Will density Manipulation be possible?

[Sythrin]

Storing weight is one of the strangest abilities of Feruchemy. You can increase and decrease your weight without affecting significantly your body autonomy, but it does not affect your density.

It seems also to be unable to give you access to the energy from hauling around heavy arms. Which results in close combat only be able to be used in „falling“ kind of attacks.

But you are still accessible to the force of the weight and can move heavy metals that would normally be outside the physical strengh of a coinshooter.

Than there are the medallions that can decrease not only ones weight, but everything that you can carry. Otherwise the airships would not be able to carry cargo.

And than you have the iron shackles that Sigzil endured on Canticle that made him heavier but do that he felt it and was sluggish.

So. Iron feruchemy seems to have many applications and can be altered.

Do you think in the future its possible to alter alter density and make somebody not only heavier but also tougher and stronger?

 

Or maybe create swords that wield like normal blades for the wielder but heavier for the attacked one.

Edited Friday at 05:26 PM by Sythrin

[Frustration]

I don't think so. I think it's just a power Brandon didn't think out very well and he's tried to make it only do the things he wants but that results in a patchwork that doesn't fit together.

[Trusk'our he/him]

6 hours ago, Sythrin said:

Do you think in the future its possible to alter alter density and make somebody not only heavier but also tougher and stronger?

Using pewter Allomancy in combination should yield similar results. 

Aside from that, I don't believe there's anything in the Cosmere forbidding such a power from existing, but you'd probably need to tweak Feruchemy enough that it wouldn't exactly be the same thing.

[Returned he/him]

I think it's just magic fuzzing the boundaries of real-world mechanisms in uneven ways. Iron stores weight but not all associated properties, which is part of the magic. And magically manipulating weight without needing to account for those other properties should allow for all sorts of tricks we haven't seen yet. Wax certainly made interesting use of it.

That said, I think that iron will mostly stick to manipulating weight and not branch out into density (density-as-toughness sounds like a pewter-type effect), though I wouldn't want to bet a lot on it.

[Treamayne]

22 hours ago, Sythrin said:

Storing weight is one of the strangest abilities of Feruchemy. You can increase and decrease your weight without affecting significantly your body autonomy, but it does not affect your density.

<snip>

Do you think in the future its possible to alter alter density and make somebody not only heavier but also tougher and stronger?

Or maybe create swords that wield like normal blades for the wielder but heavier for the attacked one.

The thing to keep in mind is that, based on current data, what Iron is really manipulating is the Higgs Field. Density is the ratio of mass and volume and changes to density (Wikipedia):

Quote

In general, density can be changed by changing either the pressure or the temperature. Increasing the pressure always increases the density of a material. Increasing the temperature generally decreases the density, but there are notable exceptions to this generalization. For example, the density of water increases between its melting point at 0 °C and 4 °C; similar behavior is observed in silicon at low temperatures.

The effect of pressure and temperature on the densities of liquids and solids is small. 

Higgs fields naturally interact with energy density, but not physical density - though my physics education falls far short of really understanding the interactions at play. Possibly @DrPhysics will find time to weigh in (pun totally intended)

WoBs:

Spoiler

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Questioner

I remember in, I believe it was Hero of the Ages, when Sazed was helping TenSoon escape. When he had fallen on the guard, he said that, by increasing his weight he also increases his density so he doesn't <hurt> himself. Then in The Alloy of Law, it also says that when Wax increases his weight he said that he didn't.

Brandon Sanderson

So, Sazed is just making a mistake. He's mistaking the fact when he increases his weight his musculature changes to be able to handle the new weight and that was what he was talking about. Strength and muscle tone and things like that. I might have just gotten it wrong in the original one [scene], I can't honestly remember, but this is what we kinda decided it needs to be. 

 

Shadows of Self San Jose signing (Oct. 9, 2015)

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Phantine

I actually asked Peter Ahlstrom (who tends to handle math and magic system interactions with physics for Team Sanderson) about this a little while ago

A couple of friends and I are discussing if the iron feruchemy causing changes in speed is a retcon (since there's a mention in AoL that "increasing his weight manyfold would not affect his motion"), or if the effect is just more complicated (like only causing an instant change in speed if Wax changes weight while actively pushing on something).

