# The search for atoms of space and time

## Quantum gravity experts to meet at FAU in July

Albert Einstein’s general theory of relativity – which is 100 years old this year – is essential for describing our universe at a large scale, from our solar system, to galaxies, to the earliest stages of the universe. However, whether and to what extent Einstein’s theory can also be applied at the microscopic scale has not yet been sufficiently researched. Together with international colleagues, researchers at FAU’s Institute of Quantum Gravity are working on developing and researching a theory that combines general relativity with the laws of quantum physics – a quantum theory of gravity. From 6 to 10 July 2015, around 200 experts from all over the world will be meeting at the Loops ’15 conference in Erlangen to discuss the results of the latest research in quantum gravity. The general public are also invited to attend the popular science lecture by Italian researcher Prof. Carlo Rovelli. The lecture, which will be given in English, will be held at 8.30 p.m. on 9 July at Heinrich-Lades-Halle in Erlangen. Rovelli will take his audience through Einstein’s work, explain what it says about black holes and the big bang, and outline the search for a quantum theory of gravity.

Exactly 100 years ago, Einstein revolutionised our understanding of space and time with his general theory of relativity. He showed that space and time do not exist independently of other physical processes but interact with them dynamically. His theory is not only essential in order to understand our universe, it also plays an important role in everyday life. For example, it has to be considered in GPS positioning. Yet the general theory of relativity also has a few unanswered riddles for researchers. The theory describes the beginning of our universe with the big bang, but it appears to lose its predictive power here, at the beginning of space and time, as the physical quantities that it defines would take on infinite values. This phenomenon is known as a singularity. The same applies to what it says about black holes. Einstein’s theory implies that gravity causes particularly heavy stars at the end of their lives to collapse unstoppably and a singularity – a hole in spacetime – is what remains.

It is not unusual for a physical theory to reach its limits in certain areas, and in the history of physics this has always served as motivation to question old concepts and develop new theories that are able to describe nature even in its extremes. A particularly impressive example of this was the introduction of quantum theory at the beginning of the last century which allowed physical models to be applied at the atomic scale, an area in which classical physics at the time was unable to provide an adequate description of the laws of nature. Quantum theory describes the world at small scales, while the general theory of relativity describes its at large ones.

To answer the questions about the big bang and black holes that cannot be explained by the general theory of relativity, gravity – and therefore the geometry of space and time – must also be understood at the microscopic scale. Researchers assume that this requires a new type of quantum theory that can not only describe the quantum properties of atoms but is also able to describe those of space and time – and therefore gravity. What they are looking for, therefore, is a quantum theory of gravity.

What such a theory might look like and what its physical consequences would be is one area of research that FAU’s Institute of Quantum Gravity specialises in. A team at the Institute, led by Prof. Dr. Thomas Thiemann, is carrying out research on loop quantum gravity, one of several possible approaches to a quantum theory of gravity. The predictions about microscopic properties of gravity that loop quantum gravity allows for is one of the topics up for discussion at this year’s Loop ’15 conference from 6 to 10 July, which is being hosted by the Institute of Quantum Gravity. The participants will include renowned researchers such as Prof. Abhay Ashtekar, Prof. Carlo Rovelli and Prof. Lee Smolin, who are considered the founders of loop quantum gravity. Lee Smolin is also well known among a wider audience thanks to his popular science books, such as ‘Time Reborn: From the Crisis in Physics to the Future of the Universe’. The conference’s programme includes longer plenaries that provide an overview of topics such as current research in quantum gravity and short parallel sessions in which young researchers in particular have the opportunity to present their latest findings.

Further information on the event is available at www.loops15.de.

### Further information

Prof. Dr. Kristina Giesel

Phone: +49 9131 8528470

kristina.giesel@gravity.fau.de

Prof. Dr. Hanno Sahlmann

Phone: +49 9131 8528465

hanno.sahlmann@gravity.fau.de