www.UsHumans.net: Chapter 2
Nature has but a few fundamental rules; today, millions of natural phenomena are understood to be different aspects of these few rules
Physicists have studied millions of phenomena, including heat, light, motion, gravity, electricity, magnetism, gases, fluids, solid materials, sound, radiation, atoms, and nuclei. At first it seemed like the world was full of millions of unconnected phenomena, but we now understand how each of these is just one of multiple aspects of a few more-fundamental phenomena. As Richard Feynman says "The adventure of our science of physics is a perpetual attempt to recognize that the different aspects of nature are really different aspects of the same thing.," see www.aip.org/history/esva/exhibits/feynman.htm. This chapter contains a few illustrations of this reduction along with an explanation of how it may even be possible to explain all physical phenomena with a single law of nature. We will see how these few but fundamental laws govern the chemical and biological processes that occur within the atom's of our bodies. We will then begin to see that the fundamental aspects of nature are simple, that nature exhibits endless variety, and that each complicated end product–for example, a human–consists of a large number of these more-simple underlying phenomena.
This chapter also contains a description of atoms, the electrical force, radioactive dating, and the unpredictable uses of today’s science. These topics are important in our understanding of what is life and how life works. We are made of atoms. The electrical force is important to us because we are made of atoms held together by this force. Every chemical reaction–including those within our bodies–occurs through the electrical forces exerted between neighboring atoms. It is also the force behind many material interactions that you see every day, from rubber bands to light and even our sense of touch. A description of radioactive dating is included in this chapter because this technique is used to tell us the age of the Earth and the age of many materials that we find on the Earth. It also tells us the age of the first appearance of many of the different species of life and the age of many of our cultural objects, too. An accurate measurement of these ages allows us to more precisely determine the order in which interesting evolutionary steps have taken place. The power and endless usefulness of science is illustrated in this chapter by discussing the impact that 100- and 300-year-old science has on our lives today. In the same way that the people of those times could not imagine the machines that have resulted from the research of those years, nobody can imagine the machines that will soon result from today's scientific research.
Newton's motion equation, and the gravitational force
Around the year 1687, after the motion of enough systems had been studied by previous scientists, Isaac Newton (see http://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/Newton.html for his biography) deduced a single rule of nature, in mathematical form, that describes the motion of each of these special cases. He was able to begin with that single, mathematical rule of nature and, after applying a sequence of mathematical steps, obtain each of the distinct equations previously found to describe just one system. This made us understand that all of those systems previously thought to be distinct were actually just variations of the single phenomenon: motion.
Many physicists believe that all natural phenomena are governed by just one rule of nature: if you push on an object it will speed up. This is Newton's law of motion (or motion equation) which he published in 1687 in the mathematical form “force equals mass times acceleration.” This law numerically specifies the location, speed, and acceleration through time of any object that will result when any set of forces are applied to it. The mass of the object resists this change in speed: it has inertia and momentum that make the object prefer to continue moving in the same direction at the same speed. (To accelerate means to change either your speed or your direction of movement.) The law can be written in terms of either force or energy. Today, this law is written in a relativistic, quantum-mechanical form. Visit www.pbs.org/wgbh/nova/elegant/program_d_t.html for the PBS video The Elegant Universe. Visit www.mine-control.com/sand.html for an example of motion as art.
Newton's motion equation describes the motion that results from applying forces to masses. Objects are pushed or pulled with a force. Only five forces have been found to exist in nature: the gravitational, electric, magnetic, and the strong and weak nuclear forces. Gravity is the attractive force between masses. It is an attractive force that pulls two masses toward each other. In this way it keeps the Moon in orbit around the Earth and the Earth in orbit around the Sun, and it also holds us to the surface of the Earth. In the year 1680, Newton obtained the equation that describes this gravitational force. Electricity and magnetism are the forces between charges and magnets. These forces can be either attractive or repulsive. As mentioned above, all of chemistry results from the electrical force. The short-ranged, weak nuclear force is involved in the process of radioactive decay. The strong nuclear force holds together the particles, called protons and neutrons, found to makeup the nucleus of an atom, and it also holds together the three quarks that are the particles forming a proton or neutron. The weak and strong nuclear forces were found only in the last century as we became able to measure atomic-sized processes.
Recently the electric, magnetic, weak, and perhaps the strong forces have been shown to be different aspects of a single force. There have not yet been any measurements of the gravitational interactions of atomic matter, so we do not yet know how to describe gravity on an atomic scale. Many physicists hope to unite gravity with the other four forces, resulting in a single equation that describes the interactions of all the particles of the universe in a “theory of everything.” This is called the Grand Unified Theory.
