In the calculation of the precession of Mercury's orbit, why is the stress-energy tensor equal to 0? There is energy and momentum at the location of the planet.
The part of the stress-energy tensor due to Mercury itself, at the position of Mercury, isn't just comparable to the part due to the sun. It's infinitely large compared to the part due to the sun, since the sun's stress-energy tensor there is zero.It seemed to me that if you are calculating an orbit (i.e. position, momentum etc.) of an object and the stress-energy tensor has components made up of the object's momentum, etc., then those components would be comparable to the things you are trying to calculate and hence not negligible..
I don't know what Orodruin intended when he said, "To a good approximation, the stress energy tensor is zero[...]" Doesn't make sense to me. Maybe he could clarify.Still a little confused. One answer is that it's a good approximation to set the stress-energy tensor to zero. The other answer is that it's a fundamental fact that an object is not affected by its own field.