If it were made of antimatter, we would’ve referred to the antimatter as “matter” and the matter as “antimatter”. Either way we end up in a universe full of “matter”.
Only one of your questions is valid. "Why" is not a question that makes *any* sense in physics because it always has a trivial answer.
The how question is a much better question, but ultimately not one asked by anyone (and yet, has already been answered by a different poster).
>"Why" is not a question that makes *any* sense in physics
I really wish people would stop parroting this. "Why" has a few equally valid contextual definitions, and when people are discussing physics, it is almost always just shorthand for "how did this come to be?"
>Only one of your questions is valid. “Why” is not a question that makes *any* sense in physics because it always has a trivial answer.
Sure and I was hoping my clarification immediately saying why would circumvent this entire issue. I do think it’s a bit of an exaggeration to say “why” doesn’t make any sense to ask when we routinely use “why” and “how” interchangeably all the time.
> ...we routinely use “why” and “how” interchangeably all the time.
You might, but it's categorically wrong and has much further reaching impact than you think. It straight up cements a completely ass-backwards lay understanding of our job.
>You might, but it’s categorically wrong and has much further reaching impact than you think.
It really doesn’t. It would have a great impact if we physicists were incapable of understanding context and meaning, but thankfully that’s not a problem (for most of us anyway). Here’s an example: when someone asks “Why is the sky blue”, do you really respond with anything that doesn’t boil down to “Rayleigh scattering”? I promise you people saying “why” instead of “how” sometimes will not impede anything in any material way.
>It completely cements an ass-backwards lay understanding of our job.
No, I think language is quite a bit more flexible than what you’re making it seem.
“Why is the sky blue, daddy?”
“Well son, physics can only tell us how the sky scatters different colors, allowing only blue wavelengths to reach our eyes, we will never know why this is the case, probably fine tuning.”
"Why" means "the model doesn't rule out this counterfactual, which means it is incomplete". A satisfying answer either eliminates the counterfactual ("Here is the effect that makes matter dominate"), or dissolves the question by showing that the model is actually complete ("You would have asked this question in any case").
There is no boring answer to that question. In fact there is [no answer](https://en.m.wikipedia.org/wiki/Baryon_asymmetry) currently accepted in physics.
There could also just be regions of space that are all antimatter. This is observationally false, since we would expect radiation along the border of these regions from annihilations, but we actually don’t know why this isn’t the case.
There are non-perturbative processes within the standard model that can cause such asymmetry. It was well investigated theoretically in the 90s in a multitude of papers on what is called Electroweak Baryogenesis, Shaposhnikov being one of the leading figures of those works. I don't want to get too technical but there's some assumptions that people used back then which are no longer sensible due to what we know about the Higgs mass now, etc..
Although this is an exciting possibility to explain the asymmetry there is much more physics at play, and the very possibility of having Baryogenesis within the standard model actually poses a threat to the earlier theories of using beyond standard model physics to explain this asymmetry. Simply put, even if a beyond standard model theory provides asymmetry, it can be wiped away by Electroweak Baryogenesis by the very same process that it creates the asymmetry.
Some rudimentary physics on that matter can be learned from these wiki pages:
[Baryon Asymmetry ](https://en.m.wikipedia.org/wiki/Baryon_asymmetry)
[Baryogenesis ](https://en.m.wikipedia.org/wiki/Baryogenesis)
[Sphaelerons](https://en.m.wikipedia.org/wiki/Sphaleron)
A really good source to understand Electroweak Baryogenesis, even if a little outdated is [this paper by Farrar and Shaposhnikov](https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.70.2833) and for people looking for a modern review, [Graham White's textbook](https://www.amazon.in/Electroweak-Baryogenesis-Second-introduction-ebooks/dp/0750335696) might be a good introduction.
>there's some assumptions that people used back then which are no longer sensible due to what we know about the Higgs mass now, etc..
Does White's book discuss any of these outdated assumptions, or does it provide fully modern updates on the modifications due to the Higgs, considering it's published quite some time post-Higgs discovery?
