The universe in which we exist is theorized to be a projection enveloping the entire two-dimensional plane of the universe. The developmental process of the entire universe is likened to a complete holographic film. Each one of us Earthlings is an actor in this film.

Upon hearing this theory, one might instantly feel a sense of incredibility, as this is the renowned holographic universe theory. Let's analyze this virtual world of the universe from a scientific perspective.

Perhaps the universe is indeed just a holographic projection, and everything we see before us is not the real world. Over the past few decades, as many of us have spent a significant amount of time online, the real world seems to have become more expansive. However, in the field of theoretical physics, the situation appears to be developing in the opposite direction.

In the past two decades (though this article was written in 2009, it still holds reading value), string theorists have been exploring the idea that the time and space we inhabit, including ourselves, might be an illusion generated by a "certain reality," a hologram lacking a key feature of the world we perceive: the third dimension.

Professor Juan Maldacena of the Princeton Institute for Advanced Study played a crucial role in the development of holographic principles. In the 1990s, Maldacena proposed the first cosmological model implementing the holographic principle. Recently, during a visit to Cambridge, he granted an interview to the author.

The holographic principle stems from one of the greatest scientific questions of the 20th century: the incompatibility between general relativity and quantum mechanics, the two fundamental physical theories. At the beginning of the 20th century, Einstein discovered that time and space are inseparable, and he referred to the structure formed by these two as spacetime.

His general relativity posited that spacetime itself could be distorted by massive objects, and gravity is the result of this distortion. It's akin to placing a billiard ball on a trampoline, creating a depression that causes nearby marbles to roll towards it; similarly, massive objects (like planets) bend spacetime, attracting nearby objects with their gravity.

According to Einstein's perspective, gravity is not some substance propagating through space, but rather a consequence of the geometric structure of spacetime itself.

General relativity mainly describes the world of planets and galaxies, while quantum mechanics focuses on the subatomic scale, the realm of fundamental particles that make up matter. At this scale, mass is extremely small, and gravity can be disregarded.

Quantum field theory, a description of particle physics in the quantum realm, suggests that basic particles transmit forces to each other through messenger particles called gauge bosons: a fundamental particle communicates force to another by sending gauge bosons.

The conflict between general relativity and quantum mechanics does not pose a problem for most practical applications. Physicists usually study objects on large scales, where quantum effects are not apparent, or on small scales, where particles are light and gravity's influence is minimal. However, in a specific scenario, the conflict between these two theories becomes particularly evident: when a large amount of mass concentrates in a tiny region of space, a black hole is formed.

The powerful gravity generated by black holes is so intense that not even light can escape, meaning that when studying black holes, we cannot ignore the influence of gravity. Simultaneously, the small scale of black holes implies the presence of quantum effects. Therefore, to explain phenomena within black holes, we indeed need a unified theory of quantum gravity.

Black holes are the initial theoretical source of the holographic principle. They have an irretrievable boundary called the event horizon. Once you cross this boundary, you are pulled into the black hole, and there is no escape. When you fall into a black hole, much information disappears with you. This information includes not only your DNA and a couple of your best ideas but also countless combinations of blood cells in your veins and all the chaotic thoughts in your mind.

However, in the world of black holes, things appear much simpler. Classical physics assumes that nothing can escape from a black hole, and it can be fully described with just three parameters: its mass, charge, and rotation speed. Therefore, when you fall into a black hole, all the information needed to describe you is sucked into these three parameters of the black hole—your descent simplifies the universe a bit.

So far, Maldacena's model is just a model. It is unclear whether the universe we live in is a hologram, and we still lack a consistent quantum description of gravity applicable to our world. The assumption of negative curvature in Maldacena's model is crucial, but our universe shows a slight positive curvature in observational results.

Maldacena states, "We don't know if there is a similar description in the positive curvature case. People are exploring various ideas, but we don't have a complete answer yet."

Maldacena's conception is more or less accepted as plausible, but it has yet to receive cautious experimental confirmation.