We are all familiar with the adjectives “longitudinal” and “transverse”. And not just familiar, but actively use them in everyday life. But when it comes to waves, no matter what - in liquid, air, solid matter or electromagnetic fields, a number of questions often arise. Usually, hearing the words "transverse and longitudinal waves", the average person represents a sinusoid. Indeed, vibrational disturbances on the water look just like that, so life experience gives just such a clue. In fact, the world is more complex and diverse: both longitudinal waves and transverse ones exist in it.
If in any medium (field, gas, liquid, solid matter) vibrations occur that transfer energy from one point to another with a speed that depends on the properties of the medium itself, then they are called waves. Due to the fact that the oscillations do not propagate instantaneously, the phases of the wave at the starting point and at any final phase with increasing distance from the source are increasingly different. An important point that should always be remembered: during the transfer of energy through vibrations, the particles themselves that make up the medium do not move, but remain in their balanced positions. Moreover, if we consider the process in more detail, it becomes clear that not only individual particles vibrate, but their groups concentrated in any unit volume. This can be illustrated by an example with an ordinary rope: if one of its ends is fixed and wave-like movements are made from the other (in any plane), then although waves arise, the material of the rope does not collapse, which would occur if particles moved in its structure.
Longitudinal waves are characteristic only of gaseous and liquid media, but transverse waves are also characteristic of solids. Currently, the existing classification divides all vibrational disturbances into three groups: electromagnetic, liquid, and elastic. The latter, as you might guess from the name, are inherent in elastic (solid) media, so they are sometimes called mechanical.
Longitudinal waves arise when particles of the medium oscillate, being oriented along the perturbation propagation vector. An example is a blow to the end of a metal rod with a dense massive object. Transverse waves propagate in a direction perpendicular to the exposure vector. The logical question is: “Why can only longitudinal waves arise in gases and liquid media”? The explanation is simple: the reason for this is that the particles that make up these media can move freely, since they are not rigidly fixed, unlike solids. Accordingly, transverse vibrations are fundamentally impossible.
The above can be formulated in a slightly different way: if in a medium the deformation caused by a perturbation manifests itself in the form of shear, tension and compression, then we are talking about a solid body for which both longitudinal and transverse waves are possible. If a shift is not possible, then the medium can be any.
Of particular interest are longitudinal electromagnetic waves (SEW). Although nothing theoretically prevents the occurrence of such fluctuations, official science denies their existence in the natural environment. The reason, as always, is simple: modern electrodynamics proceeds from the principle that electromagnetic waves can only be transverse. The rejection of such a worldview will entail the need to revise many fundamental beliefs. Despite this, there are many publications of experimental results that practically prove the existence of SEW. And this indirectly means the discovery of another state of matter, in which, in fact, the generation of this type of wave is possible.