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Homework Statement
Show the Lorentz-Invariance of the following spatial statement: Two photons are traveling parallel to each other. The relative position vector of the two photons is orthogonal to the velocity and has length d.
Homework Equations
/ The attempt at a solution[/B]The first thing that comes to my mind is to represent the two photons with 4-Momentum Vectors.
So this is done the following way:
[itex]p_1=\hbar k=\hbar \left(\omega,k,0,0\right)[/itex]
[itex]p_2=\hbar k=\hbar \left(\omega,\alpha k,0,0\right)[/itex]
Now I need a 4-vector that connects the two photons. It is easy to see that the spatial component of that vector is just
[itex]\vec{d}=\left(0,0,d\right)[/itex]
But I am not sure what the first (time) component of that corresponding 4-vector would be?
From here on I guess it is simple. All I need to do is show that under a Lorentz-Transformation for arbitrary [itex]\vec{v}[/itex] the four-momentum of the photons is always orthogonal to the relative position vector. I might be wrong here.
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