Referred pain, also called reflective pain, is pain perceived at a location other than the site of the painful stimulus. An example is the case of ischemia brought on by a myocardial infarction (heart attack), where pain is often felt in the neck, shoulders, and back rather than in the thorax (chest), the site of the injury. The International Association for the Study of Pain has not officially defined the term; hence several authors have defined the term differently.

Radiating pain is different from referred pain; for example, the pain related to a myocardial infarction could either be referred or radiating pain from the chest. Referred pain is when the pain is located away from or adjacent to the organ involved; for instance, when a person has pain only in their jaw or left arm, but not in the chest. Physicians and scientists have known about referred pain since the late 1880s. Despite an increasing amount of literature on the subject, the biological mechanism of referred pain is unknown, although there are several hypotheses.

Pain is a distressing feeling often caused by intense or damaging stimuli, such as stubbing a toe, burning a finger, putting alcohol on a cut, and bumping the "funny bone". Because it is a complex, subjective phenomenon, defining pain has been a challenge. The International Association for the Study of Pain's widely used definition states: "Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage." In medical diagnosis, pain is a symptom.

Pain motivates the individual to withdraw from damaging situations, to protect a damaged body part while it heals, and to avoid similar experiences in the future. Most pain resolves once the noxious stimulus is removed and the body has healed, but it may persist despite removal of the stimulus and apparent healing of the body. Sometimes pain arises in the absence of any detectable stimulus, damage or disease. Simple pain medications are useful in 20% to 70% of cases.

Philosophy of pain may be about suffering in general or more specifically about physical pain. The experience of pain is, due to its seeming universality, a very good portal through which to view various aspects of human life. Discussions in philosophy of mind concerning qualia has given rise to a body of knowledge called philosophy of pain, which is about pain in the narrow sense of physical pain, and which must be distinguished from philosophical works concerning pain in the broad sense of suffering. This article covers both topics.

Historical views of pain

Two near contemporaries in the 18th and 19th centuries, Jeremy Bentham and the Marquis de Sade had very different views on these matters. Bentham saw pain and pleasure as objective phenomena, and defined utilitarianism on that principle. However the Marquis de Sade offered a wholly different view - which is that pain itself has an ethics, and that pursuit of pain, or imposing it, may be as useful and just as pleasurable, and that this indeed is the purpose of the state - to indulge the desire to inflict pain in revenge, for instance, via the law (in his time most punishment was in fact the dealing out of pain). The 19th-century view in Europe was that Bentham's view had to be promoted, de Sade's (which it found painful) suppressed so intensely that it - as de Sade predicted - became a pleasure in itself to indulge. The Victorian culture is often cited as the best example of this hypocrisy.

Pain (typeset as PAIN) is a musical project from Sweden that mix heavy metal with influences from electronic music and techno. The project started out as a hobby project for front man Peter Tägtgren, whose idea was to fuse heavy metal with 1980s-inspired electro-industrial and techno influences. Tägtgren, who is also the vocalist/guitarist of Hypocrisy and producer of his own The Abyss studios, is the only current member.

Pain's self-titled debut was released in 1997, and since then Pain has released six more albums and a DVD. Starting with their second, all of Pain's albums have made the Swedish charts, thanks in large part to hit singles such as "End of the Line", "Shut Your Mouth", and "Same Old Song". In early February 2006, Blabbermouth.net reported that Pain had signed with Roadrunner Records. Currently, Pain is under the Nuclear Blast Records banner.

In 2008, Pain was on tour as a supporting performer for the Finnish symphonic power metal band Nightwish. During this tour singer Peter Tägtgren, drummer David Wallin, and bassist Johan Husgafvel were assaulted by a gang in Leipzig. Tägtgren received 10 stitches in his face, Wallin suffered a concussion and stitches to his head, and Husgafvel had his nose broken.

In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes:

Radiation is often categorized as either ionizing or non-ionizing depending on the energy of the radiated particles. Ionizing radiation carries more than 10 eV, which is enough to ionize atoms and molecules, and break chemical bonds. This is an important distinction due to the large difference in harmfulness to living organisms. A common source of ionizing radiation is radioactive materials that emit α, β, or γ radiation, consisting of helium nuclei, electrons or positrons, and photons, respectively. Other sources include X-rays from medical radiography examinations and muons, mesons, positrons, neutrons and other particles that constitute the secondary cosmic rays that are produced after primary cosmic rays interact with Earth's atmosphere.

Radiation is a process in which a body emits energy that propagates through a medium, or through empty space, to be absorbed by other bodies. Radiation may also refer to:

Physics

Ionizing (or ionising in British English) radiation is radiation that carries enough energy to free electrons from atoms or molecules, thereby ionizing them. Ionizing radiation is made up of energetic subatomic particles, ions or atoms moving at high speeds (usually greater than 1% of the speed of light), and electromagnetic waves on the high-energy end of the electromagnetic spectrum.

Gamma rays, X-rays, and the higher ultraviolet part of the electromagnetic spectrum are ionizing, whereas the lower ultraviolet part of the electromagnetic spectrum, and also the lower part of the spectrum below UV, including visible light (including nearly all types of laser light), infrared, microwaves, and radio waves are all considered non-ionizing radiation. The boundary between ionizing and non-ionizing electromagnetic radiation that occurs in the ultraviolet is not sharply defined, since different molecules and atoms ionize at different energies. Conventional definition places the boundary at a photon energy between 10 eV and 33 eV in the ultraviolet (see definition boundary section below).