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I’ve always wondered about this, perhaps someone who understands this subject could explain. Say matter and antimatter were created in roughly equal proportion

I’ve always wondered about this, perhaps someone who understands this subject could explain. Say matter and antimatter were created in roughly equal proportions then some collided to create energy. Couldn’t then this energy coalesce back to regular matter through the mass-energy equivalence? E=mc^2? Repeat this a bit and you’d end up with more matter than antimatter. As I said, this is so simple there must be an easy argument against it but I’ve never heard the idea addressed.

fahadkhan 8y ago
I am not a physicist. But obvious question is why would the energy not coalesce back to equal matter and anti matter?
- misnome 8y ago
  This is a good question! In reality, for this process they do: see https://en.wikipedia.org/wiki/Pair_production https://en.wikipedia.org/wiki/Pair_production. But ignoring this and JBorrows (correct) comments on other properties to be conserved, we can ask: IF more matter is made (in some process) than anti-matter, then why? To explain this, we would need some sort of mechanism where matter was treated differently to antimatter in the laws of physics... and then you are back to the original question of looking for differences. Non-gravitationally, the general case of antimatter behaving differently to matter is covered by the concept of https://en.wikipedia.org/wiki/CP_violation https://en.wikipedia.org/wiki/CP_violation - we do know of cases where this is the case, but not strongly enough to explain what we observe in the universe - the article looks a little heavy but does have a section on the matter-antimatter imbalance that is a little easier to read.
jcims 8y ago
I had a similar thought but then wondered if the question would be why there's a bias in which type of matter condenses out of the energy. All this stuff is way over my head but it's fun to think about.
- MrEldritch 8y ago
  >if the question would be why there's a bias in which type of matter condenses out of the energy Yes, it's exactly this! The fact that there's more matter than antimatter in the universe means that, somewhere, some process has to break the symmetry and be 'biased', treating antimatter differently than matter. (There are known processes that do this - certain specific meson decays that are ever-so-slightly biased towards decaying into matter rather than antimatter, other weird stuff like that - but the observed phenomena are nowhere near strong enough to explain the degree to which matter predominates in the observed universe.) As far as we can tell, all interactions involving gravity, the electromagnetic field, and the strong nuclear interaction[1] are perfectly symmetric with respect to matter versus antimatter. The weak nuclear interaction (which is involved in a lot of processes that transform particles into other kinds of particles, like radioactive decay) does break it - that's what's up with those meson decays - but only a little bit, in very specific cases. [1]It's actually a bit of a puzzle why the strong force doesn't violate this symmetry; according to our understanding of the math for the strong interaction, it totally could - there are terms that naturally appear in the equations that would lead to it. But, the values for all of those terms appear to be as near to zero as we can measure. There's no obvious reason this should be the case, especially because another force - the weak nuclear force - has no problem with slightly violating that symmetry.
  - DenisM 8y ago
    There doesn’t have to be a break in rules symmetry tho. Imagine that universe is a giant dipole of a magic field F, one end of it carries huge field +F the other -F. Next imagine, that presence of +F is likely to precipitate matter from energy, while -F is likely to yield antimatter. Thus a perfectly symmetric system of rules will produce area with only matter and only anti-matter. And blazing inferno in between the two zones. We just need to find out what the F F is.
    - HeadsUpHigh 8y ago
      But we haven't observed any areas with antimatter only up to now.
JBorrow 8y ago
There are other things that must be conserved - not just energy - in the current standard model of particle physics. For example, you have to conserve charge - and matter and antimatter have opposite charges. In that case, say I have 100 electrons that I want to turn into positrons. If I was able to turn these into pure "energy", first I'd have to figure out how to give that "energy" charge (so it could conserve charge in that step), and then I would have to create some other particles to balance out the 100 positive charges that the positrons would give me, ending up with 300 particles. The reason that we think that there's more matter than antimatter in the real universe is because of a thing called "Charge-Parity Violation" [1] that is the focus of a lot of current research. [1] https://www.symmetrymagazine.org/article/charge-parity-violation https://www.symmetrymagazine.org/article/charge-parity-viola...