The single equation describing the gravitational pull that the Earth exerts on the pendulum's mass also describes the gravitational pull that the Earth exerts on the Moon's mass. The two systems, Earth-Moon and Earth-pendulum, are just two different variations of a system of gravitationally interacting masses. Some differences between the two systems include the lack of a string in the Earth-Moon system and that the Moon has enough speed or inertia to continue its motion all the way around the Earth. Instead of releasing the pendulum from rest, you could instead choose to throw it downward and sideways with some speed. If it is thrown with enough speed, it would spin all the way around your hand.
I want to stress the power of Newton's law of motion by pointing out that it describes any motion by any object that you see. If you list every object you have ever seen in motion, the motion of every one of them is described by this single equation. For example, the equation mentioned above relating the period of a pendulum to its length can be obtained from Newton's motion equation. The motion of the pendulum is what results when the force of its string and the force of gravity both act on it at the same time. Remove either the string or gravity and the motion will not be that of a pendulum. The pendulum is one example of a system of motion. That its equation of motion can be obtained from Newton’s equation is an example of the way in which Newton's single, but general, force and motion equation describes each particular system. All we do is add up the forces and apply a sequence of mathematical steps to obtain a final equation. A person could list millions of different systems that undergo motion, and distinct equations could be found that would describe the motion of each of these distinct systems. Since the entire world is the sum of these possible systems, our description of the entire world–that is, nature–would be a complicated mess if we had to use millions of unrelated equations for each of these millions of possible systems. All motion is instead described by a single, universal equation, making the universe a simpler place.
By the way, some persons enjoy applying sequences of mathematical steps to obtain the distinct equations for various systems like the pendulum. If you think this might be fun then you might become a physicist. We can summarize a physicist's college years in two sentences: A college student becomes a physicist through six years of course work and a few years of experimental work. During each day the student obtains the distinct equation for several additional systems, adding up to several thousand systems by the end of college. (I always wonder what are the major features of other person's occupations, so I'll mention this in passing.)
Newton's law is used daily by scientists and engineers. For example, it is used to determine the motion of your car as it moves and turns, the motion of the fluids in a car's fuel and hydraulic systems, the motion of the air that flows around airplanes and lifts them into the air, the movement of the Moon around the Earth, and the trajectories that take spaceships from the Earth to the other planets. In the year 1687, nobody could imagine the endless applications of this equation. The equation is a few hundred years old and will continue to be used for all centuries to come. It is a fundamental truth of nature. (Truth is measured by counting significant figures in repeatable measurements.)
When Newton first published his equation, many persons were surprised that one equation could describe both the motion of everyday objects, like pendulums, and the motion of heavenly bodies. In fact, they were astonished that a mere human could find an equation that even the heavens obeyed. Before then they had considered the heavens to be of a separate reality with its own behaviors. After Newton’s success, many scientists set out to find equations describing everything from human behavior to economics and society.
To prepare us to see the role of the electrical force in the orbital motion of two charges about each other, I want to further describe the role of gravity in the orbital motion of two masses about each other. The orbital motion of the Earth and the Moon, due to the gravitational attraction between the Earth and Moon, is similar to the way in which two persons sort of spin around each other while facing, holding hands, leaning backwards, and running sideways. If the two persons let go of each other then they will fly apart. The two ice-skaters sort of "orbit" each other. They can continue in this circular motion because of the mutual pull of each other's hands. If one skater is one hundred times heavier than the other, then you will hardly notice the motion of the larger person. The Earth and the Moon are similarly held in their circular orbit by their mutual gravitational pull; gravity enables them to pull on each other without having to hold hands. They orbit each other but the Earth moves little since it is about one hundred times as massive as the Moon.
The gravitational force is so tiny that it takes a lot of mass before it amounts to anything. We feel our own weight because that is how strongly the Earth is pulling on the matter of our body. If you stand on a scale to weigh yourself but have somebody pull down on your feet then the scale will read as if your weight has suddenly increased. When you stand on the scale, the Earth is pulling on your feet with the force indicated by the meter. It is an attractive force between each of the pieces of your body and each of the pieces of the Earth. The more pieces either you or the planet have, the larger will be the force and the higher the scale reading.
The electric force and light waves
The electric force is created either by an electric charge or by a changing magnetic force. Electric charges come in two varieties, which Ben Franklin named "positive" and "negative” in the year 1747. (For biographical information, see www.pbs.org/benfranklin/exp_shocking.html, www.soul.org/Ben%20Franklin.html and www.mos.org/sln/toe/kite.html, which has a video of lightning striking his kite.) We all remember from grade school that like charges repel and unlike charges attract. There is no magnetic charge that creates a magnetic field; it is instead created either by a moving charge or by a changing electric field. We occasionally experience electrical charges (electrons) and the electrical force as a slight shock when we touch metal objects on a hot, dry day. Lightning is an example of the flow of electricity.
