#### liz

i'm getting quite confused about this antimatter stuff. ive heard that for every particle there is a corresponding antiparticle somewhere out there in the universe. but it also said somewhere else about the big bang theory, that the universe only exists because for some unexplained reason there is far more matter than antimatter. which one is correct? and what is antimatter?
i think of particles and matter as blobs, so is an antiparticle also a blob? i read some analogy to explain antimatter as thinking of a sheet of metal and stamping circles out of it. the circles are matter. The spaces left in the sheet of metal are antimatter. but that doesnt really make sense.
If anyone can help clarify all this stuff than thank you very much.

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#### SpaceTiger

Staff Emeritus
Gold Member
liz said:
i'm getting quite confused about this antimatter stuff. ive heard that for every particle there is a corresponding antiparticle somewhere out there in the universe.
I think they probably meant that for every particle, an anti-particle can be created. It's hard to imagine how sigificant amounts of antimatter could exist in the universe. They would very quickly annihilate with matter. In the beginning, they think that there was a sea of matter and antimatter and that most of it annihilated. It didn't all annihilate, however, and they assume that was because there was more matter than antimatter (an asymmetry, as they say).

#### Norman

Couple things to clear up:

an antiparticle has the same mass and spin as its mate, but has opposite charge (this includes electric, leptonic, etc). So they are particles in our usual notion. The positron (the antiparticle of the electron) just has the opposite sign of electric charge and leptonic charge. When an antiparticle-particle collision occurs, the particles annihilate each other, leaving in the final state some sort of energy (i.e. photons) to satisfy conservation laws. You should look up material on the Dirac sea and Dirac's notions of holes as antimatter for a starting place. But it turns out that anti-particles fall out of Quantum Field Theory very nicely.

Now, knowing this and seeing the predominance of matter in our local neighborhood (someone correct me if there is proof of the dominance of matter throughout the universe) of the universe, we conclude that there is an asymmetry in the amount of matter and antimatter created in the universe. I don't know if there is any other proof for the dominance of what we have arbitrarily called matter over antimatter, but the fact that you and I are here is enough at least on a local level.
Hope this helped.

#### SpaceTiger

Staff Emeritus
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Norman said:
Now, knowing this and seeing the predominance of matter in our local neighborhood (someone correct me if there is proof of the dominance of matter throughout the universe) of the universe, we conclude that there is an asymmetry in the amount of matter and antimatter created in the universe.
Yeah, I'm not sure if such a proof exists either, but it's an interesting idea. If there were a part of the universe that was composed primarily of antimatter, then its boundary with the matter-dominated universe would be releasing tremendous amounts of energy (presumably in the form of gamma-rays). I bet we can rule out such a thing in the observable universe, but if such a boundary were to cross our horizon, it sounds like we'd have yet another doomsday scenario on our hands.

OK, possible dumb question but if there was an area of space made up of just antimatter, would the expansion of the universe actually reduce the amount of matter/antimatter collisions along this boundary? Possibly this has already happened and that's why we don't see evidence of these regions of space?

#### SpaceTiger

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Gold Member
OK, possible dumb question but if there was an area of space made up of just antimatter, would the expansion of the universe actually reduce the amount of matter/antimatter collisions along this boundary? Possibly this has already happened and that's why we don't see evidence of these regions of space?
The current rate of expansion wouldn't be very efficient at preventing matter-antimatter annihilation at the boundary, but in an inflationary epoch, that probably wouldn't be the case. This is just speculation, but if the pre-inflationary universe had regions of matter and antimatter physically separated from one another, the process of inflation may have separated them enough to keep them around to the present day, but there would still be annihilation occurring on the boundary.

I've been thinking about it a bit more, though, and I wouldn't expect much annihilation to be occurring at the present day. The initial post-inflation collisions at the boundary of the matter-antimatter regions would create large voids that would be expanded by the growth of perturbations (collapse by gravity). I'm now thinking that an indicator of an antimatter section of the universe would be a large void or set of voids inconsistent with the usual power spectrum.