- paulddraper 8y ago
  Momentum is an example of another conserved quantity.
  - MrEldritch 8y ago
    Incidentally, fun fact - you already know that X, Y, and Z linear momentum are all conserved separately. In special relativity, mass-energy conservation gets folded into this as well - an object's mass-energy is just the component of linear momentum along the time axis! (and "rest mass" is its value in the reference frame where the object is otherwise stationary and moving only through time.)
    - antidesitter 8y ago
      This is conservation of 4-momentum, whose spatial components are ordinary momentum and whose temporal component is energy. By Noether’s theorem, conservation of 4-momentum is due to the invariance of physical laws under 4-translations (spatial and temporal).
MrEldritch 8y ago
realize, It's not obviously impossible, but in fact this is never observed - no particle is ever created without a corresponding antiparticle. (The corresponding laws are "lepton number conservation" and "baryon number conservation" - basically, the total number of electrons[1] minus the total number of anti-electrons[2] remains constant, and so does the total number of quarks minus antiquarks. All of the interactions of the Standard Model respect these.[3][4] There are various beyond-standard-model theories that allow breaking baryon and lepton number conservation individually, with the combined number of (baryons - leptons) being a conserved quantity instead; but they also almost all predict that protons should be slightly unstable (because being able to go from [Exotic Mystery Particle] to baryons + leptons means you should also be able to go from baryons (like the proton) to [Exotic Mystery Particle] and leptons) but we've looked really really hard for evidence of extremely rare proton decays and have yet to find any. [1](plus muons, and tauons, and the three corresponding flavors of neutrinos) [2](plus anti-muons, and anti-tauons, and anti-neutrinos) [3]Even the observed violations of matter-antimatter asymmetry ("CP violation") still respect these conserved quantities; they just involve things like anti-kaons decaying slightly but measurably faster than kaons. [4]On the other hand, there's no particular reason to expect gravity to respect these; For instance, we think black holes can consume matter, and then convert it to energy in the form of Hawking radiation as they slowly decay, without having to bother with eating an equal quantity of antimatter. But honestly we're just guessing on that front.
- raattgift 8y ago
  > For instance, we think black holes can consume matter, and then convert it to energy in the form of Hawking radiation as they slowly decay, without having to bother with eating an equal quantity of antimatter. > we're just guessing Black holes (BHs) are not a very realistic candidate for solving baryon asymmetry. Where's the antimatter outside the horizon of a modern (as in after structure formation) astrophysical BH? If it's not there, it can't fall in. This is really hard to work around even for early direct-collapse super-massive BHs; hierarchical growth is already essentially ruled out. Worse, how do you keep signatures of annihilations out of the region near the BHs, including the accretion material and any jets? Or are you expecting primordial BHs to couple differently to baryons and their antis? How do you suppress that difference in the weak field limit, or more generally after first light? (And in either case, how do you make sure that virtually all of the antimatter is locked up in BHs?) Essentially you keep coming back to having the stress-energy already significantly (really, almost entirely) segregated into particles and their antis, around the time of gravitational collapse, or you depart dramatically from General Relativity in a regime in which it is already supported by evidence. Finally, where are you hiding all these black holes, whenever they formed? If only BHs break baryon symmetry, the contribution to \Omega implies a lot of lensing. (Speculating in the direction of a dust of tiny remnants or the like is also hard work, and usually involves beyond-the-standard-model new physics anyway, although there is a small literature that involves operators like \partial_{\mu}F(R)J^{\mu}, where J^{\mu} is the baryon or lepton current, and R is the curvature scalar or the Riemann tensor (R_{\mu\nu\rho\sigma}R^{\mu\nu\rho\sigma}) or a more complex term, and afaik none of these model-builders take backreaction into account yet.)
deleted 8y ago
[deleted]
andrepd 8y ago
>Couldn’t then this energy coalesce back to regular matter through the mass-energy equivalence? E=mc^2? That's just not how that works.
- pc86 8y ago
  [citation needed], not because you're wrong (you're not) but that's about as unhelpful of a response as you can make without just personally insulting the person.

