The Holographic Principle: What is Reality?

Is our Universe just an illusion?

How do black holes prove that our universe is a hologram?

We can all agree on the fact that the evolution of our understanding of physics hasn't been stable since ancient times. And I say this because most of the time when we try to formulate theories related to our universe, it's rarely been accurate. The Heliocentric model, dual nature of light, Einstein's Theory of Relativity, and quantum mechanics - are some of the most controversial yet brilliantly proven theories that led us to believe that what we see need not be the reality of the universe, and that the actual scenario might be a little...strange for us to perceive.

The Holographic principle is again one of the most controversial theories of this time, which was mainly brought up as a solution to the black hole information paradox. This theory suggests that the universe might be a hologram, like a 3-D projection of a 2-D surface. 

What's surprising is that most physicists actually picture the universe in this way - a hologram. And what's even more surprising is that physicists use this principle as one of the working tools to formulate the math in different areas of physics. 

But the important question is that what leads us into thinking that the universe might be a hologram?

It's black holes,..obviously. You hear about a strange theory and you decide to read about it, and the first word you see is black holes! In this case, too, it's the strange properties shown by the event horizon of a black hole, that triggered the development of a theoretical holographic universe, which we've earlier covered extensively in black hole thermodynamics. 

One of the most important conclusions of the black hole thermodynamics is that the entropy is directly proportional to the area of the event horizon of a black hole, which also implies that the information (of the infalling matter) is stored on the surface of the event horizon. So, whenever matter falls into a black hole, its information is spread out or stored on the event horizon, expanding its area with every additional bit of information, thereby preventing the loss of information. 

What is actually happening here is pretty simple: the event horizon of the black hole is acting as a 2-D surface, where the information of a 3-D reality is encoded. The 3-D reality refers to the objects that fell into the black hole (what the black hole is composed of). 

The event horizon of a black hole - Observer's perspective

But there is some interesting stuff happening with this whole 2-D event horizon concept. Imagine a spaceship falling into a black hole and another observer viewing the event. The crew of the infalling spaceship crosses the event horizon and will observe the whole journey in a 3-D manner. But the observer, who is viewing the whole event far away, will only see the spaceship falling until the event horizon. After reaching the event horizon, the observer will see that the spaceship has stopped moving and frozen on the surface of the horizon.

This is because while approaching the event horizon, spacetime gets more distorted and time gets slower. And by the time we reach the event horizon, time completely stops - or that's what an observer viewing the whole event would perceive.

 But the crew would still experience normal time regardless of time distortion, an effect called time dilation. However, there's a clash between two contrasting perspectives: the perspective of the crew in the spaceship viewing the horizon and beyond as a 3-D space, and the observer viewing the horizon as a mere 2-D surface. 

So what is reality? 

The answer is that both of them are actual realities. The observer would view the horizon as a 2-D surface and the infalling objects would experience a 3-D horizon. 

In simple words, the event horizon of a black hole is actually a 2-D surface, on which, all the information of the matter hidden inside the black hole, is encoded - like a hologram. So basically, the area of the event horizon literally gives us all the details on the information of the content hidden by the black hole. 

This strange idea of connecting black holes led to physicists wonder if our universe as a whole behaved in this very same manner, like a hologram. Just like the black holes, our universe may also be encoded on some giant two-dimensional horizon, of a giant hidden 3-D spatial stretch, and that is us. 

So is this 3-D world an illusion? 

And is our survival in this universe just defined by some encoded unrealistic sheet? 

Well...we don't for sure. Our human minds are way too primitive to understand uni-multi dimensional spacetime and quantum mechanics. 

But if there's something we're sure of, it's that our existence in this universe means so much more than the strange universe itself!! 

Click to watch Leonard Susskind speak on this topic here.