How does the mass-energy of a dead grandfather differ from the mass-energy of a live one?
Pretty drastically. One is decaying in the ground, the other is moving about in search of a mate. Most people have no trouble telling the difference.
The total four-momentum may well be the same in both case, but the stress-energy-momentum tensor is different (the blood is moving in the live grandfather but not the dead one, etc., etc.)
How does the mass-energy of a dead grandfather differ from the mass-energy of a live one?
Pretty drastically. One is decaying in the ground, the other is moving about in search of a mate. Most people have no trouble telling the difference.
The total four-momentum may well be the same in both case, but the stress-energy-momentum tensor is different (the blood is moving in the live grandfather but not the dead one, etc., etc.)