#### eNathan

liz said:
i'm getting quite confused about this antimatter stuff. ive heard that for every particle there is a corresponding antiparticle somewhere out there in the universe. but it also said somewhere else about the big bang theory, that the universe only exists because for some unexplained reason there is far more matter than antimatter. which one is correct? and what is antimatter?
i think of particles and matter as blobs, so is an antiparticle also a blob? i read some analogy to explain antimatter as thinking of a sheet of metal and stamping circles out of it. the circles are matter. The spaces left in the sheet of metal are antimatter. but that doesnt really make sense.
If anyone can help clarify all this stuff than thank you very much.
There is no difference from +matter and -matter. They just have different charges. We could all be made out of anti-matter, but we just call it matter lol. And everybody knows the Big Bang has some major problems. But some say that for some slight reason, there was 1/1000000 more matter than anti-matter in the universe after the BB, and over billions of years, matter won the battle. But its all in theory lol

#### ZapperZ

Staff Emeritus
2018 Award
eNathan said:
There is no difference from +matter and -matter. They just have different charges. We could all be made out of anti-matter, but we just call it matter lol. And everybody knows the Big Bang has some major problems. But some say that for some slight reason, there was 1/1000000 more matter than anti-matter in the universe after the BB, and over billions of years, matter won the battle. But its all in theory lol
This is not correct, and the word "theory" in physics doesn't mean "guess".

CP violation is not just "in theory" but a clear and verified experimental observation. And there are MANY solid theories that link the existence of CP violation as the possible symmetry-breaking origin on why our universe has more of one kind of matter than the other.

The BB has problems like any still-evolving idea, but OTHER models have more severe problems than the BB to account for ALL the experimental observatons.

Zz.

#### lawtonfogle

eNathan does have one good point, since matter and anti matter are opposites, we cannot tell which one is which unless we have some thing to compare them to.

close your eyes, and spin around a few times, can you tell which way is east or west with out something else to compare it to.

but then again, we are the ones who named it, so we can call it what ever we want (we as in human race)

#### eNathan

ZapperZ, we observe more matter than anti-matter, and the only explanation as of now is that there was just a little bit more matter than anti-matter after the BB. So, are you saying it's not a theory? Its certainly not a fact, and it is not just a "guess".

#### ZapperZ

Staff Emeritus
2018 Award
eNathan said:
ZapperZ, we observe more matter than anti-matter, and the only explanation as of now is that there was just a little bit more matter than anti-matter after the BB. So, are you saying it's not a theory? Its certainly not a fact, and it is not just a "guess".
1. If the creation of matter-antimatter came out of energy, then there should be an equal amount of matter and antimatter. There are no other mechanism for such creation, at least within the standard BB theory.

2. There are more matter than antimatter based on obvious observation

3. You said

"But some say that for some slight reason, there was 1/1000000 more matter than anti-matter in the universe after the BB, and over billions of years, matter won the battle. But its all in theory lol"

Where is this from? If you are criticizing BB theory as having problems, then you should at least cite the standard version of it. As it stands NOW, the only candidate for the asymmetry in matter-antimatter ratio is the CP violation.

Zz.

#### lawtonfogle

Um, could not there be equal amount of anti-matter in the 'center of the unverse', where the BB ocurred. It could be in a massive black hole. Just a guess. All alot more matter than anti-matter was pushed out of the 'eating range' of the black hole. And alot more anti-matter than matter was kept in the 'eating range' of the black hole.

Its just a thought not worth \$0.02 probally.

#### lawtonfogle

delete my earlier post, in the book 'A Breif History of Time', there is a hypothesis (or maybe a theory) about why there is more matter than anti-matter. Also, if i read right, the anti-matter is everywhere. electrons decay (this happens about a much as proton decay which takes 10000000000000000000000000000000 years to decay, that should be 31 zeros) into antiquarks which make up antimatter. it is viceversa for antimatter electrons. as i said, if i read right.

also, it had how we could tell antimatter apart from matter, it said it did not follow the rules based on three comparisons. Read the book for how or why, even though it states results, it gives the names of the ones who did the experiment and about when it was done, so you can look up the experiment if you want.

SpaceTiger said:
I've been thinking about it a bit more, though, and I wouldn't expect much annihilation to be occurring at the present day. The initial post-inflation collisions at the boundary of the matter-antimatter regions would create large voids that would be expanded by the growth of perturbations (collapse by gravity). I'm now thinking that an indicator of an antimatter section of the universe would be a large void or set of voids inconsistent with the usual power spectrum.
From everything I've read anti-matter behaves just like matter, except for opposite charges. I'm going out on a limb but couldn't it stand to reason that there are entire galaxies made of anti-matter, possibly in our observable area of the universe? If they are not in direct contact with matter galaxies, there would be no annihilations, so no massive energy would be radiating from them. Any reasons I've missed that prevent this?

