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388 years ago, Galileo worked out why human giants can't exist

scientificamerican.com

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Re: 388 years ago, Galileo worked out why human giants can't exist

#31

Post by dahart »

Retric wrote: post #28
dahart wrote: post #21

> for if his height be increased inordinately he will fall and be crushed under his own weight > scaled-up wooden houses would not support their own roofs Hmmm this argument fails to mention giraffes, elephants or dinosaurs. (Edit: ooops it does mention elephants and dinosaurs) But clearly, land animals with bones can be quite a bit larger than humans. Similarly the houses comment ignores that large multi-story woode…

Yea, we’ve scaled wooden buildings to 25 stories. Arguments around bone scaling ignores the impact forces of running. Scaling often means trading margins not just keeping all constraints the same.

Yeah exactly. There’s an implicit assumption here that everything scales together in perfect proportion. This is a large and limiting and unnecessary assumption that undermines the argument somewhat. Maybe giant humans could exist with stockier legs…

Re: 388 years ago, Galileo worked out why human giants can't exist

#32

Post by notnmeyer »

mw67 wrote: post #24

What about dinosaurs? not sure he's explanation makes sense given we have proven that giant dinosaurs where roaming on earth for ages.

i can’t read the article to see what the specifics are, but assuming it’s essentially the square-cube law it doesn’t mean giant creatures can’t exist, it’s that small creatures can’t scale to be giants while being unchanged.

again i’m guessing, but if the conclusion is something like “if giant humans existed, X, Y and Z wouldn’t work”. then a “giant humans” would have to be something decidedly non-human.

Re: 388 years ago, Galileo worked out why human giants can't exist

#33

Post by adrian_b »

boxed wrote: post #8
fragmede wrote: post #6

Earlier quoted context omitted.

The atmosphere is believed to be more oxygen rich back then, in order for those dragonflies to exist.

That seems to not be the reason from the latest data. Insect oxygen transfer basically doesn't scale cleanly with oxygen in the atmosphere like the original hypothesis thought. What IS true though is that pterosaurs and later birds and bats came onto the scene, and that's just game over for giant dragonflies.

Vertebrates have 2 essential advantages over insects, at big enough sizes.

An efficient circulatory system and myelinated nerves.

At small sizes, the circulatory and respiratory systems of insects work better (less friction for blood in the absence of capillaries and less friction for the air that circulates as a gas through the body), but at big sizes those of vertebrates work better, due to efficient pumping.

The myelinated nerves have the same speed for propagating nervous signals as non-myelinated nerves that are much thicker, so thick that an insect could not have many such nerves. At small sizes this does not matter, but at big sizes if the nerves are not fast enough the reaction times of an animal can become too slow, e.g. the head might need a big fraction of a second until noticing that something bites the tail.

The combined results are that an insect as big as a typical vertebrate would react mostly sluggishly and it would be able of only very short bursts of intense activity, before becoming tired. This would put it at a serious disadvantage.

Re: 388 years ago, Galileo worked out why human giants can't exist

#34

Post by Melatonic »

vivekd wrote: post #4

I don't know how convinced I am. First there were dinosaurs in the past, the brachiosaurus was 4 x as big as an elephant and there are probably yet undiscovered dinosaurs that were even bigger given discovery of partial fossils like the Sauroposeidon. Also we know in the past there were dargonflys with wingspans greater than 2 feet and centipedes that grew as long as a car.

Giant bugs are a totally different design though - don't they basically have a big exoskeleton made of different stuff than bone ? That's more like how we design a modern tank or airplane

It's also possible that for larger creatures a less dense and more flexible skeleton material (in general) might be ideal. Especially for animals that are not warm blooded (larger volume to mass ratio might resist temperature changes better?)

Re: 388 years ago, Galileo worked out why human giants can't exist

#35

Post by canyp »

mw67 wrote: post #24

What about dinosaurs? not sure he's explanation makes sense given we have proven that giant dinosaurs where roaming on earth for ages.

It's answered in the article. The argument is not that giant creatures can't exist, but that they cannot exist as a simple scaled-up version of the otherwise identical smaller version.

