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General Reddit 2016 ()
#51 Copy


Can Cadmium bubbles be nested if you have multiple Pulsers?

Bonus Question: add in duralumin/nicrosil to the equation.



The effects multiply.



I guess hiring 3-4 Pulsers before something you have to prepare for might be worth it. They create their bubbles one after the other at the same place, and boom, you have days instead of minutes.

Ok, lets calculate. We don't have exact figures for cadmium, but we have for bendalloy: 2 minutes into 15 seconds, that's a ratio of 8. 4 Pulsers mean 84 = 4096 ratio. So 21 second for every day goes by for every day you spend in there.

The outer Pulser burns this 168.75 second's worth of cadmium, the first inner one needs 22.5 minutes, the second inner one needs 3 hours and the innermost needs the 24 hours.

So basically for every day spent in these bubbles you need ~27.5 hours worth of cadmium, depending on how routinely they set up the bubbles one after the other.


Wait, are you mixing up sliding and pulsing? I also think you are nesting your bubbles but not your pulsers, so you are losing a lot of efficiency not to mention practicality.

Tell me if I'm misinterpreting what you're describing, but this is how I'm visualizing it:

I'm saying that you get 4 pulsers huddled together and the one that can open the biggest bubble goes first. Then the next largest one pops his. Then the next. And finally the smallest bubble fires.

In that scenario (unless there is something that prevents this) I picture it like this:

This method, 170 days pass only burning 4 hours worth of cadmium.

Well. I'm gonna do it. Gonna page /u/mistborn and ask: is this possible? Can time bubbles be nested like so and if they can do you truly get this kind of efficiency?

crosses fingers

Brandon Sanderson

This one is a RAFO. :)

Boskone 54 ()
#52 Copy


If you draw a line of forbiddance on a piece of on a chalkboard that’s sitting on the ground and then hit that chalkboard, will the chalkboard move?

Brandon Sanderson

This is the number one question I get, actually. The answer is, it depends on the size of the line and the amount of power that’s been put into it. This is actually relating back to Cosmere physics. If you look at the Cosmere physics, you can see exactly what happens with the speed bubbles, it’s the same sort of principle. It’s based on perception. So putting a movable line, oftentimes you will just have trouble engaging the magic on something that’s not stable enough to be viewed as stable. Drawing it on a chalkboard and then turning it toward somebody actually wouldn’t work, because you wouldn’t be able to engage that line very easily with the way the magic works. And if you did, it would disrupt the line, and it would be gone. Treat whatever I do with speed bubbles as the rule for Rithmatist magic, until I write the second book. If I decide to take it in it’s own direction, I will let you guys know.

Miscellaneous 2011 ()
#53 Copy


So, I was thinking how the third trilogy was mentioned as being in the future (as opposed to the second trilogy being contemporary to our time), and I wondered if the people from Scadrial would be able to visit the other shardworlds without using Shadesmar - and, if so, how would they do it?

The simplest (and most boring, and not germane to the topic) method would be FTL travel.

But then I got to thinking about Pulsers and Sliders.

My first thought was, "Hey, what if a bunch of Pulsers - or some Pulser-inspired technology - could put a bubble around the crew quarters of a starship? That would allow the crew to travel from one system to another within their own lifetimes." Just put the ship on autopilot, power up the Pulser Engine, and go have a sandwich.

Then I tried to figure out if something similar might work for Sliders, but the first bump I hit was that bendalloy bubbles - and cadmium bubbles - were stationary. Which, in turn, would probably rule out the Pulser starship.

But then I thought some more. These books take place in a universe which is, astronomically, pretty much like our own. It follows the same rules of physics. Which means that Scadrial is rotating on its axis, while it revolves around its star, while that star moves within its galaxy, and that galaxy moves within its universe.

Which means, technically, bendalloy and cadmium bubbles aren't stationary. They're stationary relative to one object - Scadrial - but they're perfectly mobile when one looks at the bigger picture.

This makes me think that a Pulser starship might be possible, provided the Pulsing can be anchored to the ship rather than Scadrial.

It also makes me wonder why the default anchor is the planet and why nobody has figured out how to anchor it elsewhere. Is it simply a mental block that could be overcome? Is a person too small to be used as an anchor (even though the bubbles pop up with the person at the center)? Can a bubble's size be altered, dependent upon the size of its anchor? (That is, could a small bubble be made around, say, a person's heart if the whole person were the anchor?)

I still dig the idea of Allomancers Iiiin Spaaaaace!, though I'm not entirely sure how it would work.


[Links out to WoBs about Metallic Arts FTL being a thing]

So FTL is confirmed

Peter Ahlstrom

There's an issue with conservation of momentum with speed bubbles.

FanX Spring 2019 ()
#54 Copy

Steeldancer (paraphrased)

 According to General Relativity, there should be spatial distortion in speed bubbles. So, why does no one notice it?

Brandon Sanderson (paraphrased)

There is spatial distortion in speed bubbles, that's why bullets are refracted when they enter a bubble. However, I played with it a bit, and ignore the redshift that should happen. The barrier of the bubble absorbs it, otherwise everyone would just be irradiated. 

