Immortality in Full Metal Alchemist: Brotherhood is achieved through the Philosopher's Stone, which contains human souls.
The energy within a Philosopher's Stone can be used to calculate the energy of one human soul.
One human soul contains 654 terajoules of energy, equivalent to 156 kilotons of TNT.
To achieve immortality, one would need the energy of 351 exajoules, which is five times the amount of electricity generated worldwide in a year.
Obtaining the energy required for immortality would require a significant amount of resources, including uranium and knowledge of alchemy.