Clarification on mass-energy tensor and 4-velocity.

MathematicalPhysicist

I have next question, we have in the next printcreen the equation:
[tex]\frac{dU^b}{d\tau}=U^a \nabla_a U^b[/tex]
why is this right?
(the printscreen is from the book of Woodhouse in GR, page 34)

Thanks.

MathematicalPhysicist

Ok, I think I can see why this is right, we pick a frame where [tex]U^a=(1,0,0,0)[/tex].

Clumsy me.
:-)

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MathematicalPhysicist	Clarification on mass-energy tensor and 4-velocity. I have next question, we have in the next printcreen the equation: [tex]\frac{dU^b}{d\tau}=U^a \nabla_a U^b[/tex] why is this right? (the printscreen is from the book of Woodhouse in GR, page 34) Thanks. Attached Thumbnails