This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: When one mentions "waves," we immediately think of a perturbation that propagates. This applies to waves on the shore, sound waves in the air or electromagnetic waves that we use to transmit information via optical fibers.
The same idea of propagating perturbations applies to gravitational waves (GWs), which entered the mainstream media a decade ago after their first direct detection. These are perturbations of the elastic fabric that we are all embedded in, called spacetime. It is as if waves do not like to stay still; on the contrary, they really like to move from the moment they are created.
However, there are some instances in which perturbations remain spatially localized, ignoring their propagating counterparts entirely, even when sharing the same space. These forever localized perturbations are called BICs (from bound states in the continuum). I discuss these in a new article published in Physica Scripta.
The bound part means something that is localized at some particular place (a set of spatial coordinates). A state is a configuration of a system. The continuum comes from quantum mechanics, the field in which BICs were first proposed in 1929.
Typical bound states of the wavefunction have negative and discrete energy values. Meanwhile, unbound wavefunctions are assigned positive energies, which form a gapless continuum. However, one can still postulate a localized wavefunction and calculate its corresponding potential.
Its energy will be in the continuum of positive energies. And voilà, a bound state in the continuum (of positive energies) is created. BICs have since expanded to different wave phenomena, such as acoustic waves in parallel plates, water waves in tubes, elastic waves in solids and electromagnetic waves in optical fibers or arrays of resonators.
Extract — continue reading at the source.
