Dale

Mentor

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## Main Question or Discussion Point

If

My question arises because of the four-velocity, which always has magnitude c. So the sum or difference of two four-velocities will not generally be a four-velocity, but will it be a Lorentz invariant four-vector? If so, does it have any physical interpretation?

**a**and**b**are four-vectors then are k**a**and**a**+**b**also four-vectors?My question arises because of the four-velocity, which always has magnitude c. So the sum or difference of two four-velocities will not generally be a four-velocity, but will it be a Lorentz invariant four-vector? If so, does it have any physical interpretation?