Matter and Antimatter?

[Iron4ever]

I beleive that it is proven (please correct me if im wrong) that every particle in the universe has an antiparticle, and it is stated that the most significant property is that when you bring the two together they annihilate and make pure energy.

The Question that I ask is that if equal amounts of matter and antimatter were produced in the big bang, what happened to the antimatter? Did it decay? Why? If they both annihilate why is matter still here and not just pure energy?

 

As far out in our galaxy and in the universe as we can see everything around us is made of matter. How did we get to this situation of having a matter-dominated universe now, when the initial condition, the big bang, made equal amounts of matter and antimatter?

[GAHD]

I've yet to find much 'hard' evidence on antimatter, so as far as I can tell that's just theory. I'd love to see any evidence on it myself.

[alxian]

last i heard during the grand annihilation most free antimatter in the universe was annihilated, leaving the normal matter that remains.

 

creating antimatter then containing it is difficult because when it comes into contact with matter they combine releasing energy.

 

so theoretically every particle has an anti particle however in terms of raw volume if there is any antimatter left it is because it has not yet combined with matter and been annihilated.

[Erasmus00]

I've yet to find much 'hard' evidence on antimatter, so as far as I can tell that's just theory. I'd love to see any evidence on it myself.

 

We use anti-matter in particle accelerators all the time. CESR (Cornell electron storage ring) is a positron-electron colider. I think some lab somewhere managed to make a few atoms of anti-hydrogen, though I'll have to go through some back issues of APA to find the article.

-Will

[Iron4ever]

The researchers at the European Laboratory for Particle Physics, or CERN, have produced antiprotons. Here is part of a quote from CNN web site relating to this.

 

"The decelerator takes antiprotons -- the opposite of protons -- which have been created in the accelerator, groups them together and then slows them down to a tenth the speed of light.

 

These can then be captured, either in electromagnetic fields or by inserting them into ordinary atoms, which is possible because antiprotons destroy normal protons but not other matter.

 

Then, positrons -- antielectrons emitted by a radioactive source -- are added to the antiprotons. Just as one proton and one electron creates hydrogen, so one antiproton and one positron creates antihydrogen. Manufacturing antiatoms is the next step to understanding the fundamental properties of an antimatter world. "

[rockytriton]

maybe when the big band happened all matter went in one direction and all anti-matter went in the opposite direction. Perhaps there is an alternate universe that is made up entirely of anti-matter.

[Iron4ever]

I had thoughts along them lines aswell, which also got me thinking when we produce antihydrogen etc. in these particle accelerators, are we actually tapping into that alternate universe?

[CraigD]

I beleive that it is proven (please correct me if im wrong) that every particle in the universe has an antiparticle, and it is stated that the most significant property is that when you bring the two together they annihilate and make pure energy.

The Question that I ask is that if equal amounts of matter and antimatter were produced in the big bang, what happened to the antimatter? Did it decay? Why? If they both annihilate why is matter still here and not just pure energy?

 

As far out in our galaxy and in the universe as we can see everything around us is made of matter. How did we get to this situation of having a matter-dominated universe now, when the initial condition, the big bang, made equal amounts of matter and antimatter?

Best current theory postdicts (predicts about the past) that shortly after the big bang, there were equal masses of matter and antimatter, but that a very small “asymmetry” in the way one or more large, unstable particle decayed caused there to eventually be slightly more matter than antimatter. All or nearly all of the antimatter annihilated with matter, adding to the background radiation energy, leaving just the small amount of matter we currently observe.

 

This asymmetry is called charge-parity (CP) violation. The well-experimentally supported Standard Model predicts it, but the resulting numbers are hard to reconcile with observed reality – there’s too much matter, and not enough energy observed. Attempts to explain this are a hot topic in particle physics and cosmology.

 

You ask a very good question, which can’t be thoroughly answered in a short post. Try starting with the wikipedia articles for “antimatter” and “CP symmetry”. Wikipedia has very good hyperlinks that allow one to quickly study this kind of stuff – I highly recommend that if you’re not already a heavy wiki-reader, you try it.

 

I've yet to find much 'hard' evidence on antimatter, so as far as I can tell that's just theory. I'd love to see any evidence on it myself.

