Derivative of Solid Angle: Lightmann & al. Explained

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SUMMARY

The discussion centers on the derivative of solid angle as presented in Lightmann et al.'s "Problem Book in Relativity and Gravitation." The expression for the derivative is given as dvxdvy, where v represents speeds. The solid angle is defined as dvxdvy/v², but in the context of photons, where speed v equals the speed of light (c = 1 in natural units), this leads to a specific interpretation of the solid angle derivative in relativistic physics.

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  • Familiarity with natural units in relativity
  • Basic knowledge of derivatives in calculus
  • Concept of photon behavior in relativistic contexts
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hello
please see attached snapshot from the book of Ligthmann & al. (problem book in relativity and gravitation).
Can somebody please explain the expression for the derivative of the solid angle ?
here it is given as dvxdvy where the v's are speeds !
How come this is so ?
Thanks,
 

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The solid angle is dvxdvy/v2 but the problem is about photons so v = c = 1 in natural units.
 
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