Posted by: Jamie | June 10, 2009

More about antimatter

Okay, first disclaimer. I am NOT an expert in antimatter. I have only a basic understanding based on a bachelor’s degree in physics and a summer of particle physics research. But I wanted to clear something up, based on a conversation I had today. Second disclaimer: I am not trying to actually get into the details of particle physics theory here (on the off chance that anyone with that sort of knowledge drops by and is all, “Hey, well, actually…”). I’m hoping to convey a lay-understanding of this topic.

There seems to be a misconception that antimatter is something straight out of science fiction. That it is nearly unreal, right up there with time travel and warp speed.

Antimatter is real. It’s as real as you, me, computers, and rain. Antimatter isn’t something that we think we might be able to detect. It exists. We play with it. We use it.

What antimatter isn’t is inexplicable or bizarre or mysterious. I find that the name “antimatter” is misleading. It makes me think of alternate dimensions and opposite realities, and anti-mass – something that is the opposite of existence. But in actuality, the “anti” in antimatter refers only to the charge of the particles. Antiparticles are opposites of their “regular” counterparts in that they have all the same characteristics except their charge. So an anti-proton has the same mass as a normal proton, but a negative charge. A positron has the same mass as an electron, but a positive charge. And so on for more exotic particles. (This works for the neutron, too, (i.e. there is such a thing as an anti-neutron) but to explain it involves talking about quarks, which I don’t want to get into in this post. The charged particles are also explained by quarks, but it’s easier to talk about charge, which more people are familiar with.) In theory, we could have come up with a totally different name for the anti-proton. We could have called it…a furton! And then defined a furton as a particle with a charge of -1e and a mass of 1.67 x 10^-27 kg and a spin of 1/2 and all that. But since ALL the information was the same as the proton except the charge, it sure as heck seems a lot simpler to just call it the anti-proton and save ourselves the effort.

So antimatter exists. And frankly, it’s more like matter than unlike. But it’s different in a mirror-image-esque way that has caused us to use this unfortunate naming convention. Physicists have a sometimes-unfortunate tendency to enjoy poetry in their science. :)

P.S. Yes, there’s that whole messy business with matter and antimatter annihilating when they collide, but frankly that’s a whole different subject and isn’t, as far as I can tell, really understood by anyone yet (I base this belief on the fact that we weren’t taught the “conservation of matterness” rule in my particle physics course. Maybe in a decade it’ll be on the list). I’m hoping the Ph.D. process will clue me in to some more knowledge on this point. I’m really just trying to emphasize that antimatter exists and is part of our reality.

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Responses

  1. I think you’ve glossed over the biggest reason lay-people have this mystical view of antimatter, which is the issue of mutual annihilation with normal matter. This directly contradicts what must be a rather quaint notion from our introductory science courses in middle school that matter is neither created nor destroyed.

    The ramifications of the mutual annihilation issue thus strongly affect how antimatter is perceived. For instance, the storage of antimatter is non-trivial (my understanding is that it involves suspension in a vacuum by very strong electromagnetic fields). The absence of antimatter on a macro-scale also doesn’t help. When it comes down to it, it belongs to that class of exotic particles which have no practical impact on our everyday existence, at least not yet. Electrons were equally mystical until we based our entire society around them. Until antimatter has a practical application, it might as well be nothing more than a flight of science fiction, right up there with sonoluminescence – it’s real, but it’s crazy, and it doesn’t help me connect to the Internet any faster.

  2. I think you’ve glossed over the biggest reason lay-people have this mystical view of antimatter, which is the issue of mutual annihilation with normal matter. This directly contradicts what must be a rather quaint notion from our introductory science courses in middle school that matter is neither created nor destroyed.

    While the issue with antimatter not existing on the macro level is certainly one that hasn’t been explained yet (there are whole research groups devoted solely to matter-antimatter asymmetry, and trying to find reasons for it), I think the issue with annihilation being seen as mystical can also be explained by terminology. When matter meets antimatter, they don’t just disappear. They are not “destroyed,” as it were. Instead, they simply change into energy. It’s like a chemical reaction, in a sense. When baking soda meets vinegar, they suddenly change into a gas, ostensibly without cause.

    I did, however, gloss over this aspect, you’re right. I made a guess at where the mystical perception comes from and I guess I got it wrong. :)

  3. “But I wanted to clear something up, based on a conversation I had today.”

