There's a straightforward physical theory: colossal magnetic fields + slightly diamagnetic materials (including a human body with small superconducting particle

There's a straightforward physical theory: colossal magnetic fields + slightly diamagnetic materials (including a human body with small superconducting particles) = magnetic levitation. But human bodies might contain paramagnetic and ferromagnetic particles too, and more importantly building magnets that are strong enough to levitate a corpse is an expensive and difficult engineering challenge.