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Is there any fundamental law of physics that says if you want to turn mc^2 energy into mass, that you have to create particle/antiparticle pairs together? Or co

Is there any fundamental law of physics that says if you want to turn mc^2 energy into mass, that you have to create particle/antiparticle pairs together? Or could you, theoretically, create exclusively antimatter, and we just don't have a known method of doing so? In theory, could you use mc^2 energy to create a mass m of antimatter, combine it with m matter (which is rather more readily available), get 2mc^2 energy back out, and repeat, effectively consuming matter to make energy?

master_crab 2y ago
IANAP (physicist, just an Engineer) but any sort of reaction like this is probably pretty hard to control so you won’t get twice the energy. Just like with combustion engines, you’re probably looking at some significant percentage loss (~50%?) in efficiency from various things. (I’m sure there are other things that would also hinder the 2x outlook you are asking about)
- JoshTriplett 2y ago
  Yeah, as the article here notes, the energy released is effectively an explosion, and harnessing that energy into something more useful is a substantial challenge. As is the concept of turning energy into specific (anti-)matter, which we have no idea how to do at the moment. This is more a theoretical question of whether any law of physics makes this impossible (e.g. you can't create unpaired particles), or whether this is theoretically possible but it's difficult to get enough efficiency to make it net positive. (We currently haven't even gotten fusion to be reliably net positive; practicality is as always a set of concerns all its own.)
  - api 2y ago
    Project Orion style pusher plate nuclear pulse designs can handle turning big boom boom into space propulsion but as the parent said you are not 100% efficient.
    - JoshTriplett 2y ago
      More interested in electrical power than propulsion, in this case.
      - lazide 2y ago
        The classic stand-in of boiling a bunch of water, then spinning turbines is likely our best bet.
  - ben_w 2y ago
    > This is more a theoretical question of whether any law of physics makes this impossible (e.g. you can't create unpaired particles), or whether this is theoretically possible but it's difficult to get enough efficiency to make it net positive. It's theoretically impossible, with the slight problem that there seems to be more matter than antimatter in the universe today and nobody really knows why. Either the theory is wrong (and it being a conservation rule, then by Noether's theorem there's an equivalent symmetry* you'd have to violate if the conservation doesn't hold), or the initial value that's getting conserved wasn't ever zero. * the wikipedia page says this is specific to continuous symmetry; but integers aren't continuous, so has this been generalised, or is it just assumed?
- EA-3167 2y ago
  You have a solid intuition, in addition to the usual efficiency losses, a large amount (20%-50% would be usual, up to 80% in some cases) of the energy released during annihilation is in the form of... neutrinos. I don't foresee a realistic means of harnessing that energy any time soon, even where "soon" indicates quite a stretch of time.
deleted 2y ago
[deleted]
wiml 2y ago
Charge is conserved, so if your energy input is in the form of (say) a photon, you'll have to produce equal numbers of positive and negative charged particles. Baryon and lepton number are almost conserved, which would require you to produce (or consume) equal numbers of particles and antiparticles, unless you can figure out a way to make nonconservation happen outside of a black hole or whatever. (Feeding matter to a black hole and using the Hawking radiation as an energy source would probably do what you describe, but there are practical difficulties)
- hnaccount_rng 2y ago
  I love the “practical difficulties”
- api 2y ago
  AFAIK a black hole could be a near perfect mass energy converter, and I think the evaporation rate (Hawking temperature) can be regulated by adjusting black hole spin. There’s just the wee problem of getting or making a black hole and then grabbing it and controlling its spin.
  - ben_w 2y ago
    There's the second problem that the temperature and power are directly related, so if you want the temperature low enough to not photo-ionise stuff much (6eV/70,000 K) then be power output is 114 microwatts. https://benwheatley.github.io/blog/2022/05/14-17.06.59.html https://benwheatley.github.io/blog/2022/05/14-17.06.59.html
- JoshTriplett 2y ago
  > Charge is conserved, so if your energy input is in the form of (say) a photon, you'll have to produce equal numbers of positive and negative charged particles. Charge alone doesn't seem like it'd be a fundamental limitation here, considering that (for instance) antineutrons exist. > Baryon and lepton number are almost conserved Is the "almost" here something other than the Hawking radiation "one half falls in a black hole and the other half doesn't"?
codethief 2y ago
One obstacle is momentum conservation: You can't just turn a single massless particle (a photon, say) into a massive one or vice versa because that would violate conservation of 4-momentum. The way out is to involve more than one massless particle in that interaction, e.g. convert two massless particles into one or more massive ones, or vice versa. (If a single massive particle is produced, the 3-momentum of the two massless particles cancels out in the center-of-mass frame, while their energy / p_0 adds up to the rest mass of the particle that's produced.) Which interactions exactly are possible depends on the particles & forces involved, and further conservation laws for quantum numbers (e.g. charge) that the force obeys. TL;DR Turning a single massless particle into a single massive one is not possible, you always need at least two.
- JoshTriplett 2y ago
  Thanks for the explanation!
- stoperaticless 2y ago
  Could two particles be: anti proton and anti electron? (What conservation law would it violate?)
  - messe 2y ago
    Lepton and baryon number.
markovs_gun 2y ago
This is an open question, and an important one to understanding the early history of the universe. Essentially, as far as everything we have seen in the lab shows, and everything we know about the laws of physics says, certain quantities like charge must be conserved, so matter and antimatter are always generated together. However, this creates a glaring issue- where the Hell is all the antimatter? The universe is, as far as we know, made almost entirely of matter with very little antimatter, and so there must be some kind of asymmetry somewhere that we haven't found yet. Otherwise the universe would be 50/50 matter/antimatter, or would just be constantly forming and destroying matter and antimatter.
qnleigh 2y ago
From Wikipedia: "The Standard Model of electroweak interactions has all the necessary ingredients for successful baryogenesis, although these interactions have never been observed[11] and may be insufficient to explain the total baryon number of the observed universe if the initial baryon number of the universe at the time of the Big Bang is zero." In other words, there is a process that can in in principle create more matter than antimatter, but it has not been observed experimentally yet. I think other than this, there are no known ways to even create more antimatter than matter in a process. But it is believed that more processes must exist, in order to explain the predominance of matter over antimatter in our universe. https://en.m.wikipedia.org/wiki/Chiral_anomaly https://en.m.wikipedia.org/wiki/Chiral_anomaly

