There was a question and answer posted about antimatter dated, Nov. 5 1999 and in reading the answer, most of my own questions were answered, except one. All atomic particles have opposites; electrons have positrons, protons have antiprotons and neutrons have antineutrons, which makes sense, but they all involve charged particles, save neutrons which are neutral. So, what is an antineutron and how if the charged particles of matter and antimatter annihilate one another when they come in contact, can you first have an opposite neutral, and then in turn how can they annihilate each other without an electromagnetic charge if there’s no attraction in their nature to bring them together?

The column in question is a Staff Report written by a staff member (in this case Karen), not one of Cecil’s own columns, so I imagine that a moderator will be moving this thread shortly.

Antimatter has everything (except mass) opposite, not just charge. This includes properties like baryon number and magnetic moment, both of which neutrons have. So it is possible to have antineutrons. They won’t be electromagnetically attracted to neutrons, but if you bring them together by some other means, they’ll annihilate (probably forming a bunch of other particles in the process, which particles would then eventually decay into photons). Note that there are some particles which don’t have any of these other properties (or looked at another way, they have them with a value of zero), and so those particles are their own antiparticle. A photon, for instance, is the same thing as an antiphoton.

Here is an article on anti-particles.

You are confused about some basic facts. An anti-particle will have the opposite charge only if the original had charge to begin with. Having a charge in no way relates to the existence of an antiparticle. Note, that from a technical point of view, all subatomic particles are defined to have anti-particles, even though (such as in the case of photons) they might be their own anti-particles.

Here’s another way to think about what an antineutron is that doesn’t require you to worry about oddball topics like “baryon number” and the quantum-mechanical notion of “spin”:

Protons and neutrons are, themselves, actually composed of smaller particles called quarks. There are six total kinds of quarks known to science, and six corresponding antiquarks. In the normal everyday world that you’re likely to encounter while walking down the street, however, there are only two kinds of quarks you have to worry about:[ul][li]up quarks, which have an electric charge of +2/3, and[/li][li]down quarks, which have an electric charge of -1/3[/ul]A proton is composed of two up quarks and one down quark. This gives it a total overall electric charge of (+2/3) + (+2/3) + (-1/3) = +1. So a proton is positively charged.[/li]
A neutron is composed of one up quarks and two down quarks. This gives it a total overall electric charge of (+2/3) + (-1/3) + (-1/3) = 0. So a neutron is electrically neutral.

Now, when we talk about antiparticles, and say that every particle has a corresponding antiparticle with the same mass but opposite charge, it’s not really the protons and neutrons themselves that have antiparticles when you get right down to it. It’s the quarks that the protons and neutrons are made up of that have antiparticles. An antiproton or antineutron is nothing more than the proton’s or neutron’s corresponding aggregate of antiquarks.

An antiproton consists of 2 antiup quarks and 1 antidown quark, while an antineutron consists of 1 antiup quark and 2 antidown quarks. As you might imagine, an antiup quark has an electric charge of -2/3, exactly the opposite of the charge on an up quark. An antidown quark likewise has a charge of +1/3, exactly the opposite of the charge on a down quark.

So, let’s compare:

particle     quarks               overall electric charge
--------     ------               -----------------------
proton       2 up, 1 down           +1
neutron      1 up, 2 down           0
antiproton   2 antiup, 1 antidown   -1
antineutron  1 antiup, 2 antidown   0

thank you, i have very limited knowledge in this area and this made it make sense a lot better. while the others replies helped somewhat i got kind of a feel of someone telling me how much i didn’t know, which i was already well aware, and how much they knew about it, which i didn’t really care. thanks for taking the time to read the question and answer it by teaching. frank

…there are only two kinds of quarks you have to worry about:[ul][li]up quarks, which have an electric charge of +2/3, and[/li][li]down quarks, which have an electric charge of -1/3[/ul][/li][/QUOTE]

Gosh. You have no idea how helpful that is.

For seven years I watched Deep Space Nine and tried to figure out whether Quark was a good guy (“up” quark) or a bad guy (“down” quark), and all the time a bit of subatomic physics would have explained the whole thing to me.


Not very edifying, but no discussion of quarks would be complete without mention of the other four kinds of quark, which you don’t have to worry about. They’re called Charm, Strange, Truth, and Beauty. Modern physicists generally refer to the last two as Top and Bottom, but I’m old-fashioned on this. And just for that extra dollop of weirdness, these aren’t refered to as “kinds” of quark, or “types” of quark, they’re flavors.

By the way, CURIOUS, I apologize if my answer wasn’t as helpful. What’s useful to some folks isn’t to others, and it’s sometimes hard to tell which explanation will be best for a particular person. tracer’s answer is also correct, and if that makes more sense for you, go with it.

That makes no sense. Everyone knows that Beauty is Truth, Truth Beauty, – that is all ye know on Earth, and all ye need to know.

Well, yes, that’s all you need to know if you’re a W boson. Well, you also need to know that Charm is Strange and Up is Down, but those are just details.

So, a deuterium necleus is like a well pitched baseball inning (three up and three down)? :stuck_out_tongue:

I dunno. Sounds pretty weak to me…

Did you come up with that yourself? 'cause I’m stealing it, and I want to know who to credit.

Yes. At least, I don’t believe I’ve ever heard it before in this context. It is a rip-off of the Radio Guy’s answer to the Seargent in “Good Morning Vietnam” (roughly: Seargent - pointing to his insignia - “Three up and three down - do you know what that means?” Radio Guy: “End of the Inning!?”); but I digress…

e-mail royalties to the address in my profile :wink:


If I discover a way to profit from adding it to my Instant Messenger profile, you’ll be the first to know. :slight_smile:

tim314, since you appear to like physics puns, it may amuse you to note that it would be (the observer’s) curiosity that killed (Schroedinger’s) cat…


Well, I can see why they say “curiosity killed the cat” . . . “Curiosity collapsed the cat’s wave function, thereby forcing him into a state of definite ‘deadness’” just doesn’t have quite the same ring to it. :smiley: