Physics suggests time bubbles should be air tight.

[DrPhysics he/him]

TLDR; Letting air molecules pass through the bubble boundary the same way as bullets creates catastrophic conditions for those inside and outside a speed bubble. The molecules should bounce off the boundary instead.

I'm a plasma physicist (really hot gasses) by training, which has made me think way too much about what would happen to air at the boundary of a speed bubble.

One tenet of physics is that whatever happens on the microscopic (molecular) level should describe what happens on a macroscopic (regular) scale.

So, I spent an afternoon building a particle simulation that shows what happens if air molecules behave the same way as bullets when they cross a time bubble boundary (i.e. they keep the same perceived speed, but are diflected in a random direction).

The results were catastrophic. On the slow side of the border, pressure rapidly drops proportionately to the time slowdown (e.g. if time is 10 times slower, pressure is 10 times lower). That pressure drop spreads out at the speed of sound, freezing any nearby air and creating a vacuum.

On the fast side, the molecules pile up, superheating the air and creating a shockwave that flies away at the speed of sound.

Dropping a bubble would create a thunderous boom as the two sides slam back into each other trying to correct the pressure imbalance.

Since we see none of this in the books, air molecules cannot interact with the boundary the same way a bullet does.

 

What do the molecules have to do in order to show what happens in the book? Bounce off the boundary instead of going through.

This makes the bubble airtight but stops the pressure drop, the freezing, the vacuum, and the loud boom, matching what we see in the books. (No one in the stories has stayed in a bubble long enough to come anywhere near the point where there is noticeably less oxygen).

This matches what we know about the cognitive realm. Things are either all in or all out of a bubble. If the air sees itself as a complete fluid inside a bubble, its individual molecules won't want to leave the bubble because they all see themselves as part of the air inside.

The only other option would be some odd interchange where the boundary counts molecules trying to cross and reflects some and bounces off others so that the count of molecules stays the same on both sides, but once you get to time differences of 100 or more (and the books show that differences of thousands are easily possible), that molecular exchange makes the bubble effectively airtight anyway.

Edited July 9, 2024 by DrPhysics

[JohnnyKaizen he/him]

I really hope we get into this on the page as we get to the more advanced tech ages, because that's fascinating!

[Quantus he/him]

So, I have a disclaimer and a some additional factors to consider if you are trying to crack Time Bubbles. 

The disclaimer is that Time Bubble functionality is almost entirely Plot driven concerns over functional logic, and so far at least the instances where it breaks physics are handwaved as the Spiritual Realm filling in the energy balance gaps.  Both the deflection of bullets and the lack of Doppler Shift irradiating folks are results of those Doylistic concerns per WOB.  The air pressure changes, oxygen depletion, etc are likely to fall into the same boat.  

Also, an object is either inside or outside of the time bubble with no half-way state possible, depending on whether the object views itself as inside or outside the bubble.  So some of the issues with the transition randomizing the movement and/or forces is due to that step-change blinking into different time-frames.  

[DrPhysics he/him]

46 minutes ago, Quantus said:

Also, an object is either inside or outside of the time bubble with no half-way state possible, depending on whether the object views itself as inside or outside the bubble.

I had this in my notes, but looks like I left it out of my post (I'll add it in an edit). I'd actually add that as an argument in favor of the bouncing molecules. The air inside sees itself as inside, so all of it wants to stay inside.

49 minutes ago, Quantus said:

The disclaimer is that Time Bubble functionality is almost entirely Plot driven concerns over functional logic, and so far at least the instances where it breaks physics are handwaved as the Spiritual Realm filling in the energy balance gaps.  Both the deflection of bullets and the lack of Doppler Shift irradiating folks are results of those Doylistic concerns per WOB.  The air pressure changes, oxygen depletion, etc are likely to fall into the same boat. 

True. This will probably be outdated once we get any information on what air does in a bubble (like during space travel, though keeping air inside has some really interesting applications here).

 

This was just a simple "Here's what we know now, what would that mean if we take it to extremes".

[Steel Speedster ♂]

I was able to find two WoBs about how air behaves in bubbles.

Spoiler

Quote

timQuestioner (paraphrased)

Can you burn cadmium to trap air and move in space like that?

Brandon Sanderson (paraphrased)

That's a plausible extrapolation, but I'll give you a RAFO on that. You're thinking along the right lines.

Stuttgart signing (May 17, 2019)

Quote

Kurkistan

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.

Skyward Chicago signing (Nov. 16, 2018)

The second one definitely seems to imply that air does indeed pass through the bubble boundary and deflect.

