Is the universe really one big black hole?

The following is an excerpt from our newsletter, Lost in the Space of Time. Every month we turn the keyboard over to a physicist or mathematician to tell you about fascinating ideas from their corner of the universe. You can Register for Lost in Space-Time hereField

“So you wrote a book about black holes?”

The stranger takes a sip from his cocktail. We are at a party and I was introduced to the guests. I nod politely, fidgeting with my piña colada.

“Then tell me,” the stranger continues Really Is it true that the entire universe is a black hole? »

I'm not surprised. This is one of the most common questions I've been asked when I tell people that I've spent years talking to scientists and visiting observatories to find out what we currently know about these cosmic behemoths.

And it's no wonder people want to know. There are regular media headlines that suggest the twinkling galaxies we see when we peer into space could be caught inside Fire black holeField Videos discussing such ideas receive millions of views on YouTube. And although this sounds like something out of a science fiction novel, it is not without merit. Scientific research into this idea dates back to 1972, when physicist Raj Kumar Patria published a letter in the journal Nature called “The Universe as a Black Hole.” Since then, the stunning statement has returned from time to time.

So, is this true?

How to make a black hole

Simply put, a black hole is a region of space where gravity is so strong that nothing, not even light, can escape it.

These mysterious objects were originally discovered by the mathematics of astronomer Karl Schwarzschild during the First World War. While he could hear the rumble of battle on the French-German front, he explored what Albert Einstein's newly published general recurrence equations predicted Planetary movement and the structure of stars.

Schwarzschild clicked on a formula that describes how space and time can behave so wildly, out of sync with our experience of the world, giving in on itself and creating a type of inescapable region later called a black hole.

Schwarzschild's discovery led to a deep understanding of how black holes work. Take a given piece of mass, such as a human body, a planet, or a star. Now squeeze it inside the volume defined by the Schwarzschild formula, And voila! A black hole has formed.

This critical volume depends on the mass of the object. For the human body, this is ridiculously tiny: a hundred times smaller than a proton. For Earth, this is the size of a golf ball, while for the sun it is roughly the size of downtown Los Angeles (about 6 kilometers, or just under 4 miles, across).

As you can see, creating black holes is difficult. Under normal circumstances, Matter simply doesn't like to be compressed to such extremely high densities. Only the most catastrophic processes in the universe – such as when very massive stars explode in supernovae – can cause matter to collapse in on itself and form a black hole.

But there is a twist in the story of the creation of the Black Hole. While those created from exploding stars are associated with exceptionally dense matter, there are many more of them super massive cousinswhich are at the center of most galaxies have a fairly low density. According to the Schwarzschild formula, the larger the black hole, the larger the void it contains, and the lower its average density (in a fairly simple manual sense – in reality, the density of a complex space-time object like a black hole is not simple to determine). Thus, the largest black holes have an average density less than that of air!

So what about the universe then? Given that it is mostly made up of empty space, could its extremely low density still correspond to a black hole?

Location of the universe

Thanks to the Schwarzschild formula, astronomers are equipped with a tool to determine whether an object is a black hole: first, measure its mass; Then set its volume. If an object has a mass limited to a volume less than that determined by the Schwarzschild formula, then it must be a black hole.

So let's apply this recipe to the entire universe. To do this, we need to know its mass and volume. But since we cannot roam the whole universe with the help of a celestial ruler and measure its true breadth, it is impossible to know its general size. All we can do is observe the light and particles that reach us from the distant boundaries of space.

The oldest light we can see comes from Cosmic microwave backgroundIt was created by the field just 380,000 years after the big bang. Since the universe has been expanding, the points from which this light was emitted now lie very far from us. The total distance that light has been able to travel since the Big Bang defines observable universewhich has a diameter of 93 billion light years.

Thanks to painstaking measurements carried out over several decades, astronomers have determined how much mass is in this volume: about 10⁵⁴ KG (that's a 1 followed by 54 zeros, which has the fancy name One Septendecillion).

