A Commentary on String Theory's 'Holographic Principle'

Lately, I've been obsessed with grasping, philosophically, an understanding of current theories and stances of our reality through the lense of theoretical physics. One particular corner that's been inspiring my inner autodidact to charge is something called the holographic principle.

It's a current cornerstone of the string theories. I say string theories, plural, because from what I've gleaned there's five of them. Why it's caught my attention so much is because string theory operates on a level so small, so imperceptible, that our current technology is nowhere even close to being able to observe it in action, in order to prove it's credibility. This microscopic level is the Planck length. To put its smallness into perspective, if an atom was expanded to be the size of the observable universe, one planck unit would be roughly the size of a tree on Earth. Yet, for the last few decades, the current realm of academia and scientific study has poured vast amounts of time, money, and man-power into research on the topic.

Before I get into the thick of the Holographic Principle, I have a question.

Why—if we aren't even close to being able to prove its credibility through observation and the scientific method, do we continue to spend so much effort studying it?

It's because of one particular reason. Just as Stephen Hawking predicted the existence of black holes through seeing it in the math, we see a similar phenomenon in our study of the math in the string theories. The math tells us something astonishing is happening.

For centuries, humans have sought a so-called "Theory of Everything". We constantly strive for a methodology, or equation, or keystone discovery that reconciles multiple systems and explains our reality through their unification. Scholars once posited that Euclidian geometry explained our world thoroughly—then we discovered that Earth is a sphere—so we developed non-Euclidian geometry. Then we directed our focus to the stars and guess what, we think that space behaves, again, according to the laws of Euclidian geometry. Space is flat, or it's just so massive that we can't detect it's curvature within our observable bubble. There exist countless examples throughout history. Currently, we are searching for something that reconciles Einstein's General Theory of Relativity with our current model of Quantum Mechanics. Many theoretical physicists believe that String Theory might be just that which we seek.

Could it be? Or is History repeating itself?

In the most basic way of explaining it, through which I understand it as well, it's because even though it operates at the Planck scale—something happens in the math when we plug in the various equations across the string theories. I know this is a very rudimentary way of explaining how the vastly complex mathematics and computations that go into studying string theory operate. But at the most basic interpretation, one hundred percent of the time—a specific, theorized massless particle called a graviton is produced.

A massless, 2-spin particle—a graviton, is predicted each and every time and it emerges naturally—we don't even have to look for it. The presence of this particle reconciles general relativity and quantum mechanics, it explains how gravity fits into the quantum realm, and the fact that the math perfectly and naturally predicts this every single time—is no coincidence.

To be more precise—in most attempts to quantize gravity, you start with gravity and try to force it into quantum mechanics—and it breaks. We have a lot of trouble trying to reconcile gravity's role in the quantum realm.

Incredibly, string theory does the opposite.

It starts with something much simpler: a vibrating string, and then—almost accidentally, gravity appears as a consequence.

The graviton. The fundamental, quantized unit of gravity.

This lead me to another question. Gravity is not an actual force. It's not an actual pushing or pulling on an objects shape or trajectory toward something, it's just the curvature or distortion of spacetime in the presence of massive objects. The more massive the object, the more distorted the space around it. Think of the space around you as a 3-dimensional grid. Perfectly symmetrical square units of length, width, and heighth permeating the space all around you in every direction. Now place a massive object, like the Sun, in the middle of that grid. The cubed units surrounding the sun would bend inward toward its surface area, so that the various cubed sections making up the grid bend and contract on one side that surrounds the Sun's perimeter, and are less warped on the side of the unit facing away. A terrible visual analogy is a bowling ball on a trampoline, the ball representing the star and the fabric of the trampoline representing spacetime. The problem with the analogy is that the fabric of the trampoline only displays a flat, 2D aspect of spacetime. A more accurate description would be if we had some sort of 3 dimensional trampoline where the fabric is represented as a large, cubed environment with length, width and heighth that are being warped by the ball. The presence of massive objects and their resulting influence on the fabric of spacetime create a sort of gravity well. So when an object gets trapped in the Sun's orbit, it's not being pulled in by the Sun, it's just following the warped curvature of the space around it. For the object in orbit, it's just following a straight line, forever in freefall toward the Sun. It's kind of like if you were on a train track, and someone bent the rails to move in a circle. To the train, it's just following the path of the tracks. So back to my question: if gravity is just the curvature of spacetime, what—or why, is there a fundamental unit to it? How can there be a fundamental particle that makes up gravity, if gravity is just spacetime itself being bent?