Holiday signing ()
#55 Copy

zas678's sister

If Wayne and Breeze, like if Wayne had a time bubble up and Breeze was inside Pushing on somebody's emotions what--

Brandon Sanderson

He could still make that work.

zas678's sister

Would it affect it?

Brandon Sanderson

Not really. It wouldn't dramatically affect it. You're going to have one of these sort-of effects-- Yeah, because what he is doing is on another Realm, it's not going to affect it.

zas678's sister

Is that the same with all of the *audio obscured*

Brandon Sanderson

Not necessarily. See what's going on is if you are affecting things on the Cognitive Realm--


It's kind of time-independent?

Brandon Sanderson

Yeah? It's not as-- Really it's the Spiritual Realm that is completely time-independent, right? All time and space are irrelevant once you reach the Spiritual. You're kind of going to go over the top a little bit, it's going to work just fine. In fact you can probably-- So he could use that to make his metals last a little bit better, probably. So that is a hack of the magic systems that you could probably do.

Starsight Release Party ()
#57 Copy


Would tapping Feruchemical speed cause you to burn metals faster as your whole body speeds up?

Brandon Sanderson

Yeah. I think it probably would. I don't know if we've gotten to that interaction yet, but it probably would. Good question. If it's speeding up... Yeah, I think it would. Good question. If you're in a speed bubble and doing it, it's totally going to do it, and there's some analogies there.

Skyward Chicago signing ()
#58 Copy


What's it like inside a time bubble on a windy day?

Brandon Sanderson

So, I've had to play around a little bit with the air. Air moves in and out, you would still feel it windy, but as I have it you will not feel it from the direction the wind is coming, it will be deflected a little bit. So you might be a little bit in a wind tunnel or something, probably a swirl.

Arcanum Unbounded release party ()
#59 Copy


If Marasi could burn duralumin, would that make time go faster or her bubble get bigger? 

Brandon Sanderson

This is on tape so I have to make sure I do this right.

It is less about the size of the bubble and more about speeds. You can expand the size and change the size of the bubble, so it's possible that you could use duralumin for either one if you knew what you were doing, but the speed is the more relevant part. So, I just wanted to say that correctly. 

SpoCon 2013 ()
#60 Copy

Shardlet (paraphrased)

A slider and a pulser are standing near each other and each put up a bubble. Neither is standing close enough to the other to be within the other's bubble, but they are near enough that their bubbles would overlap what effect would you have?

Brandon Sanderson (paraphrased)

The bubbles would overlap and it would be like a Venn diagram (i.e., outside both bubbles-normal time, in sliders bubble-fast time, in pulser's bubble-slow time, in the overlap-normal time).

Firefight Chicago signing ()
#62 Copy


So time bubbles... How much control does a bubbler have over the bubble before and after it's cast? Can they just grow and shrink it or...

Brandon Sanderson

Not very much.


So Wayne could flare his metals make time go faster--

Brandon Sanderson



But if he'd stopped flaring--

Brandon Sanderson

Yeah, but-- they have a bit of control over the speed of it, but once it's up moving it or anything like that, not much. The flaring of it and things like that, yes they can-- it's mostly set when they start.


But they have some discretion when they start it.

Brandon Sanderson

They do have some discretion, yes.

Miscellaneous 2011 ()
#63 Copy

Aiken Frost

Guys, have you noticed this bit in the Bendalloy section [of the Mistborn Adventure Game]?

"A physical attack made through the bubble, whether held or thrown, is robbed of its kinetic energy, often with an audible 'pop.'"

Could this be what we are looking for when trying to figure the FTL space travel thing?

Arcanist Lupus

This statement seems to violate several things from Alloy of Law: first, Wax's "shooting the bullet" scene, and the danger of being shot while inside a cadmium bubble.

Peter Ahlstrom

Not really. A bullet shot out of a speed bubble IS robbed of kinetic energy—not all of it, but just enough to slow it down to the speed it would have been moving at had it been fired outside the bubble in the first place.

Arcanum Unbounded release party ()
#64 Copy


Is there a simple explanation of why bullets and objects that go through the time bubble wall are refracted at such random...?

Brandon Sanderson

There's two reasons. One is the outside-of-the-books reason, one is the inside-of-the-books reason. Outside the books, it made time bubbles too powerful. Limitations, that whole idea about limitations. In-world, what's happening is, there is a transfer of power that's happening right there. Which is what keeps light from irradiating people when it passes through a bubble. So, there's a transfer of energy, there's actually a thermodynamic process happening when you pass out of the speed bubble. And energy is being lost. And that has to do with cosmere physics.

Calamity Chicago signing ()
#65 Copy


<Gives text of original conversation with Brandon>

To restate the scenario in more understandable terms (phase 2 is to use diagrams, if it comes to it and I still don't manage to get it across):

Say Cory the cork-thrower is standing besides a train track. Cory is facing North and the train is running from West to East. Cory tosses a cork North up over a passing train. Normally, this cork would go over the train and land on the ground directly opposite Cory to the North.