Re: 388 years ago, Galileo worked out why human giants can't exist

#36

Post by projektfu »

twotwotwo wrote: post #20

About the argument that a beam's strength:weight ratio worsens as it grows: do the artificial structures humans use, like house frames or bridges' trusses, recover strength:weight ratio? Would a theoretical giant with a skeletal structure like a bridge or a house's frame be better off than one with a human-like skeleton of the same material? (And, related to another comment here, guessing the actual structure of bone…

Actual bone does incorporate some things we would consider "architectural" or "engineering" techniques to do more with less, not least of which they are composite materials and not mere rocks. They remodel the structure dynamically to respond to stresses as well.

Re: 388 years ago, Galileo worked out why human giants can't exist

#37

Post by projektfu »

vivekd wrote: post #4

I don't know how convinced I am. First there were dinosaurs in the past, the brachiosaurus was 4 x as big as an elephant and there are probably yet undiscovered dinosaurs that were even bigger given discovery of partial fossils like the Sauroposeidon. Also we know in the past there were dargonflys with wingspans greater than 2 feet and centipedes that grew as long as a car.

One theory about large sauropods is that they were aquatic animals that propelled themselves like hippopotamuses, using their feet against the bed of the lake/river. Just as whales can get very large, so could buoyant sauropods.

Re: 388 years ago, Galileo worked out why human giants can't exist

#38

Post by kergonath »

twotwotwo wrote: post #20

About the argument that a beam's strength:weight ratio worsens as it grows: do the artificial structures humans use, like house frames or bridges' trusses, recover strength:weight ratio? Would a theoretical giant with a skeletal structure like a bridge or a house's frame be better off than one with a human-like skeleton of the same material? (And, related to another comment here, guessing the actual structure of bone…

> do the artificial structures humans use, like house frames or bridges' trusses recover strength:weight ratio?

There is some improvement from computer design. We have better tools to know the margins that allow us to remove as much material as possible, things like that. So we can tweak existing designs to make them more efficient, like adjusting the section of beams to make them as strong but with a few percent less materials.

But the major improvements come from using different materials and new techniques, side-stepping the scaling issue.

For example, we could not scale old arch bridge designs very far. Getting steel beams let us build truss bridges, but even these cannot be that long in a single span. Suspended bridges were a step forward, with the improvement coming not from better beams, but from removing them altogether. Then, cable-stayed bridges solved some issues with older suspension designs and we can now have very large spans. Every time, scaling up is enabled by a change in strategy.

> Would a theoretical giant with a skeletal structure like a bridge or a house's frame be better off than one with a human-like skeleton of the same material?

Looking at things like elephants and dinosaurs, there certainly would be a way to have bones strong enough to support a 10m high human-like thing. Now, whether we would recognise that thing as human, I don’t know. Every time the problem was solved, there were significant compromises. I am not sure a giraffe’s vascular system could sustain a human’s brain. Elephants are not particularly agile. Whales cannot get out of the water.

Re: 388 years ago, Galileo worked out why human giants can't exist

#39

Post by kergonath »

timedude wrote: post #19

Important to keep in mind that the earth was smaller back then with lower gravity. The earth grows like all other living organisms.

What do you mean? The Earth does not "grow" and is not really bigger now than at any point in the past (since the creation of the Moon). On the contrary, it is losing mass through the escape of light atoms escaping, but even that is absolutely tiny.

Also, the Earth is absolutely not a living organism.

Re: 388 years ago, Galileo worked out why human giants can't exist

#40

Post by OrvalWintermute »

kergonath wrote: post #39
timedude wrote: post #19

Important to keep in mind that the earth was smaller back then with lower gravity. The earth grows like all other living organisms.

What do you mean? The Earth does not "grow" and is not really bigger now than at any point in the past (since the creation of the Moon). On the contrary, it is losing mass through the escape of light atoms escaping, but even that is absolutely tiny. Also, the Earth is absolutely not a living organism.

The earth is both gaining mass and losing mass at the same time

We are losing gases and energy (hydrogen, helium, radioactive decay)

Concurrently, we are aggregating cosmic dust, micrometeorites, meteoroids, and the occasional larger body

Overall a tiny loss

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