We all know that when the flashlight is turned on, we will see a beam of light projecting out. So the question is, if the flashlight is turned off, will the light disappear or continue to spread?
In fact, you may have tried this small experiment countless times, but you should not yet figure out whether the disappearing light exists. In fact, the answer to this question requires knowledge in physics.
First of all, we need to understand what light is? Light is a physical noun. It can propagate in various media such as air, water, vacuum, etc., and light can propagate in a uniform medium along a straight line. However, according to Einstein's theory of relativity, because light will be affected by the strong gravitational field of an object, the propagation path of light will undergo reflection, refraction, diffraction and other phenomena.
The first to discuss the essence of light was the Roman scientist Lucrecius, who first proposed the concept that light is a very small particle, which also laid the theoretical foundation for the particle theory of light. However, predecessors have discussed and summarized optical laws, but have not risen to the essential level of studying light. But it was not until the early 20th century that the nature of light had a specific concept. Physicists defined the nature of light as a stream of photons in a specific frequency band, mainly a phenomenon generated after the electrons are excited.
But do you know how light can be seen by humans? This is definitely indispensable for the assistance of light sources. Any object in the universe that can emit light and is emitting light is called a light source, and the electrons in the light source can obtain additional energy, mainly releasing energy in the form of electromagnetic waves. This is exactly the same as the way sunlight releases energy, both of which releases energy through electromagnetic waves. Light sources can also be divided into natural and artificial light sources, just like the sun, electric lights are light sources.
In fact, the flashlight emits the same principle as the human being able to see objects during the day. Both are derived from stimulated radiation. This is because external energy intake, the luminescent body will actively absorb energy and then release a large number of high-energy electrons. The objects seen by humans are transmitted to the human eyes through photon reflection.
If the flashlight is turned on at night, a beam of light will appear, and a bright light will be found on the wall. This is because a series of photons are released, which will be refracted to the wall soon, and then the external electrons on the wall will be released, so you can see the light from the flashlight shining directly on the wall. But if light is shot into the night sky, some photons will be absorbed by the air. Although light can theoretically spread infinitely, where can light eventually spread? The answer is in a vacuum, because light can travel about 10 billion light years, and it can spread all the time as long as it does not encounter an object. However, some unknown substances will randomly be generated in the vacuum. If these substances are encountered during transmission, the transmission will be greatly affected.
In addition, when humans turn off the flashlight, they can no longer see any light, but this must be analyzed according to different situations. Once the light source disappears, the photons will be absorbed by low-speed objects, making it difficult to continue to emit new photons. But if the light source is turned off in a vacuum, as long as there is no obstacle, even if the light source is turned off, the emitted photons will continue to spread. In other words, the photon will not disappear out of thin air. It is a kind of energy release. It is not visible at present, but it is only released because it is absorbed by other electrons.
In fact, if any energy decay is not taken into account, the propagation of light will be hindered to a certain extent. This is because the universe is not endless. The stars seen by humans and the planets observed by scientific instruments may collide with light, which will lead to energy loss. Therefore, it is impossible for light to spread all the time to the end of the universe.
