Why cosmology is not only a matter for astronomers and physicists, but also for mathematicians. How the spatial geometry of the universe can be derived by observing the cosmic background radiation. How the first nuclei of helium, lithium and other light elements were cooked up shortly after the big bang. 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.

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

About attempts to understand the beginning of our universe using different approaches to quantum gravity. The collapsing and then re-expanding quantum universe that loop quantum gravity offers as a replacement of the standard big bang models.

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

More about string theory - at present, mostly about the extra dimensions that play such a central role in that theory. Why our universe could possess dimensions beyond length, width and depth - and why those dimensions need not be noticeable in everyday life.

Is our three-dimensional world embedded in a higher-dimensional space? Ways of detecting extra dimensions - and why the fact that our earth orbits the sun is a relevant data point. Why matters that seem rather complicated might be much more simple in higher dimensions. More about loop quantum gravity, in particular its cosmological applications. The quantum structure of space according to loop 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. An overview of the causal set approach to a theory of quantum gravity. Useful physics background information that may help with a better understanding of the other spotlight texts on this page.

## Special Relativity

About the path integral approach to quantum theory. Legal notice Impressum Datenschutzhinweis. Main Navigation Home. Elementary Einstein. Spotlights on relativity. Special relativity. General relativity. Gravitational waves. Relativity and the Quantum. Complete list of spotlights.

## Why is Einstein's general relativity such a popular target for cranks?

Further reading. About Einstein Online. Einstein Online is provided by the.

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. Cosmology Relativity and the Quantum. Special relativity More about the foundations and applications of special relativity. Basics 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 Read More….

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 Read More…. The case of the travelling twins Why the so-called "twin paradox" isn't really a paradox Read More….

Twins on the road How one can picture the situation of the travelling twin, using a simple geometric analogy Read More…. 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 Read More…. General relativity Concepts and applications of general relativity. The basics 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 Read More….

Gravity: from weightlessness to curvature So what is gravity in Einstein's theory? Mass and other sources of gravity Mass and more An account of which physical properties act as sources of gravity - includes consequences for collapsing stars and for cosmology Read More…. The gravity of gravity An important property of gravity in Einstein's theory is that it can create more gravity. Light in general relativity Gravitational deflection of light On one of the fundamental consequences of general relativity: the deflection of light by gravity Read More….

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 Read More…. A brief history of gravitational lensing Historical sketch of the derivation of general relativity's prediction of gravitational lenses and subsequent astronomical observations Read More….

Gravitational redshift and White Dwarf stars One of the fundamental effects predicted by general relativity, and some of its astronomical applications Read More…. Singularities 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 Read More….

Numerical relativity The realm of relativistic hydrodynamics Modeling relativistic fluids and the phenomena associated with them - from supernovae and jets to merging neutron stars Read More…. The mathematics behind general relativity From soap bubbles to Einstein Most readers will know them from childhood: soap bubbles Read More….

### Why People Didn't Believe Einstein

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? Gravitational waves More about gravitational waves, how they are produced and how they can be detected. Basic properties The wave nature of simple gravitational waves A closer look at the way that simple gravitational waves propagate through space with time Read More….

Gravitational wave sources Chirping neutron stars For some gravitational wave signals, one can go beyond graphs and animations - they can be made audible Read More…. 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 Read More….

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 Read More…. Small vibrations Some information on how the vintage models among gravitational wave detectors work - resonant detectors Read More….

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. Cosmological applications Of gravitational waves and spherical chickens Information about a class of simple model universes, each an expanding cosmos filled with gravitational waves Read More….

Close encounters with black holes 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 Read More…. 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 Read More….

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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 Read More…. The physics of black holes How many different kinds of black holes are there?

## Will Quantum Mechanics Swallow Relativity?

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 Read More…. 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 Read More…. Physics in the background 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 Read More….

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 Read More…. 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. Basics 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 Read More…. The cosmic background radiation Cosmic Sound: Curvature and the cosmic background radiation How the spatial geometry of the universe can be derived by observing the cosmic background radiation Read More….