Can't we argue for the low amount of anti-matter as a type of anthropic principle? The early universe was super dense meaning that areas with imbalance would quickly annihilate and leave only one type of matter. Then, due to rapid expansion, our observable universe is dominated by only one type of matter. If we imagine a universe with a more even mix it would be less welcoming to life, so we are less likely to observe it. Has someone modeled something like this?
Physicists drive antihydrogen breakthrough at CERN
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Re: Physicists drive antihydrogen breakthrough at CERN
#62Earlier quoted context omitted.
As I learned it long ago in school, elements up to the mass of iron are formed by stellar fusion. That's the point where fusion is no longer exothermic. Any element on earth that is heavier than iron is the product of a supernova. So we live on a ball of supernova debris.
> elements up to the mass of iron are formed by stellar fusion And elements down to the mass of iron can also be formed. But iron is at the bottom of the well.
The elements heavier than iron are not formed by fusion because of the asymmetry in the initial conditions.
The Universe that we can see has started from a mixture of equal amounts of free neutrons and protons (at a temperature of a few tens of MeV, matter has the simplest possible structure, consisting of free neutrons, free protons, free electrons, free positrons, photons and various kinds of neutrinos; upon cooling, nuclei form, then positrons annihilate, then atoms form), which have formed in the beginning hydrogen, helium and some lithium. Then, through fusion, the next elements until iron have been generated.
Iron is not the last element generated, a few elements after it have also been generated by fusion, because while they have lower binding energies than iron, their binding energies are still greater than of the lighter elements that can fuse into them.
However after the peak of the iron, the abundance of the following elements generated by fusion drops very quickly, e.g. down to germanium that is about 8 thousand times less abundant than iron.
The elements heavier than germanium are produced only in negligible amounts by fusion. They are produced mostly by neutron capture and sometimes by proton capture, and such events happen mostly during supernova explosions or neutron star collisions, because only then high concentrations of neutrons with high energies are present.
Neutron capture produces elements with Z until 100, i.e. until fermium (after that, spontaneous fission happens too fast, before beta-decay can raise the Z and enough extra neutrons can be captured to form a nucleus with long enough half-life). However the half-life of the heaviest elements decreases very quickly with Z, so the elements heavier than plutonium usually decay before reaching a stellar system from the explosion that has generated them. At its formation, it is likely that Earth also contained plutonium (244Pu has a half-life of over 80 million years, enough to survive an interstellar journey), but it has completely decayed until now, leaving uranium as the heaviest primordial element on Earth.
Re: Physicists drive antihydrogen breakthrough at CERN
#63Can't we argue for the low amount of anti-matter as a type of anthropic principle? The early universe was super dense meaning that areas with imbalance would quickly annihilate and leave only one type of matter. Then, due to rapid expansion, our observable universe is dominated by only one type of matter. If we imagine a universe with a more even mix it would be less welcoming to life, so we are less likely to observ…
The anthropic principle doesn't imply that our entire observable universe has to contain only matter.
Why shouldn't we observe clouds of anti matter and matter annihilating millions or billions of light years away? Why does the annihilation have to have happened so early on that we can't see any evidence anywhere?
I think there does need to be an explanation and it can't be an anthropic principle cop out.
Re: Physicists drive antihydrogen breakthrough at CERN
#64Earlier quoted context omitted.
As I learned it long ago in school, elements up to the mass of iron are formed by stellar fusion. That's the point where fusion is no longer exothermic. Any element on earth that is heavier than iron is the product of a supernova. So we live on a ball of supernova debris.
Most of what we live on, the vast majority, is iron or lighter. So it's more that we're sprinkled with supernova debris. But we are made out of stardust, so that's something.
An interesting fact is that while almost all of the Solar System has started as gas, which has then condensed here into solid bodies that have then aggregated into planets, a small part of the original matter of the Solar System has consisted of solid dust particles that have come as such from the stellar explosions that have propelled them.
So we can identify in meteorites or on the surface of other bodies not affected by weather, like the Moon or asteroids, small mineral grains that are true stardust, i.e. interstellar grains that have remained unchanged since long before the formation of the Earth and of the Solar System.
We can identify such grains by their abnormal isotopic composition, in comparison with the matter of the Solar System. While many such interstellar grains should be just silicates, those are hard to extract from the rocks formed here, which are similar chemically.
Because of that, the interstellar grains that are best known are those which come from stellar systems that chemically are unlike the Solar System. In most stellar systems, there is more oxygen than carbon and those stellar systems are like ours, with planets having iron cores covered by mantles and crusts made of silicates, covered then by a layer of ice.
In the other kind of stellar systems, there is more carbon than oxygen and there the planets would be formed from minerals that are very rare on Earth, i.e. mainly from silicon carbide and various metallic carbides and also with great amounts of graphite and diamonds.
So most of the interstellar grains (i.e. true stardust) that have been identified and studied are grains of silicon carbide, graphite, diamond or titanium carbide, which are easy to extract from the silicates formed in the Solar System.
Re: Physicists drive antihydrogen breakthrough at CERN
#65Earlier quoted context omitted.
But you want that to happen in space and to control the output of energy. Otherwise you just have a bomb.
The difference between a bomb and a reactor is just clever engineering.
It's much easier to make a fission reactor than a fission bomb, and much easier to make a fusion bomb than a fusion reaction. They are not even that similar.
Re: Physicists drive antihydrogen breakthrough at CERN
#66Earlier quoted context omitted.
