Antimatter-matter annihilation: significance of opposite charge

  • #1
NothingsMatter
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What is it about having the opposite charge and same mass that makes a particle and its antimatter partner annihilate each other?
I did a forum search and couldn't find this, so forgive me if my search skills were insufficient to find a previous explanation of this.

But, I'm a bit confused as to why merely having the same mass but opposite charge would cause, for example, an electron and positron to annihilate each other. Why couldn't they just bond to each other and be a happy little neutral particle with twice the mass, give or take a bit related to the energy change required for them to bond? What I have learned from the worst source (artificial intelligence) is that it creates an unstable situation, resulting in the two converting entirely to energy. But if so, why?

So, is there more to the picture than them just having the opposite charge but same mass? If not, what makes that so volatile? Why would opposite charges but different masses not cause the same thing?

Thanks.


Sidenote: My math background maximum is upper division undergrad level. but if your answer requires graduate level stuff, I'll figure it out enough to get a better understanding than I have now, regardless of the intermediate tag on this thread.
 
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  • #2
NothingsMatter said:
But, I'm a bit confused as to why merely having the same mass but opposite charge would cause, for example, an electron and positron to annihilate each other. Why couldn't they just bond to each other and be a happy little neutral particle with twice the mass,
There is no such thing as a stable particle containing an electron and a positron.

The particles combine to form a new stable state. It just happens that the most common stable state is photons - usually gamma rays - that travel at the speed of light.

Wiki has a primer on annihilation, including an example of electron-positron collision. Give it a read and ask specific questions.
 
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  • #3
NothingsMatter said:
TL;DR Summary: What is it about having the opposite charge and same mass that makes a particle and its antimatter partner annihilate each other?

But, I'm a bit confused as to why merely having the same mass but opposite charge would cause, for example, an electron and positron to annihilate each other.
One answer is because they can. When an electron and a positron interact, there are two main processes that are allowed by the laws of physics: scattering and annihilation. In the former case, the particles scatter off each other and go their separate ways. QED (Quantum Electrodynamics) gives you the probability that this happens and the distribution of scattering angles. These calculations are done using the so-called Feynman rules.

Note that at low energy, the scattering angles are closely approximated by Rutherford Scattering - which uses only classical electromagnetism.

QED also allows the two particles to annhihilate and produce two (or more) photons. And, again, the Feynman rules give you the probability for this, given the total energy of the interaction.

NothingsMatter said:
Why couldn't they just bond to each other and be a happy little neutral particle with twice the mass, give or take a bit related to the energy change required for them to bond?
This is possible in high-energy cases, where neutral mesons may be produced. See here, for example:

https://en.wikipedia.org/wiki/Electron–positron_annihilation#High-energy_case

Again, the probability of this can be calculated, given the energy of the interaction. These particles, like most elementary particles, are unstable and soon decay into smaller particles.
 
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  • #4
The German Wikipedia article about annihilation also mentions the possibility of building a positronium for about ##0.1 \,\mathrm{ns}## before annihilation.
 
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  • #5
fresh_42 said:
The German Wikipedia article about annihilation also mentions the possibility of building a positronium for about ##0.1 \,\mathrm{ns}## before annihilation.
Or 140 ns. And even 1100 ns.
The problem is that there is a lower lying more stable state. Electron and proton are unable to annihilate. So are electron and positive muon.
But same mass and opposite charges are not required for annihilation. Antineutron and proton also annihilate.
 
  • #6
You have it backwards. Technically there could have existed particles of the same mass and energy that would not annihilate. However, being each other’s anti-particle implies that they must have the same mass and opposite charge - and that they can annihilate to photons since said charge is non-zero.
 
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  • #7
Orodruin said:
However, being each other’s anti-particle implies that they must have the same mass and opposite charge - and that they can annihilate to photons since said charge is non-zero.
Proton and antiproton annihilate to mesons. Can a proton and antiproton annihilate to photons only, without any mesons?
 
  • #8
snorkack said:
Proton and antiproton annihilate to mesons. Can a proton and antiproton annihilate to photons only, without any mesons?
Sure they can. It is just not as likely to happen.
 
  • #9
Orodruin said:
You have it backwards. Technically there could have existed particles of the same mass and energy that would not annihilate. However, being each other’s anti-particle implies that they must have the same mass and opposite charge - and that they can annihilate to photons since said charge is non-zero.
So, you are saying the mass and charge are merely consequences of them being anti-particle partners, and they annihilate because they are anti-particle partners, not the other way around. If I understand what you are saying, it is not that the opposite charge and same mass causes them to annihilate, but rather, they wouldn't have the necessary properties to annihilate if they didn't have the opposite charge and same mass. Is that an accurate or close to accurate understanding of what you said?


