Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Radiation trapping, imprisonment of resonance radiation, radiative transfer of spectral lines, line transfer or radiation diffusion is a phenomenon in physics whereby radiation may be "trapped" in a system as it is emitted by one atom and absorbed by another. Physics is a natural science that involves the study of matter and its motion through spacetime, as well as all applicable concepts, such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the world and universe behave.