Are you willing to weigh in on that, or is it just something we shouldn't be thinking too hard about?

Thanks

And his response was

I just don't know the answer to this question.

So I personally think the explanation is either 'Brandon thought it would be cooler for shifting your weight to change your velocity, and forgot he had mentioned it a couple times' or 'this is Wax's twinborn perk'. I'm leaning towards the latter, since the person who writes the magic system summaries at the end of the book specifically interrogated Wax about the effects, and mentioned she specifically was interested in his very unusual power combination.

As for the density thing, there is an explicit mention that you appear to get stronger when tapping, but only to the extent that you can still stand up and walk around - you still have more difficulty moving around overall. So (to pull out random numbers), if you're at 200% normal mass, you have 180% normal strength, and at 50% mass you have 60% normal strength. That means Wax habitually going around at 75% weight so he's 'light on his feet' makes sense - even if he's weaker overall, he's proportionally stronger.

The way I personally think about things for bullets or whatever, anything 'inside' the body (where 'inside' is defined in the same way that pushing/pulling metal 'inside' the body uses it) interacts with your body as if it were normal. So tapping iron doesn't cause your ultra-massive blood to be impossible for your heart to pump, but it also doesn't prevent a bullet from passing through your flesh. That seems to be consistent with how it's portrayed in the books.

Brandon Sanderson

Just a note: in the quote of mine above, I was trying (I believe) to find a way for Wax to indicate that weight doesn't influence the rate at which he falls. IE, acceleration in regards to gravity. It's tough, and I made the call (perhaps incorrectly) not to use modern physics terminology in the W&W books. It has been very hard then to explain:

1). Wax changing his weight doesn't change the pull of gravity on him, or the rate at which he falls. 2) He DOES follow the laws of conservation of momentum.

My talking around these things has let me to tie a few paragraphs in knots.

General Reddit 2016 (Feb. 19, 2016)

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Questioner

So, Metalminds: if you store weight, how does that work, do you decrease your mass or...?

Brandon Sanderson

So, storing weight actually plays with your mass, because if you look at how we do the physics of it… This one is really screwy, because we are changing mass and playing with it. You watch, like with Wax decreases his weight while he's in motion he'll speed up, and if he increases it, he'll slow down. The conservation of momentum and things like that, but we'll doing really weird stuff. It's like, how can you store your mass… Well, in the magic system it works, but it’s one of the weirdest things we do. *pauses to sign book* We kind of play loose and free with the physics sometimes. Like the example that I often use is Wayne doing a speed bubble, the light that is trapped in the speed bubble...like if he turns on a flashlight would actually radiate because of the redshift, and you could just kill everybody by flashing that. So, we make the speed bubbles not cause a redshift for that reason. We kind of work with what is good storytelling first, and then work the physics around it, but we have to put in all these little breaks and things like that in there regularity in order to actually have the story.

Shadows of Self San Jose signing (Oct. 9, 2015)

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Seonid

I noticed that you-- Was that a retcon on the way iron Feruchemy works?

Brandon Sanderson

What do you mean?

Seonid

There's a researcher who talks to Wax, asking him about whether he's changing his mass of whether he's changing whether the planet perceives him-- affecting his gravity.

Brandon Sanderson

Right. It's more a re-- Defining something I didn't pin down strongly enough. I wouldn't call it a retcon because it's something that nobody really did until Wax, really, in the series. The only one really capable of doing that in the original trilogy would have been the Lord Ruler, maybe some of the Inquisitors, but we don't have viewpoints from them. So I wouldn't call it a retcon I would just say it’s something that didn't come up in the first series that now I have to make sure is clear.

Seonid

So is it Higgs field stuff going on?

Brandon Sanderson

Yeah. Mmhmm.

Seonid

My idea was right.

Brandon Sanderson

Mmhmm.

Bands of Mourning release party (Jan. 25, 2016)

 

 

[alder24]

19 hours ago, Treamayne said:

The thing to keep in mind is that, based on current data, what Iron is really manipulating is the Higgs Field.

Which doesn't make a lot of sense because the Higgs Field accounts for less than 1% of the actual mass of an atom (mass of each individual elementary particle like quarks and electrons), the rest comes from the binding energy that holds atoms together. Let's just stick to saying that F-iron manipulates mass (not weight) and the magic lets the density remain unchanged. 

