In another question, I talked about a form of magic that converts metabolic energy (i.e. the energy produced by biological processes in "animals", which for this purpose includes e.g. yeast) into kinetic energy, with essentially unbounded¹ ability to precisely direct that kinetic energy.

In one answer / comment, Yakk implied that this would give someone wielding this ability nearly unlimited power:

There is enough energy in a 1 kg rock to throw everything on the island of Manhattan 100 km into the sky.

On the one hand, I can see where someone might wonder if this could incarnate Maxwell's demon. On the other hand, looking at the thought experiment literally, it would seem that opening and closing the door would itself require work, never mind all the problems that conductive heat transfer raises.

Is this — not the literal thought experiment, but the general idea — plausible? If so, what would be an example of an actual process by which one could extract "unlimited" energy using this "kinetic magic", and what limits could be applied to the wielding of magic that would prevent it, without preventing less, ah, "excessive" uses of magic? (The linked question notes some of the things I want to be able to do.)

I will assume:

  • Initiation energy is limited to, at best, 2KWHr, and can be delivered at, at best, 5KW. Any process which would require exceeding those limits to start isn't feasible.
  • Magic can't simply convert matter directly to energy.

The critical piece of the puzzle here is that magic can reduce entropy. For instance, it can turn a jumbled pile of blocks into a neat stack, or turn a bag of black and white marbles into piles separated by colors. Perhaps more importantly, it can² do these sorts of things on a molecular level, for example, fill a 1L container with pure argon taken from the surrounding atmosphere.

A related question could be, how do you measure the energy value of information of this nature? Knowing that, it may be that the "obvious" limitation is that this energy cost must also be paid.

Affirmative ("yes, this is world-breaking") answers should give a detailed explanation why this is the case, not just an assertion that it is.

(¹ Not really, but for the purpose of this question, we'll go with that.)

(² Actually, this is, at best, pushing the limits of what I'm going to allow, but again, for the sake of this question, we'll go with it.)

  • $\begingroup$ I don't think your question makes sense. Metabolic energy release is pretty well understood (at least by biologists). Nuclear energy release is well known but rather hard to achieve unless your "magic" changes atomic half-lives. So what do you want to pretend your "magic" can do? If it pulls energy from another universe or dimension, then it's unlimited until the last star dies (see Kilgore Trout) $\endgroup$ Commented Feb 5, 2020 at 16:23
  • 1
    $\begingroup$ If the only usable energy comes from metabolism then I'm unclear on how you are getting that much energy out of the rock. $\endgroup$ Commented Feb 5, 2020 at 16:28
  • $\begingroup$ To both commenters; your thoughts sounds suspiciously like an answer. @Yakk's comment suggests that some mechanism exists, but I don't understand how. This question is an attempt to ascertain if Yakk's comment is legitimate or bunk. I also don't understand how Yakk is proposing said energy conversion. $\endgroup$
    – Matthew
    Commented Feb 5, 2020 at 16:28
  • $\begingroup$ I don't think Yakk is saying you can use that energy via your magic. I think Yakk is just using nuclear energy to point out that entropy not energy is the constraining part of the problem. $\endgroup$ Commented Feb 5, 2020 at 16:33
  • 2
    $\begingroup$ "Initiation energy is limited to, at best, 5KW, and at best 2KWHr". At least use the same unit. One is a power, the other is an energy $\endgroup$
    – L.Dutch
    Commented Feb 5, 2020 at 16:52

1 Answer 1


Since you are talking magic, you can impose limits however you wish. I'll tell you what I would do though.

First limitation is to consider Magic to be energy. Seems like you are doing this already. It gives you a limit based in understood physics. You can neither create or destroy energy just like you can neither create or destroy Matter. You can rearrange things down to a molecular level, but you still do business with the laws of physics. Conservation of Mass and Conservation of Energy are key concepts here.