The electric force is very strong. It is a zillion (1045) times stronger than the gravitational force. (This means that you would have to be able to measure about forty-five decimal digits before you could see the tiny change in motion that gravity causes between two objects that are also interacting electrically.) All matter is composed of these electrical charges. Most everyday objects have equal mixtures of positive and negative charges, making them electrically neutral. In 1785, a person named Coulomb (for his biography and portrait, visit http://en.wikipedia.org/wiki/Charles-Augustin_de_Coulomb) made measurements that resulted in the equation describing the electrical force between two electrical charges.
The electric force holds atoms and molecules together, including those within your body. (Remember that there are about one hundred different kinds of atoms, from hydrogen to uranium, and that a molecule is a collection of atoms.) In the same way that the gravitational force can pull two masses–the Earth and Moon, for example–into a circular orbit around each other, the electric force can pull two or more electrically charged atoms into a circular orbit around each other. Since the electrical force is sometimes attractive and sometimes repulsive, depending on whether the involved charges are alike or unlike, all molecules do not electrically attract all other molecules. This is in contrast to gravitational attraction, which is always attractive. If two atoms, or collections of atoms, electrically repel each other then they will not join together. Those atoms electrically attracting each other will join together–indeed, they must.
It turns out that a close examination of the atoms within the pendulum's string shows that the tension in the string is transmitted along the string's length through the electrical interactions of neighboring pairs of atoms. We also see the electric force at work in springs and rubber bands. It provides the "static cling" of clear food-wrap, and it keeps you from falling through the floor. Electric charges serve many purposes in industry. They are used in Xerox machines, in electroplating, to remove pollution from smoke stacks, to separate nuts from shells and chaff from wheat. (You might like to read Electrostatics, Scientific American March 1972.) Our bone growth is electrically controlled through a pressure sensitive, piezoelectric effect. Electricity consists of moving charges and is found in nerves, muscles, eyes, brains, hearts, eels, lightning, and in the electronic machines that we use every day.
All electronic circuits make use of the electrical force. A battery contains separated positive and negative charges. The negatively charged side of a battery produces a repulsive force on negatively charged electrons, forcing them to flow through the circuit toward the other, positively charged side of the battery that is attracting the electrons. The earliest usable batteries were made in 1800 by AlessandroVolta (for his biography and portrait, see http://en.wikipedia.org/wiki/Alessandro_Volta). So, in his honor, we rate battery strengths in "volts." The electric force pushes charges, causing them to flow through an engineer's circuits as a "current." One of the first persons to make measurements of electrical current was Andre Marie Ampere (1775-1836). Today, we measure the size of electrical current in units called "amperes" that are named after him.
It was soon found that each material has a characteristic resistance to the flow of electrical current. This was studied by in 1826 by Georg Simon Ohm (see http://en.wikipedia.org/wiki/Georg_Ohm). The unit of electrical resistance is named "ohms" in his honor. It took several years of research to find a way to cause an electrical current to flow through a material for distances of just a few yards (meters) and even more years to get electricity to flow through wires for distances of kilometers and miles. This research lead to the development of the telegraph machine, which occurred in the year 1844. The trans-Atlantic cable was completed in 1857.
In 1864, James Clerk Maxwell (see http://en.wikipedia.org/wiki/James_Clerk_Maxwell) wrote a set of four equations describing all electric and magnetic phenomena. These four equations, which are called "Maxwell's equations," describe a fundamental truth of nature and will be useful for all of us humans for the rest of time. They describe every electrical and magnetic machine that will ever be made including generators, streetlights, radio and television sets, motors, MRI and CAT medical imaging devices, the circuits of a computer, and toasters. Maxwell's equations also made it clear that the electric and magnetic forces are two different aspects of a single phenomenon of nature, called electromagnetism, and that light too, is an electromagnetic phenomenon.
It was found that whenever an electric charge is wiggled it sends out electromagnetic "light waves" that move away at the speed of light. For an animation of waves emanating from wiggling charges, visit the Iowa State University website at http://www.ee.iastate.edu/~hsiu/movies/dipole.mov.The frequency with which the charge is wiggled determines the "color" of the light. Blue light has a higher frequency and more energy than does red light. (It also occurs that a hot object that glows with blue light is at a higher temperature than an object that glows with red light.) The electrical charges that make up matter are caused to wiggle whenever a light wave passes by, and this in turn causes them to emit light waves of their own. Light waves come in many colors, most of which are invisible to us. Some of these are called radio, microwave, infrared, ultraviolet, radar, x-ray, and gamma-ray. This means that the operation of lenses, mirrors, cameras, optical fibers, infrared remote control devices and nighttime viewers, radar detectors for the weather and the speed of automobiles, microwave ovens, medical x-rays, and other such devices are also described by Maxwell's equations because they involve electromagnetic waves. In addition, it has been found that each chemical element wiggles at uniquely different frequencies and that these characteristic frequencies increase as the temperature of the chemical increases; scientists have already measured millions of these frequencies. When astronomers look at the light coming from a star, they measure the received frequency and then know that star’s chemical composition and its temperature, too.
