What is the room made of?

The structure of space and time is studied by astrophysicists and quantum researchers

In classical physics, space has long been just a kind of stage on which matter, fields and forces act. He himself was made up of nothing and contributed nothing to this game. Albert Einstein changed the thought and connected space and time to an inseparable structure, space-time, which deforms depending on the objects present in it and in turn influences the paths of objects. Theorists can describe their geometry and thus gravity with the equations of general relativity, but they ask themselves new questions: Is space-time and its curvatures fundamental, or does it consist of something else? Some physicists now believe in a new way to find an answer. Your guess: Everything can be traced back to the interactions of the smallest pieces of information.

The universe as a computer
  1. Some scientists postulate connections between general relativity and the quantum mechanical effect of entanglement.

  2. The joint project "It from Qubit" brings together theorists from various disciplines. For example, string theory experts benefit from findings from quantum informatics and vice versa.

  3. The physicists have the first promising approaches to some open questions. They hope to get closer to a theory that combines quantum mechanics and relativity theory more quickly.

There is a spirit of optimism among the supporters of this approach. Hundreds of them work together as part of an international joint project founded in 2015 to bring their ideas to life in a new specialist discipline. The project is called "It from Qubit" (IfQ). Physicists want to derive "it" - meaning space-time - from qubits. This is the short form for quantum bits, a term from quantum informatics. Analogous to the electronic bits in conventional computers, qubits are a measure of information stored in quantum physics. The idea behind IfQ is the idea that cosmic processes could be programmed with some kind of code. If it were to be cracked, the quantum physical nature of gravity would be revealed. In July 2016, a meeting took place at the Perimeter Institute in Ontario, Canada, at which the IfQ organizers had expected around 90 registrations. There were more than 200, and the team eventually organized parallel events at other universities to bring everyone together.

This article is featured in Spectrum of Science February 2017

The project appeals to scientists from a wide variety of disciplines, on the one hand, for example, developers of quantum computers, on the other hand, those who deal with the theory of relativity. Researchers who would hardly think of working together on their own are specifically looking for a common denominator. The Simons Foundation in New York, a private funding institution of the US mathematician and multi-billionaire James Simons, founded IfQ in August 2015 and provided the project with a total of around ten million dollars over a period of at least four years to cover the regular meetings and the Fund the work of the coordinating scientists. Since then, IfQ has been gaining more and more attention in the research community and is networked there better and better. "We depend on intensive cooperation," explains the physicist Beni Yoshida, who works at the Perimeter Institute and for the IfQ. "The project deals with extremely important, but extremely complex questions. A single person could not handle it." Even experts with no connection to IfQ express themselves hopefully. As string theorist Brian Greene says, "If the work in this area goes as well as some expect, quantum information could spark the next revolution in our understanding of space and time. This is extremely exciting."

The idea that space-time could consist of something expands the picture of general relativity. There the geometry is a fundamental property. If it is now caused by something else, namely the qubits, the question shifts: What are these bits and what kind of information do they carry exactly? The physicists don't know. Amazingly, she doesn't seem to mind that much. Brian Swingle from the Stanford Institute for Theoretical Physics and also part of the IfQ team explains: "It is the relationships that count. It is less about the properties of the individual parts and more about how they organize themselves."

Entanglement as a builder of space-time

The key to such an organization is the quantum phenomenon of entanglement, in which two particles are linked together, even over great distances. Each of them can assume different states; but if you determine the value of one of the two objects with a measurement, that of the other is immediately clear. One of the lead scientists of the project, Vijay Balasubramanian from the University of Pennsylvania, explains the approach based on it: "Whatever the smallest building blocks look like, it is only the entanglements between them that stretch the cloth of space-time, so to speak. That is a relatively new and absolute one fascinating idea. "

The idea goes back to various discoveries made by theoretical physicists over the past decade. In 2013, in a widely acclaimed piece of work, Juan Maldacena and Leonard Susskind noted that two entangled black holes can create a wormhole, a kind of shortcut through space and time. Because of such findings, more and more physicists are investigating phenomena from quantum mechanics and relativity theory specifically for possible fundamental similarities.