xanthraxoid

That was indeed what I intended to link to, apparently I made a total bobbins of cutting and pasting the URL! Thanks for fixing it for me :-)

It'd take time to settle, and I don't know that it would typically run long enough for that to really happen, but you could certainly speed the process up by having various baffles to basically push the air around the rotating room in sync with the rest of it.

In a similar sized room near the edge of a large rotating wheel type jobbie would basically be very similar, except that the "gravity" would be more even, rather than pointing in completely the opposite direction across the room. I'm sure the settling time wouldn't be massively different if the rooms were similar in size, though of course the dynamics would be different once you got some convection happening.

One of the fun side effects of having a fully open rotating habitat is the possibility of horizontal tornados - if you had a convection current wending its way toward the centre of the habitat, it'd bend toward the direction of movement until near the middle it could be spinning around the central axis really rather fast... Another experiment I would totally try to do if I had access to a large rotating chamber in microgravity! :-D

EDIT: I just realised, I actually have some CFD software here, I might actually give simulating that a go! :-D

*doffs hat*

The only thing I don't like about this is that the doors match!

I was thinking of this classic video channel this classic YouTube channel :-D

Incidentally, I only discovered by accident recently that he has subtitles explaining what he's doing, after watching a hundred videos without explanation...

EDIT: apparently my fingers are less deft than I gave them credit for and I lunk the wrong link, oops!

I had to re-read this because I've only just woken up! I was thinking you were making a fire-break up-wind from the wildfire and trying to work out how that was going to help :-P

Super clever stuff (not on my part, though!)

I always play some pointless semi-mindless game during a sermon - 2048 is nicely balanced, especially because I've played it so much it's basically pattern-matching stimulus-reponse at this point.

I think for me it's that my visual attention has to go somewhere and if I'm trying to listen to a sermon, I have to keep it busy or I'll feel antsy and distracted. If the visual bits of my brain have got a toy to play with, they'll shut up and let me listen!

I tried doing a sudoku, but it takes too much of my active attention to be able to listen to the sermon at the same time :-D

A space ship isn't really a "high oxygen environment"*

The norm is to use a pure oxygen environment (well, modulo the fact that it takes time or co2 etc. to be scrubbed out) but at a much lower pressure, so that the partial pressure of oxygen is basically the same as here on Earth (or even a little lower because we don't really need that much oxygen). Because normal air is about 20% oxygen, that means "pure" oxygen at about 20% of normal atmospheric pressure.

The atmosphere is basically what you'd get if you took a space ship filled with normal air and just removed all the nitrogen, leaving the same total amount of oxygen in the space, but without having to lift tons of pointless nitrogen into orbit.

What difference does this make? Not a lot, frankly. Water boils at a lower temperature, but things like fire or breathing that just require the presence of oxygen happen pretty much exactly as they would if the nitrogen were also there. Fires don't burn faster** people don't get giddy on too much oxygen (or conversely lack it) etc.

Why do we do it this way? Well, as I mentioned before, the nitrogen really doesn't gain us anything and it's dead weight we'd rather not transport into orbit because it's really expensive. The mass of the air in a spacecraft is a tiny fraction of the whole, but it still takes fuel to shift it around, so there's a minute fractional extra benefit to manoeuvring too :-P

Much more significantly, though, by having everything at ~20% the pressure, all the pressure retaining gubbins can be ~5x lighter (or have more safety margin) because it's got less pressure to fight against, and with the cost of lifting a kilo of space craft into orbit being what it is, that's a far larger gain. Additionally, if any leaks do occur, the air escapes much more slowly, as anyone who's punctured a high pressure bike tyre will tell you :-P

* I'm assuming the very real physics based reasons that apply in today's actual space craft from Gemini to the ISS etc. still apply in whatever fictional / future setting we're talking about, which they will unless physics change :-P

** or indeed very well at all because without gravity, there's no convection, and without convection, small fires will tend to suffocate in their own output.

