phantoms

Phantoms are beings or phenomena perceived as real but lacking physical presence. The term derives from phantasma, meaning an image or apparition, and has been adopted across cultures and disciplines to describe supernatural apparitions as well as nonphysical representations used in science and technology.

In folklore and popular culture, phantoms are often depicted as spirits of the dead, haunting places or objects. They may be described as translucent or shadowy, and their behavior ranges from benign to malevolent. The term is sometimes used more loosely than "ghost," and in fiction it can refer to psychological or symbolic projections rather than literal entities.

In medicine and medical physics, phantoms describe models that simulate human tissue for calibrating and testing imaging devices, such as CT or MRI scanners. Separate from this, the phantom limb phenomenon describes persistent sensations, including pain, in a limb that has been amputated or is otherwise absent. Phantom concepts also appear in audio engineering as phantom power, a method of delivering electrical power through audio cables to condenser microphones.

In physics and cosmology, phantom energy is a hypothetical form of dark energy with an equation of state below minus one, which would imply unusual properties such as violation of certain energy conditions and potentially a future cosmic "Big Rip." The term phantoms in this sense is descriptive rather than normative.

While the precise meaning of phantoms varies by field, the common thread is the idea of nonphysical, elusive, or synthetic presence.