Paul Sutter is an astrophysicist at Ohio State University and Chief Scientist at the COSI Science Center. Sutter is also the managing director of Ask the Spaceman and Space Radio and leads AstroTours worldwide. The scientist presented an interesting article in the Expert Voices magazine.
In the late 1990s, theoretical physicists discovered a remarkable connection between two seemingly unrelated concepts in their science. This connection is almost incomprehensibly technical, but it can have far-reaching implications for our understanding of gravity and even the universe. To illustrate this connection, let's start with a black hole.
The influence of a black hole on the flow of information
The researchers found that when one bit of information hits a black hole, its surface area increases by a very precise amount: the square of Planck's length, equal to an incredibly small 1.6 x 10-35 m.
Initially, it may not seem entirely interesting that a black hole becomes larger when matter or energy enters it, but the most surprising thing is that the surface area, not volume, grows in direct proportion to reliable information. This is completely unlike most other known objects in the universe.
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Are we living in three-dimensional space?
For most of the objects with which we are familiar, there is a single law: if it "consumes" one bit of information, its volume will grow by one unit, and its surface area will only grow by a fraction. But with black holes, the situation is changing dramatically. It is as if information does not reside inside the black hole, but instead sticks to its surface.
Thus, a black hole is a fully three-dimensional object in our three-dimensional universe and can be fully represented by a two-dimensional surface.
How do holograms work?
A hologram is a system that uses fewer dimensions. It can package all information from the original system.
For example, we live in three spatial dimensions. When you pose in front of the camera, it records a two-dimensional image of your face, but it does not capture all the information. When you later examine your work and use the filter, you cannot, for example, see the back of your head, no matter how you rotate the image. But the hologram recording will retain all this information. Even though this is a 2D view, you can still explore it from all 3D angles.
Black hole as a hologram
Describing a black hole as a hologram could provide a solution to the so-called black hole information paradox, the mystery of where information is born when matter is consumed by a black hole. But that's a topic for another article. The concept of a "black hole as a hologram" is also a good example to keep in mind when trying to view the entire universe.
Solving private problems
The correspondence between seemingly unrelated branches of physics mentioned at the beginning of this article is another application of holographic techniques that comes from the incredible AdS-CFT model.
AdS stands for Anti-De Sitter. This model represents a particular solution to Einstein's general theory of relativity. It describes a completely empty universe with negative spatial curvature.
It's a rather boring universe: it contains no matter or energy, and the parallel lines eventually diverge based on the position of the underlying geometry. While this process may not describe the universe, it at least suggests that life on earth has a beginning. This somewhat relaxed model of the universe has the necessary mathematical properties to make compound theory relevant.
Field theory
The other side of the correspondence is a structure called conformal field theory. Theoretical physics repels with its field theories. These are the levers used by scientists to create a variety of quantum theories used to describe three of the four forces of nature.
Electromagnetism, strong nuclear force, and weak nuclear force could be described through field theory, and over the past half century, mankind has often practiced their use.
It should be understood why this connection is so important. Let's say you're trying to solve a really hard problem like quantum gravity using string theory, which is an attempt to explain all the fundamental forces and particles in the universe in terms of tiny vibrating strings. In fact, this is such a complex problem that no one has found a solution for it despite decades of trying.
The AdS-CFT correspondence tells us that holographic techniques can be used to rid the world of this headache.
Instead of trying to solve the problem of quantum gravity in our three-dimensional universe, AdS-CFT allows us to move to an equivalent problem at the edge of the universe, which is represented by only two dimensions and does not contain gravity.
Field theory equations
The almost impossible mathematical calculus of string theory is being replaced by a set of simply insanely difficult field theory equations. This allows you to find solutions to problems without any gravity, which prevents you from transferring the solution back to the normal three-dimensional universe and making any predictions. It all looks like a great idea and a way to trick nature by bypassing gravitational mechanisms. And that could turn out to be a brilliant way to "solve" quantum gravity.
Existing contradictions
But at the moment there are some contradictions. First, we do not live in an anti-de Sitter universe. Our Universe is full of matter, radiation and dark energy and has an almost completely flat geometry.
Is there a similar correspondence that works in our real universe? Maybe theorists are working hard to find the "border", taken for the AdCa-CFT correspondence to the cosmological horizon - the limit of what we can see in our observable Universe.
Everything would be understandable, except for the moment that we live in a dynamic space-time with a constantly growing space, and this border is constantly changing. This position is not well explained in modern theories.
Indeed, when we move from the model described by astrophysicist Sitter to a simpler boundary model using conformal field theory, the new systems of equations are fundamentally solvable.
They still exist, but they often look fantastic, disastrous, frightening, and insoluble.
So does a hologram exist?
Even if the AdS-CFT link turned out to be useful for solving the problem of quantum gravity and physicists could find a way to navigate the problems and make this method relevant to the universe we live in, this does not mean that we actually live in a hologram.
It is a mistake to think that the AdS-CFT model is a convenient way to solve the gravitational problems of our universe with gravity in three dimensions.
This is all an illusion, and we really live in two-dimensional space without gravity. A mathematical device as convenient as this does not change our views on the fundamental nature of reality.
If holographic principles are useful for solving problems, this does not mean that we live in a hologram. And even if we really lived in a hologram, we would not be able to tell the difference anyway.
Maya Muzashvili