Are black holes just holograms?

© 2025 Kieron Conway - All rights reserved.

Black holes are not actual holograms but can be mathematically described as if they were!

The Holographic Principle

And it’s not just black holes either - some physicists believe that the entire universe could be so described! The idea is known as the holographic principle, first proposed in the 1990s by Gerard ’t Hooft and Leonard Susskind, building on earlier work on black hole physics.

Black holes as holograms, was described in A Journey into Modern Physics Part 2 and also in Part 2 of the LIGHT series. However, an interesting analogy to how real holograms are created appeared in the LIGHT version that didn't make it into the main series. Here’s a recap of the theory sprinkled with extra detail, and including the analogy for those who missed it.

A Breakthrough in Black Hole Physics

This came in the 1970s when Stephen Hawking showed that black holes are not completely black, but radiate energy, now called “Hawking radiation”. This confirmed a bold suggestion made a few years earlier by Jacob Bekenstein, who argued that black holes must have entropy: a measure of disorder or information content. Surprisingly, Bekenstein found that this entropy is not proportional to the black hole’s enormous volume, defined by a sphere with a radius equal to that of the event horizon, but instead to the surface area of its event horizon.

This was revolutionary: until then, nobody had seriously considered that a black hole could even have entropy, let alone that its extent would be proportional to its area rather than volume. Hawking’s theoretical prediction of black hole radiation provided a definitive formula, known today as the Bekenstein–Hawking entropy law.

What happens to information that falls into black holes?

Suppose you throw a book into a black hole. Does all the information inside it, the countless quantum states making up its paper and ink particles, get destroyed for ever? Are the contents of the book lost for eternity? That’s a problem in physics, because one of the basic rules of quantum theory is that information is never truly lost. This is the famous black hole information paradox: does a black hole lose all the information that falls into it, or does it somehow preserve it?

One proposed resolution is that the information isn’t lost inside the black hole but instead becomes encoded on its event horizon. In fact, every new, tiny, bit of information, falling in would correspond to a tiny increase in the horizon’s area, roughly equal to one Planck length multiplied by one Plank length, or one unit of area at the Planck scale (the smallest meaningful length in physics). And this is how a black hole grows!

At that microscopic level, some theories even picture the horizon's surface as a kind of “quantum fluid” where gravity and quantum mechanics meet. This is highly speculative, but it does capture the idea that the event horizon itself is the key to storing information that falls into the behemoth.

So, can I get my book back one day?

If all the information in the particles of a book thrown into a black hole is somehow preserved, then in theory there would be a complete record of everything that made up the book. But the idea that you could one day reconstruct the actual pages and print is deeply speculative at best and highly fanciful at worst!

When matter falls into a black hole, its information isn’t destroyed but scrambled into a chaotic tangle of quantum data on the event horizon's surface. The patterns that once described the letters on paper get mixed beyond recognition. In principle, the universe keeps all the quantum information but in practice, it’s like shredding a book and scattering the pieces to the wind. So, while nothing is truly lost in physics, recovering something as specific as a printed page from its mass of quantum information would be difficult in the extreme.

The moral of this story is: keep your books on the book-shelf where they belong!

Black Holes as Holograms and the Analogy

If all the information about what falls into a black hole is stored on its two-dimensional surface, then the black hole we perceive could be thought of as a kind of holographic projection of that data.

This sounds bizarre, but it’s actually how real holograms work. To make a hologram, you capture the light wavefronts from a 3D object and record them on a flat surface (the DVD). Later, you use the data on the surface to reconstruct the wavefronts to reveal a 3D image of the original object.

In the same spirit, you can think of the black hole as a 3D object whose information is really stored on the 2D surface of the event horizon.

As a final thought: just remember that the holographic principle provides a mathematical model of one of nature's most mysterious objects to assist in understanding its extreme complexity.

Extending the idea to the universe

The holographic principle goes even further: some physicists propose that the entire universe might be described in holographic terms, with all the information in our 3D space encoded on the 2D boundary of the universe. How's that for a crazy idea?

Whether our own expanding universe can be explained this way is still an open question, but it remains one of the most fascinating insights in modern physics. Mathematically, physicists have shown that certain kinds of universes (including black holes) can be described holographically, as if all the information inside them were stored on a boundary surface.

Whether our own reality can be described this way is still an open question, but you have to admit, the possibility that the universe itself can be described as a hologram is one of the wildest ideas in modern physics.

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