master_crab 2y ago

IANAP (physicist, just an Engineer) but any sort of reaction like this is probably pretty hard to control so you won’t get twice the energy. Just like with combustion engines, you’re probably looking at some significant percentage loss (~50%?) in efficiency from various things. (I’m sure there are other things that would also hinder the 2x outlook you are asking about)

JoshTriplett 2y ago
Yeah, as the article here notes, the energy released is effectively an explosion, and harnessing that energy into something more useful is a substantial challenge. As is the concept of turning energy into specific (anti-)matter, which we have no idea how to do at the moment. This is more a theoretical question of whether any law of physics makes this impossible (e.g. you can't create unpaired particles), or whether this is theoretically possible but it's difficult to get enough efficiency to make it net positive. (We currently haven't even gotten fusion to be reliably net positive; practicality is as always a set of concerns all its own.)
- api 2y ago
  Project Orion style pusher plate nuclear pulse designs can handle turning big boom boom into space propulsion but as the parent said you are not 100% efficient.
  - JoshTriplett 2y ago
    More interested in electrical power than propulsion, in this case.
    - lazide 2y ago
      The classic stand-in of boiling a bunch of water, then spinning turbines is likely our best bet.
- ben_w 2y ago
  > This is more a theoretical question of whether any law of physics makes this impossible (e.g. you can't create unpaired particles), or whether this is theoretically possible but it's difficult to get enough efficiency to make it net positive. It's theoretically impossible, with the slight problem that there seems to be more matter than antimatter in the universe today and nobody really knows why. Either the theory is wrong (and it being a conservation rule, then by Noether's theorem there's an equivalent symmetry* you'd have to violate if the conservation doesn't hold), or the initial value that's getting conserved wasn't ever zero. * the wikipedia page says this is specific to continuous symmetry; but integers aren't continuous, so has this been generalised, or is it just assumed?
EA-3167 2y ago
You have a solid intuition, in addition to the usual efficiency losses, a large amount (20%-50% would be usual, up to 80% in some cases) of the energy released during annihilation is in the form of... neutrinos. I don't foresee a realistic means of harnessing that energy any time soon, even where "soon" indicates quite a stretch of time.