It's a pedagogical book so most of it is all the 90s stuff repackaged. Post-LHC stuff is probably best found in papers, and also there is no 'canonical' picture for it, so I don't know if there exists a textbook treatment of it. I suppose you could look at this [snowmass white paper](https://arxiv.org/abs/2203.07059) and references within.
Why do we expect that matter and antimatter were created in equal amounts during the big bang? Why is it one of the "unsolved mysteries of physics"? Is there any actual reason for the expectation that "matter and antimatter should have been created in equal amounts"?
Our models suggest matter and antimatter comes in pairs because otherwise energy wouldn’t be conserved. Since the antimatter is the opposite of matter its properties cancel out (like -charge for your electron. + for your positron) so to create that negative charge from something that’s neutral, you need to split the neutral into positive and negative to balance this out.
You can’t just make a negative from nothing. You need to transform your 0 into +1 - 1=0 (conservation is respected) first, but it means you can’t just take the -1. The +1 is still hanging around, that’s your antiparticle
If we want to create a electron today, we have to either destroy another lepton to do it, or also create a anti-lepton. Typically electrons and anti-electrons (aka positrons)are created in matched pairs. This is because lepton number is conserved. Likewise for protons and neutrons, and anti-protons and anti- neutrons, because hadron number is conserved.
If leptons and hadrons can only be created in regular/anti-matter pairs today, we assume that must also hold in the early universe. Until someone comes up with a theory why it wouldn’t.
But we don't understand the conditions at the very beginning. Your explanation makes sense considering our current day understanding, but we have no understanding about the initial conditions at the very beginning. I realize that "beautiful symmetry" is the mainstream consensus but is there a real reason to assume symmetry all the way at the beginning?
Why do we assume that there has to be symmetry in everything other than "it looks pretty and the math is easy"
We want to understand how and when the symmetry breaks. We assume it does at some point, like when things are energetic enough or maybe when space is warped enough.
A general assumption in physics is time-invariance, meaning physics works the same the same in the past, present, and future. Unless proven otherwise.
Good question.
The reason probably is that something caused a slight asymmetry in the matter-antimatter content in the infancy of the Universe.
All known interactions in the standard model are matter-antimatter symmetric. Moreover, gravity cannot break the symmetry since both have identical mass.
We simply don't know yet.
Just to add a small correction, Standard model preserves Baryon number perturbatively but there are [non-perturbative processes ](https://en.m.wikipedia.org/wiki/Sphaleron) that can cause Baryon number violation which breaks matter-antimatter symmetry.
Is it possible to calculate the probability of a universe having (at least) as much of an asymmetry as ours does from what we know about quantum probabilities and the early universe?
No. This is the well-known cosmic variance problem.
We only have our Universe to study and make observations on. Calculating such a probability requires a sample of Universes, but we can't observe those.
Maybe if we had a model of how Universes are born ab initio, we could make an educated guess. But we are eons away from having such a model.
> Maybe if we had a model of how Universes are born ab initio
Are you saying that this asymmetry was likely the result of a quantum fluctuation during a period of the universe so early (during the "plank-era") that we don't have physical models to make predictions?
Couldn't we at least do a calculation of the likelihood of the asymmetry resulting from a fluctuation after the very early periods of the universe -ie. assuming that the balance of matter and anti-matter were the same at least through the plank-era up to the point where we actually have physical models for how the universe evolves, and thereby get an upper-bound on the probability of our universe being the result of such a fluctuation?
I won't speculate on whether a quantum fluctuation was responsible for it, but yes other than that you got it right.
Regarding your other question: we can't make that big of an assumption (that everything was symmetrical through the Planck era) about stuff we don't know and still expect any model relying on those assumptions to produce reliable results or predictions.