Your Second limitation would be limited to the energy your Magic user can glean from metabolic processes. This takes away the ability to use the 1kg rock to toss Manhattan around. A metabolic process is loosely defined by layman like myself is the process of taking something you take in, break it down to useful compounds, then combine it to release energy. In an animal, this is breaking down food, converting it to glucose, and combining it with oxygen to release energy (laymans description)

The upshot is that your magic user cannot use any more energy than they can take in and process as food. What they move, whether it's with their body or mind, takes the same amount of calories. If it takes 20 Calories to pick up boxes on your left and move it to your right using your hands, then it will take the same amount of calories to do it with your brain. If you want to travel a certain distance with brain power, it will burn the same amount of calories as you walking or running the same distance. This puts a solid limit to magic and keeps magic users from getting ridiculously OP.

You did bring up Magic being able to combat entropy. Humans do this with their hands all the time. To stack a pile of bricks will simply cost the same amount of calories as walking over and using your hands. Separating colored marbles is the same. The thing about Entropy is that it takes over when you stop paying attention.

Now comes some of the cool stuff. Humans are prevented from ultra fine manipulation of stuff like molecules without tools because fingers prevent that kind of control. Magic is different. It is the Magic, which has no form, that does the work and can therefore grab that argon molecule, and only the argon molecule, and transfer it to the glass. The ability to manipulate the physical shifts from the skill of the hand to the skill of the brain. You are still limited by how much energy you can derive from food. You're Magic User still won't be able to lift a 20 ton block without tools and help. However, your Magic User will be able to pull the rope attached to a pulley system that can lift the 20 ton block. In addition, imagination becomes your limiting factor. Your Magic User could do whatever they imagine, like maybe assassinating an enemy by pinching the carotid artery from 30 feet away. Or spooking a general's horse from a distance. Dice manipulation, moving the barrel of a gun before it's fired, and so on.

That's how I would put limits on magic use. It's all about counting calories

  • 1
    $\begingroup$ I'm not sure this actually answers the question. You've basically stated that, at a macroscopic scale, anyway, I can create Maxwell's Demon. Take separating marbles. The argument why this doesn't decrease entropy is because the increased "information energy" is offset by the calories my brain burned in to "produce" that information. But... how do I measure that cost when I instead separate grains of sand, or molecules of atmosphere? At some point, that cost must become "very high", or I think (and @Yakk claims) it leads to world-breaking powers. $\endgroup$
    – Matthew
    Commented Feb 5, 2020 at 21:02
  • $\begingroup$ That said, thanks for the answer anyway! You're pretty much bang-on with how I envision this to work. (Hehe... hadn't thought about dice; needless to say, use of magic in a casino is very, very banned. It's off topic here, but yes, there are ways to tell when magic is used; otherwise, as you also noted, it's way to easy to do things like kill people without leaving a trace.) $\endgroup$
    – Matthew
    Commented Feb 5, 2020 at 21:03
  • $\begingroup$ @Matthew One way to prevent the world breaking aspect would be to keep the calorie cost to be the same as moving the molecule with your hand. You still have the cost of moving the arm in addition to the amount of energy required by the payload, no matter how small. If you want to fill a glass with argon then you would have to make that motion once for each molecule and that carries a caloric cost that would be incredibly high because the motion would be repeated billions of times. Call it the invisible hand. $\endgroup$
    – Paul TIKI
    Commented Feb 5, 2020 at 21:14
  • 1
    $\begingroup$ Yeah... that could work, but seems rather contrived. (Also, it would probably break a lot of the things I want to be able to do, like remove dirt from clothes.) I'd prefer to be able to quantify the associated entropy costs. $\endgroup$
    – Matthew
    Commented Feb 5, 2020 at 21:19
  • 1
    $\begingroup$ @Matthew The Maxwell's Demon effect could be mitigated by the speed of human reaction. Even if you could perceive the motion of molecules, could you react fast enough to trigger the gate? And even if you could, what would be caloric cost to trigger a neuron to fire to trigger the gate. If you figure one neuron fire to activate the gate, trying to run a Maxwell gate would light your head up like a Christmas Tree. $\endgroup$
    – Paul TIKI
    Commented Feb 5, 2020 at 21:25

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .