## Is the Klein-Gordon equation a wave equation?

The Klein-Gordon equation is the linear partial differential equation which is the equation of motion of a free scalar field of possibly non-vanishing mass m on some (possibly curved) spacetime (Lorentzian manifold): it is the relativistic wave equation with inhomogeneity the mass m2.

**What is Klein-Gordon equation for free particle?**

The equation describes all spinless particles with positive, negative, and zero charge. Any solution of the free Dirac equation is, for each of its four components, a solution of the free Klein–Gordon equation. The Klein–Gordon equation does not form the basis of a consistent quantum relativistic one-particle theory.

**What is the spin of a photon?**

Electrons and quarks (particles of matter) can have a spin of –1/2 or +1/2; photons (particles of light) can have a spin of –1 or +1; and Higgs bosons must have a spin of 0. Though particle spins are tiny, they have an impact on our everyday world.

### Why is a photon spin 1?

That’s because if you rotate polarizers by only 90∘, you will find that you can break photons down into two mutually exclusive populations of photons. That is geometrically possible only if the particle in question is a vector boson, that is, a spin 1 particle.

**Why do we need relativistic quantum mechanics?**

In physics, relativistic quantum mechanics (RQM) is any Poincaré covariant formulation of quantum mechanics (QM). This theory is applicable to massive particles propagating at all velocities up to those comparable to the speed of light c, and can accommodate massless particles.

**Is Schrödinger equation Lorentz invariant?**

Abstract. The Schrodinger equation is not Lorentz Invariant, so it cannot be applied to the wave functions of moving particles. However, the Classical Wave Equation is Lorentz Invariant and is also satisfied by particle wave functions.