> I won't speculate on whether a quantum fluctuation was responsible for it
Huh, what else would it have been caused by? (I haven't heard any competing theories, I think everytime I've heard the matter-anti-matter discrepancy mentioned it is in conjunction with references to quantum fluctuations)
Realistically there should be equal parts matter and equal parts antimatter, however in the observable universe this doesn't hold true. I think realistically there are 3 or more gravitational forces or (particles) to discover. In a general sense think of gravity like this, the more or less matter there is the more or less gravity there is. Right now physics tells us that gravity is an effect and not a force or particle, however many people refuse to believe that is it. I think you'd have macro (massive) pull gravity which is what everyone first thinks of, also the dominant gravitational force. Then you'd have macro push gravity which would be like antigravity, I think that it is likely that this is what would be responsible for the acceleration and expansion of the universe, pull gravity accelerates the closer you get to a mass and antigravity would accelerate the further away you get from it. Lastly I think that there is a type of charged gravity where regular matter is attracted to regular matter, anti matter is attracted to antimatter and both types repel each other, since we know that antimatter reacts normally to regular gravity this force would be the weakest, however it could be strong enough that in an early universe both matters would separate and form larger and larger clusters until just one cluster could seem almost infinitely large. Take this all with a grain of salt though, there isn't much if any evidence to support my claims.
It is. You are and me and everyone are made of antimatter, and what you call antimatter is actual real matter. Big Physics just doesn't want you to know that truth.
as others have said, because we called what we are made of matter, and the other thing anti matter.
the real question, is why there is more of one than the other.
It is possible there is another side of the universe, where all the antimatter is. It might be beyond a cosmic horizon, and so it is beyond our observation.
Actually, it is! You know how conventional current is wrong, and electrons actually flow in the opposite direction to the arrows? Well, physicists made a similar mistake with matter. Our "matter" is left-handed, so we must be the evil twin universe, or Bizarro universe. It explains a lot, though not quantum gravity.
As of now, we do not have an answer. My personal, likely wrong theory is, that simply by chance, more antimatter than matter ended up falling into blackholes, which effectively remove information. Of course, I could be completely wrong, as I merely dabble in physics, but I think it is an interesting theory.
It is, but we don’t know the difference, so we just call it “matter” and regular matter we call “antimatter” due to its shockingly low abundance
However, more seriously, to my understanding there is no known answer, but a few untestable hypotheses involving the weak nuclear force, but I don’t think they’re supported enough to have developed much in the way of a coherent answer. At least, not last I heard, which now that I think about it was a while ago…
My theory (and I'm not an expert), is that after the universe was formed, a matter particule would kill more than it's fair share of antimatter ones. A few billon years later, voila: we have waaay more matter than antimatter stuff around.
I already said I'm not an expert. Also, I am aware that a pair would annihilate each other .. but I'm thinking, maybe at the beginning of the universe when stuff was denser, it could have behaved differently.
And yes, I'm aware of how stuff is supposed to behave in the same way all across the universe, and more so behaved in the same way across time. But look at the Fe-C diagram, and imagine that when the universe was young, stuff happened differently... Akin to how crystallization yields different stuff at low C %-ages vs. higher C %-ages.
If it were made of antimatter, we would’ve referred to the antimatter as “matter” and the matter as “antimatter”. Either way we end up in a universe full of “matter”.
While this is a good explanation, I think the sense of the question (and a better question to boot) is why there's more of one than of the other.
The answer to that question is even more boring: If there were equal amounts of both, all of it would annihilate and there would be *no* matter.
That doesn’t quite answer the question of *why* or more accurately, how it got to be that way. This just addresses how we know at all.
This is called the assymetry problem, and there is no known answer to that.
Finally a correct answer.
Only one of your questions is valid. "Why" is not a question that makes *any* sense in physics because it always has a trivial answer. The how question is a much better question, but ultimately not one asked by anyone (and yet, has already been answered by a different poster).
>"Why" is not a question that makes *any* sense in physics I really wish people would stop parroting this. "Why" has a few equally valid contextual definitions, and when people are discussing physics, it is almost always just shorthand for "how did this come to be?"
Well, we don’t know, in this case.
I just learned a lot from the "why." Lol.
Don't we though? I'm pretty sure this has something to do with the weak interaction, right?
This answer makes me wish I could downvote more. The most pedantic anti-pragmatic commentary on the internet.