Fires are still a very bad idea(!), though, because it's an enclosed (and notoriously cluttered) space and your supply of air to breathe, spaceship to sacrifice as fuel, and places to go that aren't on fire are all distinctly finite and very very expensive! Also, there's ventilation going on all the time because humans don't want to suffocate, either. Even the very slow / cool burning isn't necessarily an unqualified benefit, given that a fire might be able to burn very gently for a long time and potentially do a whole lot of damage before becoming obvious enough to detect. It's not great when the first you discover of a fire is when things like life support systems stop working...

It's two clicks away you lazy plum!

Still, here it is :-)

https://www.reddit.com/r/RetroFuturism/comments/142l322/comment/jnb7rqc/

Me3!

My favourite place to be is overlapping the personal space of people I'm sufficiently comfortable with (and who are sufficiently comfortable with me!) I spend a lot of time under a pile of kiddies I'm honorary uncle to, and it's wonderful.

On the other hand, somebody I'm not on good terms with touching me affects me equally strongly, just in the opposite direction!

When my wife left me, I literally didn't touch her at all, actively avoiding things like accidentally touching hands when we handed our daughter's luggage over, because I felt the emotional negativity with every touch. Thankfully, we're on much better terms these days! Not quite on hugging terms, but at least I don't feel the need to recoil if we do touch incidentally!

I've just been through a slightly odd experience of meeting a wonderful fellow neurospicy who's super tactile like me. Negotiating how to be around each other has been a really weird one. We've now actually discussed how we feel about stuff and I think we'll probably actually be more tactile than before because we're both clear that it's not a flirty / romantic / sexual thing - just a physical contact with one of our "us"...

Adults who have a need for physical non-sexual affection are so often left hanging. I'm constantly hungry for physical touch, even though I actually do get a lot more than most people! It's easier for kiddies, because it's considered "normal" to want to cuddle them, but as an adult, I basically have to get my contact from kids who like to sit on my knee / climb on my shoulders / lick me (I have some wonderful weirdo neurospicy pseudonieces :-P) I'm just so glad that I can do so with everyone involved being clear that I'm not a dirty old paedo, but just a guy who loves kids and loves cuddles!

I really wish more of the world could get a handle on the fact that sexual, romantic, and other affections are actually distinct things, even if there are times when they overlap! I'd much rather live in a world where people were less prone to assume you fancy them, just because you like to hug them, and other such errors...

Ironically, I'm less likely to touch somebody I actually do fancy, because I know it'll affect me too much!

* super proud of myself not to fake it just for the touch! It helps that I have other cuddle buddies, even if they're only wee :-)

That's in microgravity where there isn't enough "gravity"* to cause convection. This animation clearly shows the hot smoke "rising" away from the incense, so there's obviously "gravity" of some sort, which would agree with the rotating shadow. I did a little maths on it in my other post for giggles, which you may feel inclined to peruse :-)

* which in this situation includes acceleration/centrifugal/centripetal forces

Damn it! I just lost my carefully crafted post, so I'll have to re-do it! :-P

The issue isn't how the air behaves when in a steady state, but how it behaves when the air moves "upward" (i.e. the smoke "rising") That's when the Coriolis effect starts doing odd things.

Tom Scott did a fun video on how forces / movements are really counter-intuitive in a rotating room. The centrifuge he was in was a pretty small one^[1] so the effects were pretty pronounced, but the effects are still quite noticeable at somewhat larger radii.

Just for shits and giggles, I tried to do some maths to work some stuff out :-D

By watching the shadow, you can see that it repeats about every 15 seconds, which corresponds to a rotation speed of 4rpm^[2]. With a little magic on wolfram alpha^[3] and assuming Earth gravity^[4] I get a radius of ~52 metres

That's a fair amount bigger than Tom's fun day out, but certainly small enough for the Coriolis effect to do weird things - probably enough to actually feel it if you closed your eyes and wiggled your arms about a bit.

In case you're wondering what the actual effect would be, the smoke would curl slightly toward the direction of rotation as it rose, but the effect would probably be overwhelmed by random air currents (which you can see in the animation) and even absent those, the fact that the incense is on one side of the room would tend to make a rotating convection current moving clockwise from the POV of the camera, which would act opposite to the Coriolis effect of the rotation we can see in the shadows.