If so, it then makes me wonder what other thing about them makes them annihilate each other, but I expect the answer is the same answer for why water freezes at 0 degrees C: that's just how ("god", "nature" etc) made it.

However, my guess is that this happens simply because it's a lower energy state after the annihilation. That seems to be why most things happen in physics, as far as I can tell, so it makes sense to me here. But I know nothing so \_(0_0 )_/
 
  • #10
Consider, for example, neutrino and antineutrino.
Can they annihilate?
If yes, to what?
 
  • #11
snorkack said:
Consider, for example, neutrino and antineutrino.
Can they annihilate?
If yes, to what?
Given that they have no charge, this further elucidates what Orodruin said (if I understood it correctly). So, if I'm on the right track in understanding it, then again it would boil down to the annihilation being a lower (lowest possible?) energy state of the system. As for what they become, I cannot say, since I don't really know what neutrinos are. I don't want to cheat and look it up, so I'm going to guess ether photons or another particle that corresponds to the electromagnetic spectrum. :) Maybe it depends upon the energy of the particles when they collide.
 
  • #12
NothingsMatter said:
So, you are saying the mass and charge are merely consequences of them being anti-particle partners, and they annihilate because they are anti-particle partners, not the other way around. If I understand what you are saying, it is not that the opposite charge and same mass causes them to annihilate, but rather, they wouldn't have the necessary properties to annihilate if they didn't have the opposite charge and same mass. Is that an accurate or close to accurate understanding of what you said?

Yes. For example, for all we know (although that may not be the whole story), the muon could have just as well had the same mass as the electron. There are a number of theoretical points to be made here about how such a world would look like or even if it would actually be possible, but I am not going to go further into that detail here as that would be an A+ level discussion. The positron would then not annihilate with the negative muon even if they had the same mass.

NothingsMatter said:
If so, it then makes me wonder what other thing about them makes them annihilate each other, but I expect the answer is the same answer for why water freezes at 0 degrees C: that's just how ("god", "nature" etc) made it.
That's not the reason. The reason is that Anders Celsius defined 100 °C as the freezing point of water and 0 °C as the boiling point and that this was later reversed so that the lower fixed point of the scale (0 °C) instead referred to the freezing point.

If your question is instead "Why 273 K?" apart from the choice of the numerical value of the Boltzmann constant, then it is ultimately due to the value of the fine-structure constant.

NothingsMatter said:
However, my guess is that this happens simply because it's a lower energy state after the annihilation. That seems to be why most things happen in physics, as far as I can tell, so it makes sense to me here. But I know nothing so \_(0_0 )_/
Things happen because they can happen - there is a non-zero amplitude for it to happen, so it happens.

snorkack said:
Consider, for example, neutrino and antineutrino.
Can they annihilate?
If yes, to what?
Yes. Depends on the energy.

NothingsMatter said:
since I don't really know what neutrinos are
Me neither! That makes two of us! 😂

NothingsMatter said:
I don't want to cheat and look it up, so I'm going to guess ether photons or another particle that corresponds to the electromagnetic spectrum. :)
No. Neutrinos are neutral (no electric charge) leptons. Essentially relatives to electrons, muons, and taus. They only interact through the weak interactions mediated by W and Z bosons, where the interactions with the charged W bosons turn them into charged leptons or create them from charged leptons. Neutrinos have extremely small masses, which allow them to exhibit the phenomenon known as neutrino oscillations, where a neutrino originally created in an interaction with a muon can later be detected interacting with an electron. (This would not be possible were they massless.)

NothingsMatter said:
Maybe it depends upon the energy of the particles when they collide.
Indeed. Neutrino collisions are, however, extremely rare due to neutrinos only interacting through the weak interaction.
 
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  • #13
Orodruin said:
The reason is that Anders Celsius defined 100 °C as the freezing point of water and 0 °C as the boiling point and that this was later reversed so that the lower fixed point of the scale (0 °C) instead referred to the freezing point.
I'm getting dizzy. o0)

(not your fault, you're just presenting facts)

Orodruin said:
Me neither! That makes two of us! 😂
Your PhD thesis and many peer-reviewed journal articles notwithstanding. :wink:
 
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  • #14
berkeman said:
Your PhD thesis and many peer-reviewed journal articles notwithstanding. :wink:
I don’t even know if they are Dirac or Majorana fermions! 😭
 
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  • #15
Orodruin said:
I don’t even know if they are Dirac or Majorana fermions! 😭
… although when a I think about it, nobody else knows either … 🤔
 
  • #16
Orodruin said:
… although when a I think about it, nobody else knows either … 🤔
Kind of reminds me of an event long ago. A fellow student entered our lounge, constantly shaking his head and mumbling: "Zero divisors, zero divisors! There are no zero divisors at all."
 
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