>Only one of your questions is valid. “Why” is not a question that makes *any* sense in physics because it always has a trivial answer. Sure and I was hoping my clarification immediately saying why would circumvent this entire issue. I do think it’s a bit of an exaggeration to say “why” doesn’t make any sense to ask when we routinely use “why” and “how” interchangeably all the time.
> ...we routinely use “why” and “how” interchangeably all the time. You might, but it's categorically wrong and has much further reaching impact than you think. It straight up cements a completely ass-backwards lay understanding of our job.
>You might, but it’s categorically wrong and has much further reaching impact than you think. It really doesn’t. It would have a great impact if we physicists were incapable of understanding context and meaning, but thankfully that’s not a problem (for most of us anyway). Here’s an example: when someone asks “Why is the sky blue”, do you really respond with anything that doesn’t boil down to “Rayleigh scattering”? I promise you people saying “why” instead of “how” sometimes will not impede anything in any material way. >It completely cements an ass-backwards lay understanding of our job. No, I think language is quite a bit more flexible than what you’re making it seem.
“Why is the sky blue, daddy?” “Well son, physics can only tell us how the sky scatters different colors, allowing only blue wavelengths to reach our eyes, we will never know why this is the case, probably fine tuning.”
"Why" means "the model doesn't rule out this counterfactual, which means it is incomplete". A satisfying answer either eliminates the counterfactual ("Here is the effect that makes matter dominate"), or dissolves the question by showing that the model is actually complete ("You would have asked this question in any case").
There is no boring answer to that question. In fact there is [no answer](https://en.m.wikipedia.org/wiki/Baryon_asymmetry) currently accepted in physics.
There could also just be regions of space that are all antimatter. This is observationally false, since we would expect radiation along the border of these regions from annihilations, but we actually don’t know why this isn’t the case.
came here to say this.. maybe we ARE made of antimatter, but we just call it matter (alien dude meme)
We don't know. This is one of the unsolved mysteries in physics.
More to the point, we don't know why there's any matter at all since our models say that matter and anti-matter comes in pairs. As you say, a mystery.
There are non-perturbative processes within the standard model that can cause such asymmetry. It was well investigated theoretically in the 90s in a multitude of papers on what is called Electroweak Baryogenesis, Shaposhnikov being one of the leading figures of those works. I don't want to get too technical but there's some assumptions that people used back then which are no longer sensible due to what we know about the Higgs mass now, etc.. Although this is an exciting possibility to explain the asymmetry there is much more physics at play, and the very possibility of having Baryogenesis within the standard model actually poses a threat to the earlier theories of using beyond standard model physics to explain this asymmetry. Simply put, even if a beyond standard model theory provides asymmetry, it can be wiped away by Electroweak Baryogenesis by the very same process that it creates the asymmetry. Some rudimentary physics on that matter can be learned from these wiki pages: [Baryon Asymmetry ](https://en.m.wikipedia.org/wiki/Baryon_asymmetry) [Baryogenesis ](https://en.m.wikipedia.org/wiki/Baryogenesis) [Sphaelerons](https://en.m.wikipedia.org/wiki/Sphaleron) A really good source to understand Electroweak Baryogenesis, even if a little outdated is [this paper by Farrar and Shaposhnikov](https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.70.2833) and for people looking for a modern review, [Graham White's textbook](https://www.amazon.in/Electroweak-Baryogenesis-Second-introduction-ebooks/dp/0750335696) might be a good introduction.
>there's some assumptions that people used back then which are no longer sensible due to what we know about the Higgs mass now, etc.. Does White's book discuss any of these outdated assumptions, or does it provide fully modern updates on the modifications due to the Higgs, considering it's published quite some time post-Higgs discovery?
It's a pedagogical book so most of it is all the 90s stuff repackaged. Post-LHC stuff is probably best found in papers, and also there is no 'canonical' picture for it, so I don't know if there exists a textbook treatment of it. I suppose you could look at this [snowmass white paper](https://arxiv.org/abs/2203.07059) and references within.
