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The dicarbon molecule, C₂, does exist in nature. It has been detected in stellar atmospheres, the interstellar medium, and cometary comas. The fluorescence of C₂ in the latter contributes to the green appearance of certain comets, including C/2022 E3 (ZTF) currently approaching Earth.

However as discussed in this paper (link to abstract only), the 4th inter-carbon bond does not make for a 'stronger' molecule:

>Quantum chemical calculations using the complete active space of the valence orbitals have been carried out for HnCCHn (n=0–3)...

>The bond dissociation energies and the force constants suggest that C₂ has a weaker C−C bond than acetylene, C₂H₂.

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Essentially an offshoot of a Dyson sphere. I‘ve always wondered about the mechanics of those. ;-)

Pregnancy is an inherently dangerous for us, mammals.

I’ve read of lion cubs in breach position who would have died if not for veterinary assistance. And, of course, the whole body of literature on medical problems in domesticated animals.

A free neutron can decay because its mass-energy is greater than that of the resulting particles, proton + electron + antineutrino (and because it meets a few other conditions). But the binding energy that keeps a neutron in a nucleus is negative (and therefore the mass of a nucleus is less than the sum of the masses of its constituent protons & neutrons). If the neutron decayed it would violate conservation of energy, and therefore it must be stable.

However, in some neuclei the energies work out such that a neutron can still decay! We call those radioactive isotopes. For example ^(14)C decays into ^(14)N by emitting an electron+antineutrino and changing one of its neutrons to a proton - sound familiar?

Matt Strassler has a good article on exactly this topic, which also links to his articles about particle decay in general: https://profmattstrassler.com/articles-and-posts/particle-physics-basics/mass-energy-matter-etc/the-energy-that-holds-things-together/neutron-stability-in-atomic-nuclei/

As with all population-wide things, it’s a range: some bodies mature sooner, some later in life. The number 25 is a convenient mid-range estimate.

Let’s take an example that we can actually see, and use it as a rough marker for physical development: wisdom teeth. The majority of people get them between 18-26. In some instances, however, the wisdom teeth don‘t erupt until the age of 40! This indicates that the individual’s body is still developing at that age.

Hope this makes sense.

There’s also the issue of the invasive placenta, another issue caused by big brains—the human placenta has blood vessels that burrow into the uterine lining to get maximum oxygen and nutrients from the mother’s blood supply. This can easily go wrong—too invasive and the placenta can cause bleeding and/or the placenta getting stuck, to little and the embryo can’t develop normally.

Thank you.. I know nothing about anything but understood most of what you said.

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No. The ring particles are in orbit, and orbits that are closer to the planet always go faster. So the inner particles are always moving faster than the outer particles, and can’t stick together.

If you took Saturn’s rings and added more ice particles to them, they would not weld together. Instead, collisions between particles would knock more of them into higher orbits and more into lower orbits. The ring would get wider, and a lot of the mass you add would fall into Saturn.

Even if you tried to build a solid structure shaped like Saturn’s rings from scratch out of steel, the difference in gravity between inside and outside would create tremendous forces that would rip it apart.

Ringworld is a popular science fiction based on (sort of) the same idea. The ring in it is essentially a huge ring around a star instead of a planet, some 100s of million miles in diameter, and is artificial. Also, it's facing the sun. The science isn't actually accurate I think but it's a good story if you want to read.

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The rates of pregnancy mortality are naturally far higher than other mammals. This is hard to quantify, but pregnancy used to be a significant mortality risk not that long ago. I can't think of another mammal where this is the case.

Most of the reason why is walking upright. Evolution has to work with what it has and to take a quadruped and make a biped it came up with some less than ideal solutions. Our spines for example are terrible need to balance weight towards the back let's add some S curves. An "intelligent designer" would have been fired for that work around.

Our hips also had to change shape and shift back and forward and needed greater flexibility in the ball joints. Initially the sacrum became broader allowing the birth canal to become larger allowing for larger head seizes, but then larger head sizes were selected for. Birth canal size limited by the pelvis and baby weight (too low lower baby survival too high birth mortality) led to a high selective pressure around an ideal baby weight. Until recently it was of the best examples of optimized selection. Even with the high birth risks larger head size was still favorable so fetus skulls are born not fully formed which is why babies have soft spots in there head. The unfused skull can deform during birth to squeeze through the pelvis and why they can come out looking like cone-heads.

Walking upright and selection for increasing large heads made for a dangerous combination to human women and if there was an "intelligent designer" they really phoned it in.

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Orbital mechanics, has something to say about stable orbits. Material closer to planet must travel faster, material further away must travel slower. A ring of any sizeable width will swirl over time, spinning faster or slower depending on distance from the body it's orbiting.

Not an astrophysicist, but I believe that's the same driving force that can make rings. When a moon's orbit degrades to the point where the difference in gravity between the near-side and far-side is greater than the moons own binding gravity, the near side will naturally accelerate away from the moon while the far-side luffs off behind.

So no, a ring cannot be a solid plate. But a series of hoops with bearings between them? Well probably not that either since rings aren't flat but undulate up and down in the plane of their orbit due to... Science.

Well first of all, matter doesnt compress in that way. A ring would be far too thin and mostly empty to form. Not only that but tidal forces and impacts would damage a ring very quickly. Technically a solid ring around a planet is possible, but hardly if ar all through natural formations, and would probably have to be made

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It can. Carbon can actually form a quadruple bond with itself but the fourth bond is extremely weak because of the way the hybrid orbitals are arranged. Strength of bond depends on orbital overlap and these fourth orbitals are pointing in opposite direction (think the hydrogens in acetylene) so there's little overlap.

So C2 isn't a very stable molecule; it's also not a particularly interesting one since it's literally just two carbons.

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This is the best answer. Other animals can die, but Humans, and some select animals like hyenas, have an issue of trying to pass a large thing through a small hole which is especially dangerous.