Since 2002, several thousand atoms totaling about 1.5 nano-grams (1.5*10^-9) of antimatter (anti-hydrogen) have been created and stored by 2 separate systems at CERN. Slowing (cooling) antiparticles from cyclotron collisions enough to make atoms was and continues to be an impressive accomplishment. Storing them is surprisingly easy. (see http:// http://en.wikipedia.org/wiki/Antimatter#Antimatter_production and http://ffden-2.phys.uaf.edu/212_fall2003.web.dir/tyler_freeman/modern.htm )

 

As any trekie will tell you, there’s no better fuel than antimatter. The cost of producing it by current methods, however, is staggering: at present, taking into account the cost of building, maintaining, and powering the necessary devices, $US 62,500,000,000,000/gram! Technologists like the late Robert Forward have suggested that this cost could be dramatically reduced by specially designed accelerator/collectors, possibly placed in a close orbit of the sun to provide ample solar power.

 

Very exciting, big-budget stuff.

[CraigD]

maybe when the big band happened all matter went in one direction and all anti-matter went in the opposite direction. Perhaps there is an alternate universe that is made up entirely of anti-matter.

I had thoughts along them lines aswell, which also got me thinking when we produce antihydrogen etc. in these particle accelerators, are we actually tapping into that alternate universe?

The problem with the idea that the primordial matter and antimatter didn’t annihilate, but physically separated, is that the anti-particles of particles with charge (such as electrons/positrons and quarks/antiquarks, which make up protons/antiprotons) have opposite electromagnetic charge. They’re strongly attracted to one another. Keeping them separate in the early universe would be nearly impossible.

 

A couple of potential misconceptions about antimatter need to be confronted:

• Antimatter isn’t an energy source, but a means of energy storage. Like a storage battery, more energy has to go into the accelerators that create antimatter than you could get out of the antimatter by allowing it to annihilate with matter. Unlike coal and oil, there doesn’t appear to be any sizable supplies of naturally-occurring antimatter anywhere, so to make antimatter will always take lots of energy from a conventional source.
  
• The production of antimatter is predicted by the Standard Model. There’s no great mystery where it comes from. Most antimatter is created via the high-energy collision of atomic nuclei in accelerators like the ones at CERN, but small amount of it is produced by low-energy sources such as the tiny amount of radioactive fluorine a radiologist injects into your vein when they do a PET scan. What the PET scanner is actually measuring are the gamma-ray emissions of matter-antimatter annihilations in your body!
  

Alternate universe theories can be a lot of fun, and maybe even good physics, but they’re not necessary to explain antimatter.

[Qfwfq]

As far out in our galaxy and in the universe as we can see everything around us is made of matter. How did we get to this situation of having a matter-dominated universe now, when the initial condition, the big bang, made equal amounts of matter and antimatter?

Actually, this is more of a cosmological topic so it should have gone into the Astronomy and Cosmology forum, I'll move it.

 

The problem with the idea that the primordial matter and antimatter didn’t annihilate, but physically separated, is that the anti-particles of particles with charge (such as electrons/positrons and quarks/antiquarks, which make up protons/antiprotons) have opposite electromagnetic charge. They’re strongly attracted to one another. Keeping them separate in the early universe would be nearly impossible.

This argument doesn't show anything about entire galaxies or clusters of them. If our galaxy can electrically neutral, so can a galaxy of positrons, antiprotons and antineutrons.

 

The force between astronomical bodies such as stars and galaxies is essentially gravitational afaik.

[UncleAl]

I beleive that it is proven (please correct me if im wrong) that every particle in the universe has an antiparticle

Obviously false. What is the antiparticle of a photon? There is no common occurance of antimatter anywhere in the visible universe, or we would see 511 keV annihalation radiation at its boundary with ordinary matter. Energetic processes (relativistic jets from collasped matter sources) can locally produce some antimatter.

 

if equal amounts of matter and antimatter were produced in the big bang

They weren't. There is parity asymmtery in the Standard Model. A sock will fit equally well upon either foot, but a given single shoe will not. The Big Bang generated matter and antimatter in unequal quantities The net discrepancy is the visible universe.

[CraigD]

The problem with the idea that the primordial matter and antimatter didn’t annihilate, but physically separated, is that the anti-particles of particles with charge (such as electrons/positrons and quarks/antiquarks, which make up protons/antiprotons) have opposite electromagnetic charge. They’re strongly attracted to one another. Keeping them separate in the early universe would be nearly impossible.

...This argument doesn't show anything about entire galaxies or clusters of them. If our galaxy can electrically neutral, so can a galaxy of positrons, antiprotons and antineutrons.

 

The force between astronomical bodies such as stars and galaxies is essentially gravitational afaik.

I believe you’re correct that a far-away galaxy or cluster might be composed almost entirely of antimatter, and be indistinguishable from one composed of ordinary matter by any sort of remote measurement we might make.