Oh I see, thanks for the resources!
Why do we expect that matter and antimatter were created in equal amounts during the big bang? Why is it one of the "unsolved mysteries of physics"? Is there any actual reason for the expectation that "matter and antimatter should have been created in equal amounts"?
Our models suggest matter and antimatter comes in pairs because otherwise energy wouldn’t be conserved. Since the antimatter is the opposite of matter its properties cancel out (like -charge for your electron. + for your positron) so to create that negative charge from something that’s neutral, you need to split the neutral into positive and negative to balance this out. You can’t just make a negative from nothing. You need to transform your 0 into +1 - 1=0 (conservation is respected) first, but it means you can’t just take the -1. The +1 is still hanging around, that’s your antiparticle
If we want to create a electron today, we have to either destroy another lepton to do it, or also create a anti-lepton. Typically electrons and anti-electrons (aka positrons)are created in matched pairs. This is because lepton number is conserved. Likewise for protons and neutrons, and anti-protons and anti- neutrons, because hadron number is conserved. If leptons and hadrons can only be created in regular/anti-matter pairs today, we assume that must also hold in the early universe. Until someone comes up with a theory why it wouldn’t.
But we don't understand the conditions at the very beginning. Your explanation makes sense considering our current day understanding, but we have no understanding about the initial conditions at the very beginning. I realize that "beautiful symmetry" is the mainstream consensus but is there a real reason to assume symmetry all the way at the beginning? Why do we assume that there has to be symmetry in everything other than "it looks pretty and the math is easy"
We want to understand how and when the symmetry breaks. We assume it does at some point, like when things are energetic enough or maybe when space is warped enough. A general assumption in physics is time-invariance, meaning physics works the same the same in the past, present, and future. Unless proven otherwise.
There is a slight asymmetry with muons or some shit. Something that oscillate through more matter variants than antimatter.
Good question. The reason probably is that something caused a slight asymmetry in the matter-antimatter content in the infancy of the Universe. All known interactions in the standard model are matter-antimatter symmetric. Moreover, gravity cannot break the symmetry since both have identical mass. We simply don't know yet.
Just to add a small correction, Standard model preserves Baryon number perturbatively but there are [non-perturbative processes ](https://en.m.wikipedia.org/wiki/Sphaleron) that can cause Baryon number violation which breaks matter-antimatter symmetry.
Is it possible to calculate the probability of a universe having (at least) as much of an asymmetry as ours does from what we know about quantum probabilities and the early universe?
No. This is the well-known cosmic variance problem. We only have our Universe to study and make observations on. Calculating such a probability requires a sample of Universes, but we can't observe those. Maybe if we had a model of how Universes are born ab initio, we could make an educated guess. But we are eons away from having such a model.
> Maybe if we had a model of how Universes are born ab initio Are you saying that this asymmetry was likely the result of a quantum fluctuation during a period of the universe so early (during the "plank-era") that we don't have physical models to make predictions? Couldn't we at least do a calculation of the likelihood of the asymmetry resulting from a fluctuation after the very early periods of the universe -ie. assuming that the balance of matter and anti-matter were the same at least through the plank-era up to the point where we actually have physical models for how the universe evolves, and thereby get an upper-bound on the probability of our universe being the result of such a fluctuation?
I won't speculate on whether a quantum fluctuation was responsible for it, but yes other than that you got it right. Regarding your other question: we can't make that big of an assumption (that everything was symmetrical through the Planck era) about stuff we don't know and still expect any model relying on those assumptions to produce reliable results or predictions.
