Radio astronomy is currently undergoing a major revolution with the
introduction of digital phased arrays, of which LOFAR (Low-Frequency
Array) is the first of its kind. This new type of telescope lets one
explore an abundant range of signals and sources never "heard" before in
the radio: from the earliest phase of the universe to the most violent
explosions in space and down to relativistic particles hitting the Earth.
The foundation for the latter is the geosynchrotron effect which leads to
strong radio emission when an ultra-high energy cosmic particle hits the
earth atmosphere and interacts with the geomagnetic field. This effect was
predicted analytically and has now been modelled with a sophisticated
Monte Carlo code. To test this prediction, a LOFAR Prototype Station
(LOPES) has been installed at the "Forschungszentrum Karlsruhe" in Germany
next to the cosmic ray detector array "KASCADE Grande". The experiment now
has detected the radio emission from cosmic rays and confirmed the
geosynchrotron effect. The radio emission seems to be a faithful tracer of
primary particle energy and allows detection of rather distant and
inclined events. Future steps will be the installation of radio antennas
at the AUGER experiment to measure the composition of ultra-high energy
cosmic rays and the usage of LOFAR as a cosmic ray detector. Here an
intriguing additional application may be the detection of radio emission
from neutrinos and cosmic rays interacting with the lunar regolith. This
promises the best detection limits for particles above 10^21 eV and allows
one to go beyond current ground-based detectors.