads every space point closer together, intensifying density. In this context, the beginnings of the Big Bang culminate in a singularity. So, for black holes, this mathematical singularity lies in the future; for our expanding universe, it exists in the past. In both instances, the complexity indicated signifies just how little we understand about these dense, enigmatic points.

Sum it all up—the disparities in expansion, event horizon, and singularity—paint a convincing picture of our universe: it’s not a black hole. It just doesn’t fit that label!

“But wait,” the stranger interjects, feeling disheartened, “I thought we calculated that the universe met the criteria for a black hole.”

“While the computations are indeed accurate,” I explain, “we observe that mathematical relationships akin to Schwarzschild’s also align within the context of an expanding universe. This isn’t exclusively characteristic of black holes.”

It suggests that strange phenomena exist at the largest cosmic scales, beyond our observational reach with telescopes. However, according to models of non-rotating, expanding black holes, our universe lacks the definitive traits that categorize it as a black hole. What to make of it? Personally, I view it as a testament to gravity’s versatility, crafting magnificent structures that encapsulate the essence of time and space.

Jonas Enander is a Swedish science writer with a PhD in physics. His newly released book Infinites Faced: Black Holes and Our Places on Earth (Atlantic Books/The Experiment, 2025) examines the impact of black holes both universally and on humanity. To delve further into these ideas, he created a video narrating the story using light blue illustrations.

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