Although there are many kinds of force, modern science has proved that,natureThere are only four basic forces (or interactions) in. The other forces are different manifestations of these four forces.[1]These four forces are: gravityElectromagnetic interaction、weak interaction 、strong force 。[1]
In life, we can detect the buoyancy of sea water on the ship, the adhesive force of glue, the attraction or repulsion between magnets, etc.In addition to the forces we can perceive in the macro world, there are also forces of one kind or another in the micro world.For example, the attraction or repulsion between molecules or atoms, the attraction between electrons and nuclei in atoms, and the repulsion and attraction between particles in nuclei.[1]Although the types of forces are so complex, modern science has proved that there are only four basic forces (or interactions) in nature, and other forces are different manifestations of these four forces, which are gravity, electromagnetic force, strong force, and weak force.[1]
Type of force
Interacting objects
Strength of force
Range of force
Universal gravitation
All particles
ten-34N
Infinity
weak force
Most particles
ten-2N
Less than 10-17m
Electromagnetic force
charge
tentwoN
Infinity
Strong
Nucleons, mesons, etc
tenfourN
ten-15m
1、 Gravity
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Gravity refers to the attraction between any two particles of matter.Its law was first discovered by Newton and is called the law of gravitation. This law says that any two particles attract each other, and the magnitude of the gravitation is proportional to the product of their masses and inversely proportional to the square of their distances.[1]
Electromagnetic force refers to the force between charged particles or charged macroscopic objects.The force between two stationary charged particles is governed by a Coulomb law similar to the law of gravity.Coulomb's law says that two static point charges in vacuum repel or attract each other, and the magnitude of the repulsion or attraction
And two point charges
and
Is proportional to the product of
Is inversely proportional to the square of.[1]
The mathematical expression of electromagnetic force is:
[1]
among
and
Represent the electric quantity of two point charges respectively;
Represents their distance;
Is a scale factor, and its value is
[1]
The electromagnetic force is much larger than gravity, for example, the electric power between two adjacent protons can reach
Is the universal gravitation between them
Of
Times.[1]
Electric power and magnetic force are collectively referred to as electromagnetic force: in addition to electric force, there is also magnetic force interaction between moving charges. The electromagnetic force between charges uses photons as the transmission medium.Magnetic force is actually a manifestation of electric power. The relationship between electric field and magnetic field can be determined byMaxwell's equationsTo represent.[3]
The elastic force, friction force, fluid resistance, surface tension, gas pressure, buoyancy, adhesive force, etc. between the objects in contact with each other are the macroscopic manifestations of the forces between atoms or molecules that are close to each other, so they are also electromagnetic forces in essence.[1]
3、 Strong
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We know that there is more than one proton in most atomic nuclei.The electromagnetic force between protons is repulsive, but in fact, all parts of the nucleus do not fly away automatically, which indicates that there is a natural force stronger than the electromagnetic force between protons. It is this force that tightly binds protons and neutrons in the atomic nucleus.[1]This exists inproton、neutronThe force between hadrons such as mesons and mesons is called strong force.[1]
Strength is the expression of the force between the "color charges" carried by quarks - color force, which uses gluons as the transmission medium.[1]
Strong range
The distance between hadrons exceeds about 10-15M, the strength can become very small and negligible;Less than 10-15When the distance is about 0.4 × 10, the strength is dominant-15When the distance is smaller, the strength will be shown as repulsion.[1]
4、 Weak force
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Weak force is also an interaction between various particles, but it only shows its importance in some reactions among particles (such as beta decay).The weak force is expressed as W+,W-,ZzeroAnd so onIntermediate bosonAs a medium of transmission.[1]Its force range is shorter than the strength, and the force is very weak.The weak force between two adjacent protons is only about 10-2N。[1]
Unified theory of weak electricity
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In the 1960s, Grashaw, Weinberger and Salam were in theWeak interactionOn the basis of theory, through the differences in the apparent forms of electromagnetic action and weak action (for example, their strength, force process, and action time are different), we can gain insight into the identity of their internal essence (for example, they are universal, vector type interactions, all in the form of current - electromagnetic action presents electromagnetic current, weak action presents weak current).According to Yang Zhenning Mills gauge field theory, it has independently put forward the idea that electromagnetic action and weak action have unity, and established the weak current unified theory.[4]
