Pique the Geek: The Weak Nuclear Force 20100103

(10 pm. – promoted by ek hornbeck)

Hello, everyone.  I hope that all of you had a wonderful holiday season and are refreshed and recharged for the new year.  Mine was particularly busy, with two 1200 mile round trips to Arkansas, first for Eldest Son’s wedding and then for Christmas, the former Mrs. Translator graciously inviting me to spend with the family.  Everyone was there, and it was a wonderful, but low-key, get together, just like they should be.

It is COLD here in the Bluegrass.  As I edit this Sunday evening, my outdoor thermometer shows 19.2 degrees F, nearly 20 degrees below normal for this time of the year.  It has not made freezing since 30 December, and is not predicted to exceed freezing for many more days.  I finally settled on 58 degrees F as the minimum comfortable temperature during waking hours, and 52 whilst sleeping.

Now, on with the topic.  There are four known fundamental forces in nature.

1)  The gravitational force, familiar to everyone who has fallen down and can’t get up.  This is weakest force, as far as forces go, but because of the enormous amount of mass around us, and in the universe, has very significant effects.  It is theorized to be mediated by massless particles called gravitons, although they have yet to be detected.  This force follows an inverse square relation, meaning that the force is four times stronger when the distance between two interacting bodies is halved.

2)  The electromagnetic force, also familiar to everyone who has seen light or felt the warmth of a hot stove.  It is a stronger force than the gravitational one (actually, it is the second strongest force), but in common human experience is overwhelmed by the huge amount of mass around us.  This force is mediated by photons, most commonly observed as light.  These massless particles have been proven to exist for many decades.  This force also follows an inverse square relation.

3)  The strong nuclear force is not commonly observed except by physicists directly, but is extremely important, because it holds atomic nuclei together.  It is the strongest of the four fundamental forces, being around 100 times stronger than the electromagnetic force, and many, many orders of magnitude (like 40) times stronger than the gravitational force.  It is the force that binds quarks into protons and neutrons, and that also binds nuclei together.  It is mediated by gluons, which are gauge bosons that come in eight different species, unlike the single kind of graviton and photon.  They are theorized to be massless, but have not yet been definitively detected, although the evidence for them is pretty overwhelming.  This force follows an inverse sixth power law, so it operates only in very close quarters, like elementary particles and atomic nuclei.  In other words, if the distance is halved, the intensity of the force increases by 64 times.

4)  The weak nuclear force is a real oddball.  Once again, it is not one that is encountered in everyday life, but it critical to how matter “works”.  It is the weakest force, other than gravity, known.  The most well-known effect of it is beta decay, where a neutron is changed into a proton and an electron (and a electron antineutrino, for those who are very technical).  Alternately, a proton can be transformed into a neutron and a positron (and a electron neutrino).  More about this in a bit.  The really interesting part is that the bosons that are the vectors for transferring the force have mass, unlike the ones for the other three forces.  In fact, they have a mass that is around 100 times that of the proton and neutron, which makes them very heavy particles indeed.  This is part of the curious nature of this force.  Like the strong force, it seems to follow an inverse sixth power relation.

The thing about the weak force is that it violates most rules that other forces have to follow.  First, it discriminates between different particles depending on their “handedness”.  The weak interaction operates almost exclusively on “left-handed” particles, and some suggest this is why there is much more matter than antimatter in the universe.  However, it also operates almost exclusively on “right-handed” antiparticles, so that is probably not a very good argument.  I solicit those with more expertise to comment in this area.

Probably the most important aspect of the weak force is that it is the only one of the four forces that change the flavor of a quark.  This is what makes beta decay work, because to change a neutron to a proton and electron requires that the flavor of one of the neutron’s quark to change, and no other force can do that.  A neutron has two down quarks and one up quark, whilst a proton has two up quarks and one down quark.  (Up and down are the “flavors” of quarks, and up quarks carry an electrical charge of +2/3 whilst down quarks carry an electrical charge of -1/3, so two downs and one up comes to (-1/3 + -1/3) + (+2/3) = 0 for neutrons, and (+2/3 + +2/3) + (-1/3) = 1 for protons.  Antiquarks are the opposite).  Thus, without the weak force, beta decay could not happen, and the universe as we know it would not exist.

What does this mean to you?  It means that without the weak force, we could not exist.  In stars, all of the elements up to and including iron can be created, but iron is a dead end.  It turns out that the iron nucleus is the most stable one that is known to exist, and so after everything lighter has been converted to iron, a star just dims out, unless something else happens.  In small stars, that is pretty much what happens (and also is responsible for iron being a fairly common element).  To make elements heavier than iron, other processes must occur.  Well, iron is only element number 26 in the Periodic Table, and life as we know it require elements of higher atomic numbers.

Enter the supernovae.  A supernova is a relatively large star that, instead of just “going out” undergoes a cataclysmic explosion that initiates an extremely complex cascade of nuclear reactions, forming heavy, less stable nuclei.  Many of those nuclei are produced by the weak force, and without that phenomenon, life as we understand it would not be possible.  A short list of elements required by humans (not all of them, but many of them produced by the weak force) include copper, zinc, molybdenum, iodine, and several others.

I know that this is all pretty much very geeky indeed, but it is important for the universe to operate as it does.  I also wanted to start out the new year with something more technical than I have been writing last year, at least for a while.

Well, you have done it again.  A whole set of the bosons known as photons have been wasted by you reading this drivel.  And even though Senator Demented, sorry, Senator DeMint, removes his hold on the candidate for the TSA administrator when he reads me write this, I always learn much more than I ever could possibly hope to teach when I get feedback from you.  Thus, please keep those comments, questions, corrections, especially tips and recs coming!  I am merely the catalyst for the reaction that makes this series special.  Remember, no scientific or technical issue is ever off topic here, so fire away with your ideas.

Finally, I have a request.  I am seriously considering (meaning that I intend to do so) starting my own blog to address topics like this, and much more.  I need readers, and showing your support by tipping and recommending would be very much appreciated.  More importantly, please tell your friends, your family, and your online acquaintances about this series so that I can be more assured of success when I launch.  Thank you!

Warmest regards, and the happiest of holidays to each of you,

Doc

Crossposted at Dailykos.com