    I was delighted to see that our kitchen conversation sparked a blog post.

    ;)

  4. “Antiparticles are opposites of their “regular” counterparts in that they have all the same characteristics except their charge.”

    I want to emphasize, as you mention a few lines later, this isn’t a sufficient definition. For example, the kaon (or k-meson) comes in four varieties: positive, negative and two neutral species. The two neutral species are the antiparticles of one another. In addition, the neutron has an anti-particle and photons (which are chargeless AND quarkless) are their own antiparticles.

    You are correct in that we know lots about antimatter because it acts like normal matter. There are events all around us in which antimatter is created, but the amount is tiny and short-lived.

    The big mystery with anti-matter is, in fact, why the universe decided to favor what we perceive as “normal matter” and not anti-matter.

  5. Thanks for emphasizing those points, Jason. I do, however, have a slight addendum with regards to your statement that this isn’t a sufficient definition. Amongst scientists, I agree that that’s completely true, and I would never consider this post an adequate explanation of antimatter for a scientific audience. But I would propose that for the lay-person (the audience I indicate I’m addressing at the start of the post), it is, in fact, sufficient. What do you think?

  6. Jamie, let me first say that I think your goal here is excellent, and you have taken upon yourself a difficult job. Describing physics, and particularly basic physics like particles, is hard…most of it exists as math and a weird bunch of various characteristics that have no basis other than “we observe them” (strangeness, I am looking at you).

    That said, I would argue that since your goal here is to expose non-physicists to physics concepts you absolutely must do so with precision. This doesn’t mean you have to delve into QCD, but you should be careful with your language especially when you are giving a simple case.

    For example, the point of my previous post was to point out that anti-matter isn’t as simple as being JUST about charge or JUST about quarks, which is a topic you, maybe inadvertently, broached.

    In your post, you chose to talk about things in terms of charge, which is straightforward for an electron/positron and an excellent choice for an example because charge is a familiar concept. However, you rightly point out that this cannot apply to neutrons because they have no net charge and that the anti-neutron needs to be explained in terms of quarks, which is where you end.

    The problem here is you’ve introduced two examples, one in which the anti-particle is defined by charge, and one in which it is defined by quarks, but there is no overlap between your two examples (no quarks in electrons, no charge in neutrons). Would a lay person pick up on or be confused by this? I don’t know, but it is a potential issue and I wanted to address that what makes something an anti-particle is a little bit more complicated than what you covered. Which is completely fine; after all your main point is that anti-matter is just matter, and behaves as such, but I thought it was worth noting.

    While I am replying, I’d also like to address this passage; you wrote:
    “But since ALL the information was the same as the proton except the charge, it sure as heck seems a lot simpler to just call it the anti-proton and save ourselves the effort.”

    Which is almost true. All the PHYSICAL characteristics except charge are the same. This is different from saying ALL the INFORMATION (which includes flavor quantum numbers [I think this may be what you are referring to as “matter-ness,” but I’ve never heard that term], like baryon number) is the same . You’d never have to talk directly about flavor quantum numbers, but your wording can still be clear and consistent with the larger picture at the same time.

    I really like your post, and I like it more the more I read it; keep up the good work. Forgive the wordiness of my response, as well…I’d like to see you succeed with this and am merely trying to be of some use!

  7. Jason, I agree with basically everything you say. Which just goes to show I need practice. I think I might attempt to rewrite this post (which I would not put over this one, but rather as a new post to demonstrate the changes), and see if maybe I can’t do it better. Yay feedback!

  8. One thing I might note is that at the C.P. Snow conference I attended, one thing that was brought up was that one of the issues scientists have in conversing with the public is that they are never willing to be inaccurate in favor of giving a basic idea. I do not want to fall in the trap of sacrificing simplicity of concept for the sake of detail which the layperson will never need. Striking this balance is where I (and most of the rest of the scientific community ^_^) need practice.

  9. Like I said, it is extremely difficult. There are ways of presenting information and giving clear examples that are illuminating as well as rigorous…but coming up with them isn’t so easy.

    Part of the problem with the written form over conversation is whatever you write has to stand on its own – an added challenge. It is more difficult for a reader to ask for clarification or other questions (though not impossible, hence the comments section). But again, I applaud your work!


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