There have been several proposals. This paper proposes a feasable mechanism[1]: -"a SBH could be artificially created by firing a huge number of gamma rays from a spherically converging laser. The idea is to pack so much energy into such a small space that a BH will form." 1. https://arxiv.org/abs/0908.1803
The biggest problem is that if you're creating it with lasers, you're only going to get the energy out that you put in. You really want to be able to feed it matter, which would effectively make it an anything-to-gamma-radiation converter, which means you have to feed it quite a lot of matter, against the radiation pressure of all that energy coming out. The paper mentioned assumes a worst case of not being able to f…
Does anyone address the fact that a black hole will be falling towards the center of the earth at 1g? How do you handle a black hole?
Re: Physicists drive antihydrogen breakthrough at CERN
#67Can't we argue for the low amount of anti-matter as a type of anthropic principle? The early universe was super dense meaning that areas with imbalance would quickly annihilate and leave only one type of matter. Then, due to rapid expansion, our observable universe is dominated by only one type of matter. If we imagine a universe with a more even mix it would be less welcoming to life, so we are less likely to observ…
Not only there is no evidence for the existence of antimatter in quantities comparable with matter, but there also is no logical necessity for this.
People who entertain the idea of an initial state with equal amounts of matter and antimatter do this because thus the properties of the matter that are conserved, except the energy, would sum to zero in the initial state.
However, such people forget that not only the particle-antiparticle pairs that can be generated or annihilated through electromagnetic interactions have this property that the conserved quantities except the energy sum to zero.
The particle-antiparticle symmetry is important only for the electromagnetic interactions, while other interactions have more complex symmetries.
All the so-called weak interactions are equivalent with the generation or annihilation of groups of 4 particles, for which all the conserved properties except energy sum to zero. Such a group of 4 particles typically consists of a quark, an antiquark, a charged lepton or anti-lepton and a neutrino or antineutrino.
For instance the beta decay of a neutron into a proton is equivalent with the generation of 4 particles, an u quark, an anti-d quark, an electron and an antineutrino. The electron and the antineutrino fly away, while the anti-d quark annihilates a d quark, so the net effect for the nucleus is a change of a d quark into an u quark, which transforms a neutron into a proton.
The generation and annihilation of groups of 4 particles in the weak interactions are mediated by the W bosons, but this is a detail of the mechanism of the interactions, which is necessary for computations of numeric values, but not for the explanation of the global effect of the weak interactions, for which the transient existence of the W intermediate bosons can be ignored.
So besides the symmetry between a particle and an anti-particle, we have a symmetry that binds certain groups of 4 quarks and leptons.
There is a third symmetry, which binds groups of 8 particles. For instance, there are 3 kinds of u quarks, 3 kinds of d quarks, electrons and neutrinos, a total of 8 particles that belong to the so-called first generation of matter particles (i.e. the lightest such particles).
All the conserved quantities except energy sum to zero for this group of 8 particles. The neutrino is necessary in this group so that the spin will also sum to zero, not only the electric charge and the hadronic charge.
These 8 kinds of particles are exactly those that are supposed to compose in equal quantities the matter of the Universe at the Big Bang.
So all the conserved quantities except energy sum to zero for the Universe at the Big Bang, when it is composed entirely of ordinary matter, without any antimatter.
Therefore there is no need for antimatter in the initial state.
There is no known reason for this symmetry between the 8 particles of a generation of quarks and leptons, except that this allows for the initial state at the Big Bang to have a zero sum for the conserved properties.
It can be speculated that this symmetry might be associated with a supplementary hyper-weak interaction, in the same way as the symmetry between certain groups of 4 quarks and leptons is associated with the weak interaction. Such an interaction would allow the generation and annihilation of ordinary matter, without antimatter, but with an extraordinarily low probability.
Re: Physicists drive antihydrogen breakthrough at CERN
#68Earlier quoted context omitted.
The biggest problem is that if you're creating it with lasers, you're only going to get the energy out that you put in. You really want to be able to feed it matter, which would effectively make it an anything-to-gamma-radiation converter, which means you have to feed it quite a lot of matter, against the radiation pressure of all that energy coming out. The paper mentioned assumes a worst case of not being able to f…
Does anyone address the fact that a black hole will be falling towards the center of the earth at 1g? How do you handle a black hole?
Black hole is the safest energy generator per unit of energy produced.
Re: Physicists drive antihydrogen breakthrough at CERN
#69Earlier quoted context omitted.
Minor nit-pick but Hawking Radiation hasn't been observed and remains a theoretical prediction.
It's a pretty fundamental prediction though, and it's been derived in many different ways, all of which give the same prediction. It's closely related to the Unruh effect, which is a direct consequence of pure QFT. The Unruh effect describes how an accelerated observer sees a different vacuum from an inertial observer - they see radiation that the inertial observer doesn't. Hawking radiation is essentially this same…
A lot of great science progress followed after some "fundamental prediction" turned out to be wrong :). Wouldnt it be awesome to learn that blackholes, in fact, do not evaporate at all? That would be exciting
Re: Physicists drive antihydrogen breakthrough at CERN
#70Earlier quoted context omitted.
The difference between a bomb and a reactor is just clever engineering.
It's much easier to make a fission reactor than a fission bomb, and much easier to make a fusion bomb than a fusion reaction. They are not even that similar.
It's way easier to make a fission bomb than a fission reactor. I reactor has to stay in the very narrow window where it's critical but not prompt critical. Even pure fission bombs can be marvels of engineering but the simplest gun-type bomb is easier to build than the simplest nuclear reactor.