People have long been accustomed to the fact that one of the characteristics of any matter is mass. It is inherent not only in such large objects as planets and stars, but also in their counterparts from the invisible microcosm - protons and electrons. Sir Isaac Newton at one time brilliantly proved the relationship of gravitational forces and mass, which the body possesses. In the framework of his theory, calculations of celestial mechanics are still being successfully performed. A time after the creation of Newton's theory, the need arose for its substantial refinement, since some phenomena remained inexplicable. A. Einstein solved this problem by formulating his “special theory”. Then the famous formula E = m * (c * c) appeared, indicating the relationship of energy, mass and speed of light. Applying the formula to particles, it quickly became clear that the mass of the photon (particles of light) is zero. At first glance, this contradicts common sense, but this is exactly the case. The mass of a photon at zero speed of its motion is zero. But when a particle overcomes 300 thousand km / s - it acquires the usual mass. However, recently it is believed that the mass of the photon is, nevertheless, zero. And the value that follows from the formula H * v = m * (c * c) is a relativistic mass. So what exactly is the mass of a photon? There is indeed a formula. Only it is more complex and the calculation is performed through the momentum of a given particle.
Since the energy E for the photon is equal to H * v, then the mass can be determined from the formula:
m = (H * v) / (c * c)
But since the photon, in fact, being light, cannot fundamentally exist at speeds less than “s” (300 thousand km / s), the mass found above is true only for the state of motion.
Momentum can be found through
p = (m * v) / sqrt (1- (v * v) / (c * c))
The presence of an impulse indicates energy. Indeed, if you put your hand under the sun's rays on a summer day, you can clearly feel the heat. This phenomenon can be explained through the transfer of energy by any particle having a certain mass moving at high speed. This is precisely what is observed in relation to light. Therefore, the mass and momentum of a photon are so important, although in this case it is not always possible to operate with familiar concepts.
At numerous forums on the Internet, there is debate about the nature of the world and how to make calculations. Obviously, the question of what is the mass of a photon cannot yet be considered closed. New models make it possible to completely explain the observed processes. This always happens in science: for example, at first Newton's theory was considered complete and logical, but it soon became clear that a number of corrections were needed. Despite this, nothing prevents already now using the well-known properties of the light flux: a person has learned to use instruments to see in the dark; supermarket doors automatically open in front of the visitor; optical networks made it possible to achieve previously unprecedented digital data transfer speeds; and special devices made it possible to convert the energy of sunlight into electricity.
Why does a photon at rest have no mass (and do not exist at all)? There are several explanations for this. First, this conclusion follows from the formulas. The second - since light has a dual nature (it is both a wave and a stream of particles), then, obviously, the concept of mass is completely inapplicable to radiation. The third is logical: imagine a rapidly spinning wheel. If you look through it, then instead of the needles you can see a certain fog, haze. But it is worth starting to reduce the speed of rotation, as the haze gradually disappears, and after a complete stop only spokes remain. In this example, haze is a particle called a "photon." It can be observed only in motion, and with a strictly defined speed. If the speed drops below 300 thousand km / s, then the photon disappears.