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>> the Big Bang should have produced matter and antimatter in equal amounts, and over time that all would have collided and annihilated, leaving the cosmos a ve

• laurowyn 5y ago
  I'm not reading that as the matter/antimatter didn't annihilate each other after the big bang. Rather, that matter and antimatter were not produced in equal amounts - if they were produced in equal quantities, why do our observations show such a large amount of matter and not equal amounts of antimatter? production and annihilation are balanced processes, so why the heavy sway to one side? Th obvious suggestion is that if there was equal amounts of antimatter near us, we would likely be annihilated already. But that doesn't explain why so little can be found remotely either. The potential for matter and antimatter to alternate is an interesting proposal that could explain our little island of stability in the universe. Or it could be something else entirely. I'm a software engineer, not a physicist.
• eigenket 5y ago
  Two reasons: 1. Because there isn't even close to the amount of radiation around we would see from such incredible amounts of anihlillation 2. Matter/antimatter annihilation is symmetric - it removes the same amount of matter and antimatter from the equation so however much stuff we started with we expect to still see the same amount of matter and antimatter and the antimatter doesn't seem to be around Its worth emphasising that there is some matter/antimatter asymmetry in the standard model, they don't behave as exact "mirror opposites" particularly in the context of some kaon physics, but there isn't even close to enough asymmetry to explain the amount of matter and the lack of antimatter we observe.
  • fb13 5y ago
    Thanks for the information. Does dark matter ever enter the discussion in terms of "there isn't even close to enough asymmetry to explain the amount of matter and the lack of antimatter we observe."
    • eigenket 5y ago
      I'm not really an expert on that so I can't comment definitively, I think the answer is a tentative "yes" but I don't think theres really enough evidence to favour any proposals there.
    • ephimetheus 5y ago
      We don’t know a ton about dark matter. Basically (and I’m simplifying a bit) you need CP violation (and more than is explained by the standard model) to account for the asymmetry. If your dark matter model of choice can generate CP asymmetry, then it could enter the discussion.
      • ineedasername 5y ago
        I'm pretty sure dark matter just represents the part of the universe that respects the privacy rights of matter, compared to the intrusive light emitting matter the blasts its details out into the light spectrum for all the universe to see. Think of dark matter as an effective equivalent of the GDPR for matter.
  • adrian_b 5y ago
    There is no reason to believe that matter and antimatter was produced in equal quantities in the Big Bang. 2 particles, one of which is the anti-particle of the other form a system where the sum of all quantities that are conserved can be 0, so a transformation generating or destroying both particles is possible. Nevertheless there are also other systems of particles where the sum of all conserved quantities can be 0 so there should exist transformations that generate all of them simultaneously. Besides the systems of 2 particles, where generation and annihilation is well known, there are systems of 4 particles with zero sum of all conserved quantities (e.g. a quark, an anti-quark, an electron and an anti-neutrino) and also systems of 8 particles e.g. the 3 kinds of u quarks + the 3 kinds of d-quarks + electron + anti-neutrino. The systems of 4 particles can actually be generated and destroyed in weak interactions, similarly like the the systems of 2 particles can be generated and destroyed in electromagnetic interactions. For the systems of 8 particles, there is currently no theory about a mechanism of generation or annihilation, but my bet is that this is how matter was created during Big Bang (those 8 particles aggregate into 1 proton, 1 neutron, 1 electron and 1 neutrino). For now we have a theory of Big Bang not from the starting point but from a little later when there already was normal matter as we know it. There is no theory yet for the origin of Big Bang, but there is absolutely no reason to believe that at the beginning there was an electromagnetic interaction generating simultaneously equal numbers of particles and anti-particles. For that to be true, the matter and anti-matter should have been preceded by electromagnetic waves i.e. photons, of equivalent energy with the mass of the generated matter and anti-matter, which would then annihilate restoring the previous photons. Such a theory goes nowhere, so it does not match reality. Whatever started Big Bang, it was not an electromagnetic field generating pairs of particles and anti-particles.
    • canadianfella 5y ago
      > There is no theory yet for the origin of Big Bang There are many.
      • adrian_b 5y ago
        None of them can explain anything besides what is already explained without them. The Big Bang theory that is useful starts with matter at very high temperature and density, but otherwise not different from the matter that we know. That happens at some uncertain time interval after the beginning of Big Bang. We may try to extrapolate towards time 0 and increasing temperatures and densities, but that reaches soon values of temperature and pressure high enough that we do not really know how matter behaves in those conditions and it does not matter anyway because it does not influence what happens later. For the later evolution, it is enough to start the modeling of Big Bang from the moment when the temperature became low enough, e.g. of some tens of MeV, i.e. when matter was too hot for nuclei and atoms to exist, but cold enough so that it consisted of a plasma composed of protons, neutrons, electrons, positrons, photons and neutrinos, with only negligible quantities of heavier particles. For the time 0 there is no theory that can predict anything quantitative.
