Before discussing forces, a brief fairy tale about the types of matter.
Once upon a time, in a land far, far away (Greece) and long, long ago (600 BC), the wise men determined that everything is made of four ingredients–earth, water, air, and fire. Over the subsequent centuries, other wiser men discovered that everything is actally composed of atoms–there are 94 different natural elements found in the familiar Periodic Table.
About 100 years ago, even more wiser men perceived that atoms, in turn, consisted of electrons, protons, and neutrons. Today, the list of sub-atomic particles is fast approaching 300. But wait–protons and neutrons are actually combinations of quarks. At first there were only three types of quarks; but presently there are believed to be at least 12; and who knows what the future will bring.
Almost simultaneously with the discovery of quarks, String Theory was developed by the wisest of the wise. Like atoms, strings are defined to be the ultimate element. Originally strings were two-ended linear things (strings). But strings yielded to loops, then multiple loops. And single dimensional strings lead to multi-dimensional
strings. Will the unraveling ever stop?
[READ MORE: String Theory Unraveled.]
Unlike chaotic elementary matter, the situation with forces is simple and straight forward. There are four forces–no more, no less. Case closed–according to the scientific establishment.
However, only 200 years ago there were six forces known to mankind. Only one of them–gravity–has survived until today.
electro-magneticforce, or light, as we commonly call it.
In the mid 1930s, two new forces were theorized: the weak nuclear force and strong nuclear force. Today, the four canonized forces (gravity, electro-magnetic, weak, and strong) are not as absolute as they might first seem.
electro-weakforce. (They were: Sheldon Lee Glashow, Abdus Salam, Steven Weinberg.)
unifythe electro-weak and strong forces in a Grand Unified Theory. No doubt they will succeed some day. How many forces will we have then?
The strong force, or forces, is, or are, very unusual. This was originally called the strong nuclear force because it is much stronger than the other three forces and because its attractive strength held the protons and neutrons together in the atomic nucleus (using mesons).
residual strong forcewhen it was learned that the
strong color force[
Coloris Quantum Theory terminology.] uses gluons to bind quarks into protons and neutrons with a strength 100 times more powerful than the original (residual) strong force.
How many forces are actually at work here depends on how you define them. Is
a repulsive core and
an attractive well one or two forces? Is
acting directly through gluons on quarks and
acting indirectly through mesons on protons and neutrons the work of one or two forces?
There are more cracks in the
solid wall of exactly four forces.
fundamentalforces are attributed to the curvature of differently scaled dimensions, which implies that all forces are pseudo forces.
anti-gravity. This new force is gradually gaining adherents. [I am one, so it must be real.] For the last decade many astronomers have searched in vain for missing
dark matter(hot dark matter, cold dark matter, any dark matter) that would provide the mass needed to hold together galaxies and clusters of galaxies. They haven't found any but they know it is precisely 26% of the Universe. Anti-gravity does a much better job of explaining why individual galaxies and clusters of them do not fly apart.
dark energy. They don't know what it is, but the are sure it comprizes exactly 69% of the Universe.
How many other forces are out there waiting to be discovered? Are we walking in Thales footsteps 2600 years later? Are we on the verge of discovering a vast array of forces heretofore unimagined? Here are some potential candidates:
color, etc. Or maybe a force for each of these properties.
And this brings us to our last topic–variable forces. There is a nearly-universal assumption that the strength of forces is constant and unchanging. I am not so sure.
Everything in nature vibrates–unless it is at absolute zero temperature: light waves, sound waves, electrons in an atom, neutrons and protons in a nucleus, quarks in neutrons and protons, gas molecules in the air, water molecules in the ocean, iron molecules in steel. Even Earth and Sun vibrate. Probability distributions are equally ubiquitous.
So my thought is that perhaps the strength of forces is not absolutely the same and identical all the time. The strength of some forces could slowly oscillate over eons of time–periods too long for the human race to have noticed during its short history. The strength of other forces could vibrate with such a rapid staccato that we will never be able to measure the changes. Some forces may have so little variation that it cannot be detected. Other forces may have only occasional spikes or dips. In many situations, matter and energy are controlled by opposing forces–certain events may only happen when the strength of one force jumps while the strength of the opposing force drops.
If forces are variable, it would explain several puzzling phenomena:
over the topof Coulomb's barrier. However, temperatures needed to overcome the Coulomb barrier turn out to be smaller than expected due to quantum-mechanical
tunneling, in which objects that do not have enough energy to go over the top still manage to get to the other side.
half-life. There are three types of decay:
Beta minusresults in the emission of an electron and an anti-neutrino when the change of a
downquark to an
upquark causes a neutron to become a proton.
Beta plusresults in the emission of a positron and a neutrino when the change of an
upquark to a
downquark causes a proton to become a neutron.
The important point in these examples is that they are all random processes that function according to probability distributions. This implies that the forces that control these processes are not constant in strength, but rather fluctuate according to probability distributions.
[You may have noticed that I did not discuss gravity here at all, because gravity has its own page.] [READ MORE: Gravity is Attractive]