1
vote
1answer
167 views

Lorentz Invariant Equation of Motion for Scalar Field

I'm trying to understand why you can't write down a first order equation of motion for a scalar field in special relativity. Suppose $\phi(x)$ a scalar field, $v^{\mu}$ a 4-vector. According to my ...
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1answer
368 views

Deriving the action and the Lagrangian for a free particle in Relativistic mechanics

My question relates to Landau, Classical Theory of Field, Chapter 2 - Relativistic Mechanics, paragraph 8 - The principle of least action. As stated there, To determine the action integral for a ...