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# Complete list of spotlights

## Complete Spotlights

Black holes, cosmology, gravitational waves - our "Spotlights on Relativity" section invites you to take a look at some of the many facets of relativity. The following is a complete list of all our current spotlight texts. All but a few of these texts are completely independent of each other, so you can browse to your heart's content - it would help, however, if you already had some previous ideas about relativity, on the level of our introduction Elementary Einstein.

## Special relativity

More about the foundations and applications of special relativity.

## Waves, motion and frequency: the Doppler effect

How motion influences waves, or other kinds of ever-repeating signals, in classical physics and in special relativity.

## The dialectic of relativity

How relativity can reconcile statements that, at first glance, appear to be contradictory

## Special relativity and time

More about simultaneity, time dilation and the famous case of the travelling twin

## The definition of "now"

Why it is necessary to define simultaneity, and how best to go about defining it.

## Time dilation on the road

How you can picture the relativity of simultaneity and time dilation, using a simple geometric analogy

## The case of the travelling twins

Why the so-called "twin paradox" isn't really a paradox

## Twins on the road

How one can picture the situation of the travelling twin, using a simple geometric analogy

## Energy and mass

Some background information about the most famous formula in all of physics

## Is the whole the sum of its parts?

Why Einstein's famous formula tells us that the whole, as far as mass is concerned, is often less than the sum of its parts

## From E=mc² to the atomic bomb

The subtle connections between Einstein's formula, nuclear fission and nuclear fusion

## General relativity

Concepts and applications of general relativity

## The elevator, the rocket, and gravity: the equivalence principle

Information about the principle that Einstein took as a starting point for developing his general theory of relativity

## Gravity: from weightlessness to curvature

So what is gravity in Einstein's theory? The answer: in part, an illusion; in part, an aspect of geometry.

## ...that all coordinate systems are created equal

Why, in general relativity, all observers are on an equal footing - and why, nevertheless, you can say that the earth orbits the sun, but not the other way around

## Mass and more

An account of which physical properties act as sources of gravity - includes consequences for collapsing stars and for cosmology

## The gravity of gravity

An important property of gravity in Einstein's theory is that it can create more gravity. The result is "non-linearity" - the gravitational influence of two bodies isn't just the sum of their separate influences!

## Gravitational deflection of light

On one of the fundamental consequences of general relativity: the deflection of light by gravity

## The equivalence principle and the deflection of light

The connection between one of the fundamental principles of general relativity and the gravitational deflection of light

## A brief history of gravitational lensing

Historical sketch of the derivation of general relativity's prediction of gravitational lenses and subsequent astronomical observations

## Gravitational redshift and White Dwarf stars

One of the fundamental effects predicted by general relativity, and some of its astronomical applications

## Spacetime singularities

Information about the most disturbing feature of Einstein's theory - ragged edges of spacetime known as singularities.

## Of singularities and breadmaking

About some characteristic properties of spacetime near singularities - and the violent deformations they cause for any object unlucky enough to approach a singularity

## The realm of relativistic hydrodynamics

Modeling relativistic fluids and the phenomena associated with them - from supernovae and jets to merging neutron stars

## Varying Newton’s constant: A personal history of scalar-tensor theories

Information about a modification of Einstein's theory of general relativity in which the gravitational constant is not a constant.

## From soap bubbles to Einstein

Most readers will know them from childhood: soap bubbles

## The many ways of building an empty, unchanging universe

More information on one particular answer to the question of how much variety is permitted in general relativity - how many ways are there of constructing a universe that is completely empty of all matter?

## Einstein's Nobel heritage

An overview of Nobel prizes connected with relativistic physics

## Gravitational waves

More about gravitational waves, how they are produced and how they can be detected

## The wave nature of simple gravitational waves

A closer look at the way that simple gravitational waves propagate through space with time

## Chirping neutron stars

For some gravitational wave signals, one can go beyond graphs and animations - they can be made audible

## White Dwarf binaries as gravitational wave sources

White Dwarf binaries, their properties, and the role they will play for the planned space-borne gravitational wave detector LISA.

