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The connection between mass and energy: How did Einstein change our understanding?
In physics and chemistry, the law of conservation of mass or the principle of conservation of mass states that for any closed system, the mass of a substance must remain constant over time. This law means that mass cannot be created or destroyed, although it may be reorganized in space, or the entities associated with it may change form. In a chemical reaction, the mass of the chemical components before the reaction is equal to the mass after the reaction, so in a low-energy thermodynamic process in an isolated system, the total mass of the reactants must equal the mass of the products.
The concept of conservation of mass is widely used in many fields, such as chemistry, mechanics and fluid dynamics.
The idea of conservation of mass dates back to 520 BC, when Jain philosophy stated that the universe and its components could not be created or destroyed. This idea evolved over time and was finally confirmed in the 18th century when scientists discovered that changes in mass do not exist during chemical reactions. Antoine Lavoisier's experiments first clarified the principle of conservation of mass, showing that within a closed system, the total mass remains constant regardless of how the form of matter changes.
With the progress of science, the application of the law of conservation of mass in chemical reactions becomes increasingly important. For example, when one molecule of methane (CH4) and two molecules of oxygen (O2) are converted into one molecule of carbon dioxide (CO2) and two molecules of water (H2O), the masses before and after the reaction are equal, which is a clear example of the conservation of mass.
The establishment of this law and its importance in modern natural science marks the evolution from alchemy to modern chemistry.
Although the law of conservation of mass has become a scientific consensus, it does not always apply accurately in every situation. The equivalence between mass and energy, based on quantum mechanics and relativity, requires us to re-examine this basic idea. In a famous 1905 paper, Einstein introduced the principle of mass-energy equivalence, which states that mass and energy are actually two forms that can be converted into each other. The introduction of this concept has enabled us to no longer limit our understanding of the conservation of mass, but to begin to consider how energy interacts with mass at a deeper level.
Going further, Einstein's theory revealed that in high-energy systems such as nuclear reactions, mass exists only as a form of energy. This mass conversion can not only be observed in the laboratory, but also be demonstrated in many phenomena in the universe. For example, the explosion of an atomic bomb and the nuclear fusion reactions that occur in stars are direct evidence of the conversion of mass and energy.
The principle of mass and energy conversion has allowed us to reach a new level of understanding of the material world and has also enabled us to think about the deeper laws of the universe.
However, relativity's definition of conservation of mass is not global; on large scales in the structure of the Universe, the representation of mass and energy becomes complicated. Relativity introduced concepts such as rest mass and relativistic mass, which forced us to reconstruct our understanding of mass and energy. We begin to learn how to define these quantities in different reference frames and explore how they flow through the Universe.
Combining this knowledge, the progress of modern science depends not only on the principle of conservation of mass, but also on our constant challenge and rethinking of this principle. From ancient astronomical observations to modern particle physics, scientists have always been exploring the deepest truths of nature and seeking higher understanding.
How does the connection between mass and energy affect our technological future and the way we live?
