A mathematical description of the Universe called the holographic principle states that the Universe only has two dimensions of length. This principle was proposed for the first time in 1997. This means that what we perceive as a third dimension is actually a two-dimensional event of the horizon of an image which is two-dimensional.

So far this principle was studied only in unusual spaces with negative curvature. From a theoretical point of view this might be interesting, but such exotic spaces are different from the spaces in our Universe.

However researchers at the Vienna University of Technology (TU Wien) have developed the mathematical model and say that the holographic principle can also apply in a flat space like the one in our Universe. This means that the Universe is a hologram and that we are all living in two spatial dimensions. The study was published in the journal *Physical Review Letters*.

The behavior of quantum particles in calculated with only two spatial dimensions, whereas gravitational phenomena are described with three spatial dimensions. However both calculations are corresponding. It is surprising how they can both ne mapped onto each other.

Daniel Grumiller from the Vienna University of Technology assumed that such a correspondence can also apply in the case of universes with negative curvature and flat universes like ours. He remarked:

“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.”

In mathematics the pairs of entangled quantum particles cannot be considered separate objects irrespective of the distance between them. The measure for the degree of entanglement in a particular quantum system, the entropy of entanglement, was proved to be the same in theories of quantum mechanics and gravity in a universe which only as two dimensions. Thus theories of quantum effects reckoned in two dimensions can be mapped onto gravitational models which have three dimensions. Such an analogy is strange. It is as if using an astronomy book to fix a CD-player or as if a cake recipe could be found in a dishwasher manual.

Grumiller commented that this theory confirms their assumption according to which the holographic principle can also be applied in flat spaces. It is a proof that correspondence is valid in our Universe. He added that a few years ago it would have been unconceivable that in a theory of gravity one should put the entropy of entanglement and quantum information together.

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