What caught my eye was the oscillation in the abundancy graph, there is a tendency for even atomic number elements to be more abundant than odd atomic number elements. Looking at the original Wikipedia article leads to the Oddo-Harkins rule http://en.wikipedia.org/wiki/Oddo%E2%80%93Harkins_rule. There is more discussion on the stability of even vs odd atomic number elements here: http://en.wikipedia.org/wiki/Even_and_odd_atomic_nuclei. From the latter link, roughly 60% of stable nuclei have an even number of protons and an even number of neutrons. Only 2% have an odd number of protons and an odd number of neutrons.
It would be nice if someone could explain any of the exceptions to the Oddo-Harkins rule, such as the dip at atomic number 44, Ruthenium.
The underlying mechanics are highly theoretical, but it has something to do with the quarks that compose protons and neutrons. The Strong force is theorized to be caused by color-charge attraction. It would be the same situation as if photons (light, etc) were highly magnetic, they'd attract molecules; in this way the charge carriers of the 3-way color force are highly (and mutually) attracted to quarks for their color-charge.
There's a radius for color-charge interaction. This radius is thought to be one cause for larger elements being less likely to be stable; when protons are too far apart to exchange color-charge carriers, their magnetic repulsion can disrupt nucleic stability.
And different quarks have different energies. Every neutron has 2 Down quarks and 1 Up quark (UDD); every proton has 1 Down quark and 2 Up quarks (UUD). Down quarks are more energetic (massive) than Up quarks. After about 5 minutes, a neutron (UUD) decays into a proton (UDD), an electron, and an electron neutrino. This would seem to imply that an electron and a neutrino would equal the difference between an Up and Down quark.
All protons and neutrons have 3 quarks. There are other particles with 2, but they're much more rare. Nuclei with an odd number of nucleons (protons and neutrons) would have to have an even number of quarks. There may be something to the number of quarks, research into that is difficult because the act of pulling quarks apart requires so much energy that it just creates new quarks.
when you roll 2 dice, you get a lot more evens than odds.
i imagine the same principle holds. if an odd (Hydrogen) forms with another odd, you get even. Hydrogen+helium=odd, but helium + helium = even. as the evens outnumber the odds, even more evens are forming with evens.
This is a really interesting thought. Assuming you can only add two atoms at random, there are four options:
odd + odd = even (odd reduced by 2, evens increased by 1)
odd + even = odd (evens reduced by 1)
even + odd = odd (evens reduced by 1)
even + even = even (evens reduced by 1!)
When the evens outnumber the odds, odd+odd will be rare, so the percentage of evens will tend to decrease until it reaches 50%.
No matter many of each type you start with, the equilibrium position is 50-50% odd and even.
However: there may be an exception to this. If all the odds are in one place, then odd-odd may be more likely than random. If you have all evens in one place, you can't get back to having odds again - you can't (ever) increase the number of odds that already exist to balance things out, you can only decrease the evens. 0-100% odd and even could also be an equilibrium position.
Note that the very interesting graph near the end of the article actually displays element abundance in the solar system, not in the universe. (Found that out when looking it up in Wikipedia.) The article misrepresents this!
The cosmological principle works when considering a large enough scale. A solar system of a particular type of star, even though that star is pretty average and unremarkable, is not really large enough.
While water will break down at high temperatures I would find it surprising that 1st and 3rd most common elements in the whole universe, that readily combine to form water would not result in substantial amounts of water.
It's probably like saying we shouldn't find H2 because "nothing says they are found bound together"
Most atoms- and certainly most hydrogen- are in stars, no? Not exactly places where water "breaking down at high temperatures" (really, never forming) can be ignored.
You provided a conjecture based on incomplete data as fact, he stated that it's conjecture until additional data to support it is there... the burden in this situation is not on him.
> You provided a conjecture based on incomplete data as fact,
No, I never said it is a fact, it is, as you pointed, a conjecture, and I provided a source (ok, wikipedia) for the amount of water in the universe
If you or him knows of a reason for why the most common elements in the universe that combine easily wouldn't result in an abundance of their combination I'm all ears.
(Which doesn't mean the amount of water is going to be near the amount of H2 or just the amount of Hydrogen present in the stars)
As for lithium (the third-most abundant element after the Big Bang, at 0.00000001% of nuclei), it so happens I was just reading the James S. A. Corey novel Cibola Burn where it plays a role:
"People used to think gold was worth fightin' over, and that shit gets made by every supernova, which means pretty much every planet around a G2 star will have some. Stars burn through lithium as fast as they make it. All the available ore got made at the big bang, and we're not doin' another one of those. Now that's scarcity, friend."
Naw, or at least according to what I've been reading lately we get lithium and a number of other light elements from cosmic ray spallation: (https://en.wikipedia.org/wiki/Cosmic_ray_spallation so it's happening all the time.
Reminded me how crazy it is that we're in a time where we've legitimized the fabled goal of alchemic transmutation - we can turn mercury to gold. Turns out the philosopher's stone was a particle accelerator.