We see the Sun because its wiggling charges emit light, and since these charges wiggle at many frequencies, the Sun emits many different colors of light. But because of its temperature, the Sun emits most of its light between the red and blue colors and much less beyond the infrared and ultraviolet colors. This is the reason our eyes are sensitive to the red through blue colors. It wouldn't help for Earthlings to see colors that our Sun doesn't produce. Since many other stars emit most of their light in colors not emitted by our own Sun, the eyes of creatures who might live around those stars would be more sensitive to those other colors, which might be infrared, ultraviolet, or even x-ray. The eyes of the nighttime creatures of the Earth–snakes, for example–are more sensitive to infrared light than are those of daytime creatures. Flowers are brightest in the ultraviolet colors because the eyes of their "partners," the bees, are most sensitive to these colors.
At the time of the publication of Maxwell's equations in 1864, it became clear that it was possible to generate electromagnetic "radio waves" using oscillating, electrical circuits in which current flows back and forth between capacitors and inductors (in many ways, this oscillatory motion is similar to that of the pendulum). It took about twenty years before Heinrich Hertz was first able to do so, and we have named the unit of frequency after him. We hear television and radio station frequencies given in terms of kilohertz, megahertz, and gigahertz. (My computer keyboard is operated at a speed of three nanohertz.) In 1888 Marconi was able to invent the machine we call a "radio-frequency detector" or "radio" by electrically producing an electromagnetic wave in one place and detecting it in another. The detector is nothing but another circuit containing the same capacitor-inductor combination. The frequency to which the circuit reacts is adjusted by altering the circuit components, which we are doing as we turn the radio knob. (In Chapter 16 we will see that the radio business did not blossom until the 1920s.)
The first radios consisted of a number of vacuum tubes, see http://en.wikipedia.org/wiki/Vacuum_tube, in which electrons are greatly accelerated before they are suddenly stopped by a collision with metal tube-components. Since the sudden stop is equivalent to a very high frequency wiggle, the stopping electrons emit high frequency light. In the year 1895, research involving the light emitted from vacuum tubes accidentally stumbled across the ability of certain frequencies to pass through body-sized pieces of matter. This was the discovery of x-rays by Wilhelm Roentgen, see www.xray.hmc.psu.edu/rci/ss1/ss1_2.html.
It was claimed above that many seemingly unrelated phenomena are simply different aspects of a more fundamental law of nature. The above list of electrical machines and the following list of light-phenomena illustrates this point. Some examples of light phenomena described by Maxwell's electromagnetic equations include polarized sunglasses, the rainbow patterns seen on spilled oil sheets and soap bubbles (see www.geom.uiuc.edu/graphics/pix/General_Interest/Digital_Art/sullivan-120cell.html), the highly reflective paint used on highway signs, telescopes, binoculars, a mirage on a hot day, the colors separated by water drops and the resulting rainbow, the halo that is sometimes seen around the Sun or the Moon, the blue sky, the red sunset, the color of every object, and the streaks of light you see when you squint your eyes while looking at a lightbulb. Each of these is simply a different aspect of electromagnetism. Each is described by Maxwell's equations and results from pushing on an object with the electromagnetic force. It is impressive that humans figured this out–in the year 1864, no less. There is no end to the usefulness of this understanding and its applications. In fact, humans are another example of this fundamental law of nature at work in that the atoms within our body are held together by the electrical force.
In the year 1864, nobody could imagine what sorts of machines would be made using the electromagnetic equations. In the same way, we cannot imagine the future machines that will result from today's scientific research. What sort of machines and medicines will be developed 150 years from today that are based on the just-completed human genome project, or that are based on the quark research of today's elementary particle accelerator projects?
Phenomena that involve heat are now seen to be yet another example of motion and so are not a unique or independent aspect of nature. The equations for phenomena involving heat were obtained in the last three centuries. These equations provide mathematical relationships between an object's temperature, pressure, volume, and its type of material and physical structure. It has been found that a material's temperature is a measure of the speed of its constituent atoms. The atoms of a gas bounce around, colliding with other atoms and with the walls of the container. The pressure of a gas is due to the force of the atoms colliding with the container walls. In this way it has been found that heat phenomena are also described by Newton's motion equation. That is, heat is not a separate phenomenon but is another aspect of motion. The atoms of a hotter material are jiggling faster than are those of cooler ones. When a fast moving atom runs into a slow moving atom, it is slowed by the collision; the slower atom’s speed is increased. This transfer of the speed-of-motion from one atom to another is the flow of heat. Your food heats as its slower-moving atoms are brought in contact with the more energetic atoms of the surrounding fire or air. (A microwave oven passes electromagnetic waves through food in order to make the atoms of the food wiggle more quickly and become hotter.) Other examples of heat machines include steam, gasoline, and diesel engines.
