# Are space and time two separate dimensions

*10.07.2019 10:20*

#### Possible connection between quantum physics and space-time discovered

##### Stefan Meisterle *Public and communication*

Austrian Academy of Sciences

* Quantum physicists from the Austrian Academy of Sciences and the University of Vienna were able to prove that the quantum physical law of area is also valid in the space-time described by Einstein, i.e. including the dimension of time. The new study was published in a "Nature" journal. *

Locality is the essential principle between all physical interactions: It states that every physical system can only interact with systems in the immediate vicinity or that there must be a mediating “medium” in the case of systems that are distant. This is known from making calls with mobile phones, for example, in which the data is transmitted via electromagnetic waves in order to be able to hear the other party.

Quantum researchers from the Austrian Academy of Sciences (ÖAW) and the University of Vienna have now found that a connection between modern quantum mechanics and space-time can be drawn based on this principle. As a reminder: space-time is the space described by Einstein that unites the three spatial dimensions with the fourth dimension of time (past, present, future). The new study has now been published in "Quantum Information", a journal published by "Nature".

Correlation of independently generated measurement results

In order to understand the initial scientific situation in three-dimensional space, i.e. without taking time into account, imagine two fictitious observers Alice and Bob. Both examine the components of a physical system, whereby Alice can only examine those parts that lie in a limited area ("region of space"). In turn, Bob can only examine the parts that are outside of the limited area.

The area law of entropy (“area law”), an essential law in quantum physics, states that the correlation between the measurement results of Alice and Bob is proportional to the area of the border area - but not to its volume, as one simply imagines in three-dimensional space yes could assume. The area of the border thus determines the extent to which the two measurement results generated independently of one another are related to one another. How is it when a fourth dimension, namely that of time, is added?

Possible bridge between spacetime and quantum physics

This is where the new study comes into play, for which the researchers have designed the following scenario within space-time: Alice carries out her measurements in a delimited space in a certain period of time. Bob is outside of this realm and has access to every other point there is at any point in time. The researchers from the Austrian Academy of Sciences and the University of Vienna now investigated what role the border area in spacetime between Alice and Bob has for the correlation of the measurement results.

The result: The law of area also applies in spacetime as long as the objects interact locally with one another (principle of locality). This means that, even taking into account the dimension of time, the correlation of the measurement results from Alice and Bob increases in direct proportion to the area of the limit area. The volume in space-time, on the other hand, does not play a role in the extent of the correlation.

“We succeeded in finding an important connection between quantum correlation and space-time,” says Časlav Brukner, group leader at the Institute for Quantum Optics and Quantum Information at the Academy and one of the authors of the study. "These results could help us to move closer to a unified theory that physicists are looking for worldwide and that unites the two still separate worlds of quantum physics and gravity."

##### Scientific contact:

Institute for Quantum Optics and Quantum Information Vienna

of the Austrian Academy of Sciences

University of Vienna

Boltzmanngasse 5, 1090 Vienna

M + 43 664 602777 2582

[email protected]

##### Original publication:

"A Spacetime Area Law Bound on Quantum Correlations", Ilya Kull, Philippe Allard Guérin, Časlav Brukner, Nature Partner Journal Quantum Information, 2019 (Open Access)

DOI: https://www.nature.com/articles/s41534-019-0171-x

##### Additional Information:

https: //www.oeaw.ac.at/detail/news/moegliche-verbindungen- between-quantenphysik-u ...

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