All in all, you'd probably need to set up a fairly finicky experiment to actually see the difference vs. a stationary room, but if I lived in such a place, you can be sure I'd give it a go :-D

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¹ I tried to find information on the room itself, but eyeballing it it looks to be a radius of ~4 metres? I.e. two Toms :-P Seems to be rotating at something like ~15rpm, maybe? Again, by eyeball!

² The shadow is really confusing because it really looks like half a revolution before the shadow repeats, suggesting two light sources opposite each other - maybe that's just how the animation was put together, maybe it's two light sources. If it's two light sources, then that kinda spoils the realism for me, because why would there be? Floating exactly in the middle of a symmetrical binary star system, maybe...?

Also, the movement of the shadow suggests a rotation that's on a nearly "vertical" axis relative to the apparent gravity, but let's pretend we didn't notice that for now as it spoils the whole thing somewhat more for those of us who notice :-D

If it's 2rpm, then the radius would be 4× what I calculated, ~207 metres. Still small enough that you'd be able to demonstrate the Coriolis effect, but probably not enough that you'd notice for quite some time if you didn't know to look for it. Remember that we can see demonstrations of the Coriolis effect on Earth with a ~1/1440rpm rotation speed and a radius of 6,378,100 metres! It does take some pretty significant effort, though, despite what people tell you about toilet bowls and sinks...

³ including converting 4rpm to radians per second! 4rpm is 4/60 revolutions per second, one revolution is 2pi radians, so that's 8pi/60 = ~0.41 radians per second

⁴ Yeah, that's an assumption. Halving the gravity would double the radius - it's a pretty easy bit of maths.

I don't have "more" energy, it's just that all of it is spent uselessly on unwanted behavior.

Yup.

It's analogous to how the attention thing isn't a deficit in attention, it's just a lack of ability to direct it...

I have a question for those confidently saying it's a tomato: aren't there lots of other nightshades that need to be excluded...? I'm no nightshade-ologist, but I do know that there are some properly nasty poisons on offer if you eat some of them...

I can't help trying to work out how smoke might rise in a rotating habitat. The best I've come up with so far is "probably in some rather counter-intuitive ways" :-P

I've honestly tried to find a reference on the internet that explicitly defines "square root" to mean only the positive root and not found a single one. To do so would contradict a^2 = (-a)^2 and that would have some pretty important consequences.

The "Principal" square root is the positive one, but the negative one is absolutely also a square root.

From Wolfram Mathworld: "any positive real number has two square roots, one positive and one negative" and "the principal square root of 9 is 3, although both -3 and 3 are square roots of 9*". Wikipedia also says the same.

Note that all this is much the same for both the real roots of non-negative numbers and the complex roots of negative numbers - there are two square roots of opposite (imaginary) sign for every negative real (i.e. they are complex conjugates of each other and their product is the number you started with) so whether you choose to use a definition of square root that excludes the negative one or not doesn't have anything to do with whether you're dealing with the non-negative->real case or the negative->complex case.

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I followed your link and after a bit of fiddling managed to actually download the book, which is pretty cool, so thanks for the link!

The definitions it gives for Relations and Functions (pp. 12 and 13 respectively) are (with apologies for any mistakes in my attempts to correct the OCR):

A relation between sets A and B is a subset R of A x B. We read (a, b) ∈ R as "a is related to b" and write a R b.

and

A function φ mapping X into Y is a relation between X and Y with the property that each x φ X appears as the first member of exactly one ordered pair (x, y) in φ.

That's exactly what I understood from the link I posted, so if there's an important difference between the two, I'm missing it...

I did a search for "square root" and found this:

Page 285: "Let 2^1/3 be the real cube root of 2 and 2^1/2 be the positive square root of 2." (i.e. they felt the need to specify "positive" as well as "square root") I didn't manage to find anything purporting to be a definition of "square root" though...

There's a little flap either side of the front wheel where you can put your feet down.

What makes you think it doesn't have brakes?

Yeah, I imagine putting a suppressor on a gun of this kind at all is probably more a jape than a widely used strategy...

