Is the 3D Universe Just a Hologram?

It seems obvious, that the great, vast Universe is 3-D, but now scientists are challenging this assumption, claiming that the Universe is really just a hologram, according to a new study.

Holograms can be found in everyday life, from credit cards to banknotes. They are two-dimensional, but to us they appear 3-D. Our Universe could behave the same way.

According to the "holographic principle," a mathematical description of the Universe actually requires one fewer dimension than it seems. This means that what we perceive as 3-D may in fact just be the image of 2-D processes on a huge cosmic horizon.

Until now, scientists have studied the holographic principle in exotic (anti-de-sitter) spaces with negative curvature - those in which any object thrown away on a straight line will eventually return. But this time a team at the Vienna University of Technology (TU Wien) suggests the principle can be applied to flat space-time such as our Universe.

"Our Universe, in contrast, is quite flat - and on astronomic distances, it has positive curvature," Daniel Grumiller from (TU Wien) said in a statement.

To test this hypothesis, the team constructed several gravitational theories, which do not require exotic anti-de-sitter spaces, but live in a flat space.

"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 explained.

For example, quantum mechanics - quantum entanglement - has to appear in the gravitational theory. When quantum particles are entangled, they cannot be described individually. They form a single quantum object, even if they are located far apart. There is a measure for the amount of entanglement in a quantum system, called "entropy of entanglement."

Grumiller and his colleagues found that this 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," said researcher 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," Grumiller added, "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."

However, it should be noted that these findings alone don't prove that we are indeed living in a hologram. But it is does add to growing evidence of such, and serves as a step towards validating the correspondence principle in our own Universe.

The results are described in more detail in the journal Physical Review Letters.

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