# Relativity and the Quantum

Relativistic quantum theory, string theory, loop quantum gravity and other attempts to unify Einstein’s gravitation with quantum theory; the uses of extra dimensions; quantum gravity and the big bang

**This page features an overview of all our spotlight texts dealing with the interplay of relativity and quantum theory – relativistic quantum theories as well as string theory, loop quantum gravity and other attempts to unify Einstein’s theory of gravity with quantum theory. The spotlight texts already completed deal with General aspects of quantum gravity as well as with String theory, Loop quantum gravity as well as with Other approaches to the problem of quantum gravity. Physics in the background is the heading for texts providing background information that is helpful for a better understanding of the spotlight texts presented on this page.**

**Useful background information can be found in our introduction Elementary Einstein, especially in the chapter Relativity and the quantum.**

## General aspects of quantum gravity

Some aspects of quantum gravity that are independent of which of the possible approaches is chosen.

### Actors on a changing stage: quantum gravity and background independence

The principle of background independence – space and time are no fixed structure, but take part in the dynamical evolution of the world – and its consequences for the problem of quantum gravity

## String theory

More about string theory – at present, mostly about the extra dimensions that play such a central role in that theory

### Extra dimensions – and how to hide them

Why our universe could possess dimensions beyond length, width and depth – and why those dimensions need not be noticeable in everyday life

### The embedded universe

Is our three-dimensional world embedded in a higher-dimensional space?

### Particle accelerators as black hole factories?

The intriguing possibility that the next generation of particle accelerators might produce – and allow the detection of – miniature black holes

### Hunting for extra dimensions

Ways of detecting extra dimensions – and why the fact that our earth orbits the sun is a relevant data point

### Simplicity in higher dimensions

Why matters that seem rather complicated might be much more simple in higher dimensions

## Loop quantum gravity

More about loop quantum gravity, in particular its cosmological applications.

### Avoiding the big bang

The collapsing and then re-expanding quantum universe that loop quantum gravity offers as a replacement of the standard big bang models

### Taming infinity with loops

How loop quantum gravity could replace the absurd state of infinite density, the big bang with which, according to Einstein’s relativity, the universe began

### The fabric of space: spin networks

The quantum structure of space according to loop quantum gravity

## Other approaches to the problem of quantum gravity

While string theory and loop quantum gravity are the most prominent approaches to the problem of quantum gravity, they are not the only ones. Some other approaches are described in the following spotlights.

### Searching for the quantum beginning of the universe

About attempts to understand the beginning of our universe using different approaches to quantum gravity

### Geometry from order: causal sets

An overview of the causal set approach to a theory of quantum gravity

## Physics in the background of quantum theory

Useful physics background information that may help with a better understanding of the other spotlight texts on this page.

### The sum over all possibilities: The path integral formulation of quantum theory

About the path integral approach to quantum theory