Cosmic Rays: Alien Invaders from Outer Space

Cosmic rays are microscopic, charged particles that permanently bombard Earth from outer space. 100 years after their discovery their origin is still a mystery. It is also not clear how cosmic rays can obtain energies that are sometimes billion times larger than what can be produced in the most powerful particle accelerator on Earth, the LHC, where the Higgs particle was discovered last year. Possible particle accelerators that nature provides are very exotic sites in the universe like exploding stars, massive black holes, gamma-ray bursts, and pulsars. To find out more about these enigmatic particles and their origin a number of experiments on ground and space have been put into operation over the past ten years and provide us with stunning results.  I will give an introduction to cosmic rays, how we detect them, what we have learned from recent measurements about the origin of cosmic rays, and how cosmic rays are used to test the foundation of modern physics.