fahadkhan 8y ago

I am not a physicist. But obvious question is why would the energy not coalesce back to equal matter and anti matter?

misnome 8y ago
This is a good question! In reality, for this process they do: see https://en.wikipedia.org/wiki/Pair_production https://en.wikipedia.org/wiki/Pair_production. But ignoring this and JBorrows (correct) comments on other properties to be conserved, we can ask: IF more matter is made (in some process) than anti-matter, then why? To explain this, we would need some sort of mechanism where matter was treated differently to antimatter in the laws of physics... and then you are back to the original question of looking for differences. Non-gravitationally, the general case of antimatter behaving differently to matter is covered by the concept of https://en.wikipedia.org/wiki/CP_violation https://en.wikipedia.org/wiki/CP_violation - we do know of cases where this is the case, but not strongly enough to explain what we observe in the universe - the article looks a little heavy but does have a section on the matter-antimatter imbalance that is a little easier to read.

jcims 8y ago

I had a similar thought but then wondered if the question would be why there's a bias in which type of matter condenses out of the energy. All this stuff is way over my head but it's fun to think about.

MrEldritch 8y ago
>if the question would be why there's a bias in which type of matter condenses out of the energy Yes, it's exactly this! The fact that there's more matter than antimatter in the universe means that, somewhere, some process has to break the symmetry and be 'biased', treating antimatter differently than matter. (There are known processes that do this - certain specific meson decays that are ever-so-slightly biased towards decaying into matter rather than antimatter, other weird stuff like that - but the observed phenomena are nowhere near strong enough to explain the degree to which matter predominates in the observed universe.) As far as we can tell, all interactions involving gravity, the electromagnetic field, and the strong nuclear interaction[1] are perfectly symmetric with respect to matter versus antimatter. The weak nuclear interaction (which is involved in a lot of processes that transform particles into other kinds of particles, like radioactive decay) does break it - that's what's up with those meson decays - but only a little bit, in very specific cases. [1]It's actually a bit of a puzzle why the strong force doesn't violate this symmetry; according to our understanding of the math for the strong interaction, it totally could - there are terms that naturally appear in the equations that would lead to it. But, the values for all of those terms appear to be as near to zero as we can measure. There's no obvious reason this should be the case, especially because another force - the weak nuclear force - has no problem with slightly violating that symmetry.
- DenisM 8y ago
  There doesn’t have to be a break in rules symmetry tho. Imagine that universe is a giant dipole of a magic field F, one end of it carries huge field +F the other -F. Next imagine, that presence of +F is likely to precipitate matter from energy, while -F is likely to yield antimatter. Thus a perfectly symmetric system of rules will produce area with only matter and only anti-matter. And blazing inferno in between the two zones. We just need to find out what the F F is.
  - HeadsUpHigh 8y ago
    But we haven't observed any areas with antimatter only up to now.

JBorrow 8y ago

There are other things that must be conserved - not just energy - in the current standard model of particle physics. For example, you have to conserve charge - and matter and antimatter have opposite charges. In that case, say I have 100 electrons that I want to turn into positrons. If I was able to turn these into pure "energy", first I'd have to figure out how to give that "energy" charge (so it could conserve charge in that step), and then I would have to create some other particles to balance out the 100 positive charges that the positrons would give me, ending up with 300 particles. The reason that we think that there's more matter than antimatter in the real universe is because of a thing called "Charge-Parity Violation" [1] that is the focus of a lot of current research. [1] https://www.symmetrymagazine.org/article/charge-parity-violation https://www.symmetrymagazine.org/article/charge-parity-viola...

paulddraper 8y ago
Momentum is an example of another conserved quantity.
- MrEldritch 8y ago
  Incidentally, fun fact - you already know that X, Y, and Z linear momentum are all conserved separately. In special relativity, mass-energy conservation gets folded into this as well - an object's mass-energy is just the component of linear momentum along the time axis! (and "rest mass" is its value in the reference frame where the object is otherwise stationary and moving only through time.)
  - antidesitter 8y ago
    This is conservation of 4-momentum, whose spatial components are ordinary momentum and whose temporal component is energy. By Noether’s theorem, conservation of 4-momentum is due to the invariance of physical laws under 4-translations (spatial and temporal).

