Just Antimatter

[cadbrowser]

When scientist talk about antimatter are they generally referencing anti-elements or anti-particles specifically, or is there reason to assume that there is actually a collection of molecules that could form anti-water (or whatever)?

Would the properties be exactly the same with an opposite charge?

Trying to understand this a bit better.

Thanks!

[Solauren]

IN THEORY, Anti-Water might exist.

Creating it would be an absolute bitch, given the nature of our universe, however (mostly matter, meaning the anti-matter would be annhilated quickly).

However, for the most part, they are talking about atomic and subatomic anti-matter particles.

[Imperial528]

I believe we have actually created stable anti-hydrogen, a few dozen atoms of it if I am not mistaken. We've yet to make molecular anti-hydrogen, but that is more because of how hard it is to even trap enough antiprotons and positrons to make atomic hydrogen, rather than any properties inherent in antimatter that prevents such formations.

[Simon_Jester]

Antiparticles are perfectly capable of forming anti-atoms, which in turn could form anti-molecules and even large objects such as antirocks, antitrees, and antiSDNposters.

There is absolutely nothing in the laws of physics that prevents antiparticles from having the same range of 'chemical' and 'nuclear' interactions among themselves that normal particles do. Antiuranium atoms could undergo nuclear fission and form smaller antiatoms, liberating the same energy that normal uranium atoms do in the process. Antihydrogen could fuse into antihelium, liberating the same energy that normal hydrogen atoms do. Antiwater would have the same density, specific heat capacity, and other properties as regular water... as long as you don't touch it with normal matter.

Indeed, as far as I know, if by some act of God every particle in the universe were swapped out with a corresponding antiparticle all at once, I'm not sure we'd actually notice, except for certain specialized experiments and equipment.

The only really noteworthy property of antimatter is that it explodes on contact with normal matter, because a particle and its antiparticle cancel each other out and liberate their combined "m c squared" rest-mass energy.

[Batman]

Depends on how the swap happens. If the universe always has been an anitmatter one, nobody'd notice a thing. If the modern day universe were suddenly turned all antimatter, there still wouldn't be any noticeable effects but I think all the electrical charges suddenly being reversed would cause some comment.

[HMS Conqueror]

Swapping charges would be detectable. It is thought that CPT is a fundamental symmetry of nature, but that would involve a little more. Also it is not exactly known how anti-matter behaves - that is why anti-hydrogen is produced, to test, for instance, whether the atomic spectra are the same as for hydrogen.

[Simon_Jester]

It'd be detectable- what I mean is that for routine day-to-day stuff, I'm not sure we'd notice. I think the first sign would be physicists doing something moderately complicated in a lab and going "Huh, that's funny..." But Bob the plumber might be able to carry on just the same without knowing or caring that the whole world had suddenly been turned into antimatter.

As for whether we know it behaves the same- all I can say is that it damn well ought to behave the same as equivalent amounts of normal matter, as far as light and chemistry and so on are concerned. Unless I'm badly mistaken about that, of course.

[Batman]

Bob the plumber, Lorna the clerk and I suspect Harry the electrician (as well as 99+% of the rest of the population) likely would never notice a thing. I do think the sudden reversal of polarities in electrically charged particles would be noticed a bit more widespread than people working on the LHC or in JPL, though.

[Akhlut]

Bob the plumber, Lorna the clerk and I suspect Harry the electrician (as well as 99+% of the rest of the population) likely would never notice a thing. I do think the sudden reversal of polarities in electrically charged particles would be noticed a bit more widespread than people working on the LHC or in JPL, though.

How? All the machinery that would recognize it has also changed polarity.

[Simon_Jester]

I'm pretty sure the Hall effect would change in a noticeable way, for one. But I'd have to dig back through the experiment and look to be sure.

[cadbrowser]

That's what I thought, but I wanted to make sure I was thinking correctly. So, is my understanding correct that there either should be an equal amount of matter/antimater as a result of the big bank; or none at all? This is something else that I am trying to nail down so please bear with me.

Is there a big "?" mark on the physicists minds wondering why the imbalance of matter to anti-matter? If so, can anyone point me to an article that has a decent explaination of this phenomenon?

Is there an idea that possibly there is more anit-matter, but we just haven't detected it yet?

[Winston Blake]

That's what I thought, but I wanted to make sure I was thinking correctly. So, is my understanding correct that there either should be an equal amount of matter/antimater as a result of the big bank; or none at all? This is something else that I am trying to nail down so please bear with me.

Is there a big "?" mark on the physicists minds wondering why the imbalance of matter to anti-matter? If so, can anyone point me to an article that has a decent explaination of this phenomenon?

One of the unsolved theoretical questions in physics is why the universe is made chiefly of matter, rather than consisting of equal parts of matter and antimatter. It can be demonstrated that, to create an imbalance in matter and antimatter from an initial condition of balance, the Sakharov conditions must be satisfied, one of which is the existence of CP violation during the extreme conditions of the first seconds after the Big Bang. Explanations which do not involve CP violation are less plausible, since they rely on the assumption that the matter–antimatter imbalance was present at the beginning, or on other admittedly exotic assumptions.

