Holograms are two-dimensional, but appear three dimensional to the human eye, and new research suggest the same may be true for the universe we live in.

The universe appears three dimensional from a human perspective, but a theory developed over only the past two decades suggests a mathematical description of the universe requires only two dimensions, Vienna University of Technology reported.

Until a recent study, the "holographic principle" had only been looked at in exotic space with negative curvature., which is much different from the space of our own universe. This new research suggests the holographic principle holds up even in a flat spaceline.

"In 1997, the physicist Juan Maldacena proposed the idea that there is a correspondence between gravitational theories in curved anti-de-sitter spaces on the one hand and quantum field theories in spaces with one fewer dimension on the other," said Daniel Grumiller of TU Wien. 

Gravitational phenomena are described in a theory with three spatial dimensions, but the behavior of quantum particles is calculated in a theory with just two; the results of both of these calculations can be mapped onto each other. This correspondence has surprised scientists.

"It is like finding out that equations from an astronomy textbook can also be used to repair a CD-player. But this method has proven to be very successful," the researchers said.

The researchers believe the correspondence principle is also applicable for our real universe as opposed to negatively curved anti-de-sitter-space.

"Our universe, in contrast, is quite flat - and on astronomic distances, it has positive curvature," Grumiller said.

To test this hypothesis, the researchers spent three years constructing gravitational theories that do not require exotic anti-de-sitter spaces.

"If quantum gravity in a flat space allows for a holographic description by a standard quantum theory, then there must by physical quantities, which can be calculated in both theories - and the results must agree," Grumiller said.

For example, the concept of quantum entanglement must appear in the gravitational theory. When quantum particles are entangled they cannot be described individually, but rather as one unit. The measurement of the amount of entanglement present in a quantum system is called the "entropy of entanglement." The researchers succeeded in demonstrating that entropy of entanglement has the same value in flat quantum gravity as it does in a low dimension quantum field theory.

"This calculation affirms our assumption that the holographic principle can also be realized in flat spaces. It is evidence for the validity of this correspondence in our universe", says Max Riegler (TU Wien). "The fact that we can even talk about quantum information and entropy of entanglement in a theory of gravity is astounding in itself, and would hardly have been imaginable only a few years back. That we are now able to use this as a tool to test the validity of the holographic principle, and that this test works out, is quite remarkable," Grumiller concluded.

The researchers noted this study does not concretely prove that the universe is a hologram, but adds to the growing evidence in support of the holographic principle.

The findings were published in a recent edition of the journal Physical Review.