## On the road to detection

More about gravitational wave detectors on earth and in space

## Listening posts around the globe

Overview of the gravitational wave detectors currently operational, or under construction

## Einstein@Home - gravitational waves for everybody

Informations about how you personally can help with the search for gravitational wave - by donating processing time on your private computer

## Catching the wave with light

Some information on how interferometric detectors such as LIGO or GEO600 work

## Small vibrations

Some information on how the vintage models among gravitational wave detectors work - resonant detectors

## eLISA - Hunting waves in space

Information about the latest version of the most ambitious gravitational wave project - a detector in space

## Observation of Gravitational Waves from a Binary Black Hole Merger

One hundred years ago, Albert Einstein predicted in his general theory of relativity the existence of gravitational waves. These ripples in space-time propagate at the speed of light and were directly observed for the very first time on September 14, 2015.

## Of gravitational waves and spherical chickens

Information about a class of simple model universes, each an expanding cosmos filled with gravitational waves

## Black Holes & Co.

Black holes, neutron stars and supernovae: Flight into a black hole, the black hole in the center of the Milky Way, how many different kinds of black hole are there, how black holes light up their neighbourhood

## Descent into a black hole

The story of an expedition's closer and closer approach to a black hole - too close?

## How to track compact objects

More about the gravitational influence of black holes and neutron stars on their cosmic surroundings, from the orbits of nearby stars to accretion disks and the associated luminous phenomena.

## The dark heart of the Milky Way

Information about the closest supermassive black hole - the central object of our own galaxy

## Luminous disks: How black holes light up their surroundings

How the fact that black holes are very efficient in attracting surrounding matter leads to some of the most spectacularly luminous phenomena in the whole of the cosmos

## Active black holes: Ultra-hot cosmic beacons

What astronomers can see once a black hole has heated up its cosmic neighbourhood, stimulating it to emit bright radiation

## How many different kinds of black holes are there?

Once they have settled down, there are actually only very few different kinds of black hole - find out which, and how black holes shed other distinguishing marks.

## 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

## Changing places - space and time inside a black hole

How, in one sense, space and time switch their roles inside a black hole - and why this leads to a black hole's most characteristic property, namely that nothing can get out

## What figure skaters, orbiting planets and neutron stars have in common

Some information about what is called the conservation of angular momentum, and its consequences for neutron stars, black holes and the matter disks around them

## Heat that meets the eye

The connection between temperature and the emission of electromagnetic radiation, as well as the consequences for stars, matter disks around black holes, and cosmology

## Cosmology

The big bang and all the rest: The geometry of the universe, the formation of the first light chemical elements, cosmology and quantum gravity

## A tale of two big bangs

In cosmology, "big bang" has two different meanings - and if you want to understand what's going on, you should be aware of that difference.

## The shape of space

The different space geometries allowed by the big bang models - do we live on a hypersphere?

## The mathematical universe

Why cosmology is not only a matter for astronomers and physicists, but also for mathematicians

## Cosmic Sound: Curvature and the cosmic background radiation

How the spatial geometry of the universe can be derived by observing the cosmic background radiation

## Big Bang Nucleosynthesis: Cooking up the first light elements

How the first nuclei of helium, lithium and other light elements were cooked up shortly after the big bang

## Equilibrium and Change: The physics behind Big Bang Nucleosynthesis

The physics behind Big Bang Nucleosynthesis, the period shortly after the big bang that saw the first production of light elements such as helium and lithium

## Elements of the past: Big Bang Nucleosynthesis and observation

How to reconstruct the abundances of light elements shortly after the big bang, and thus test some important predictions of the big bang models against observation

## Cosmology and quantum gravity

More information about possible cosmological consequences of the attempts to formulate a theory of quantum gravity.

## Searching for the quantum beginning of the universe

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

## 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

## Heat that meets the eye

The connection between temperature and the emission of electromagnetic radiation, as well as the consequences for stars, matter disks around black holes, and cosmology

## 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

## 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.

## The fabric of space: spin networks

The quantum structure of space according to loop quantum gravity

## 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

## 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

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