The edifice of modern physics has two cornerstones: the theory of relativity and quantum mechanics, which govern the macrocosm and the microcosm, respectively.
Among them, the theory of relativity is almost "equivalent" with Einstein, and quantum mechanics also has Einstein's indelible credit, which is enough to show how great Einstein is!
At the beginning of the 19th century, Einstein successively proposed the great special theory of relativity and the general theory of relativity. Among them, the special theory of relativity states that the speed of light is the ultimate speed of the universe and the fastest speed at which any information, matter, and energy can travel.
At first, the idea of "speed of light limit" was difficult for the general public to accept, after all, people have the inherent impression that as long as an object is constantly exerted force, the object will always accelerate, which is also one of the essences of Newtonian mechanics.
However, after the birth of the special theory of relativity, the speed of light limit has been continuously verified by scientists in experiments, so it has gradually been accepted by the public.
But here is the question, why is the speed of light so special? How does light travel at the speed of light? And instantaneously, and what is the power of a photon to travel at the speed of light?
To find out the answer to these questions, we need to go deep into the microcosm.
Before we begin, we would like to emphasize that the speed of light does not refer to the "speed of light", the speed of light is the inherent speed of the four-dimensional space-time, which is only related to the four-dimensional space-time itself, and can be regarded as the speed at which the law of cause and effect is transmitted. It's just that people define the speed of light in terms of the speed of light in the first place, so this habit continues. In addition to photons, there are many velocities that are also the speed of light, such as gluons, gravitational waves, etc. Of course, the speed of light in a vacuum is equal to the speed of light, which is not accidental, but also inevitable.
To get back to the point, to understand why photons must travel at the speed of light, we first need to understand the Standard Model of particles.
There are many elementary particles in the Standard Model of particles, and these elementary particles took a long time to be discovered, and the first discovery came from Rutherford's famous experiment "Alpha Particle Bombardment Experiment", which gave us a clearer understanding of the atomic model.
Since then, physicists have been "drawing a scoop from a gourd", constantly using the collision between particles to find new elementary particles. As a result, many elementary particles were discovered, as many as hundreds.
The question is, so many particles feel too chaotic, how to classify them effectively? After in-depth exploration, physicists have finally established the Standard Model of Particles, which classifies the elementary particles that look unusually chaotic in detail.
In simple terms, all elementary particles fall into two main categories: fermions and bosons. Fermions are actually what we usually call elementary particles, such as electrons, quarks, etc. Bosons, on the other hand, are the elementary particles that bind fermions together and act like glue.
For example, elementary particles are like bricks, while bosons are like cement, and bricks are bonded together by cement to form tall buildings, which are macroscopic objects that we usually see.
There are four kinds of bosons, all of which belong to the canonical boson, which are gluons, photons, bosons, and gravitons, which are the propagators of strong force, electromagnetic force, weak force, and gravitational force, respectively, and these four forces are also the four basic forces of nature. The four canonical bosons are like glue that bind various fermions, and the four basic forces are transmitted by these four bosons. To emphasize, gravitons are still an illusion, and no evidence has been found for their existence.
Specifically, nucleons such as protons and neutrons are bonded together by gluons that transport strong interactions (strong forces) to form atomic nuclei. Whereas, the nucleus and electrons transmit electromagnetic force through photons to form atoms.
Seeing this, the partners should have a general understanding of the composition of microscopic particles, but what does all this have to do with photons and the speed of light?
If you think about it, you will find a fatal question: where does the mass come from with so many elementary particles? In other words, what is it that gives the mass to elementary particles?
According to the Standard Model of Particles, all elementary particles should have no mass and should travel at the speed of light. But in reality, this is not the case.
Physicists have calculated that 99% of the mass of matter comes from strong forces, or strong interactions. The three quarks bond together to form neutrons and protons through strong interactions, and protons and neutrons are also bonded together to form nuclei through strong interactions, and the mass of the nucleus is almost equal to the mass of the atom, and the mass of the electrons is so small that it is almost negligible.
For example, it is equivalent to a quark throwing a gluon around, and in the process it can show a huge amount of energy, which can also be understood as the energy that binds the quark or the proton neutron together, and this energy is actually nuclear energy.
According to Einstein's mass-energy equation, energy can also be expressed as mass, so 99% of the mass of an object actually comes from energy. But the question is the remaining 1% of quality, what is it exactly?
Theoretically, it must be the elementary particles themselves! Because in the Standard Model of Particles, in addition to the elementary particles, it is the interaction between the elementary particles. Since the strong interactions between particles make up 99% of the mass of matter, then the remaining 1% of the mass must come from elementary particles.
But as mentioned earlier, the Standard Model of Particles shows that elementary particles are supposed to have no mass, so why do they have mass, and how do they come about?
Physicists have proposed the famous Higgs mechanism, which suggests that there is another boson in nature, the scalar boson, that is, the Higgs boson, which gives mass to elementary particles.
What is a Higgs boson? To put it simply, the universe is full of Higgs fields, and the perturbations of the Higgs fields form Higgs particles. It can be understood in this way that the Higgs field is like a calm ocean, and when the sea is disturbed, it will become turbulent, and it will splash small water droplets, and those small water droplets are equivalent to Higgs particles.
How exactly do Higgs particles give mass to elementary particles?
In layman's terms, most elementary particles interact with the Higgs particle, decelerating and gaining mass in the process. In other words, elementary particles are supposed to travel at the speed of light, but now with the Higgs particle, they have to slow down and gain mass, that is, static mass.
But not all particles are blocked by the Higgs particle, for example, photons and gluons do not, so photons and gluons retain their original characteristics: they travel at the speed of light, and they are born at the speed of light, without any acceleration process, and the static mass is of course zero.
Whether or not it interacts with the Higgs particle depends on the intrinsic properties of the elementary particle, such as angular momentum, spin, etc.
Of course, there is no evidence, but do the Higgs particles really exist, physicists found evidence for the existence of the Higgs particles in 2012, and Higgs himself won the Nobel Prize in Physics for it!
Finish!