About the year 1900, scientists began to be able to measure nature on an atomic scale. Examples of atoms include the basic and familiar chemicals hydrogen, helium, carbon, and oxygen. It has been found that atoms consist of a massive, central core or nucleus composed of positively-charged protons and a number of uncharged neutrons. This nucleus is orbited by negatively-charged electrons, see www.lbl.gov/abc/Basic.html. The electrons are held in orbit around the protons by their mutual electrical force in a manner analogous to the way in which the Earth and Moon are held together by their mutual gravitational force. Visit VisionLearning at http://web.visionlearning.com/custom/chemistry/animations/CHE1.3-an-animations.shtml for animations of various atoms) It takes some force to pull an electron away from the nucleus to which it is electrically attached. Protons and neutrons are about 2,000 times more massive than electrons.
This picture of electrons orbiting a massive clump of protons and neutrons was determined in the year 1911 by Ernest Rutherford. He passed a beam of low-mass helium nuclei through a thin sheet of high-mass gold atoms and measured the resulting trajectories of the helium nuclei. Gold can be hammered into very thin sheets; Rutherford's sheet was so thin that it contained only a few layers of gold atoms. Usually the beamed helium nuclei passed right through the thin gold sheet but sometimes they struck a gold nucleus and bounced straight back toward the incoming beam. This revealed that a nucleus consists of lumps of mass and that there is mostly empty space between the adjacent nuclei of the sheet. The mass and charge of these lumps can be measured in many ways. The lumps were later named protons and neutrons. For an animation of this scattering process visit http://galileo.phys.virginia.edu/classes/109N/more_stuff/Applets/rutherford/rutherford.html
Inside the nucleus, the positively charged protons are repelled from each other by the electric force; this is a tremendously large repulsive force. Despite this large repulsive force they are held together by the even-stronger but short-ranged and attractive "strong nuclear force." That is, the protons are subject to both the electrical and the strong nuclear forces. This nuclear force is about a million times stronger than the electrical force with which the orbiting electrons are held to the nucleus (this is also the reason nuclear explosions are a million times stronger than chemical explosions). When a nucleus is split into two pieces, say by the collisional force of an incoming projectile particle, the two separated pieces are no longer close enough to each other to be held together by the short-ranged and mutually attractive strong-nuclear force. The separated, positively charged pieces will then fly apart due to their mutual electrical repulsion.
Normally, atoms are electrically neutral because they have equal numbers of protons and electrons. When an atom is heated, its electrons gain speed. When sufficiently heated they will gain enough speed to break free from their electrical bond with the nucleus and move away, leaving behind a positively charged atom. The positively charged atom is called an ionized atom, or ion. This means that the atom is now electrically charged instead of being neutral because it is missing some negatively charged electrons. The temperature at which each chemical element ionizes has already been measured.
The nucleus of each type of atom always contains a fixed number of protons but it can have a bit of a range in its number of neutrons. Each variation will then have a different mass and is called an isotope of that particular type of atom. For example, a carbon nucleus always contains six protons but has either six, seven, or eight neutrons. Uranium has ninety-two protons, ninety-two electrons and 140 to 150 neutrons. Isotopes and their variations in mass make possible the techniques of radioactive dating and such that are used to study our own history..
Scientists have found that only ninety-two different atoms or chemical elements–from hydrogen to uranium–occur in nature, see http://education.jlab.org/itselemental/index.html. Each different chemical element contains from one to ninety-two protons inside its central nucleus and an equal number of orbiting electrons–unless sufficient heat is added that the electrons begin escaping. The number of neutrons varies for each particular chemical atom but the number of protons does not. That is, hydrogen always has one proton, helium always has two, and uranium always has ninety-two.
Hydrogen atoms are the smallest of all and consist of a single proton orbited by a single, electrically-bound electron. Hydrogen atoms are so small that 100 million of them fit across the width of your finger. Most often, hydrogen nuclei have no neutrons, but about 0.8% of them are found to contain both a proton and one neutron. Since the mass of protons and neutrons are about the same, this variety of hydrogen is twice as massive as the form that contains no neutron.
Helium is the next largest atom and contains two protons, two electrons, and usually two neutrons. It has been found that about 0.3% of helium atoms have three neutrons instead of two. (Helium is the gas inside a child's balloon; it also makes your voice sound funny when you breathe it.) If you press two hydrogen atoms together with a megaton force then they will merge into a single helium atom and release a lot of previously-stored nuclear energy.
Atoms can become electrically attached to other atoms. We use the term molecule to refer to any collection of two or more atoms. Large molecules can be built by combining many smaller ones. The molecule's collection of atoms remains electrically stuck together unless it is sufficiently heated or comes into contact with another molecule that has the right charge distribution to disrupt it.