MrEldritch 8y ago

realize, It's not obviously impossible, but in fact this is never observed - no particle is ever created without a corresponding antiparticle. (The corresponding laws are "lepton number conservation" and "baryon number conservation" - basically, the total number of electrons[1] minus the total number of anti-electrons[2] remains constant, and so does the total number of quarks minus antiquarks. All of the interactions of the Standard Model respect these.[3][4] There are various beyond-standard-model theories that allow breaking baryon and lepton number conservation individually, with the combined number of (baryons - leptons) being a conserved quantity instead; but they also almost all predict that protons should be slightly unstable (because being able to go from [Exotic Mystery Particle] to baryons + leptons means you should also be able to go from baryons (like the proton) to [Exotic Mystery Particle] and leptons) but we've looked really really hard for evidence of extremely rare proton decays and have yet to find any. [1](plus muons, and tauons, and the three corresponding flavors of neutrinos) [2](plus anti-muons, and anti-tauons, and anti-neutrinos) [3]Even the observed violations of matter-antimatter asymmetry ("CP violation") still respect these conserved quantities; they just involve things like anti-kaons decaying slightly but measurably faster than kaons. [4]On the other hand, there's no particular reason to expect gravity to respect these; For instance, we think black holes can consume matter, and then convert it to energy in the form of Hawking radiation as they slowly decay, without having to bother with eating an equal quantity of antimatter. But honestly we're just guessing on that front.

raattgift 8y ago
> For instance, we think black holes can consume matter, and then convert it to energy in the form of Hawking radiation as they slowly decay, without having to bother with eating an equal quantity of antimatter. > we're just guessing Black holes (BHs) are not a very realistic candidate for solving baryon asymmetry. Where's the antimatter outside the horizon of a modern (as in after structure formation) astrophysical BH? If it's not there, it can't fall in. This is really hard to work around even for early direct-collapse super-massive BHs; hierarchical growth is already essentially ruled out. Worse, how do you keep signatures of annihilations out of the region near the BHs, including the accretion material and any jets? Or are you expecting primordial BHs to couple differently to baryons and their antis? How do you suppress that difference in the weak field limit, or more generally after first light? (And in either case, how do you make sure that virtually all of the antimatter is locked up in BHs?) Essentially you keep coming back to having the stress-energy already significantly (really, almost entirely) segregated into particles and their antis, around the time of gravitational collapse, or you depart dramatically from General Relativity in a regime in which it is already supported by evidence. Finally, where are you hiding all these black holes, whenever they formed? If only BHs break baryon symmetry, the contribution to \Omega implies a lot of lensing. (Speculating in the direction of a dust of tiny remnants or the like is also hard work, and usually involves beyond-the-standard-model new physics anyway, although there is a small literature that involves operators like \partial_{\mu}F(R)J^{\mu}, where J^{\mu} is the baryon or lepton current, and R is the curvature scalar or the Riemann tensor (R_{\mu\nu\rho\sigma}R^{\mu\nu\rho\sigma}) or a more complex term, and afaik none of these model-builders take backreaction into account yet.)

deleted 8y ago

[deleted]

andrepd 8y ago

>Couldn’t then this energy coalesce back to regular matter through the mass-energy equivalence? E=mc^2? That's just not how that works.

pc86 8y ago
[citation needed], not because you're wrong (you're not) but that's about as unhelpful of a response as you can make without just personally insulting the person.