Hadrons
Published on Sep 10, 2008 at 1:23 pm.
4 Comments.
Filed under physics.
Despite what some of the doomsayers had been predicting, the world did not end this morning. Sometimes I wonder about people who seem to always believe that the world is coming to an end soon due to some catastrophe that only they and their friends know about. If I had a dollar for every time that I’ve heard that the world was going to come to an end, I’d be rich! One of the latest crazes was that the Large Hadron Collider (LHC), a giant high energy physics particle accelerator in Europe, was going to bring about the end of the world when it was fired up this morning. Well, the LHC was fired up, and it works fine, and we are still all here. Oh, sure, now that we are all still around, the doom-and-gloom folks are going to be saying that what they really meant was that we’d all be wiped out later in the year when the LHC achieved full power rather than when it was undergoing its initial tests. When we are still around after that, they will then claim that we will still be destroyed when the LHC actually begins its colliding experiments. After that happens and we are still here, then they’ll say that we’ll be destroyed when it does something else. I have given up hope on some of these people. Every time that we survive one of their dire predictions, they just say that the next thing will do us in. For some reason, they never go back to find out if perhaps they did not fully understand the physics in the first place. In fact, it never ceases to amaze me that people who read a book or two about something, or study the introductory part of some topic, think that they know more about the field of study than people who have spent a lifetime studying it. And, even people who should KNOW better fall into this trap. Sometimes scientists and engineers will do this as well (not the good ones, of course). Unfortunately, they lend credence to the doom-and-gloom people who don’t understand the sciences. For example, if a retired molecular physicist were to claim that he was worried about the LHC (I don’t know of one who says this, but I am using this as an example), then we should listen, right? That is what the public might think. But, if someone really understood physics, they’d know that atomic and molecular physics deals with electrons and electron structure, not with high energy physics, particle physics, and relativity. Particularly for someone who is not keeping up with things in subfields outside of their own, they might not really be qualified to talk about these topics. It would be about as logical as going to a dermatologist to get treatment for a heart attack. After all, a dermatologist is a doctor and knows medicine, right? So, when the experts in high energy physics insist that the world is safe, including those who do not work on or support the LHC, then I am inclined to believe them over someone who has read a layman’s book on the subject.
OK, so now I’ll get off of my soap box. Since the LHC is in the news, it might interest some people to know a little about hadrons. To discuss hadrons, I need to also mention the fundamental forces. We know of only four fundamental forces. All of the forces that you normally run into in everyday experience are really manifestations of these (usually only two of them). The most familiar of the fundamental forces are gravity and the electromagnetic force. Gravity is an attractive force acting between two particles that have mass. Anything that has mass has a gravitational attraction for any other thing that has mass. The electromagnetic force acts between objects that have charge. Magnetism and electric forces are different aspects of the same force. Gravity and the electromagnetic force constitute the bulk of what most people experience because they are the only two long range forces. At very short distances, though, two other much stronger forces work. These are known as the weak force and the strong force. Years ago, when I was in school, they were called the weak nuclear force and the strong nuclear force because they act over distances so short that objects have to be about as close to one another as an atomic nucleus in order for the forces to manifest themselves. Indeed these forces are important in atomic nuclei, and without them nuclei would not hold together as they do. However, since the forces do operate outside of the nucleus (particles only need to be very close to one another, not in a nucleus in order for the forces to act on them), then the word “nuclear” is generally no longer used in the forces’ names.
As with the electromagnetic and gravitational forces, particles must have certain properties in order for the strong and weak forces to operate on them. I defined the electromagnetic and gravitational forces in terms of the property of the particles that was required for these forces to act. Likewise, the strong force only acts on particles that have a certain property. Unfortunately, that property is called “color.” I say that this is unfortunate, because this use of the word color is entirely different from what people think of when they think color. Most people think of color in terms of the wavelengths of light that a body reflects. Yes, that is color. But, for historical reasons, in the early days of the study of the strong force, physicists studying the particles that were influenced by the force grouped them into groups that they labeled with colors. So, the term “color” began being applied to those particles. It is important to know that these particles do not have “color” in the normal sense of the word because they do not reflect light in that manner. In other words, if you could see them, they would not look red, blue, green, etc. to your eyes. It would be more appropriate to call this property “color charge” rather than color. Even better would be if particle physicists were to come up with some other name for this property, but that is not likely to happen. Particles that have this color charge are quarks and gluons. Quarks are interesting particles, but I don’t have the time or inclination to go into all sorts of details about them in this single blog entry (I teach a whole lecture on this in my second semester general physics survey class). Among the unusual properties of quarks is that they are not found by themselves. Quarks always are bound with other quarks. A particle composed of quarks in this manner is a hadron. So, hadrons are composed of particles that experience the strong force, and thus so do hadrons themselves. It is these particles that the LHC is slamming together with high energies. Hopefully, the LHC will help us understand more about these fundamental forces, and that may tell us more about the universe itself.
Plenty of other people have written about the LHC, so I won’t do that. But, often they don’t write about the hadrons themselves, so I decided to fill in the void.
-Astroprof
Tom on September 11, 2008 at 8:09 am: 1
Good points! The idea that people who know very little about something are somehow better equiped to criticize it than experts is really toxic, and I think in ways that’s more dangerous than just fringe wackos. Look at the trade in contempt for ‘experts’ and ‘insiders’ and ‘elites’ that one of our political parties makes such good coin with. Somehow, we’ve gotten to the point where we seem to think that ignorance deserves equal treatment with understanding. I’m not much of a historian, but somehow that seems like a sign of a declining empire.
Sili on September 11, 2008 at 11:10 am: 2
I think “colour” is a beautiful simile, since it’s such a nifty way of conveying confinement. Of course there much be equations one can write down to explain how three (or two) different charges need to be present for a particle to exist, but saying that they have to be ‘white’ is so much more concise.
Astroprof on September 11, 2008 at 6:27 pm: 3
Sili, I do think that the term has its nice points. However, it is just confusing for students and people not familiar with particle physics. It is SO confusing that I feel the negatives outweigh the positives that it has for the particle physicists.
Astroprof on September 11, 2008 at 6:30 pm: 4
Tom, this country does seem to glorify ignorance. In fact, it never ceases to amaze me how many of my students proudly declare that they can’t do math (something that is said in shame in the rest of the world). This is one of the few cultures where the smart kid in school is shunned. And, of course, only in America can a movie titled “Dumb and Dumber” be so successful that it has a sequel.