#### SpaceTiger

Staff Emeritus
Gold Member
From everything I've read anti-matter behaves just like matter, except for opposite charges. I'm going out on a limb but couldn't it stand to reason that there are entire galaxies made of anti-matter, possibly in our observable area of the universe? If they are not in direct contact with matter galaxies, there would be no annihilations, so no massive energy would be radiating from them. Any reasons I've missed that prevent this?
That's right, in fact that's what I was tacitly assuming when I referred to a separate antimatter portion of the universe. If matter and antimatter aren't exactly the same (as implied by an asymmetry), then there might be some process which occurs differently in an antimatter dominated universe. I don't think it would be a problem for the formation of galaxies, however. I wouldn't expect matter-antimatter galaxies to be colliding and annihilating (though that would be quite an event), but I would expect their intergalactic media to be doing so.

#### DaveC426913

Gold Member
liz said:
...for every particle there is a corresponding antiparticle somewhere out there in the universe...
It is not meant to mean for every single individual particle there is a counterpart particle.

It means for every type of particle there is a counterpart type.

There are protons and there are antiprotons; There are electrons and there are antielectrons, etc.

#### lawtonfogle

electrons decay into anti-quarks, and anti-elctrons decay into quarks

after the BB, anti-electrons decayed much more, creating more matter than anti-matter.

Maybe I missed something but how can a tiny electron decay into a massive anti-quark? Or a positron decay into an equally massive quark? Did I misunderstand the standard model?

#### Norman

Maybe I missed something but how can a tiny electron decay into a massive anti-quark? Or a positron decay into an equally massive quark? Did I misunderstand the standard model?
No you have not mis-understood the standard model (SM). In the SM protons and electrons are stable. And as far as anyone has experimentally seen, they are completely stable. Now an experiment was done where they took a large amount of pure water and watched for proton decay for a long time. This is what set the ridiculously large limit on proton lifetimes. I have never heard of any experiment where electrons were tested for decay. And if electrons are decaying, expecially into anti-quarks (only antiquarks?) they must be decaying into baryons (only color neutral particles are present in nature), which seems ridiculous to me since that kind of reaction would violate baryon AND lepton number... hard for me to imagine- that doesn't mean it is not true though. This must involve one of Hawkings GUT's.
Cheers

#### juvenal

Maybe I missed something but how can a tiny electron decay into a massive anti-quark? Or a positron decay into an equally massive quark? Did I misunderstand the standard model?
Here's a paper I found, re electron decay:

http://arxiv.org/abs/hep-ph/9808252

Keep in mind that this is all theoretical speculation, and not proven experimentally.

But I don't think that the standard model alone can account for the observed level of baryon asymmetry in our universe, so something else is also going on. Standard model CP violation is not enough.

BTW - a particle cannot decay into a heavier particle, if we assume energy conservation holds, so the electron cannot decay into a quark, since even the lightest quark is heavier than an electron. And I don't think there are any theoretical models out there that violate energy conservation. Non-crank models, that is.

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#### Mk

liz said:
i'm getting quite confused about this antimatter stuff. ive heard that for every particle there is a corresponding antiparticle somewhere out there in the universe. but it also said somewhere else about the big bang theory, that the universe only exists because for some unexplained reason there is far more matter than antimatter. which one is correct? and what is antimatter?
i think of particles and matter as blobs, so is an antiparticle also a blob? i read some analogy to explain antimatter as thinking of a sheet of metal and stamping circles out of it. the circles are matter. The spaces left in the sheet of metal are antimatter. but that doesnt really make sense.
If anyone can help clarify all this stuff than thank you very much.
Yes matter and antimatter are both blobs, but matter is a black blob and antimatter is a white one. I've heard that analogy before, that the spaces left are antimatter, I don't know what the creator was going for but... that's not right. Maybe if you put the circules back in the hole it just makes a sheet again, the sheet being a p-brane, or spacetime? To add something, Dirac said E=±mc2, meaning since antimatter's the opposite of matter, energy can equal negative or postive charged mass times speed of light in a complete vacuumn squared. Negative matter and energy is something else, don't get them mixed up.