Each atom within a solid piece of material, such as a block of iron, behaves as if it is attached to each of its neighbors with little springs, see www.physics.brocku.ca/courses/1p21_reedyk/images/F09001.jpg; the springs represent the electrical force. As this material is heated, the atoms are seen to jiggle more rapidly, see http://vis.lbl.gov/Vignettes/vanhove-98.ijs/output.mpg. At a certain temperature the atoms are no longer able to hold each other in place and the material melts. The melting-point has been measured for thousands of types of atoms and molecules.
Those one hundred or so varieties of atoms combine into endless varieties of molecules. A molecule consists of two or more atoms that are electrically bound together. For example, we all remember that water, H-2-O, consists of two hydrogen atoms and one oxygen atom. The largest molecules within our bodies consist of billions of atoms and are electrically neutral because they contain equal mixtures of positive and negative charge. Chemists study the ways atoms interact with each other. They have found many rules that help them figure out which final chemicals will result after several chemicals have been mixed together. (During each day of an eight-year college curriculum, a chemistry student will study many different chemical reactions; by graduation, the properties of thousands of chemicals have become familiar.) We use many chemicals in our daily lives. The most familiar everyday uses include medicine, soap, glue, oil, paint, and cleaning products. Our bodies consist of millions of interrelated chemical reactions.
What's the difference between chemistry and physics? Physicists are interested in the nature of the electrical force between atoms. Some chemists might think this is an interesting aspect of interacting atoms but they are usually more interested in the properties of the millions of chemicals that result from these electrically bound combinations. Chemists want to know how atoms interact and how more-complex molecules can be formed. They study the properties of known chemicals and look for uses for them. They also look for new chemicals to serve specific purposes. Physicists want to know why atoms and molecules occur. They look for the fundamental building blocks of atoms instead of new combinations of atoms.
The electrical bonding between the atoms of a molecule occurs in a few ways. In one situation, the electrical binding-force occurs when an electron simultaneously orbits two nearby atoms. In another situation, two neutral atoms can become electrically bound when their component charges become displaced. This happens, for example, when a charge is placed near an electrically neutral block. When that neutrally charged block is undisturbed, it consists of little packets–its atoms–of equal amounts of positive and negative charge. When an exterior positive charge is held near the block, the block's positive charges are slightly repelled while its negative charges are slightly attracted toward that exterior charge. This makes a slight separation between the positive and negative charges within the block. The near side of the block is then slightly negative, while the far side is slightly positive. The result is that the neutrally charged block is slightly attracted toward the exterior charge. The same thing can occur in nearby molecules. The electrical charge of a large molecule is unevenly distributed about its three-dimensional shape. When two multi-atom molecules face each other, a slightly positive charge of one side of the first molecule and a slightly negative charge of one side of the second molecule can result in an electrical force that holds the two molecules together. We will see that, inside our bodies, this process builds very large molecules containing thousands to billions of atoms.
The difference in the mass of different chemicals also allows us to identify substances. To do this, a small amount of an unknown substance is heated until it is vaporized into a gas of ionized molecules. The gas molecules have varying speeds and bounce around within a container. The container has a tiny hole that allows those molecules moving in the right direction to escape into an adjacent tube. There are both magnetic and electric fields within the tube and each exerts a force on the moving molecules. The magnetic field does not exert an equal force on every molecule; instead, its force is larger on faster-moving molecules. The force of the electric field does not vary with molecular speed. Those molecules moving with a certain speed will experience a force from the magnetic field that is exactly counterbalanced by the force of the electric field. These molecules then move straight down the tube while all others are pushed into the walls of the tube. The combination of these two fields has the property that it allows only those molecules with a certain preselected speed to pass along the tube. The researcher selects the desired speed by altering the ratio of electric and magnetic fields. Those molecules having non-selected speeds will not traverse the entire length of the tube. This means that each molecule emerges from the end of the tube with the same speed. Those emerging molecules next pass into an area containing a second magnetic field forcing them into a circular orbit. For each different molecule, the size of its circular orbit depends on its mass: more-massive molecules move in a larger circle than do less-massive molecules. Measuring the radius of motion allows the mass of the molecule to be measured. This so-called mass spectrometer is used to identify a chemical by measuring its mass and then comparing it with previously known molecular masses. The mass of tens of thousands of different molecules have been measured and tabulated.
The mass spectrometer has many uses. It can be placed on a rocket and used to identify the chemicals of the upper atmosphere or of the atmospheres and surfaces of other planets and moons. Also, differences in the chemical contents of different geological sources of obsidian and such can be measured and tabulated. When archaeological excavations find an obsidian artifact, the artifact’s chemical composition can be compared with those tabulated sources to determine its geographical source. This tells much about the people who used the artifact, including their trading patterns. Criminal investigators use mass spectrometers to identify the tiny chemical remnants found in clothes, cars, rugs, hair, poisons, pencil marks, and arson materials gathered at the scene of a crime. The mass spectrometer is also used in the radioactive dating procedure.
