If a farmer has three sheep in his herd then, of course, he would label them with unique names and distinguish them by their individuality (due to a slightly different feature). But the farmer with thousands of sheep in his herd would not do this. In this case, for the farmer they would all be just sheep. It is the same with other bodies, especially for elementary particles in physics. Thus, atomic and elementary particles (protons, neutrons, electrons, photons, neutrinos, etc.) are considered without individuality. However, depending on the problem which we are dealing with, there is a need to distinguish between particles of the same type in terms of velocity, position, etc. A concrete question of this kind would be: for how long would the photons released in the center of a star from nuclear reactions reach its surface?
Photon
Photon is an elementary particle, which presents the quantum of light and other electromagnetic radiations. The photon has mass, therefore light and other radiations have momentum and pressure. It always moves at the speed of light in a vacuum.
“Creation” of photons in stars
According to the theory of stellar evolution, which is mainly supported by confirmed laws of physics and by observations, stars are formed under the influence of gravity. Stars are born from collapsing clouds of gas and dust, called nebulae. Over the course of millions of years, we have a ball with great mass, which is called proto-star. The constant increase and compression of this mass lead to an increase in pressure and temperature, which is the largest in its center. Under these conditions, nuclear reactions began, marking the birth of the star. Nuclear reactions are the source of star energy. Stars emit this energy through the radiation of photons. So, photons are released by nuclear reactions, which are “created” in the star nucleus.
Why does a photon delay from the center of a star to its surface for thousands of years?
The Sun’s radius is close to 700,000 km. So, a “created” photon in its center, if it had the free path, would reach the surface within 2.3 seconds. In fact, photons “created” in the center of the Sun appear on the surface after 10,000 to 17,000 years. Why? This is because the path of a photon from the center to the surface is filled with matter, which has a high density. This matter is made up of elementary particles (photons and other particles), but especially with ions whose size is much larger than that of photons. Therefore, on the way to the surface, at best, the photon collides billions and billions of times, bending its path multiple times. But the photon can also be absorbed by these ions to be re-emitted in another case. There are statistical methods of how many collisions and how many zigzags will make a photon go up to the surface. And through these methods it has been concluded that photons from the center to the surface of the Sun make a path, which is passed within a time of 10,000, up to 17,000 years. This happens to all stars. A similar thing would happen to us if we were in the hall of a crowded station. Of course, the time we spend walking when the station is crowded is much longer than the time we move when the station is empty.