This is the million dollar question.

Using our beloved analogy, as physics loves to abuse—think of spacetime as a surface of a lake. When you throw a stone into the lake, the water ripples out. Now imagine you took those ripples and quantized them into individual, equal, and discrete packets. Essentially making each individual group of excitations a quanta of gravity. The warping of the lake itself IS the graviton. It's the excitations of that field of spacetime—a quanta represents the motion of the rippling of spacetime itself. We just call those individual, quantized ripples a graviton. Remember, waves and particles act similarly at the quantum level—or more accurately, our perception of particle behavior is just our inability to see that its actually just a quanta of waves moving around down there.

Alright, let's talk about the strangeness of the Holographic Principle.

So now that I've laid down the reason why the academic community takes string theory so seriously, here's another facet of string theory that again, we are unable to prove, but have essentially and irrefutably implied via other, various indirect methods.

I'll just come right out and say what the Holographic Principle is—it's the idea that our 3D reality, everything we see, our bodies, buildings, cars, planets, solar systems, the universe itself, are all just emergent properties of quantum information encoded on a distant, 2-dimensional boundary—like a hologram. A hologram, from the side, is a 2D surface, but when you look at it from the top, it appears to be 3D. There are a couple of important discoveries that lend credibility to the idea that at the most fundamental level, our reality is actually a 2-dimensional surface and everything we experience is being projected from said surface. I'll go over each of them in short:

1) The AdS/CFT correspondence (Anti de-Sitter Space/Conformal Field Theory)

The AdS/CFT correspondence, discovered in 1997 by Juan Maldacena, showed that one aspect of our physics, mathematically describes another aspect of physics, perfectly. Not approximately, but perfectly.

It showed that our universe, complete with black holes, spacetime, atoms, solar systems, gravity, and all its complexity, can be described perfectly by a quantum field theory living on the boundary of that space's volume.

So basically gravity in d+1 dimensions = quantum field theory in d dimensions. Or—a quantum field theory explained in the surface area of 2 dimensions is the exact equivalent of what's happening in a 3-dimensional volume of space.

How Anti de-Sitter Space works is a whole other ballpark that I implore you to research on your own.

The general takeaway is this—any 3D object or area containing a 3D reality can be perfectly described by the information on its corresponding 2D surface area, not by the contents of its volume. We once thought that spacetime and gravity were fundamental and that quantum field theory lived inside that spacetime, but AdS/CFT suggests the opposite, that the geometry of spacetime and gravity are the emergent, resulting properties and that quantum information, or quantum bits (i.e., qubits) are fundamental.

How we deduced that 3D volume is described from its corresponding 2D surface area will be touched on next.

2) Studying black holes

This is one of the reasons we came to the previous conclusion. When looking at how black holes absorb matter, we came to an astonishing discovery. A black hole will spaghettify (break down matter into a string of its fundamental particles) matter, and it will absorb said matter. Naturally, we figured it just went straight into the black hole, crossed the event horizon, and filled the volume of the black hole. But thats not what we observed—instead, we saw that it took that string of information and smeared it across its 2-dimensional surface area. The matter was broken down into its fundamental information, encoded onto the boundary of the black hole, and THAT, astonishingly, was what increased its volume! Matter never actually went into volume area of the black hole, rather, matter encoded as information on the surface area, resulted in the volume size increasing.

The term holographic or just the idea of holography in general, is one of many poor analogies in physics. We are using everyday examples from our cultured human experience to describe phenomena that is ancient and not of human origin. So many terms we use are just the best example we have to help our brain interpret what's going on—just like The Big Bang, another terribly worded phrase.

The holographic principle is a radical idea in modern physics—but almost all of our current theories, laws, and understandings were radical ideas at first.

I hope this commentary inspires you to look more into the more current ideas floating around in the scientific world. I've never been more understanding of the phrase, 'Fact is stranger than fiction' until I started reading about advancements in physics over the last thirty to forty years. We even think that regions of space that are closer together, appear to be so because they are more highly entangled, and less entangled regions result in greater distances between regions—meaning that the geometry and shape of spacetime itself is a dictated and emergent result from levels of quantum entanglement between those regions! Even the proximity and perceived distances between regions of space and their geometry are possibly just the results of the quantum information dictating their levels of entanglement.

The ideas laid out here have the potential to send you down a rabbit hole of wonder and awe if you harbor such desire and curiosity for it. There is always something more to learn.