Our knowledge of the nucleus has given us lots of useful machines. The medical imaging process called Magnetic Resonance Imaging (MRI) is an important example. To understand the operation of these imaging devices recall that the magnetic needle of a compass always points toward the north pole of the Earth. It has been found that the moving, positively charged protons inside each nucleus act as a pointing magnet and will line up with an external magnetic field. If that external magnetic field is suddenly turned off, each different nucleus–that is, each different chemical–will take a different amount of time to become unaligned from that previously existing field. MRI machines makes use of the alignment and un-alignment times of different nuclei in order to determine the types of material found inside your body. Some of these materials include bone, tissue, normal cells, and cancerous cells. This allows a picture to be made of your interior without sawing you in half.
If energy is added to a nucleus, it will soon re-emit that energy to return to its less-energetic state. Since the nucleus of each chemical emits a different spectrum of energy, a chemical can be identified by measuring the energy emissions of its nucleus. This is called neutron activation analysis. For example, after you fire a gun there is an invisibly tiny amount of gunpowder left on your palms. The personnel in a crime lab can collect a remnant from the palms of a suspect and then examine the spectrum of that heated remnant to determine if that person had recently fired a gun.
Quantum Mechanics is the description of nature on the atomic level. It was developed in the 1920s (quantum mechanics is what happens when nobody in the U.S. is allowed to drink for ten years) as a necessary refinement of Newtonian mechanics. For large-scale objects, Newtonian and quantum mechanics agree to about thirty decimal places. In 1926, Erwin Schroedinger found the version of Newton's equation that describes atomic-sized particles. Schroedinger's equation describes the behavior of the atoms inside all materials. After a few decades, people learned to use the equation to make lasers and transistors and such–like those used inside computers and cd-players. Nobody in the 1920s could imagine the machines that would result from the application of Schroedinger's equation.
Electric charges were found to come in two varieties, positive and negative, but the carriers of the strong-nuclear force have been found to come in three varieties. During this century, we will begin to make machines that use the strong nuclear force. Nobody today can imagine the future machines that will be made whose operation will be governed by the strong nuclear force. The strong nuclear force is not yet fully understood, in fact, there is much left to be learned–you might like to join in the research.
The age of many objects can be measured by the technique of radiocarbon dating. This physical process will be described here so that we can refer to it throughout the remaining chapters. As mentioned above, the nuclei of a particular chemical element can contain a small range in its number of neutrons. The number of neutrons in a given nucleus can change when an external neutron collides with it and either knocks away others or becomes absorbed. That colliding neutron may have been emitted by the chemicals of the Earth, the Sun, or even another star. Certain numbers of neutrons result in an unstable nucleus, like having an overcrowded house. Stability is reestablished when the nucleus emits "radiation." This radiation has been found to occur in three forms: an electron (named beta radiation); a light wave, like an x-ray (named gamma radiation), or a helium nucleus (named alpha radiation) that consists of two protons and two neutrons. The proper mispronunciation of "helium nucleus" is "helius nucleum."
X-rays, electrons, and helium nuclei are often useful, and like everything else, they can also be harmful. One hundred years ago, Madam Curie was one of the first scientists to study radiation. From the studies of these early scientists, we began learning the hard way about the dangers of radiation. During the last hundred years, physicists have measured millions of facts concerning radiation. Today, the most familiar use of radiation is to create monster movies. Radiation can also be used to fight cancer. It can be used to kill microscopic germs in newly harvested potatoes, fruit, and meat and such. This process is called pasteurization and gives food a longer shelf life. Radiation is used to provide power in spacecrafts and in heart pacemakers. Radioactive tracers are used in medical tests. For a list of additional uses you might like to read The Ubiquitous Atom by Grace and Larry Spruch. Radiation is emitted from the dirt below us, the bricks around us, and from the stars above us. Every day our bodies absorb a small amount of radiation.
Next, we define the term "half-life" so that we can then go on to understand the radioactive dating technique. Imagine that you shake a bag of one thousand coins and then pour the coins onto the ground. Next, pick up the coins that show "heads" and place them back into the bag while taking away those showing "tails." Pretty close to half the coins will be heads and half will be tails so that the bag will now contain about five hundred coins–that is, the bag has lost half its original contents. (By the way, five years after finishing a course at school, I have forgotten about half of the material covered. After five more years, I have forgotten half of what remained, leaving one-quarter of the original amount.) Shake the bag again and then dump the coins onto the ground once more. Again, half the remaining coins will be heads, and half will be tails. If you pick up the heads, you will find about 250. We see that about half the contents of the bag are lost after each shake. Initially the bag had 1,000 coins. After shaking and removing "tails" the bag contained 500, then 250, then 125, 63, 32, 16, 8, 4, 2, 1, and finally zero coins. (See Student Study Guide for Energy for a Technological Society by Joseph Priest, page 89.)
