if you would like some background on this question, as I do, there is a SE discussion that makes it a bit easier... https://physics.stackexchange.com/questions

if you would like some background on this question, as I do, there is a SE discussion that makes it a bit easier... https://physics.stackexchange.com/questions/3189/is-the-abraham-minkowski-controversy-resolved https://physics.stackexchange.com/questions/3189/is-the-abra... There is a summary statement that I found to be especially helpful in framing the question: "To summarize... it's probably OK to "redo" the budget in such a way that a part of the momentum of the photon is attributed to the dielectric material when the photon enters it, and then it is returned back to the photon. In this way, one may justify the Abraham's form - and probably many other forms - but why should one really do it?"