Glad to see that you were able to explain to me the workings behind the "dummy index":smile: ! This also answers my question on why ##\eta^{\mu \nu }\partial _{\nu }\phi + \eta^{\mu \mu }\partial _{\mu }\phi## was incorrect to start with as I was replacing ##\rho## with an index that was...
Hi @Orodruin ! :)
My understanding is that in 1.151 we replaced ##\mu## with ##\rho## and ##\nu## with ##\sigma## which we called our dummy indices. I understand that in the line above 1.153 we consider the case where ##\delta _{\rho }^{\mu }## is equal to 1 which happens when ##\delta...
Homework Statement
Hello all !
Over the past few day's, I've been trying to understand how Sean Carroll comes to the conclusion that he does on equation 1.153. I've tried to look for various resources online but I still have trouble understanding how he is able to add both partial derivatives...