[alder24]

20 hours ago, DrPhysics said:

TLDR; Letting air molecules pass through the bubble boundary the same way as bullets creates catastrophic conditions for those inside and outside a speed bubble. The molecules should bounce off the boundary instead.

I'm a plasma physicist (really hot gasses) by training, which has made me think way too much about what would happen to air at the boundary of a speed bubble.

One tenet of physics is that whatever happens on the microscopic (molecular) level should describe what happens on a macroscopic (regular) scale.

So, I spent an afternoon building a particle simulation that shows what happens if air molecules behave the same way as bullets when they cross a time bubble boundary (i.e. they keep the same perceived speed, but are diflected in a random direction).

The results were catastrophic. On the slow side of the border, pressure rapidly drops proportionately to the time slowdown (e.g. if time is 10 times slower, pressure is 10 times lower). That pressure drop spreads out at the speed of sound, freezing any nearby air and creating a vacuum.

On the fast side, the molecules pile up, superheating the air and creating a shockwave that flies away at the speed of sound.

Dropping a bubble would create a thunderous boom as the two sides slam back into each other trying to correct the pressure imbalance.

Since we see none of this in the books, air molecules cannot interact with the boundary the same way a bullet does.

 

What do the molecules have to do in order to show what happens in the book? Bounce off the boundary instead of going through.

This makes the bubble airtight but stops the pressure drop, the freezing, the vacuum, and the loud boom, matching what we see in the books. (No one in the stories has stayed in a bubble long enough to come anywhere near the point where there is noticeably less oxygen).

This matches what we know about the cognitive realm. Things are either all in or all out of a bubble. If the air sees itself as a complete fluid inside a bubble, its individual molecules won't want to leave the bubble because they all see themselves as part of the air inside.

The only other option would be some odd interchange where the boundary counts molecules trying to cross and reflects some and bounces off others so that the count of molecules stays the same on both sides, but once you get to time differences of 100 or more (and the books show that differences of thousands are easily possible), that molecular exchange makes the bubble effectively airtight anyway.

It's really interesting to consider "realistic" time bubbles. They would make a fine weapon if they behaved like this while attached to a primer cube. But just like redshift, those problems are handwaved as the Spiritual Realm shenanigans. 

However we do know that air is passing through a bubble, but it's also possible to somewhat trap the air inside a bubble. It seems like both of those things can't work together, but if air molecules are bounced at random directions, can't some of them randomly be bounced off the bubble instead of passing into it and the air in the bubble would be reflected back inside as you proposed? But because it was all very random, some air would still pass through the bubble. The rate at which air passes through depends only on a compression factor - the more time is being slowed down or sped up, the less air can pass through the bubble. This matches with the example of the Wayne's superbubble at the end of TLM, which had a solid, crystalized barrier.

Spoiler

Kurkistan

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.

Skyward Chicago signing (Nov. 16, 2018)

 

Spoiler

timQuestioner (paraphrased)

Can you burn cadmium to trap air and move in space like that?

Brandon Sanderson (paraphrased)

That's a plausible extrapolation, but I'll give you a RAFO on that. You're thinking along the right lines.

Stuttgart signing (May 17, 2019)

 

[Steel Speedster ♂]

6 minutes ago, alder24 said:

However we do know that air is passing through a bubble, but it's also possible to somewhat trap the air inside a bubble. It seems like both of those things can't work together,

Cadmium bubbles would trap air, because due to the molecules inside the bubble moving slower than the outside ones, more would be coming in from outside than going out from the inside.

[alder24]

3 minutes ago, Speeding Steelrunner said:

Cadmium bubbles would trap air, because due to the molecules inside the bubble moving slower than the outside ones, more would be coming in from outside than going out from the inside.

And you don't see any problem with that? Just like @DrPhysics described in his post, without any other interaction, pressure inside a cadmium bubble would mount up and eventually would be unbearable, if the air was allowed to freely move in and out of time bubbles, like bullets do. This doesn't happen, as neither Wayne or Marasi felt any difference in pressure - and Wayne created a bubble that almost stopped the time itself, which would make it a perfect vacuum in a blink of an eye. 

And the WoB was about a cadmium bubble in the vacuum of space, where there is no air going into the bubble and it should get depressurized very quickly. There is some mechanism preventing this from happening, if you can somewhat trap the air in a bubble and go to space. 

[DrPhysics he/him]

15 minutes ago, Speeding Steelrunner said:

Cadmium bubbles would trap air, because due to the molecules inside the bubble moving slower than the outside ones, more would be coming in from outside than going out from the inside.

