How can absorbing the life force of human sacrifices to fuel spells decrease your own life span?

[Erebus]

Alchemy is a branch of magic practiced by witches that involves transmuting materials in the natural environment into various other materials through the use of mana, akin to the life force within humans. The relationship between mana and magic operates similarly to currency in trade and commerce. It revolves around the 1st law of alchemy known as equivalent exchange, in which the level of input to magic be matched by an equal amount of output resulting from said magic. In simplified terms, the amount of mana applied to a spell will determine how powerful the spell will be. The amount of mana content in a human being is determined at birth, ranging from power levels between 100 and 8999, with exceedingly rare individuals reaching levels over 9000. Mana level determine a person's magical potential and affinity. However, the average human cannot access their mana all at once, effectively killing them by draining their life force. Instead, and individual uses a limited amount of mana at one time, similar to how a human uses a limited amount of brainpower as needed to avoid over-stimulation, limiting their abilities.

When a person dies, the mana contained within the body is released in a metaphysical burst, quickly dissipating with no trace. A clever witch use this knowledge to capture that mana at the point of death and use it to fuel their own magic to make a stronger spell, or to create powerful magical items. Whenever a witch lacks the appropriate level of power for their usage, they have the option of using the power of others to amplify their magic. This is summed up within the 2nd alchemic law better known as the law of compound interest, in which the accumulation of mana from others (the sacrifice) added to the original principal (user's mana) leads to stronger magic. Due to this effect, ritual human sacrifice has become the holy grail of alchemy, providing for potentially unlimited returns in power, and has allowed for a black market to develop using living beings as magical resources.

There is a trade-off within the rules of magic that prevent this tactic from becoming a common occurrence, otherwise witches would be killing people left and right for power. This leads to the third rule, in that a witch who uses this tactic in turn shortens their own lifespan. However, this final rule sounds nonsensical, as absorbing the life force of others to empower yourself should increase one's own life by adding the years of the victim to your own. Instead, compound interest is working in reverse, as the user gains in power but decreases the number of years they have to live.

How can adding the life force of others to your own actually decrease your lifespan instead of increasing it?

 

[Queshire]

Gotta use your lifeforce in order to chain up the other person's lifeforce instead of actually using either to, ya know, live.

 

[shangrila]

I mean, there's a couple of different options.

My main thought is to view it like building a fire. Yes you can take the wooden logs off of an extinguished fire but on their own they do nothing. You'd require a spark (the witch's life energy) to actually reignite them (i.e., use them for the spell). Then you just give it a rough ratio, like 80-20 dead life to witch life force to explain why they'd bother going through with the whole procedure.

 

[Eduardo Ficaria]

How can adding the life force of others to your own actually decrease your lifespan instead of increasing it?

The most simple explanation to this would be to think of each person as a lifeforce battery of sorts. Your own lifeforce growths and evolves within your body, so your body is only prepared to hold so much lifeforce. Trying to squeeze more in puts a strain in your body, and the larger the lifeforce that's absorbed, greater the damage. But instead of just saying that any lifeforce absortion process always shortens the lifespan of a witch, you could play more loose with this:

• Small absortions and good training can reduce the strain/damage and make it tolerable or could even being healed completely.
• It's not only the amount, but also how fast the witch is trying to do the absortion. A veteran/skilled witch will be faster and safer than a rookie.
• There may be tricks to avoid damage like storing the lifeforce in alchemical devices, although there's still a risk for the witch because she has to channel the lifeforce through her (like a copper cable channeling electricity).

On the other hand, it doesn't seem very natural to me that someone is born with a certain amount of mana and that's it. Were not machines, we change over time so that mana amount should be affected too. You could say that people in your worldbuilding are born with a natural potential for a certain maximum amount of mana, in other words, a soft/imprecise mana limit. That maximum can be increased with some sort of magical training or enhanced with alchemical skills/devices, and that with old age that natural mana limit usually decreases.

 

[pmmg]

The star that burns twice as bright burns half as long.

If this was a star, and another star was feeding it, it would eventually collect so much energy that it exploes.

Suppose a witch, which can max out at 9000, can only super max to a certain level, such as 15000, and then they explode or the difficulty of containing the extra power starts to exponentially increase, such that the amount of personal life force required to contain 9000 is 0, 10000 is 2, 11000 4, and so on. Eventually the life energy required to store exceeds the mana, and Pop...its all comes exploding out. Maybe different individuals have different tolerances, but it all end the same if one goes down that road.

 

[Fettju]

If lifeforce is the fire, the mana could be the air of the fire. It makes it burn stronger and hotter, but uses up the fuel, the body, faster. A person who is born with much mana is a larger fire, and can take more air before burning out, while a person with little mana cannot take too much air before burning out, or even become extinguished with too much air