It's all relative

In the previous message we mentioned an interesting article on relativity: Relativity at the centenary, which pointed out that gravitational physics has become an experimental science. There's a lot going on with studies of black holes, the search for gravitational waves, detailed tests of special and general relativity. And on the theoretical side, there's a lot of activity in the (as yet still unsuccessful) quest for a theory of quantum gravity.

Of course, the theory of relativity is intimidating to a lot of people, but it doesn't need to be. Special relativity actually involves little more that basic physics (ideas like mass, velocity, force, energy) and high school algebra with rudimentary calculus. The mathematics needed for general relativity is somewhat more sophisticated. But the basic concept described by the math is pretty simple: concentrations of matter cause space to curve, and the motion of two (or more) massive objects that interact gravitationally can be understood as "straight lines" in the curved space.

Once you've read some overviews, like the Wikipedia articles just referred to, you will have the basic ideas needed to learn more about relativity. Fortunately, there's an excellent online reference with a large number of review articles that explain in more detail many of the most interesting topics in the contemporary theory of relativity. It's called Living Reviews in Relativity -- and it's all free.

The journal, which covers both theory and experiment, is now in its 9^th year. Some of the articles are valuable for understanding basic topics in cosmology. Here are some of the more generally accessible articles:

• Loop Quantum Gravity (1998)
  
• Stationary Black Holes: Uniqueness and Beyond (1998)
  
• The Cosmic Microwave Background (1998)
  
• Gravitational Wave Detection by Interferometry (2000)
  
• The Cosmological Constant (2001)
  
• Computational Cosmology: From the Early Universe to the Large Scale Structure (2001)
  
• The Thermodynamics of Black Holes (2001)
  
• Experimental Searches for Dark Matter (2002)
  
• Gravitational Waves from Gravitational Collapse (2003)
  
• Testing General Relativity with Pulsar Timing (2003)
  
• On the History of Unified Field Theories (2004)
  
• Quantum Gravity in Everyday Life: General Relativity as an Effective Field Theory (2004)
  
• Brane-World Gravity (2004)
  
• Measuring our Universe from Galaxy Redshift Surveys (2004)
  
• Quantum Gravity in 2+1 Dimensions: The Case of a Closed Universe (2005)
  
• Modern Tests of Lorentz Invariance (2005)
  
• Binary and Millisecond Pulsars (2005)
  
• Loop Quantum Cosmology (2005)
  
• The Confrontation between General Relativity and Experiment (2006)
  

Note that there have been updated versions of some articles. In each case, only the most recent update (as of this writing) and its corresponding date are listed.

Tags: relativity, special relativity, general relativity, black holes, quantum gravity, pulsars