If that is true, it would behave exactly as described in my post. The heating was a result of the massive compression air due to having much more air coming in than going out. That's what I simulated.

And I have seen the WOB on the topic (I should have addressed them initially). I'm operating under the principle that it isn't Canon until it is in the books, time bubbles being air tight make for some potentially interesting story points, and people from Dragonsteel pop up occasionally in the forums.

[Quantus he/him]

17 hours ago, DrPhysics said:

This was just a simple "Here's what we know now, what would that mean if we take it to extremes".

Oh, yes, and Im entirely down for the ride, just wanted to set the starting position that a lot of the logic will need to start at the desired narrative Effect and work backward to Cause, so there will narrative pressures instead of a purely scientific and data-based approach. 

With that said, lets look at that Data!

1. Bubbles are subject to the Intent of their user. 
   1. So Perception effects and modifiers are in the mix
   2. So behaviors could Change in with training and/or cultural understanding in later Era's.
2. Different things behave differently as they cross the boundary.  By Default:
   1. Light & Radiation are unaffected
   2. Air/wind and airborn objects will transition but are deflected.
   3. The User will Pop the bubble if they cross the boundary.
   4. Other People can pass in and out (Confirm?)
   5. Aluminum Will Pop the Bubble
      1. Silver is likely but untested to do the same, given it's Investiture Disruption effect.
3. An "Object" is either inside or out with no* discernable transition time.
   1. An "Object" is not necessarily a single molecule, it can be any random volume of air from a waft to a breeze to a tornado, depending on how it views itself in the moment on the I Am A Stick level, in the same way one Object can encompass anything from a single grain of sand to a boulder to a whole stacked stone keep.  
4. Physics like to do things with the least amount of energy possible at all times. 

 

I propose that the Random Deflection of air current and ballistic objects is happening because random volumes of Air are popping across into the Bubble, and it's creating a sort of frothy effect that randomly bumps the objects to impart unexpected vectors and spin, and disrupts the air currents coming it as the cohesive 'school' of individual wind currents get scattered.

23 minutes ago, alder24 said:

It's really interesting to consider "realistic" time bubbles. They would make a fine weapon if they behaved like this while attached to a primer cube. But just like redshift, those problems are handwaved as the Spiritual Realm shenanigans. 

However we do know that air is passing through a bubble, but it's also possible to somewhat trap the air inside a bubble. It seems like both of those things can't work together, but if air molecules are bounced at random directions, can't some of them randomly be bounced off the bubble instead of passing into it and the air in the bubble would be reflected back inside as you proposed? But because it was all very random, some air would still pass through the bubble. The rate at which air passes through depends only on a compression factor - the more time is being slowed down or sped up, the less air can pass through the bubble. This matches with the example of the Wayne's superbubble at the end of TLM, which had a solid, crystalized barrier.

  Hide contents

Kurkistan

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.

Skyward Chicago signing (Nov. 16, 2018)

 

  Hide contents

timQuestioner (paraphrased)

Can you burn cadmium to trap air and move in space like that?

Brandon Sanderson (paraphrased)

That's a plausible extrapolation, but I'll give you a RAFO on that. You're thinking along the right lines.

Stuttgart signing (May 17, 2019)

 

So we know at a high level that when the math break reality the hand-wavy explanation is that Spiritual Realm spillover make up the difference.  But we also know it's supposed to be a relatively hard magic system that can and will be quantified, so there are always limits.  The Super-Bubble example seems to fit that concept: lets assume the Bubble itself is providing the Investiture/Energy to transition.  It's generally easy for light, and mass can work too but for the Identity Froth (tm) described above, but it makes sense that a Duralumin Super-bubble could create such a massive differential that it overloads the bubble's capabilities and makes that crystal effect as it strains against it's limits.  

For the Space Age implications to FTL and Air Bubbles, and looking at Rosharan development as an example, I think that it'll either be a matter of specific Understanding and Intent (the way Soulcasting could do Isotopes or ignore Conservation in some circumstances, or Lightweaving can eventually do high energy weapons) or it'll be a matter of mechanically modifying the Bubble's behavior more like the Aluminum&Conjoiner development opened up so many options in RoW.

[Steel Speedster ♂]

4 minutes ago, alder24 said:

And you don't see any problem with that? Just like @DrPhysics described in his post, without any other interaction, pressure inside a cadmium bubble would mount up and eventually would be unbearable, if the air was allowed to freely move in and out of time bubbles, like bullets do.

Well, no, of course that would be problematic. That just seems like the only explanation for the apparent discrepancy between the two WoBs.