From the frame of reference of Cory and his cork, the train is moving West->East. From the frame of reference of the train, the train isn't moving at all and the cork is moving both South->North and East->West (i.e., Northwest). So if we were to draw a line describing the cork's movement, Cory's line would have the cork moving South->North over a moving train. The train's line would have the cork travelling Southeast->Northwest as it described a diagonal across the train.

If there's a bubble on the train, that's where things get complicated. When the bubble hits the cork, does the train's frame of reference "take over" so far as it's direction of travel goes? So far as the train is concerned, nothing really changes: the cork is still describing that same diagonal, just more quickly/slowly. But so far as Cory and his cork are concerned, all the sudden the cork is moving laterally (East->West) corresponding to the train's frame of reference. The question, then, is where the cork lands when all's said and done: does it still land directly North of Cory after it passes over the train, or does it land a bit to the West or East as well?


My thoughts/model on this would be that it also lands West/East. If the bubble was a bendalloy bubble, then the corks diagonal passage would be accelerated, meaning that it pops out of the bubble off to the West of where it would have otherwise. A cadmium bubble would still move the cork to the West according to its frame of reference, but because of how slow the bubble itself is in motion the cork would still end up East of Cory.

Peter Ahlstrom

The bubble's frame of reference would take over while it's inside. But you also need to include the fact that bubbles deflect things. The cork would be deflected both when it enters and when it leaves the bubble. So you can't completely predict the path it will take.


<At this point the conversation kept on for a bit as things grew... complicated. We misunderstood one another [which I take the blame for] on several crucial fronts and ended up talking past one another. Long story short is that I'd been implicitly assuming absolute relativity of reference frames in the cork-bubble system—so while both types of bubble would drag the cork along for a bit, that dragging would also be offset (to varying degrees based on bubble type/compression) by lateral movement of the cork within the bubble. This is wrong.>

Peter Ahlstrom

If the train is moving east, and he throws the cork over the train, a bubble that slows the cork down will mean the cork ends up east of him.

If the train is moving east, and he throws the cork over the train, a bubble that speeds the cork up will mean the cork ends up on the other side of the train faster than it would have with no bubble. It doesn't move west.

If the speed bubble only very slightly increases the flow of time, then the cork could even end up slightly east of him, depending on the speed of the train.

So depending on the speed or slowness of the bubble, and the speed of the train, the cork will either end up exactly where the thrower expects it to, but more quickly, slightly east of where he expects, but more quickly, or quite a bit east of where he expects, more slowly. The cork doesn't move west.

In fact, I think it's safe to assume that the train is always moving to the east faster than the thrower is throwing the cork to the north. In that case, both types of bubbles will always end up pushing the cork at least somewhat to the east.

Let's do the math here.

Say the bubble is 10 feet in diameter and the cork toss hits the bubble right in the center. He tossed the cork at 5mph. The bubble is 2x speed. That means the cork goes 10 mph across the train (measuring from the frame of reference of the tosser). The train is moving at 50 mph. The cork crosses the train in 0.682 seconds. In that time the train moves 50 feet to the east. So the cork ends up 50 feet to the east of where the tosser expected it to.

If the bubble is 100x speed, the cork goes 500mph across the train, and in that time the train moves 1 foot. The cork ends up 1 foot to the east of where the tosser expected it to, but much faster than he expected.

If the bubble is 1/2 speed, then the cork goes 2.5 mph across the train. The cork crosses the train in 2.727 seconds. In that time the train goes 200 feet to the east. The cork ends up 200 feet to the east of where the tosser thought it would end up.

If the bubble is 1/100 speed, then the cork goes 0.05 mph across the train. The train moves 1.9 miles in the time it takes the cork to cross the train. The tosser has no idea where it ends up, but he watches it hovering over the train as the train goes off into the distance.


As far as the cork is concerned, it can't tell the difference whether it's moving through a stationary bubble or a (laterally) moving bubble. From the cork's point of view it moves in a straight line either way.


<Some doodles got involved at one point or another, and it was also confirmed that the path of the cork (barring refraction) would stay the same once it left the bubble, still going directly north>

FanX Spring 2019 ()
#67 Copy

Steeldancer (paraphrased)

Have you ever heard of the Alcubierre Drive? 

Brandon Sanderson (paraphrased)

Yes, I know about the Alcubierre drive. 

Steeldancer (paraphrased)

So, if we took two speed bubbles--mechanized, because Allomancers aren't powerful enough to pull it off--could we create a functioning Alcubierre drive?

Brandon Sanderson (paraphrased)

You are theorizing in the right direction. 

17th Shard Forum Q&A ()
#68 Copy


If you are standing inside of a time bubble, and throw a spear out of the bubble, what happens to that spear as it traverses the border of the bubble? Are different parts of the spear ever in different "time zones," going fundamentally different speeds?

On that line of reasoning, what would happen to a train and its occupants if Marasi stood next to railroad tracks holding up a Cadmium bubble while that train sped by?

Brandon Sanderson

In general, a large object going through a time bubble is not going to notice. An object is either in or out, and it depends in part on how the object views itself. People inside the train would be inside of its influence, and wouldn't notice the bubble. The spear would go from one to the other, but would never be in both.