Sep 182010

What is a fundamental? Something that is not derived. Something that cannot be explained in terms of something else. For example, our understanding holds the following to be fundamentals: mass, length, time, energy, force, charge…

We have trouble really understanding these, because understanding is done through analogy and definitions. Normal definitions are based upon deeper concepts, and when we finally arrive at the deepest concepts of all, we cannot “take them apart” into their fundamental pieces. What is charge? What is mass? What is time? This is like asking “what is ‘WHAT’?” or “what is ‘IS’?” Very hard to answer.

1) What is a force?

According to the Standard Model… In the conceptual model of fundamental interactions, matter consists of fermions, which carry properties called charges and spin ±12 (intrinsic angular momentum ±ħ/2, where ħ is the reduced Planck constant). They attract or repel each other by exchanging bosons.

The interaction of any pair of fermions in perturbation theory can then be modeled thus:

Two fermions go in → interaction by boson exchange → Two changed fermions go out.

The exchange of bosons always carries energy and momentum between the fermions, thereby changing their speed and direction. The exchange may also transport a charge between the fermions, changing the charges of the fermions in the process (e.g. turn them from one type of fermion to another). Since bosons carry one unit of angular momentum, the fermion’s spin direction will flip from +12 to −12 (or vice versa) during such an exchange (in units of the reduced Planck’s constant).

Because an interaction results in fermions attracting and repelling each other, an older term for “interaction” is force.

The modern (perturbative) quantum mechanical view of the fundamental forces other than gravity is that particles of matter (fermions) do not directly interact with each other, but rather carry a charge, and exchange virtual particles (gauge bosons), which are the interaction carriers or force mediators. For example, photons mediate the interaction of electric charges, and gluons mediate the interaction of color charges.

2) What is a field?

In modern physics, the most often studied fields are those that model the four fundamental forces

A field may be thought of as extending throughout the whole of space. In practice, the strength of every known field has been found to diminish to the point of being undetectable.

Defining the field as “numbers in space” shouldn’t detract from the idea that it has physical reality. “It occupies space. It contains energy. Its presence eliminates a true vacuum.”[2] The vacuum is free of matter, but not free of field. The field creates a “condition in space””[3]

If an electrical charge is moved, the effects on another charge do not appear instantaneously. The first charge feels a reaction force, picking up momentum, but the second charge feels nothing until the influence, traveling at the speed of light, reaches it and gives it the momentum. Where is the momentum before the second charge moves? By the law of conservation of momentum it must be somewhere. Physicists have found it of “great utility for the analysis of forces”[3] to think of it as being in the field.

“The fact that the electromagnetic field can possess momentum and energy makes it very real… a particle makes a field, and a field acts on another particle, and the field has such familiar properties as energy content and momentum, just as particles can have”[3].


Thoughts and questions on fields and forces and matter and particles…

What is the difference between a particle and its field? Where does one end and the other begin?

In one of the paragraphs above, an electrical charge is described as if it is a physical thing, rather than some property of a thing. Is this true? What does it mean to speak of interactions between charges, as opposed to speaking of interactions between particles (which may “carry” a charge)?


3) What is a charge?

Electric charge is a physical property of matter which causes it to experience a force when near other electrically charged matter.

Let’s restate that, with our standard model version of force:

Electric charge is a physical property of a fermion which causes it to exchange bosons when near other fermions.

The electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. Electrically charged matter is influenced by, and produces, electromagnetic fields. The interaction between a moving charge and an electromagnetic field is the source of the electromagnetic force, which is one of the four fundamental forces (See also: magnetic field).

Follow up questions: When we say electric charge, are we saying the same thing as “electron?” Are these terms equivalent? No. Because protons also have charge, as do positrons and other particles. But we can say that an electron IS a certain type of electric charge. Likewise, we can say that a positron is another certain type of electric charge. A proton, however, is more than just an electric charge? Charge and Electricity are the same thing, but the word electricity is commonly used to mean electromagnetic energy, which is something different. Charge is not electromagnetic radiation, but when a charge moves, it creates electromagnetic radiation.

Charge is also not energy. Charge is to energy what air is to sound waves. Charge is what energy moves? Charge is the pole (+) and (-) of matter

Charge is…

…the stuff that flows during an electric current.
…the stuff that appears on a balloon when you rub it on your hair.
…the stuff that comes in two kinds: positive and negative.
…the Plus and Minus electric poles (as opposed to North and South magnetic poles.)
…the stuff that causes electrical forces.
…charge is the “glue” that connects all of the flux-lines of electrostatic fields to protons and electrons.
…charge is the positive and negative stuff that forms atoms.
…charge is the stuff that is carried by electrons, protons, positrons, and other particles.
…charge is the medium that energy flows through (like sound flows through air.)
…charge is the stuff that, when it wiggles fast, creates light.
…charge is the stuff that, when it wiggles slower, creates radio waves.
…charge is the stuff that, when it wiggles very slowly, creates energy in electric circuits.
…charge is the stuff that, when it flows or spins, creates magnetism.
…charge is the stuff that reflects light and makes objects visible.
…charge is the stuff that makes metals look metallic or “silvery.”
…charge is the stuff that causes electrical attraction and holds everyday objects together.
…charge is the stuff inside of wires that is movable, almost fluid.
…charge is the stuff inside of nonconductors that is immobile and “frozen” in place.
…charge is the stuff that is measured in units called Coulombs.
…charge is the stuff that scientists once called “quantity of electricity” and “particles of electricity.”

4) What is electricity?

 Posted by at 10:35 pm

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