Spoiler

Questioner

Does Iron store mass or weight?

Brandon Sanderson

Excellent question. The thing is it really does involve mass, but I’m breaking some physics rules, basically. I have to break a number of physics rules in order to make Magic work in the first place. Those whole laws of Thermodynamics, I’m like “You are my bane!” (laughter) But I try to work within the framework, and I have reasonings built up for myself, and some of them have to be kind of arbitrary. But the thing is, it does store mass if you look at how it interacts, but when a Feruchemist punches someone, you’re not having a mass transference of a 1000 pounds transferring the mass into someone else.

So there are a few little tweaks. You can go talk to Peter, because Peter has the actual math. Oh Peter’s back there. Peter is dressed up as Allomancer Jak from the broadsheet. In fact we’re giving some out broadsheets, aren’t we Peter. So when you come through the line, we’re giving out Broadsheets. Please don’t take fifty—I think we might have enough for everybody. The broadsheets are the newspaper from the Alloy of Law time. It’s an inworld newspaper. It’s actually reproduced in the book in four different pages, and we put it together in one big broadsheet.

So anyway, you can talk with him, he’s got more of the math of it. I explained the concept to Peter and he’s better with the actual math, so he said “We’ll figure it out.”

Alloy of Law release party (Nov. 7, 2011)

 

Spoiler

Brandon Sanderson

Chapter Six

The fight in the ballroom

From the early days of the Mistborn books, I'd been planning how an Allomantic gunfight would go down. I felt it the next evolution in what has been stylistically a big part of these books.

There is a fine line to walk in a lot of these sequences. I've made something of a name for myself in the fantasy world by attempting to mix some scientific reasoning with my magic systems. At the same time, Allomancy was designed precisely with action sequences in mind. I wanted them to be powerful and cinematic—and a cinematic fight sequence is often at odds with realism. (Watch two people who really know what they're doing fight with swords sometime, then watch any fight sequence in a film. Most of the time, the film sequences stray far from what would really happen.)

So, as I said, I walk a line. Sometimes, there are things I just can't do because they violate what I've set up as the rules of the world. Other times, I design the setting and nature of the fight specifically to allow for certain types of cinematic sequences. One thing I like a lot about Wax’s abilities is the power he has to manipulate his weight. There's some realism to what he does—for example, increasing his weight doesn't make him fall more quickly, but it allows him to do some powerful things while falling. Destroying the chandeliers is an example.

At the same time, I acknowledge that the weight manipulation aspect of Feruchemy is one of its more baffling powers, scientifically. Is he changing his mass? If so, he should become more dense, which I don't actually make the case when it plays out in fights. (Otherwise, increasing his weight enough would make him impervious to bullets.) So, if it's not mass manipulation, is it gravity manipulation, like Szeth and Kaladin do? Well, again, not really—as when his weight increases, his strength and ability to uphold that weight increase as well. Beyond that, Wax can't make himself so light that he has no weight at all.

So . . . well, at this point, the ability to explain it scientifically breaks down. I do like what it does, but I have to set its boundaries and stick to them—and accept that some of what's going on is irrational. (And don't get me started on what should really be happening scientifically when Wayne speeds up time.)

Footnote: Brandon has stated that iron Feruchemy works by manipulating the Higgs field.
The Alloy of Law Annotations (March 14, 2014)

 

On 6/12/2026 at 7:24 PM, Sythrin said:

Do you think in the future its possible to alter alter density and make somebody not only heavier but also tougher and stronger?

The Focused Ones are achieving the same effect but with Tension. When relaxed they are fat and large, but they can compress themselves down to the size of a normal Singer with Tension, infusing their body with Voidlight and making it incredibly tough. They may not be manipulating density directly, but they kind of manipulate the volume of their body, F-iron manipulates mass directly, so I think it's not a stretch to say that there might be a way in Cosmere to manipulate density directly, without changing mass and volume (but it's unlikely we see it as just mass manipulation creates a lot of problems). But F-iron can't do it, as it doesn't affect density. 

On 6/12/2026 at 7:24 PM, Sythrin said:

Or maybe create swords that wield like normal blades for the wielder but heavier for the attacked one.

No, it's either heavier for both or not at all.