deleted 2y ago

[deleted]

wiml 2y ago

Charge is conserved, so if your energy input is in the form of (say) a photon, you'll have to produce equal numbers of positive and negative charged particles. Baryon and lepton number are almost conserved, which would require you to produce (or consume) equal numbers of particles and antiparticles, unless you can figure out a way to make nonconservation happen outside of a black hole or whatever. (Feeding matter to a black hole and using the Hawking radiation as an energy source would probably do what you describe, but there are practical difficulties)

hnaccount_rng 2y ago
I love the “practical difficulties”
api 2y ago
AFAIK a black hole could be a near perfect mass energy converter, and I think the evaporation rate (Hawking temperature) can be regulated by adjusting black hole spin. There’s just the wee problem of getting or making a black hole and then grabbing it and controlling its spin.
- ben_w 2y ago
  There's the second problem that the temperature and power are directly related, so if you want the temperature low enough to not photo-ionise stuff much (6eV/70,000 K) then be power output is 114 microwatts. https://benwheatley.github.io/blog/2022/05/14-17.06.59.html https://benwheatley.github.io/blog/2022/05/14-17.06.59.html
JoshTriplett 2y ago
> Charge is conserved, so if your energy input is in the form of (say) a photon, you'll have to produce equal numbers of positive and negative charged particles. Charge alone doesn't seem like it'd be a fundamental limitation here, considering that (for instance) antineutrons exist. > Baryon and lepton number are almost conserved Is the "almost" here something other than the Hawking radiation "one half falls in a black hole and the other half doesn't"?

codethief 2y ago

One obstacle is momentum conservation: You can't just turn a single massless particle (a photon, say) into a massive one or vice versa because that would violate conservation of 4-momentum. The way out is to involve more than one massless particle in that interaction, e.g. convert two massless particles into one or more massive ones, or vice versa. (If a single massive particle is produced, the 3-momentum of the two massless particles cancels out in the center-of-mass frame, while their energy / p_0 adds up to the rest mass of the particle that's produced.) Which interactions exactly are possible depends on the particles & forces involved, and further conservation laws for quantum numbers (e.g. charge) that the force obeys. TL;DR Turning a single massless particle into a single massive one is not possible, you always need at least two.

JoshTriplett 2y ago
Thanks for the explanation!
stoperaticless 2y ago
Could two particles be: anti proton and anti electron? (What conservation law would it violate?)
- messe 2y ago
  Lepton and baryon number.

markovs_gun 2y ago

This is an open question, and an important one to understanding the early history of the universe. Essentially, as far as everything we have seen in the lab shows, and everything we know about the laws of physics says, certain quantities like charge must be conserved, so matter and antimatter are always generated together. However, this creates a glaring issue- where the Hell is all the antimatter? The universe is, as far as we know, made almost entirely of matter with very little antimatter, and so there must be some kind of asymmetry somewhere that we haven't found yet. Otherwise the universe would be 50/50 matter/antimatter, or would just be constantly forming and destroying matter and antimatter.

qnleigh 2y ago

From Wikipedia: "The Standard Model of electroweak interactions has all the necessary ingredients for successful baryogenesis, although these interactions have never been observed[11] and may be insufficient to explain the total baryon number of the observed universe if the initial baryon number of the universe at the time of the Big Bang is zero." In other words, there is a process that can in in principle create more matter than antimatter, but it has not been observed experimentally yet. I think other than this, there are no known ways to even create more antimatter than matter in a process. But it is believed that more processes must exist, in order to explain the predominance of matter over antimatter in our universe. https://en.m.wikipedia.org/wiki/Chiral_anomaly https://en.m.wikipedia.org/wiki/Chiral_anomaly