Renormalization

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Renormalization is a technique in theoretical physics that is used to address divergences that arise in quantum field theories. In quantum field theory, particles are represented by fields that interact with each other, and the interaction strengths are described by coupling constants. When we calculate the behavior of these fields and their interactions, we often encounter infinities that arise from the mathematical formalism used in the calculations. These infinities can make the theory meaningless or impossible to work with.
Renormalization involves a process of redefining the physical quantities of the theory in a way that removes these infinities while still preserving the predictive power of the theory. The process involves separating out the "bare" quantities (which are the original, unrenormalized values) from the "physical" quantities (which are the observable quantities we can measure in experiments). The bare quantities are then adjusted by counterterms, which are chosen to cancel out the infinities that arise in the calculations.
The process of renormalization can be complex and involves a great deal of mathematical manipulation. However, it has been an essential tool in the development of modern particle physics, enabling us to make precise predictions for a wide range of phenomena, from the behavior of subatomic particles to the structure of the early universe.