### Gravitational waves / Elementary tour part 3: Gravitational wave astronomy

Every single atom can radiate and absorb electromagnetic waves. The light reaching us from astronomical sources is a hodgepodge of little snippets of radiation, each snippet produced by one of the object's myriads of atoms. That's good news and bad news. ...

### Gravitational waves / Elementary tour part 2: Making waves

In our universe, gravitational waves are produced in many different ways. Almost every occasion in which masses are accelerated leads to the generation of travelling space distortions, be it two heavenly bodies orbiting one another or stellar matter ...

### General relativity / Elementary Tour part 4: The light side of gravity

For the propagation of light, Einstein's theory makes a clear prediction: Light is deflected by gravity. Just as test particles move on the straightest-possible lines in curved spacetime (i.e. on spacetime geodesics), so does light. The most basic example: ...

### Special relativity / Elementary Tour part 4: The speed of light

On the previous pages, relativity reigned supreme. Although we usually think of lengths and times as absolute, they turned out to be observer-dependent. On this page, the shoe is on the other foot. Ordinarily, we think of velocities as relative, but one of ...

### Cosmology / Elementary Tour part 4: A mysterious beginning

From the first millionth of a second on, the big bang models are on fairly safe ground. Standard theories of physics such as the standard model of particle physics tell the researchers how matter behaves under the temperature conditions in question, and the ...

### General relativity / Elementary Tour part 2: The cosmic dance

In this new picture, there is no gravitational force that masses exert on other masses. Instead, there are spacetime distortions. Spacetime in the presence of a mass is curved. In flat, empty spacetime, small test particles follow straight lines. However, ...