5 minutes ago, alder24 said:

This doesn't happen, as neither Wayne or Marasi felt any difference in pressure - and Wayne created a bubble that almost stopped the time itself, which would make it a perfect vacuum in a blink of an eye.

That's true, the evidence we have for this question seems to point many different ways. I haven't come to any definitive conclusions, because I don't think there's any explanation that's consistent with all the information we have.

7 minutes ago, alder24 said:

And the WoB was about a cadmium bubble in the vacuum of space, where there is no air going into the bubble and it should get depressurized very quickly. There is some mechanism preventing this from happening, if you can somewhat trap the air in a bubble and go to space. 

Okay, true. Technically, depending on the compression factor, the bubble should hold the air in for a long time from an outside perspective. From the inside, no, that air is just gone instantly.

7 minutes ago, DrPhysics said:

If that is true, it would behave exactly as described in my post. The heating was a result of the massive compression air due to having much more air coming in than going out. That's what I simulated.

Yes.

[DrPhysics he/him]

2 hours ago, Quantus said:

I propose that the Random Deflection of air current and ballistic objects is happening because random volumes of Air are popping across into the Bubble, and it's creating a sort of frothy effect that randomly bumps the objects to impart unexpected vectors and spin, and disrupts the air currents coming it as the cohesive 'school' of individual wind currents get scattered.

There just isn't enough momentum in the air to explain the deflection of ballistic objects.

Also, the frothy effect can't be explained on a molecular level. To have wind change direction, the bubble would have to actively create (on the input side) and destroy (outgoing) matter.

 

2 hours ago, Quantus said:

Different things behave differently as they cross the boundary.  By Default:

1. Light & Radiation are unaffected

 

Actually, two things happen: 

1. They are energy-shifted so they maintain relative frequency across the border.
2. Photons are added/removed so that the intensity of light is the same on both sides. Otherwise, the inside of a speed bubble would be very dim, and the inside a slow bubble would be blindingly bright.

My current working theory: the edge of the bubble uses light weaving-like effects to essentially project the proper images like a television screen. That could explain the faint shimmer at the edge. 

 

2 hours ago, Quantus said:

Other People can pass in and out (Confirm?)

Yeah, we see Wax get knocked out of a bubble in the Lost Metal. 

2 hours ago, Quantus said:

Aluminum Will Pop the Bubble

In the Alloy of law, chapter 18, an aluminum bullet actually goes through a bubble without popping it. Could be a plot hole, might need a retcon. Or, aluminum might not pop bubbles. 

 

 

Some other rules that I've noticed:

1. They bend space-time so that gravity is what you expect inside the bubble (Gravity should be much weaker in speed bubbles and much stronger in slow ones so that dropped objects all accelerate at the same rate according to an outside observer).
2. When an object crosses into a speed bubble, it considers the center of the bubble to be "at rest" (see this discussion about a cork and a  train: https://wob.coppermind.net/events/10/#e6589)
3.  Objects aren't deflected if they leave a bubble as it drops/appears (See Wax's trick shot where he shoots another bullet at the end of Alloy of Law. He clearly fires, then the bubble drops).

4. The center of the bubble stays at rest according to what the "user" sees as at rest (like the train). You could actually launch spaceships at incredible speed by getting them to move along a rail (to prevent deflection) into a speed bubble created by an etmetal cube, then somehow attaching the cube to the spaceship and convincing the cube that the spaceship is the rest frame.

5. Our understandings of Special and General Relativity cannot describe how a bubble is made, so using them to describe what happens as you enter/exit is equally as useless.

[Rorzikel]

Sometimes I think we have to accept that at a hyperspecific level the Required Secondary Powers trope kicks in to suit the story’s needs rather than Brandon’s writing ever matching a physics simulator. If Brandon’s unable or unwilling to implement that stringent adherence to our reality, then no calculation on the matter will accurately predict future ability mechanics.

I may come at this very differently than the rest of you though. My philosophy is that hard magic systems exist so that the story can’t cheat when convenient for the plot, not that it’s airtight (pun not intended).

[drunkenbotanist]

On 7/9/2024 at 2:13 PM, DrPhysics said:

I had this in my notes, but looks like I left it out of my post (I'll add it in an edit). I'd actually add that as an argument in favor of the bouncing molecules. The air inside sees itself as inside, so all of it wants to stay inside.

True. This will probably be outdated once we get any information on what air does in a bubble (like during space travel, though keeping air inside has some really interesting applications here).

 

This was just a simple "Here's what we know now, what would that mean if we take it to extremes".

Cadmium feruchemical power storing breath is a fun coincidence here

Edited July 13, 2024 by drunkenbotanist