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I am reading Weinberg's book and in the part on symmetries he speaks about rays, and says basically that 2 vectors [tex]U,V[/tex] which are on the same ray can only differ by a phase factor [tex]\phi[/tex], so that [tex]U=e^{i\phi}V[/tex].

Is "ray" meaning "direction" here ? Can I rephrase it and say that 2 colinear vectors can only differ by a phase factor ?

Thanks for your help!

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# Ray vs vector

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