 Solution

ID: past-exam-of-the-symmetry-and-relativity-course-of-the-university-of-oxford/2017/2/c/b/solution

V_{CM} = \frac{c ^{2} p _{tot}}{E _{tot}} = (\frac{c}{2}, \frac{c}{2}, 0), ∣ V_{CM} ∣ = \frac{c}{2} .

A boost in this direction with

Γ_{CM} = 2

gives zero total spatial momentum and total energy

2 ℏ ω

. The constituent photons remain moving at

c

in that frame.

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