eNathan said:
ZapperZ, we observe more matter than anti-matter, and the only explanation as of now is that there was just a little bit more matter than anti-matter after the BB. So, are you saying it's not a theory? Its certainly not a fact, and it is not just a "guess".
Science is a cycle of theory and experiment. Scientific theories are created to explain the results of experiments that were created under certain conditions. A good theory should also make predictions about new experiments under diffrent conditions. If a experiment comes along that shows the theory is not a good approximation of completely wrong, the theorists make another, or change the first. Theories are predictions and explinations, with good proof to go with it and back it up.
From everything I've read anti-matter behaves just like matter, except for opposite charges. I'm going out on a limb but couldn't it stand to reason that there are entire galaxies made of anti-matter, possibly in our observable area of the universe? If they are not in direct contact with matter galaxies, there would be no annihilations, so no massive energy would be radiating from them. Any reasons I've missed that prevent this?
Nope, maybe matter-antimatter annihilation is the source of the mysterious gamma-ray bursts cosmologists have been trying to figure out. Most of the EMR from annihilation comes out in gamma wavelength.
lawtonfogle said:
delete my earlier post, in the book 'A Breif History of Time', there is a hypothesis (or maybe a theory) about why there is more matter than anti-matter. Also, if i read right, the anti-matter is everywhere. electrons decay (this happens about a much as proton decay which takes 10000000000000000000000000000000 years to decay, that should be 31 zeros) into antiquarks which make up antimatter. it is viceversa for antimatter electrons. as i said, if i read right.

also, it had how we could tell antimatter apart from matter, it said it did not follow the rules based on three comparisons. Read the book for how or why, even though it states results, it gives the names of the ones who did the experiment and about when it was done, so you can look up the experiment if you want.
Well, the half-life is 1035, meaning theoretically (in perfrect conditions with all variable accounted for) exactly half of the protons will have decayed. In half of that period 1/4 of the protons will have decayed, in half of that, 1/8 and half of that 1/16. So, since there's a hell of a lot of protons around us, there's always a bunch decaying. As I recall, just like neutrino observatories, proton observatores use huge vats of pure liquid, usually ultra-pure H2O.

The simplest way we tell antimatter from matter:
Shoot the antimatter/matter particles between a magnet. If there's a proton that goes towards one pole, the antiproton will go towards the other, because antimatter has opposite charges as matter.

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#### lawtonfogle

Norman said:
No you have not mis-understood the standard model (SM). In the SM protons and electrons are stable. And as far as anyone has experimentally seen, they are completely stable. Now an experiment was done where they took a large amount of pure water and watched for proton decay for a long time. This is what set the ridiculously large limit on proton lifetimes. I have never heard of any experiment where electrons were tested for decay. And if electrons are decaying, expecially into anti-quarks (only antiquarks?) they must be decaying into baryons (only color neutral particles are present in nature), which seems ridiculous to me since that kind of reaction would violate baryon AND lepton number... hard for me to imagine- that doesn't mean it is not true though. This must involve one of Hawkings GUT's.
Cheers
actualy what i was saying was something i read in A Breif History of Time, by Stephen Hawking

pages 79 to 81 in the updated and expanded tenth anniversary edition, or at the end of the chapter'elementary particles and the forces of nature

#### ZapperZ

Staff Emeritus
2018 Award
lawtonfogle said:
actualy what i was saying was something i read in A Breif History of Time, by Stephen Hawking

pages 79 to 81 in the updated and expanded tenth anniversary edition, or at the end of the chapter'elementary particles and the forces of nature
You should NEVER, EVER, use a pop-sci book as a physics reference text!

Zz.

#### lawtonfogle

what do you mean by a pop-sci book, it is not a sci-fi type thing is it?

i thought it was just a book about the universe

and what classifies a pop-sci book

#### Stefan Udrea

Norman,you said :

<<an antiparticle has the same mass and spin as its mate, but has opposite charge>>

I don't pretend to understand these things profoundly,but I wil quote from Feynman's "Lectures on Physics" :

<<The most important characteristic [of antimatter] is that when a proton and anti-proton come together they can anihilate each other.The reason why we accentuate this is because people don't understand when we say that there is a neutron and an anti-neutron,because they say "a neutron is a neutron,so how can it have opposite opposite charge".The rule of "anti" is not that it has opposite charge,but that it has a lot of other properties which are opposed.The anti-neutron distinguishes itself from a neutron this way : if we bring together two neutrons,they remain two neutrons,but if we bring together a neutron and an anti-neutron,they anihilate each other with a big explosion of released energy,with many $$\pi$$ mesons , gamma rays and many others.>>

(actually it was a romanian translation that I've put back into english )

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