Electromagnetic action is parity conservation, and weak action is parity nonconservation.They can be accommodated simultaneously by SU (2) × U (1) group, which has four generators, three of which are SU (2) and one of which is U (1).These four generators correspond to four weak charges carried by leptons and quarks and four basic gauge fields generated by them
。There is a scalar field called Higgs field in nature.The above four basic gauge fields are recombined in pairs in the interaction with the Higgs field.[4]
and
Intermediate vector boson field combined into two kinds of electrification
and
, they are coupled with the weak band current formed by charged particles;
and
Combined into electromagnetic field
And weak neutral field, that is, neutral intermediate vector boson field
They are coupled with weak band current and weak neutral current composed of neutral particles.[4]electromagnetic field
Charged intermediate boson field
And weak neutral field
The observable photon γ transmitting electromagnetic interaction and the charged intermediate boson transmitting weak interaction
、
And neutral intermediate boson
。
The lowest energy state of the field is called the ground state. When all fields overlapping in a certain space are in the ground state, it corresponds to the physical vacuum in the space range, and it does not show any physical effect of releasing energy.[4]In 1964, the British physicist Higgs introduced the concept of spontaneous breaking of vacuum symmetry in quantum field theory: when the field quantity of Higgs field is zero, its energy is not minimum;The field energy is the smallest when the field value is a nonzero value.In the physical vacuum state where the total energy of all fields reaches the minimum, the vacuum expectation value of the field quantity of the Higgs field is not zero in some directions, and the physical vacuum deviates from the state where the field quantity of all fields is zero, so it no longer has the invariance under the SU (2) × U (1) localized gauge transformation, that is, it no longer maintains the SU (2) × U (1) symmetry, which is called the spontaneous breaking of vacuum symmetry.[4]
The field quantum of Higgs field isSpin quantum numberThe scalar particle of zero, in which the particle with static mass is called Higgs particle;The particles without static mass are called Goldstone particles.Intermediate boson with weak interaction
and
Under the spontaneous breaking of the vacuum symmetry, it interacts with the Higgs field in the ground state, but the vacuum mean value of the field is not zero.Wave function of Goldstone particle of Higgs field, converted to weak field
and
Longitudinal component of, equivalent to
、
and
The Goldstone particle and its moving mass are absorbed, thus obtaining a large static mass.[4]
Because the force path of the interaction is inversely proportional to the mass of the gauge particle transmitting the interaction;And the greater the mass of the gauge particle, the weaker the role it transmits.Therefore, the weak action becomes a short-range action, and the effective strength is greatly reduced.Because the U (1) gauge symmetry corresponding to the electromagnetic interaction does not have the phenomenon of spontaneous vacuum breaking, there is no Higgs field interacting with the electromagnetic field, and the quantum photon of the electromagnetic field cannot obtain the static mass.The electromagnetic action still remains long range and strong.[4]
Standard model
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The standard model is a theory that describes the three basic forces, strong, weak and electromagnetic forces, and the basic particles that make up all substances.According to the standard model, particles are divided into two categories: fermions (including quarks and leptons) and bosons (including gluons, photons, W particles, Z particles, Higgs particles). According to the prediction of the standard model, there are 61 particles in these two categories.Except Higgs particle, other particles have been supported and verified by experimental data.[5]
Higgs particle is the last particle to be discovered in the standard model. It has zero spin, mass, no charge and is very unstable.[5]Higgs bosonIt was proposed in 1964 for the purpose of imparting mass to other elementary particles through spontaneous symmetry breaking in the non Abelian gauge theory.It is a key link in the long-term lack of validation of the particle standard model.[6]
stayStandard Model of Particle PhysicsNeutrinos are massless elementary particles.[7]Discovery by Japanese physicist Takashi Kajida and Canadian physicist Arthur McDonnellNeutrino oscillationPhenomenon, which proves that neutrinos have mass.In 2001 and 2002, the Canadian Sudbury Neutrino Observatory (SNO) published experimental results twice, confirming the solar neutrino oscillation.These two discoveries opened the door to new physics in the micro world and had a significant impact on the origin and evolution of the universe and celestial bodies.[7]
