Speed Bubble Deflection

[Gray to]

Why do speed bubbles deflect projectiles that enter or exit it? And would aluminum bullets get deflected?

[HSuperLee]

So, based on the fact that we know the speed bubbles steal/give kinetic energy of objects that travel through them, I would guess that the energy isn't applied uniformly (or it is, and since it's a sphere parts of an object pass through at different angles) and thus the object is deflected.

[Calderis]

It's exactly as @HSuperLee says, and it's mainly there for meta reasons.

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Brandon Sanderson

Chapter Twelve

The group investigates the railroad tracks and canal

So, let's talk about the realities of speed bubbles. I did research on this, and got different answers from people on what really should happen if you could slow time like this. One of the issues is that light doesn't change speeds based on this sort of issue, so there was discussion of what things would look like inside looking out or outside looking in. It seems likely that there'd be some sort of red shift, and also that things might grow more dim inside a speed bubble. This is all really very theoretical, however, and so, in the end, I decided that there was enough disagreement among scientists with whom I spoke that it wouldn't be glaringly irregular if I just had the shimmer at the borders and stayed away from dealing with speed of light issues.

There's a much larger issue dealing with slowed time that rarely gets addressed by this type of fiction. I considered using it, and it's this: conservation of energy. Inside the speed bubble, Wax and Wayne are moving far more quickly, and therefore have a ton of kinetic energy compared to those outside of it. And so, a coin tossed from inside the bubble going outside would suddenly move with a proportional increase in speed (proportional to how much slower things were outside).

In essence, speed bubble = railgun.

This is dangerous for narrative reasons. I've often said that the limitations of a power are more interesting than the powers themselves. (It's Sanderson’s Second Law of Magics: Limitations > Powers.) One of the reasons for removing Mistborn and Full Feruchemists from the setting was so that we could focus in on the usefulness of the individual powers in Allomancy and Feruchemy. That falls by the wayside if any of the individual powers become too strong on their own.

I didn't want Wayne to be able to slow time, then sit inside his bubble and leisurely pick off enemies one at a time. And so, I had to place strong limitations on the speed bubbles. (Much stronger limitations than on other aspects of Allomancy. Pushing and Pulling, for example, have their limitations based in solid science. With speed bubbles, I eventually decided that solid science made them way too powerful. So I had to change things.) Therefore, the rules became: No shooting/throwing things out of speed bubbles, no moving speed bubbles, and a required couple second cool-down between creating different speed bubbles. The first rule broke required objects to be deflected when leaving the bubble and that we have the bubble absorb excess kinetic energy when something leaves it.

Disappointing for the scientists, I know, but it makes for a stronger story.

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[Scion of the Mists]

I've always imagined it as similar to the refraction (i.e. deflections things undergo when changing medium).  Like how light bends when entering water.  Plus it acts as a necessary nerf to speed bubbles (otherwise you could freeze time and line up perfect shots on all of the enemies without them being able to react).  

As far as aluminum bullets, I think that they'd either "pop" the bubble or would be affected by the deflection (because the Investiture isn't directly affecting it, it's more a byproduct of the magical effect).  

[Stormfather-in-Law]

I never stopped thinking that the actual effect of a speed bubble would be to mess up anything that went in or out. Like a bullet leaving would have the forward part moving faster than the rear, causing it to rip itself apart and leave more like a shotgun blast than a bullet. Or if a cadmium bubble, it would compress itself into minimum space as it leaves. 

Same thing with an arm or leg, really. Pretty much anything that goes in or out should be destroyed.

[Quantus]

Adding to what @Calderis said, he has currently RAFO'd what would happen if somebody shot a time bubble with an aluminum bullet, but for what it's worth we do know that if you tried to raise a time bubble with aluminum crossing the boundary, the Time bubble would fail to form and you'd get hit with some kind of backlash:

 

 

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Questioner

What would happen--

Imagine I had-- imagine Wayne is standing near the end of an aluminium tube. He tries to set up a speed bubble such that he radius would go through the tube, what would happen?

Brandon Sanderson

Okay standing at the end of an aluminum tube, well I don't know--

Oh I see what you're saying. Yeah, yeah yeah yeah yeah yeah yeah. I think that if it's trying to be set up through aluminum it's gonna' disrupt it, you're gonna' have that sort of the "backlash" that you get when-- yeah.

Questioner

Oh so you can't even set it, it won't be there *inaudible*--

Brandon Sanderson

I don't think you can set it up, I think it's gonna' cause it to collapse the second that it tries to pop up around the aluminum.

Questioner

Okay that makes sense.

Brandon Sanderson

[...]

Yeah, it's probably gonna' act like you tried to set up a speed bubble on something that's too small and moving.

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[CalaCrisp88]

On 11/5/2018 at 1:38 PM, Stormfather-in-Law said:

I never stopped thinking that the actual effect of a speed bubble would be to mess up anything that went in or out. Like a bullet leaving would have the forward part moving faster than the rear, causing it to rip itself apart and leave more like a shotgun blast than a bullet. Or if a cadmium bubble, it would compress itself into minimum space as it leaves. 

Same thing with an arm or leg, really. Pretty much anything that goes in or out should be destroyed.

Objects are either in or out. They don't split.

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Kurkistan

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.

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