Now let's calculate the hypothetical size of a black hole with a mass of one sependiatencilionth of a kilogram. Plug the number into the Schwarzschild formula, let the reels roll, and a few maths later we were faced with a startling answer: such a black hole would be 300 billion light years away, about three times larger than the observable universe. In other words, just by looking at the size and mass contained in the observable universe, it matches the count of a black hole.

“Wow,” exclaims an inquisitive stranger at a cocktail party, “So the universe really is a black hole?” »

“Not so fast, grasshopper,” I reply. To really get to the bottom of this question, we need to take a closer look at the inside of a black hole.

Into the darkness

Black holes are weird. One of their many strange aspects is that from the outside they appear to be of a fixed size, but on the inside they are constantly changing. According to the Schwarzschild formula, the space inside them is stretched in one direction and simultaneously twisted together in the other two. (If a black hole spins, its interior still gets weirder, but that's a story for another post.)

Cosmologists call this type of structure anisotropicField Tropical means “direction” iso means “equal” and anon means denial. The anisotropic dynamics inside a black hole mean that of the three spatial directions, one will expand and the other two will contract – for example, a rubber sheet will be stretched into a thin string. This distortion is closely related to the tidal stretching of all wavy substances, which Stephen Hawking and his trademark linguistic talent call spaghettification.

Unlike the case with black holes, as the universe expands isotropically (That is, it expands equally in all directions). Doesn't look like the inside of a black hole, does it?

But this does not yet exclude the Black Hole universe. This is because black holes share two features with our universe that appear familiar on the surface: the event horizon and the singularity.

A event horizon it is a surface from which light cannot appear. In the case of a black hole, it marks a passage of no return from which matter can never escape after passing through. In the case of the universe, this occurs because the expansion of space occurs so quickly that it prevents light from very distant galaxies from ever reaching us.

This cosmic event horizon is like an internal version of a black hole's event horizon: the latter prevents us from seeing into the depths of the black hole's abyss, while the former prevents us from seeing out to the furthest reaches of space.

This inverted relationship also holds for the ominous doom-point singularity, where the density of matter and space-time curvature becomes infinitely greater. According to the Schwarzschild formula, the singularity is a future point in time when any unfortunate astronauts falling into the black hole should meet after they pass the event horizon. Likewise, our cosmological model also contains a singularity – but in the past. As we extrapolate backwards from the expansion of the universe, all points in space become closer and closer, while densities become higher and higher. As the unbound density increases, the mysterious starting point of our Big Bang model ends in a special one. Thus, for black holes, mathematically the singularity lies in the future, whereas for our expanding universe it lies in the past. In both cases, the features that emerge in our models signal a lack of understanding of what is happening at these unexplained dense points.

Adding all this together – the differences in expansion, horizon and singularity of events – paints a pretty convincing picture that our universe No Black hole. It just doesn't look like one!

“But hold on,” says the stranger, with a whiff of disappointment, “I thought we had just calculated that our universe met the criteria for a black hole. This doesn't make sense!

“Well, although the calculation is correct,” I respond, “it turns out that similar mathematical relationships, like Schwarzschild’s, are also buried deep in our model for an expanding universe. It's not unique to black holes.”

Who knows what weird things happen on the largest cosmic scales beyond what we can probe with our telescopesField But according to our fundamental models of expanding universes and non-fermenting black holes, our universe bears no sign of being inside a black hole. What should we make of this? Personally, I think this demonstrates the universality of gravity, creating such amazing structures as cosmic time, crunching black holes, and an accelerating expanding universe all at once.

Jonas Enander is a Swedish science writer with a PhD in physics. His recently published book Pillars of infinity: black holes and our place on earth (Atlantic Books/The Experiment, 2025) explores the impact of black holes on the universe as well as humanity. To explore these ideas, he Created a video that tells a story using watercolor paintingsField

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