Tuesday, January 25, 2011

What’s the Matter?

The crystal structure 
of cellulose. The black 
spheres are carbon, 
the red spheres are 
oxygen and the white 
spheres are hydrogen.

In physics, matter is the stuff that everything is made of, but let’s explore that, shall we? Take a pencil, for example. It’s made of wood for the most part. But what is wood made of? The main component of wood is the organic compound cellulose, composed of carbon, hydrogen and oxygen which forms very long chain molecules. It’s organic because it contains carbon, but what is carbon made of?
   Carbon is the element in chemistry with atomic number 6. One atom of carbon has six protons, six electrons and either six, seven or eight neutrons which make up the three isotopes of carbon: carbon-12, carbon-13 and carbon-14, respectively. The nucleus of the carbon atom is composed of the protons and neutrons tightly held together by a strong nuclear force. The six electrons orbit the nucleus, creating an “electron cloud” and held within this cloud by an electromagnetic force that exists between the electrons and protons. Drilling down further, lets look at the proton. Protons are subatomic particles with an elementary electric charge of +1 that live in the nucleus along with neutrons. The number of protons in the nucleus is the defining characteristic of an element. Hydrogen, the lightest element, has but a single lonely proton and therefore is said to have an atomic number of one. Element 118, known as ununoctium, has the highest number of protons in its nucleus, but it’s highly unstable. Only three or four atoms have been produced and detected.
   But what is a proton made of? Can we drill down farther? Protons are composed of yet smaller fundamental particles called quarks: two “up” quarks, each with a charge of +2/3 and one “down” quark, with a charge of -1/3. Quarks are exceedingly small and cannot exist in isolation, so much of what we know about them is inferred by observing the various particles they form. The name quark comes from the line in Finnigan’s Wake “Three quarks for Muster Mark!” which is fitting since they like to hang out in threes.
   There have been attempts to drill down further still. String theory asserts that quarks and electrons are made up of 1-dimensional vibrating strings. String theory requires the existence of extra dimensions beyond the normal four dimensions of space and time, although the precise number of dimensions is up for debate. The most popular variant of string theory, called M-theory, requires 11 spacial dimensions  where the strings are cross sections of 2-dimensional vibrating membranes. The main problem with string theory, though, is that it doesn’t put forth any predictions which can be tested. Until it does that it will belong more to the realm of math or philosophy than the world of science.

1) True or false: Atomic number is controlled by the number of particles in the nucleus.

2) Protons and neutrons are held together by ____________.
a) gravity  b) strong nuclear force  c) electromagnetic force  d) weak nuclear force

3) True or false: The heaviest isotope of carbon is carbon-14.

4) The proton is composed of ________________.
a) two “down” quarks and one “up” quark  b) three “up quarks”  c) three “down” quarks  d) two “up” quarks and one “down” quark

5) The variant of string theory that requires 11 spacial dimensions is called ______________.

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