> Basically, the hydrogen-helium abundance helps us to model the expansion rate of the early universe. If it had been faster, there would be more neutrons and more helium. If it had been slower, more of the free neutrons would have decayed before the deuterium stability point and there would be less helium.
> If it had been faster ...
> If it had been slower ...
Isn't the inflation conceived to be as fast and long as necessary so that inputs to baryogenesis give result with hydrogen to helium ratios that are in line with experimental data?
As I understand it, something like the big bang produces mostly light elements -- hydrogen and helium. Everything else is produced in the stellar fusion machine plus supernovas.
So, by the time that the heavier elements are forming, the big bang has been done with and forgotten about for at least, like a microsecond. ;-)
I was referring to creation of hydrogen, helium and traces of some others like lithium.
Thinking about what you said I think necessary condition to get big bang hydrogen/helium ratio is that although there must be very high energy density we must not have too much of gravitational confinement because that would spark fusion and mess up the ratio bringing to closer to what we have currently in the universe.
I've always wondered how elements produced in past stars end up in our solar system. I wouldn't think the whole universe is getting remixed all the time. It seems like areas stay pretty isolated.
At the universal scale, we can observer several galaxies in various stages of colliding with each other (1). In fact our galaxy and Andromeda are on course to collide with each other in about 4 billion years (2).
Massive stars end their lifecycle in a supernova explosion, which blasts much of their mass off into space. the remaining stellar core either forms a neutron star or a black hole. The mass that is blated off contains many heavy elements formed in the star by nuclear fusion, and contributes to nebula formation. These nebulas coalesce to form new stars and their associated planetary systems. We can actualy see this happening in various places throughout our galaxy, with nebulas in various stages of coalescing and with multiple stars forming within them. Absorbtion spectra tell us about the materials these nebulae are composed of.
There is some speculation that heavy elements such as iron are also produced and scattered about in nutron star collisions.
This is actually my PhD research! Yes the current thought is that neutron star mergers are the source of heavy elements (iron and greater) over supernova. Looking at the elements produced by nucleosynthesis from the outflow yields very positive results when compared with abundance curves in our solar system.
Also because we know how much material is released in a mrger and how much material there is in our galaxy, we can work out how frequent neutron star mergers are and these results agree with other independent estimates of frequency of merger.
Interesting. So where did our sun come from? Are you saying it started from a multilight year wide cloud?
Why is it 4+ light years from any other stars? Did our sun pull everything out of that radius when it was forming leaving a whole bunch of empty interstellar space?
Bear in mind the galaxy is continuously rotating, our sun is orbiting the galactic nucleus, as are the other stars around it. Right now the nearest star is 4 lightyears away, but that's not always the case and it's quite likely other stars have passed ours by much closer than that during it's lifetime. In fact our sun has orbited the galactic core many times; it does so roughly every 250 million years.
The sun would have accumulated material from the nebula it formed in as it drifted though it. The stars near us now are not the ones our sun was near when it formed though (except by extemely unlikely co-incidence), as each star is on a slightly different course round the galaxy, like water droplets in a very slowly rotating cyclone.
If another star were to pass by very close, it could be disastrous for us as it could severely disrupt the planetary orbits in our system, but that's fairly unlikely and there's no prospect of that happening for many millions of years at least. The space between stars is vast, even by comparrison to the size of stars themselves and their solar systems.
EDIT - on that last point, 4 ly is ~250,000 AU (the distance from the earth to the sun). If we asume out solar system is 100 AU across, that's still only 1/2500 the distance to the next star.
Assuming I remember correctly, I should clarify that specifically it's the supernova itself that produces the heavy elements. The fusion that occurs during the bulk of the star's life doesn't tend to get much beyond oxygen.
(Maybe it was XKCD that gave me the idea?) But I remember thinking it interesting that humans are the chemical/physical process that creates those highest elements.
Well, yeah. I thought it was carbon, and I thought it was way ahead of the others. But instead there are actually a bunch of elements vying pretty closely for third position: oxygen, carbon, neon, nitrogen, magnesium, silicium, iron, sulphur. (Although one should keep in mind that the graph is logarithmic.)
Note that the graph actually shows the estimated abundance of elements in the solar system (found that on Wikipedia), not the universe or the Milky Way. The article misrepresents that!
I thought he was making a Terry Pratchett reference.
> The world is made up of four elements: Earth, Air, Fire and Water. This is a fact well known even to Corporal Nobbs. It's also wrong. There's a fifth element, and generally it's called Surprise.
I think in cases where the original comment appears to be made in good faith, it's OK to explain what's wrong with it/what to do instead. That's how people learn.
(Obvious spam/flames/etc. should just be downvoted, ofcourse.)
It seems like about half of ilovefood's comments are of the "wow! great article!" type. I'm not sure whether this indicates that comments saying "don't do that" are likely to be helpful or not...
(If it were 100%, I'd conclude that it's a would-be spammer's account, building up a bit of history before starting to try to fill HN with spam. But I don't think that's what's going on here.)
It would be nice if someone could explain any of the exceptions to the Oddo-Harkins rule, such as the dip at atomic number 44, Ruthenium.