timberwind - Tumblr blog

[timberwind]

this is a nice little article on the views from starships traveling at high fractions of the speed of light. A little sad that the "starbow" of classic SF isn't real, but the more realistic luminous clustering of stars in the direction of travel is kind of cool in its own way I think.

[timberwind]

This is a fun paper - I'd always kind of assumed the reason Io and Europa are relatively* dry is because of their high tidal heating having desiccated their surfaces. Seems this is plausibly not actually the case! More likely that they just formed inwards of the ice-line of the jovian circumplanetary disk, similarly to how the inner planets in the Solar System are rocky and the outer planets and moons are volatile-rich.

Particularly interesting to me for worldbuilding was this bit:

Actual numbers for the correlation between tidal heating and ice shell thickness! I've always wondered just how much internal heat flux you'd need for a super-thin ice shell that could let some visible light through (like you see under the thin sea ice in the Arctic and Antarctic oceans) in areas with locally thinned ice above hydrothermal upwellings. Turns out the answer is "quite a bit, probably a bit more than 10x the heat flow of present-day Io", but plausibly not completely unachievable**, especially with the mention of periods of high-eccentricity - and concomitant high tidal heating - in the histories of moon systems that exhibit Laplace resonance. The more exciting thing is that this implies that a moon with a higher water mass fraction could migrate into an Io-like orbit and not be desiccated, which could yield some interesting cryovolcanism from the thinned out ice shell - plausibly even temporary melt lakes like the ones which we've seen frozen-out remnants of on Triton!

(*) Europa is of course famous for being a wet moon with an ocean, but notably it only has a water mass fraction of about 5-9 percent. While being about three times the mass of all the water in all the oceans on Earth, this is teeny-tiny in comparison to Ganymede's water mass fraction of 50 to 30 percent - tens of times the total surface water inventory of the Earth! Io, on the other hand, is very very dry to the best of our knowledge. Unpleasant place.

(**) This becomes far more reasonable with a larger icy moon in a younger star system like Epsilon Eridani (age cca 400-800 million years), where the residual heat of formation and radionuclide decay in the hearts of these worlds has had less time to diminish.

[timberwind]

[timberwind]

when you're 32 you will meet someone who will change your life forever

i believe you.

[timberwind]

a summer nargagooga for @renekton :3c (2022)

[timberwind]

Having now read approximately 100,000 papers on the topic, I can emerge from my chrysalis to share with you my divine knowledge: planetary climates are complicated and annoying

[timberwind]

type of guy who invariably buys the worst salami in the store because he was cursed by god himself never to buy good salami: you know I don’t like salami very much

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how far are you in children of the sky?

I actually ended up getting sidetracked by Seth Dickinson's Exordia! It completely overtook my brain by virtue of being really extremely good. Honestly I think it might be a strong contender for new favorite novel. I did in fact start CotS this morning though! The complicating factor that had me going for Exordia instead of CotS was that the copy I got was, for some reason, just A Deepness In The Sky repeated twice back to back - I didn't realise this until I was about to start reading it on the bus lol.

[timberwind]

— have you tried the peat over here — yes. i have tried all of this peat — i do not think you have tried this peat. if you had tried it you would have remarked upon it — i have tried it — you would have said, "this peat is as salty as day's honest work, and as sweet as the first sip of vodka past my lips at sundown" — is that something i say? — yes. you say it all the time — i don't think i say it all the time — yes, you do. and you would have said it when you tried that peat — let me try it again, then — oh, now he's interested — mm. wow. ok — you're not going to say it? — say what — you know what — it's nice peat. no strong associations

[timberwind]

reminder to worldbuilders: don't get caught up in things that aren't important to the story you're writing, like plot and characters! instead, try to focus on what readers actually care about: detailed plate tectonics

[timberwind]

ooo yeah classic werewolf in a weird pose

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ID Cinquecento, 1992, by Italdesign. Giorgetto Giugiaro's Fiat Cinquecento-based concept was a cute mono box small car that was developed into the Lucciola concept a year later and, with 4 doors, became the first generation Daewoo Matiz

[timberwind]

The word "time" and the suffix "-like" have both been in the English language for a very long time, but it's only in the past century or so that anyone's had much reason to put them together. You could've made the adjective "timelike" a thousand years ago, but what would you have used it to describe?

[timberwind]

yeah that's the part where the extra sideways speed you get from the spinny isn't enough to compete with the extra gravity. i'm pretty sure there's a geometric explanation due to the non-euclideanality of space near there kinda similar to how there are no stable orbits in 4 or more (spatial) dimensions (because gravity falls off as 1/r^(dim-1) for a potential shaped like 1/r^(dim-2) but the spinny™ (angular momentum of your orbit) adds a fixed effective potential ∝L²/r² which can only make a local minimum for 2 ≤ dim < 4, so in 4 dimensions it ends up flat, so any orbit will just keep spiraling in whatever direction it's spiraling in, and for 5 and above, the spiraling gets worse) the unstable orbit i'm talking about is kinda like how it is in dimension > 4, where you can have a circular orbit, but any perturbation is amplified until you either get zooped up by the black hole or yeeted away. i think it's technically the infinitely long whirl phase of a zoom-whirl orbit with maximum whirl.

it's cool for spaceships because if you have a binary blackhole system, you can jump between these knife-edge orbits around each of them and steal the pair's spinny to get going inordinately fast (i think there was one paper on the topic that boasted a claim of unbounded kinetic energy in finite experienced time). then you can zoom off to another binary blackhole system in another galaxy and do the process in reverse (giving the pair more spinny to slow yourself down). don't miss though!

Oh yeah, zoom-whirl orbits! I do know about these actually. I didn't know you could get a sort of infinite (if perfectly unperturbed) whirl phase though, that's really interesting. I actually learned about the "no stable orbits exist in >4 spatial dimensions" from it being a plot point in Greg Egan novel Diaspora, lol.

Extremely swagged out multiple-black-hole gravity assists are a very fun idea! Ultrarelativistic travel made easy*. A shame (?) most star systems don't happen to have binary black holes in their vicinities. Would be a fun thing for a setting to have the conceit that mystery precursor aliens/retrocausal superintelligent AIs/wizards dropped a bunch of planet-mass binary black holes in the Sednian depths of star systems for fast interstellar travel purposes. Could be coy and say that's what Planet 9 is, too...

[timberwind]

opinions on how you can always find a (unstable) circular orbit around a black hole no matter how fast you are going?

Prefacing this with a disclaimer that I have basically no in depth knowledge of the physics of black holes aside from like, vague ideas about hawking radiation and ergospheres lol

I thought that was only true of rapidly rotating black holes, because of the whole relativistic frame dragging thing they have going on? I was distinctly under the impression that non-rotating black holes have an inner boundary where all unpowered circular orbits with periapses inside inevitably spiral inwards past the event horizon.

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they just woke up from a nap

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I was told she pets other dogs but I wasn’t ready for how funny it is