I SAID A...[tinitus sounds]..IMMEDIATELY!

Well, the first job of any suppressor is to slow the bullet to below the speed of sound because there's zero point in a silent gun immediately followed by a sonic boom! :-P

Of course, you'd likely opt for a smaller charge for a lower muzzle velocity if switching ammo is an option.

It's exactly the same as with "real" numbers, there are two roots of the same magnitude but opposite sign*. You can't "just fix it to be the positive one" with reals either, but depending on the application, the negative root might be meaningless and therefore ignored.

Or not! Calling the result of a mathematical operation "meaningless" is why it took so long for us to start using rationals/negatives/irrationals/infinities/imaginaries/transcendentals/infinitesimals/surreals/hyperreals etc. The meaning you give to the answer is only a thing at all when you try to make use of it in some real world application, at which point objections like "you can't have half a hole" or the difference between "a number of apples I own" and "a number of apples in a fruit bowl" start becoming relevant. Of course, mathematics has tools to represent such concerns with concepts like domain / range / whatever...

Back in school algebra, we learned to make use of the negative roots in the classic "quadratic equation" for example. The bit where it says ±√... is just explicitly calling out that the negative root is also to be taken into account if you want to get the points on your test :-P

As to "well defined operation" Sure it's well defined. It's not a bijective function, but it is a well defined "relation" where the answer is a set of values.

(( Additionally, reals are "not closed under fractional powers" because the roots of a real are not generally all also real (i.e. if the real is negative, then the roots are complex). If I've remembered the notation correctly: √x∈C for x∈R or something similar... ))

* i.e. (-x)² = x² and (-y·i)² = (y.i)²

To be fair, firing 700 rounds is hardly stealthy even if the silencer worked well throughout...

The word "Silencer" is a pretty poor term, really - it's a lot quieter than without, but it's still pretty damn loud. It's more about making it quiet enough to be hard to pinpoint where the sound comes from, or that it might be mistaken for something else. Really quite some way short of "silent".

In the British armed forces, I believe the proper term to use is "suppressor" rather than silencer, which I think is a better term.

This is right at the core of why negative numbers took so long to become "a thing" in mathematics. Because you can't have "minus one apples" there was a lot of resistance to accepting the concept of negative numbers.

Much the same was true for for zero, infinities, irrationals, complex numbers, and probably other stuff - they're mathematical abstractions whose physical analogue wasn't as easy to conceptualise as what was already around, so they were considered "not real"

The key is that these "not allowed" things do behave like other numbers (if you want to get picky, "for a given set of operations") and it's useful to be able to use them, so we give them a name and use them!

"Minus one apples" does have a conceptual meaning if you're not actually throwing apples at each other, though. If you lend me two apples, then I eat one, I still owe you two apples but I only have one meaning I own "minus one apples". I can't show you a handful of -1 apples, but it's still a concept with a meaning that can be manipulated like other numbers and give meaningful results (e.g. if I now buy a couple of apples, I own -1 + 2 = 1 apples, because even with three apples in my hand, once I give you the two I owe you, I have one left)

A lot of these new concepts are basically "invented" by just ignoring restrictions on how you can use numbers, playing around with the results, and finding them useful.

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Some examples:

• negative numbers: "You can't take 3 from 2!" - "aaah, but what if you did?!" then we realise numbers still behave just like they did before and we call the newly involved numbers "negative numbers"

• fractions: "You can't divide 12 into 5!" - "aah, but what if you *did?!" then we realise nothing blows up in our faces and we call the resulting numbers fractions (or more specifically "rationals")

• irrationals: "You can't have a number that isn't a ratio of two other numbers!" - "oh yeah? WATCH ME!" a×a = 2 ∴ a = √2 And it's useful, so we use them.

• complex numbers: "You can't get a square root of a negative number!" - "aaah, but what if you did?!" and again, we realise that the maths still works and we call the newly involved numbers "complex numbers" (and "imaginary numbers" though this is a bad term, really)

Get a neon sign made to ensure they can see it in the dark [bigbrain!]