 

There are a some reasons to doubt this has actually happened:

• To avoid the annihilation I described, the big bang (or whatever created primordial matter and energy) must have occurred in a “clumpy” manner at multiple distant locations. Current theory, supported by data such as the uniformity of the cosmic background radiation, doesn’t support this.
  
• Collisions between galaxies occur frequently. If there were many “antigalxies” or cluster of antigalaxies scattered more-or-less randomly among the ordinary ones, collisions between an anti- and a normal galaxies should occur. These would be tremendously energetic events. No such events have been observed

And the reason I find most persuasive (though understand least well)

• The CP symmetry violation thought to be responsible for the slight excess of primordial matter over antimatter explicitly predicts more matter than antimatter, not simply more of one than the other

The idea of antiuniverses is certainly exciting. When I was a astronomy student in the 1970s, I recall reading and speaking to several professional astronomers who thought that super-energetic light sources such as quasars might be collisions between anti- and normal galaxies. Since then, though, explanations not involving antimatter (though no less exciting) seem to have captured the scientific consensus.

[infamous]

I believe you’re correct that a far-away galaxy or cluster might be composed almost entirely of antimatter, and be indistinguishable from one composed of ordinary matter by any sort of remote measurement we might make.

 

.

Possible but highly unlikely because the asymmetric conditions that gave us our universe would apply everywhere within it, especially when the universe was young and universal evolutionary events were more closely associated with each other. Not much chance for any anti-matter to survive this epoch.

[Qfwfq]

Obviously false. What is the antiparticle of a photon?

A photon! Of course.

 

Goodness Unc, you can be disappointing sometimes!

 

There is no common occurance of antimatter anywhere in the visible universe, or we would see 511 keV annihalation radiation at its boundary with ordinary matter.

That would depend on the quantity of particles going between them.

 

Anyway, I doubt the annihilation would be so much along "the border". How much would it really be noticeable? How much would the spectrum be sharply peaked at 511 keV?

 

CP symmetry violation for weak interactions has more to do with it, though I'm not expert on the details.

 

To avoid the annihilation I described, the big bang (or whatever created primordial matter and energy) must have occurred in a “clumpy” manner at multiple distant locations.

I wouldn't be too sure.

 

Collisions between galaxies occur frequently.

Yeah, I know, true.

 

'Frequently' doesn't mean every few weeks though. :hihi: I wouldn't even be so sure of exactly how great the effect would be. AFAIK hardly any of the stars actually bump into each other during such collisions. Reckon it on the ratios of distances. I'm not sure even the solar winds would give all that great an effect.

[Jay-qu]

so if there is anti-matter regions of the universe that have eluded annihilation, does an antiparticle look different? does it produce anti-photons or something that would distinguish it from a distance? anyway why would there be more matter than anti-matter in the universe, for some reason it would make sense if there where equal quantities of each... but who knows really

[CraigD]

so if there is anti-matter regions of the universe that have eluded annihilation, does an antiparticle look different? does it produce anti-photons or something that would distinguish it from a distance?

Antimater interacts gravitationally with normal matter and other antimatter in a way indistinguishable from normal mater. They emit ordinary photons (with the defining difference that the photons of magnetic force emitted by anti-protons and anti-electrons (positrons) are swapped – that is, an anti-proton has the charge of an ordinary electron, a positron the charge of an ordinary electron.

 

Since the only interactions (fundamental forces) measurable at astronomical distances are gravity and light, not magnetism, there seems to be no way to disprove that a distant galaxy is not made of antimatter.

 

It 2 distant galaxies are observed to interact (collide), however, they’re proven to be either both ordinary matter, or both antimatter. Otherwise, we’d observe tremendously energetic gamma-frequency light emissions, secondary radiation, and physical features from matter/antimatter annihilation. The consensus is that this has never been observed.

… anyway why would there be more matter than anti-matter in the universe[?]…

The best explanation at present is know as CP symmetry violation. It’s complicated, and requires a good knowledge of quantum physics to understand well. Though it’s the best explanation most people believe we have, the prediction appears to be off by about a factor of 100 – it doesn’t predict as much matter as we observe.

…for some reason it would make sense if there where equal quantities of each... but who knows really

It certainly does make sense that there would have been equal quantities of both, and theory postdicts (predicts about the past) that there very nearly was.

 

:evil: It’s fortunate for us that the amount were not exactly equal, or there’d likely be no or very little matter in the universe (and a bit more energy), and we wouldn’t exist.

[Aki]

There's actually more matter than antimatter because the universe isn't perfectly symmetrical.

And in a vaccum, even though it is considered as "empty space", it is not. In fact there is a constant creation of particles, and anti particles, and that annihilate all the time.