Bringing the Supermarket to the Apocalypse Chapter 415: Energy (2)

Energy is one of the basic concepts of physics. From classic mechanics to relativity, quantum mechanics and cosmology, energy is always a core concept. ↑

In common language or popular science, energy refers to the energy that a system can release or obtain from it, which can be equivalent to doing a certain amount of work. For example, 1 kilogram of gasoline contains 12 kilowatt hours of energy, which means that if all the chemical energy in 1 kilogram of gasoline is released, it can do 12kwh of work.

Energy is a physical quantity that describes a system or a process in physics. The energy of a system can be defined as the sum of work from a zero-energy state to the current state of the system. How much energy a system has is not a definite value in physics, it changes with the description of the system. During the life activities of the human body, all life activities require energy, such as the synthesis reaction of material metabolism, muscle contraction, gland secretion and so on. And these energies mainly come from food. The nutrients contained in animal and plant foods can be divided into five categories: carbohydrates, lipids, proteins, minerals and vitamins, plus water into six categories. Among them, carbohydrates, fats and proteins can release energy through oxidation in the body. The three are collectively referred to as "productive nutrients" or "heat source substances."

The law of conservation of energy indicates that energy will not be created or vanished, it can only be transformed from one form to another, and the total amount of energy remains unchanged. Energy is a scalar quantity, not a vector, and no direction. As for positive matter and antimatter, it is not to say that mass has positive and negative, but the electrical properties of the atomic nucleus are opposite. After meeting, the mass is converted into energy. Any movement requires energy. There are many forms of energy, such as light energy, sound energy, heat energy, electrical energy, mechanical energy, chemical energy, nuclear energy, etc. As an example, observe the energy of a solid with a mass of 1kg:

In classical mechanics, its energy is the sum of work done from acceleration to static speed.

In classical thermal science, its energy is the sum of work done by heating the existing temperature from absolute zero.

In physical chemistry, the energy is the sum of the work added to the raw materials when synthesizing this solid.

In atomic physics, the energy is the sum of the work done from the state where the atomic energy is zero to the current state.

The energy contained in this solid can also be defined in the opposite way. Give two examples:

The internal energy of the solid is the sum of the work released by cooling it to absolute zero.

The atomic energy of the solid is the kinetic energy that releases its binding energy into the reaction product during nuclear fission or fusion reactions.

Although energy is a commonly used and basic physical concept, it is also an abstract physical concept.

In fact, physicists did not really understand the concept of energy until the mid-19th century. Before here, they were often confused with concepts such as force and momentum.

The energy requirement of the human body means that the body can maintain good health for a long time, and individuals with good body shape, body composition and activity level can achieve energy balance and can maintain the energy intake necessary to engage in productive labor and social activities. the amount.

In Einstein ’s special theory of relativity, energy is a component of four-dimensional momentum. In any closed system, when observing in any inertial system, each component of this vector (one of which is energy and the other three is momentum) will be conserved and will not change with time, the length of this vector will also be conserved (Minkowski modulus length ), The vector length is the rest mass of a single particle, and is also the constant mass (ie constant energy) of the system composed of multiple masses particle.

So as long as the observer ’s reference system has not changed, the conservation of energy in time in the special theory of relativity still holds true, and the energy of the entire system remains unchanged. The energy measured by observers in different reference systems will be different. But the energy value measured by each observer will not change with time. The constant mass is defined by the energy-momentum relationship, which is the minimum value of the system mass and energy that all observers can observe. The constant mass will also be conserved, and the values ​​measured by all observers are the same.

In quantum mechanics, the energy of a quantum system is described by a self-adjoint operator called the Hamiltonian operator. This operator acts in the Hilbert space (or wave function space) of the system. If the Hamiltonian operator is a time-invariant operator, as the system changes, the measurement of its occurrence probability does not change with time, so the expected value of energy does not change with time. The conservation of local energy under quantum field theory can be obtained by using the energy-momentum tensor operator and Noord's theorem. Since there is no global time operator in quantum theory, the uncertain relationship between time and energy will only be established under certain conditions, and the uncertain relationship between position and momentum is the essence of quantum mechanics. Different (see principle of uncertainty). The energy at each fixed time can be accurately measured without being affected by the uncertain relationship between time and energy, so even in quantum mechanics, energy conservation is a clearly defined concept.

Energy must obey the law of conservation of energy. According to this law, energy can only be changed from one form to another and cannot be produced or destroyed out of thin air. Conservation of energy is a mathematical conclusion drawn by the translation symmetry (translation invariance) of time.

According to the law of conservation of energy, the energy flowing in is equal to the energy flowing out plus the change in internal energy. This law is a fairly basic criterion in physics. According to the translation symmetry (translation invariance) of time, the laws of physics (theorems) hold at any time.

The law of conservation of energy is characteristic of many physical laws. From a mathematical point of view, the conservation of energy is the result of Noord's theorem. If the physical system satisfies continuous symmetry when it shifts in time, its energy (conjugate physical quantity of time) is conserved. Conversely, if the physical system has no symmetry when it shifts in time, its energy is not conserved, but if this system is considered to exchange energy with another system, and the resulting larger system does not change with time, the energy of this larger system will be Conservation. Since any time-varying system can be placed in a larger non-time-varying system, the conservation of energy can be achieved by appropriate redefinition of energy. For the theory of physics in flat spacetime, because quantum mechanics allows non-conservation in a short period of time (such as positive-reverse particle pairs), energy conservation is not observed in quantum mechanics, but in the special theory of relativity, the law of conservation of energy is converted into a prime Conservation law.

The law of conservation of mass energy means that in an isolated system, the sum of the relativistic kinetic energy and static energy of all particle remains unchanged during the interaction. The law of conservation of mass energy is a special form of the law of conservation of energy.

Energy, what Lin Feng is very eager for. If there is not enough energy, you ca n’t do anything. What you can do now is to continuously enhance your energy.