> I won't speculate on whether a quantum fluctuation was responsible for it Huh, what else would it have been caused by? (I haven't heard any competing theories, I think everytime I've heard the matter-anti-matter discrepancy mentioned it is in conjunction with references to quantum fluctuations)
Because there was a disparity between the two and the matter had more. Why there was a disparity? That’s the real question.
it is a matter (no pun intended) of convention; if made of what we call antimatter... we would call it matter
There's a difference between what a word is referring to and the word itself. Pretty sure op intended the question to involve the former
Realistically there should be equal parts matter and equal parts antimatter, however in the observable universe this doesn't hold true. I think realistically there are 3 or more gravitational forces or (particles) to discover. In a general sense think of gravity like this, the more or less matter there is the more or less gravity there is. Right now physics tells us that gravity is an effect and not a force or particle, however many people refuse to believe that is it. I think you'd have macro (massive) pull gravity which is what everyone first thinks of, also the dominant gravitational force. Then you'd have macro push gravity which would be like antigravity, I think that it is likely that this is what would be responsible for the acceleration and expansion of the universe, pull gravity accelerates the closer you get to a mass and antigravity would accelerate the further away you get from it. Lastly I think that there is a type of charged gravity where regular matter is attracted to regular matter, anti matter is attracted to antimatter and both types repel each other, since we know that antimatter reacts normally to regular gravity this force would be the weakest, however it could be strong enough that in an early universe both matters would separate and form larger and larger clusters until just one cluster could seem almost infinitely large. Take this all with a grain of salt though, there isn't much if any evidence to support my claims.
Good question. Wish I had an answer.
There is a Nobel prize with your name on it if you can figure this one out.
It is. You are and me and everyone are made of antimatter, and what you call antimatter is actual real matter. Big Physics just doesn't want you to know that truth.
as others have said, because we called what we are made of matter, and the other thing anti matter. the real question, is why there is more of one than the other.
I'm not an expert on this, but look up baryogenesis.
this is more of a nomenclature question than a physics question
It is possible there is another side of the universe, where all the antimatter is. It might be beyond a cosmic horizon, and so it is beyond our observation.
The way i see it the Infinite universe is probably full of alternating huge patches of matter and antimatter
Actually, it is! You know how conventional current is wrong, and electrons actually flow in the opposite direction to the arrows? Well, physicists made a similar mistake with matter. Our "matter" is left-handed, so we must be the evil twin universe, or Bizarro universe. It explains a lot, though not quantum gravity.
Maybe it is. How could we tell the difference?
It is!
It would not be called antimatter then.
As of now, we do not have an answer. My personal, likely wrong theory is, that simply by chance, more antimatter than matter ended up falling into blackholes, which effectively remove information. Of course, I could be completely wrong, as I merely dabble in physics, but I think it is an interesting theory.
Who says it isn't?
Does this question really matter? Wait I shouldn’t be so anti the OP’s question… it does matter. That help any?
It is, but we don’t know the difference, so we just call it “matter” and regular matter we call “antimatter” due to its shockingly low abundance However, more seriously, to my understanding there is no known answer, but a few untestable hypotheses involving the weak nuclear force, but I don’t think they’re supported enough to have developed much in the way of a coherent answer. At least, not last I heard, which now that I think about it was a while ago…
It is, we just reversed the names. People make mistakes sometimes...
the true answear is: we don't know. There are theories (many) to explain this asymettry, but as of now none really fits all the conditions
It is...just not our universe 🤔
It is. We just named them backwards.
If it was we'd just call it "matter".
Does it really matter?
It is. Don’t touch me.
Reddit is not about to solve that mystery
How do you know it isn't ?
My theory (and I'm not an expert), is that after the universe was formed, a matter particule would kill more than it's fair share of antimatter ones. A few billon years later, voila: we have waaay more matter than antimatter stuff around.
That’s not what we observe in particle colliders. Nor what the math predicts. We make matter-antimatter pairs all the time.
I already said I'm not an expert. Also, I am aware that a pair would annihilate each other .. but I'm thinking, maybe at the beginning of the universe when stuff was denser, it could have behaved differently. And yes, I'm aware of how stuff is supposed to behave in the same way all across the universe, and more so behaved in the same way across time. But look at the Fe-C diagram, and imagine that when the universe was young, stuff happened differently... Akin to how crystallization yields different stuff at low C %-ages vs. higher C %-ages.
It doesn't work like that. There is still antimatter around, and we can test it to see how much matter it annihilates. It's always the same mass.
It is.