The baryon asymmetry problem in physics refers to the apparent fact that there is an imbalance in baryonic matter and antibaryonic matter in the universe. Neither the standard model of particle physics, nor the theory of general relativity provide an obvious explanation for why this should be so; and it is a natural assumption that the universe be neutral with all conserved charges.[1] The Big Bang should have produced equal amounts of matter and antimatter, as such, there should have been total cancellation of both. In other words, protons should have cancelled with antiprotons, electrons with antielectrons (positrons), neutrons with antineutrons, and so on for all elementary particles. This would have resulted in a sea of photons in the universe with no matter. Since this is evidently not the case, after the Big Bang, some physical laws must have acted differently for matter and antimatter.

There are competing hypotheses to explain the matter-antimatter imbalance that resulted in baryogenesis, but there is as yet no one consensus theory to explain the phenomenon.

Mention me when you collect your Nobel prize.

---

Also IIRC studies of antihydrogen are actually extremely important, because we don't even have experimental evidence that antiparticles are attracted in 'right' direction by gravity fields. For decades everyone has 'known' what antimatter is like, but there is a paucity of strong empirical evidence.

In fact, I just found a Wikipedia article on this topic, from googling 'antimatter antigravity':

The gravitational interaction of antimatter with matter or antimatter has not been conclusively observed by physicists. While the overwhelming consensus among physicists is that antimatter will attract both matter and antimatter at the same rate that matter attracts matter, there is a strong desire to confirm this experimentally, given that consensus in science is for this to be true, but the hypothesis still open to falsification.

Antimatter's rarity and tendency to annihilate when brought into contact with matter makes its study a technically demanding task. Most methods for the creation of antimatter (specifically antihydrogen) result in high energy atoms unsuitable for gravity-related study. In recent years, the ATHENA and ATRAP consortia have successfully created low-energy antihydrogen, but observations have thus far been methodically limited to annihilation events that yield little-to-no gravitational data.

[cadbrowser]

I remember reading the first Wiki reference before...thank you for reminding me of it.

I've often wondered about that whole anti-mater and it's attraction in a normal gravitation vs anti-gravitation.

Any recent word on the detection of a graviton yet? I haven't come across anything as of late.

[Irbis]

Let me hijack this thread a bit for one question I had and not sure where to look for answer - I know matter annihilates with antimatter, but what happens if we try to use 'mismatched' matter? Say, used positrons with neutrons or protons? Would they still annihilate each other? If so, what about huge mass difference? Would more normal matter be annihilated, or only part equivalent to positron's mass?

[Eternal_Freedom]

Positrons and protons have the same charge so would repel each other. As for positrons and neutrons I have no idea.

[Imperial528]

Let me hijack this thread a bit for one question I had and not sure where to look for answer - I know matter annihilates with antimatter, but what happens if we try to use 'mismatched' matter? Say, used positrons with neutrons or protons? Would they still annihilate each other? If so, what about huge mass difference? Would more normal matter be annihilated, or only part equivalent to positron's mass?

I believe that if a positron hit a neutron you'd end up with just a proton left, since the component electron in the neutron would have been annihilated with the positron. Either that or a bunch of quarks and gluons or whatever neutrons and protons and electrons are made of. But I'm no particle physicist so don't take my word for it.

[Irbis]

Huh? There are electrons in the neutrons? I thought they're made from quarks?

As for positrons and protons having the same charge, I know, but we do have ways to make them come into contact, and I was just curious what would happen. Would it be, say, possible to cut on amount of antimatter fuel carried by only using positrons to somehow annihilate heavier, normal matter particles? It would also have advantage over 'normal' antimatter that positrons are much easier contained than neutral particles, but if I never heard about such idea being even contemplated it's probably impossible for some reason.

Another question then, if it is impossible, and you can only annihilate the same particles, can you make an atom from protons, antineutrons, and electrons?

[Imperial528]

Huh? There are electrons in the neutrons?

I read somewhere that it is speculated that neutrons can actually decay into a proton and an electron. But like I said, I don't have any formal education in the area so don't quote me on it.

[Winston Blake]

Huh? There are electrons in the neutrons?

I read somewhere that it is speculated that neutrons can actually decay into a proton and an electron. But like I said, I don't have any formal education in the area so don't quote me on it.

It's very much not speculation. It doesn't mean neutrons 'contain' a proton and electron, though.

At the fundamental level (as depicted in the Feynman diagram below), this is caused by the conversion of the negatively charged down quark to the positively charged up quark by emission of a W− boson; the W− boson subsequently decays into an electron and an electron antineutrino:

Would it be, say, possible to cut on amount of antimatter fuel carried by only using positrons to somehow annihilate heavier, normal matter particles?

I don't think so. Stable matter is made of electrons, up-quarks, down-quarks, and their antiparticles. The ups and downs form protons or neutrons and their antiparticles, and can't be 'separated out'. So you either have a electron-positron annihilation or quark-antiquark annihilation, or electron/positron interaction with a proton or neutron. The third one would resemble some kind of beta decay process, with the 'terms' shuffled around appropriately. E.g. beta+ decay is [proton -> neutron + positron + e_neutrino], so presumably if you could actually get them to 'react' reliably in the first place, [positron + neutron -> proton + e_antineutrino].

Another question then, if it is impossible, and you can only annihilate the same particles, can you make an atom from protons, antineutrons, and electrons?

Well, the protons are made of up and down quarks, and the anti-neutrons are made of anti-ups and anti-downs, so I would expect the usual annihilation to occur on the quark level.