 1. vadim_romansky says:

Well, how to say it… Energy is defined really differently in “school physics” and deep theoretical physics. But wherever several approaches are applied, the values obtained from different definitions are the same.

In school, energy is defined as the ability to do work, and in theology, it is defined as the integral of motion associated by Noether's theorem with invariance with respect to time shifts.

But the general essence, in simple terms, remains unchanged-a scalar quantity, which is a single measure of all movements and interactions

“Everything is energy” is nonsense, of course. It is more correct to say “everything has energy”

2. alexander_boronnikov says:

Energy is the equivalent of mass. In classical mechanics, it is expressed in terms of potential energy (for a body at rest). In relativistic theory, the very concept of “mass” becomes very vague and velocity-dependent.

Is “energy” a measure of the ability to do work?

I choked on my cigarette butt…

Why is it often said that “everything is energy”, and is this statement true?

Of course not. Even to justify laziness. Everything is matter and fields.

3. andrey_dyuk says:

I'll start at the end, perhaps.

1. No. The statement “everything is energy” is incorrect. There is a long-standing philosophical concept – the unity of matter and motion. Matter is inseparable from motion. Neither matter nor its motion is annihilated or added. Matter and motion exist only together. It is impossible to physically separate one from the other. It is from this impossibility that the “incomprehensible”, though obvious, conclusion follows : matter and its motion exist EVERYWHERE. In particular, space itself is a state of moving matter. At least for this reason, it is impossible to separate motion from matter (try to do this with space? 🙂

Actually, all the laws of conservation (momentum, energy…) are based on this unity of matter and motion. It is important to understand that the unity of matter and motion is the fundamental basis of all laws in general. Those laws themselves are formulated on the basis of observation of PHENOMENA. In other words, everything we know is different manifestations of just one fundamental property of nature-the unity of matter and motion. In this aspect, the statement ” everything is energy “(if taken literally) immediately points to a dead end.

1. About the difference in the concepts of “energy”.

The term energy originated in the framework of Newtonian mechanics. The mechanical equivalent is the ability to perform a certain amount of work to accelerate the mass of a material body. The term “work” here is almost equivalent to the term energy. It's not difficult. So you need to look at-and what is mass in Newtonian mechanics?

1. Mass (in Newtonian mechanics) is a measure of the inertia of a body. It is wonderful that PRACTICE always confirms – by the mass of a body, you can judge the amount of matter (tangible) in it! Just wonderful. Mass can be used as the equivalent of weight even on the Moon. To do this, you just need to use a lever scale, not a force meter. In other words, in the observed phenomena, the masses of material bodies are comparable! Even somewhere in the universe, where there is practically no gravity, the masses of bodies can be compared based on the acceleration that the “dimensional force”gives them. However.

The nature of inertia has not yet been determined. Although it is clear that this must be something from the interaction of the material body with space. But still, we don't know the nature of inertia. From what is obvious – we do not know the nature and mass, too. And without knowledge of nature, the term mass can only be used conditionally in the microcosm ( in quantum mechanics). And here's why.

1. We all know perfectly well that the mass of a material body is not equal to the sum of the masses (atomic) of the atoms included in this body. Actually, this is the history of the origin of the term “atomic mass “(atomic weight). It was immediately stated that this is not the same as the mass of a tangible (material) body. Atomic weights (masses) they were calculated based on almost different reactions. This can be found. In general, the term “atomic mass” is used only to compare atoms with each other. And to use the law of conservation of mass in relation to chemical reactions.

2. Quantum mechanics ALREADY started from the parameters of atoms. So it wasn't about “Newtonian mass”either. For example, it is known that the mass of any atom is less than the sum of the masses of the nucleons included in this atom.

3. And so the “defect” of the masses of nucleons combined into an atom dictates the iron condition – this can only be the case if part of the total movement of the nucleons that formed the atom is bound inside the atom and does not appear as a mass. So in quantum mechanics, “inside the term” mass”, it is no longer possible to ignore motion. Well, it (quantum mechanics) doesn't do that. It just takes into account the movement. Unlike Newtonian mechanics.

4. It turns out that there is no definition of the nature of mass, but what about energy? – Yes, so far, maybe it's better in no way. Motion is not separable from matter, and energy is a separate manifestation of the motion of matter. The term energy is convenient for practical application in the framework of phenomena that describe precisely the selected movement of material bodies. The nature of mass can be determined, but the nature of energy (the term) does not need to be determined. This is unnecessary. Nature does not use two tools where one is sufficient.

You might be interested.

https://infra-e.ru/products/structureofspaceandmatter

4. evgeny_lepeshev says:

Let's start with the fact that there is a law of conservation of energy and no one has canceled it, that this law is written using different formalisms does not change or cancel it.

There are two types of matter: matter and radiation, radiation can be considered energy, but matter cannot be, although there is an obvious mechanism for turning matter into radiation and, perhaps, there is a state of the Universe when everything is energy, i.e. when all black holes will evaporate, but we exist in the gravitational cycle of the Universe, so part of matter is matter.

5. kirill_kapitonets says:

Neither is true. Neither the third (as it is sometimes written: “energy is a general measure of various forms of motion”).

For starters, energy is a physical quantity, a calculated formula. It is not a substance. Therefore, “everything is energy” is absurd. Moreover: the energy is in principle defined up to an arbitrary constant.

Further:

Energy in physics is a scalar quantity determined by the parameters of motion, which is independent of time for closed physical systems.

In quantum mechanics (non – relativistic), the energy operator, the Hamiltonian, plays a special role.