We all know that the hydrogen atom contains a proton and an electron and is the simplest atom. The mass of the hydrogen atom should also be equal to the mass of the proton plus the mass of the electron.
But if you think so, you're dead wrong. The mass of a hydrogen atom is smaller than the mass of a proton and an electron combined. Why is that?
This needs to start with Einstein's mass-energy equation E=MC², which can also be expressed in another way: M=E/C², which tells us exactly what the mass in the formula means.
There is often a view on the Internet that mass and energy are equivalent, and that mass is a form of energy. In fact, this view is not rigorous, but it is just popularly understood.
So how to understand the formula M=E/C² more deeply?
As mentioned at the beginning of the article, the mass of a particle is usually not equal to the sum of the masses of the smaller particles that make up that particle. The mass of an object consists of two aspects: its composition (such as the protons and electrons of hydrogen atoms) and the way the object moves.
As a simple example, suppose there are two identical cars, then the mass of the cars after the movement will be greater. Why? Why does exercise lead to an increase in mass?
The car is in motion, which means that the internal engine of the car, various gears, etc. are in motion, so they all have kinetic energy, and the car is bound to generate heat during the movement, so that the microscopic particles that make up the car move more intensely, forming thermal energy, which can also be considered irregular kinetic energy.
The formula M = E / C² expresses exactly this: the kinetic energy, thermal energy, etc. inside the car can be used as part of the mass of the car, and the sum of these energies is divided by C², and the mass is obtained.
So the moving car will be more massive than the stationary car, but because the square of the speed of light is too large, even if the energy is very high, the increase in mass is very small, completely negligible, we are even less likely to feel the increase in mass.
In general, we will default to M is static mass (rest state mass), but we will not say static mass, the default is to replace with mass.
But we need to know that moving objects are usually more massive than resting objects.
To give another example, in the 1980s and 1990s, due to insufficient power resources, there were frequent power outages, and flashlights became a must-have for families. But did you know that when you turn on the flashlight, the quality of the flashlight becomes smaller, but the magnitude of the smaller is so limited that you can't feel it.
Why is it getting smaller?
Or is the same thing. The light emitted by the flashlight has energy, and this energy is always stored in the battery of the flashlight, and when it is emitted in the form of energy, the energy is reduced, which means that the mass will also become smaller.
Back to the question at the beginning of the article: Why is the mass of a hydrogen atom smaller than the mass of protons and electrons combined?
Because there is potential energy between protons and electrons. If the distance between the electron and the proton is infinite, the potential energy is zero. When protons and electrons are close to each other, the potential energy becomes smaller and negative potential energy appears. Although electrons have kinetic energy around the movement of protons, the negative potential energy and kinetic energy add up to negative, and the negative potential energy is greater.
According to the formula M=E/C², mass M is also negative, so the mass of hydrogen atoms is smaller than the sum of proton and electron masses.
So where do the most basic particles, such as electrons, and the quarks that make up protons come from? Related to the Higgs field, it can be seen that the elementary particles interact with the Higgs field and have potential energy.
Perhaps you should understand that the so-called "mass" is not an inherent thing, just an attribute, a form of energy, and energy is a more essential thing, not quality!