2013/01/14

The Lord Abhors Dishonest Scales

Proverbs 11:1 (well, if we add in "...but accurate weights are his delight"). I assume it's partly metaphorical, since "preferring the lesser good to the greater" is the only smart definition of ill-will (one cannot actually desire evil).

Anyway, this is a reality check for meself. Remember, few posts back, when I talked about how you should keep gravity in mind, designing an alien world? It occurred to me, I probably omitted the square-cube law, the bane of so many science fiction writers (e.g., this).

See, presumably, a difference of gravity would have an effect on the mass, therefore the volume, of colonists, and their height would vary by the cubic root of that ratio. Thus, if your planet is like the one where most of my first SF book takes place, and has a surface gravity 92% of Earth's, the inhabitants are going to be [1/(3√(.92))=1/.97=1.03] 3% taller than Earth-humans. Of course, zled colonists on the same world, since their homeworld has a surface-gravity 8% higher than Earth's, will be living in 85% gravity (relatively speaking). So their colonists will be [1/(3√(.85))=1/.95=1.05] 5% taller than Lhãsai-zledo. ("Lhãsai" is pronounced "ɬasai", with the vowel of its first syllable "purred", because I am a crazy person.)

I don't know if I'm right in assuming height varies by the cube-root of the gravity difference, but it seems reasonable given the effect a thing based on mass (like gravity) tends to have on single dimensions.

Incidentally, if this principle is applied to Niven, Crashlanders being 24% taller than Flatlanders means that We Made It would have to have 52% Earth's gravity, or 37% higher than Mars. Actually, that sorta seems closer to what Niven was describing, although it's even lower than the old number I calculated.

3 comments:

Anonymous said...

Scaling by gravity when comparing species assumes that there's an optimum height for sentient creatures in any given gravity, and there's not much variation from that height. But for all we know, in our own gravity, it may be possible for sentient creatures to vary from two to twenty feet high; and the single species we have for reference, our own, has subpopulations (pygmies) which are about 25% shorter than the norm. Also, IIRC, the reason some dinosaurs could get stupidly big was higher oxygen levels in the atmosphere; not that the dinosaurs were sentient, but the effect might be important.

Note especially that we have no idea what the minimum size of a sentient creature would be. It's usually assumed that one would need a brain roughly the size of a human's to run a human-level intelligence, but there are hydrocephalous people with a far smaller volume of brain tissue than normal who show above-average intelligence. (Cf.) A sci-fi author is additionally at liberty to propose that the brain tissue of their aliens is denser, faster, more efficient, etc., which should provide ample excuse to write aliens whose brain is less than 1% of the volume of ours. Sci-fi authors seldom do this, however, and usually only when inventing non-carbon-based lifeforms, which are sufficiently exotic to allow authors to throw existing preconceptions out of the window.

Sophia's Favorite said...

Only...I wasn't scaling by gravity when comparing species, because I wasn't comparing species at all.

All my comparisons were within species, between the home planet and colonists on planets with different gravity, "all other things being equal". The closest thing to comparing two species that I did is mentioning that a species whose home gravity is heavier would experience more low-gravity effects than a human would, on the same planet.

And pygmies don't count; they are that small because, for about 3000 years, the farmer-cultures took the tallest hunter-gatherer women off to be their wives, which selectively bred the hunter-gatherers for shortness. Wolves are an apex predator in parts of their range, and the domestic dog is a subspecies of wolf—but that doesn't make chihuahuas a valid basis for statements about apex predators.

As for "higher oxygen levels in the atmosphere", it depends on when; in some parts of the Mesozoic O2 levels were about half what they are now. Of course, effectively, that means they were the same—the dinosaur respiratory system is about twice as efficient as the mammal one, that's why modern dinosaurs can fly much higher than bats.

penny farthing said...

"As for "higher oxygen levels in the atmosphere", it depends on when; in some parts of the Mesozoic O2 levels were about half what they are now. Of course, effectively, that means they were the same—the dinosaur respiratory system is about twice as efficient as the mammal one, that's why modern dinosaurs can fly much higher than bats."

This makes me very happy.

I'm glad there is someone out there who does this type of math for books. At Barnes and Noble I had to suffer through a guy telling me about this great hard science fiction he was reading, and how it detailed how this one species had evolved into energy beings. I was torn between rage and pity.