A Physics Illusion
We, as humans, have a variety of senses that we use to experience the world around us. But perception can be a tricky thing. It can be fooled by, say, two dimensions of light working together to create the appearance of a 3D object or form. This is how real-world holograms are achieved, and some suggest this illusion could be extended far beyond the confines of some stage or exhibit. In fact, some scientists believe that, at least theoretically, it's possible that our entire universe is a hologram.
The first inklings of this strange idea emerged in the 1970s when scientists debated the properties of a black hole and how an object's entropy could be lost while adhering to the second law of thermodynamics. It was found, as stated by Paul Matt Sutter, an astrophysicist, in an interview with Fraser Cain that, "when it comes to black holes, the information content of a black hole is proportional not to its volume, but to its surface area."
In other words, the information going into a black hole might be directed and maintained onto its event horizon, which is 2D — essentially 3D information stored in 2D space. This field of thought expanded in the 1990s when physicists discovered that when you assume that universe is a hologram, gravity vanishes when you can take away one from whatever number of dimensions you are working with.
These phenomenon are described in the "holographic principle," which states, simply, that all objects can be explained by the information stored on their surfaces — so the space around you might be 3D, but if you rest on a 2D surface, then perhaps a shadow or reflection of you exists within that 2D space. In other words, a higher dimension of information is, essentially, encoded in a lower dimension of space.
However, the most intensively explored instance of the holographic principle works only under very special circumstances — when 5D space-time is bent back on itself, as New Scientist put it, "rather like the surface of a Pringle." This "trick" of bending space-time, eliminating gravity, and working under the constraint of the universe being a hologram, has had a variety of practical applications. The holographic principle, a part of string theory, has helped with the advancement of supercomputers and physics problems like explaining why particles have mass.
Raphael Bousso, who has been working on the principle at Stanford University, has confidently stated that "The world doesn't appear to us like a hologram, but in terms of the information needed to describe it, it is one."
While its llikely not literally true that the universe is a hologram, the potential for 3D information to be stored in two dimensions has been shown with black holes. This might cause you to yell, "A-Ha! Nothing is real!" at your computer screen, but, as Sutter concretely puts it, the holographic principle is just "a convenient mathematical tool because some questions in physics are super hard."