  • scotty79 5y ago
    Can radiation be absorbed by matter and and turned into kinetic energy? Because matter in the universe has plenty of that when super massive blackholes and things that fly around them run away from each other.
    • eigenket 5y ago
      Sure, but the amount of kinetic energy (in sensible frames of reference) isn't really significant compared to the amount of energy locked up as mass energy of stuff. To close approximation the kinetic energy of something is 1/2 * mv^2 and the mass energy is m c^2 so to have a meaningful contribution to the total energy thespeed has to be close to the speed of light. We generally don't observe big things (stars, black holes, galaxies) moving anywhere near to that fast and their energy is basically entirely due to their mass rather than their speed.
      • ganzuul 5y ago
        Wouldn't that stuff have taken leave right at the beginning?
        • eigenket 5y ago
          Things can't really "leave", well they can, but the best guess we have is that there is no particularly special place in the universe, everywhere is roughly the same. So if even if all the really speedy stuff from here "left" we'd see the speedy stuff arriving from other places.
          • ganzuul 5y ago
            I thought 'no special place' was meant to say physics was the same everywhere; not the environment. If you have a sparse gas with a random distribution of velocities and you let it sit for a while, you will find that the outliers on the upper end have have moved further away from cluster center. They have boiled off.
            • 5y ago
  • dnautics 5y ago
    Suppose the amount of matter/antimatter produced at creation is chi-distributed. So there's some random variation, and each universe gets a different random value. Then if it's too close, then there's too much background radiation and the universe doesn't support life.
• AnimalMuppet 5y ago
  Tangentially related, but veering off-topic very quickly: We define "matter" to be what there is in greater abundance in the local neighborhood. Thus we define protons and neutrons (or up and down quarks) as matter, along with electrons. But what if that's wrong? What if electrons are anti-particles? That would go some distance toward "matter and antimatter in equal amounts" (though not, I think, all the way there). Is there any physical reason that, if we identify the up quark, say, as matter, then the electron also has to be matter rather than antimatter? (I think there is reason that if the up quark is matter, the down quark has to also be matter, but I could be wrong on that one, too.) Can anyone with better knowledge than mine shed some light here?
  • Filligree 5y ago
    Arguments about matter-antimatter balance are actually per quantum field. Electrons can't, in any sense, be "antimatter". That's because there antimatter as a concept only applies to a particle's relationship to its antiparticle -- it's not a feature of a single type of particle, only of two types of particle. Which must be variant excitations of the same quantum field. That's almost irrelevant, however. The big bang should have created roughly equal amounts of matter and antimatter for each quantum field; an excess of protons cannot be balanced by deficit of positrons, as I believe you were suggesting. Protons and positrons do not annihilate, nor would protons and electrons for that matter. Only protons and anti-protons, or electrons and positrons, have that reaction. (Though, aside: Protons are composite particles. None of the composites are electrons, though, so this still applies.)
    • ben_w 5y ago
      This reminds me of a question that popped into my mind earlier this year. Forewarning: I’m not a professional physicist. If the Big Bang didn’t create an equal quantity of matter and antimatter, and given that antimatter is still being produced by various cosmological sources and at a lower rate for proton-antiproton pairs than for electron-positron pairs, would that imply that the universe has a non-zero net electric charge which is still changing over time? And if so, what would a universe with a significant non-zero electric charge look like? And if not, because Noether, could the combination of e.g. antiprotons and positrons into anti-neutrons turn out to be stable and one possible candidate for dark matter? (Full blogpost: https://kitsunesoftware.wordpress.com/2021/02/09/baryon-asymmetry/ https://kitsunesoftware.wordpress.com/2021/02/09/baryon-asym...)
• dokem 5y ago
  Wouldn’t this just produce energy in the form of photons which are neutral in terms of being matter or antimatter which could then turn back into matter? I don’t see how anything has to be lost in this situation. Other than a large amount of entropy being produced.
• philipov 5y ago
  My baseless speculation of choice is that if antimatter is basically regular matter moving backwards in time, all the antimatter we expect to see from the big bang went flying out into negative time, into an anti-universe temporally disjoint from our own.
  • scotty79 5y ago
    That would mean we should see the events where anti-particle flies, absorbs (or emits, or does none of that) some energy and turns into normal particle. Unless the moment of big bang was totally unique time when such things happened.
    • ben_w 5y ago
      Isn’t that a valid description of both pair-creation and pair-annihilation events? (Serious question; I’m not a professional physicist)
      • scotty79 5y ago
        No. Pair creation is two photons disappearing and turning into particle and antiparicle. And annihilation is turning particle and antiparticle into two photons. When particle and photon meet the result is particle and photon just moving differently. You probably might think of this as old particle and photon disappearing and new paricle and new photon appearing.
        • ben_w 5y ago
          Ah, I misread your original post. Sorry!
        • philipov 5y ago
          Shouldn't you be able to rotate the Feynmann diagram in all directions and get a valid interaction, though?
  • whatshisface 5y ago