In the same way it has been measured that half the radioactive atoms of an unstable material will emit radiation during each half life. This changes the unstable atoms into a stable non-radioactive form. For example, if you have 10 kilograms (22 pounds) of a radioactive material then half of it will change into another chemical during a period of time equal to its “half life.” The half life of each type of radioactive atom has been measured. The half life of an atom never changes. Radiation is a natural process. Just as a hammer will always fall whenever it is pushed off a table, during each half-life, half the nuclei in a radioactive material will become more-stable by radiating either light waves, electrons, or helium nuclei.
Different radioactive chemicals have different half lives; this makes them suitable for determining different sizes of time spans. For example, one can measure how much time has elapsed since a rock had last been in a molten state. This shows that the molten Earth solidified about 4.5 billion years ago. This technique can also be used to measure the age of a given volcanic eruption.
It was mentioned above there can be a small range of numbers of neutrons within a nucleus. For example, we saw that carbon atoms always have six protons but six, seven, or eight neutrons for a total of twelve, thirteen, or fourteen neutrons and protons. The percentages of each type (each type is called an isotope) of carbon have been measured. If you start with 1,000 atoms of radioactive carbon-14, you will find that after 5700 years have elapsed , which is its half-life, only 500 of these carbon-14 atoms will be remaining; the other half of them will have emitted radiation and turned into a more-stable atom. After another 5700 years elapse, only one-fourth of the original carbon-14 atoms remain.
When the Earth formed it contained a certain amount of carbon; a small percentage was the radioactive carbon-14 variety. The carbon-14 essentially disappears within about ten half lives, which would be 57,000 years. The Earth is much older than 57,000 years. (We have measured the age of the Earth by counting radiation tracks and by measuring the relative amounts of radioactive uranium and thorium, as described in Chapter 4.) Since the Earth is much older than 57,000 years it means that carbon-14 is continually being produced, otherwise it would all be gone.
Scientists have found that energetic neutrons from the Sun and the other stars collide with nitrogen nuclei in the Earth's atmosphere and create carbon-14. This collision rate will certainly be variable but not drastically so. Little variation is likely to have occurred in the last 50,000 years because the Sun's lifetime is much longer than that. Some carbon-14 combines with oxygen to form a carbon-dioxide molecule. Living things absorb this as they breathe. Every living creature contains carbon, and all living creatures have identical relative mixtures of the non-radioactive carbon-12 and the radioactive carbon-14 varieties. After death, the relative proportion of carbon-14 steadily decreases in time. Every 5700 years after death, half the remaining carbon-14 will have undergone radioactive decay. A measurement of the relative proportions of carbon-12 and carbon-14 atoms makes it possible to determine how many carbon-14 half-lives have occurred since the object died. This is the radioactive dating technique. The greater the number of years since the death of the creature, the longer its carbon-14 has been radiating away.
We see how it can be said that millions of seemingly unrelated phenomena are just different aspects of a small number of more-fundamental phenomena. We saw how all motion can be described by a single equation, that heat is nothing but the energy of motion, and that there are many manifestations of electromagnetism.
We have also seen something of the scientific process and its accumulation of knowledge and techniques through the centuries. We see that with each generation of us humans, we add to our collective knowledge of nature. It is certain that we will continue to build additional knowledge forever. Knowledge is an important part of our civilization. We often look back at the knowledge of previous generations as we discuss the building blocks of our own knowledge. Today's knowledge forms the foundation for that of tomorrow.
The topics of this chapter provide a basis for the descriptions, in the next few chapters, of the gravitational formation of the Earth and of the electrical formation of the molecules of life. The technique of radioactive dating will appear many times in the coming chapters. The following six chapters present our understanding of the nature of a human. This knowledge has been gained through the application of the scientific process. For more information about physics, visit http://textbookrevolution.org/Textbooks/Physics.html.
We saw that some persons do science just for the pleasure of satisfying their own human curiosity; others hope to contribute to the well-being of every person on the planet–for centuries to come. The mathematics and science of the Renaissance and Enlightenment were done more for pleasure than profit. For example, nobody asked Mr. Bessel how much money he could make from his new function, and he did not demand royalties for its use. (Bessel's function appears in the mathematical solution to any system that has the shape of a cylinder or a sphere.) There are scientists who enjoy the attempt to understand the rainbow–even though they will not obtain any financial profit from this. (Each time you see a rainbow, please send some money to my friend James Clerk Maxwell.) Some of us humans enjoy music, cooking, or just eating; others follow sports or climb mountains–because "they are there"–and yet others simply want to understand the world. These are things that humans do. If you are not amused by studying the world then you might still be amused to know that there are people who are amused by studying the world.
Questions
1. List the motions of some objects. These motions can be described by Newton's equation.
2. How many electric and magnetic machines do you use every day?
3. Describe a phenomenon that involves light.
4. Describe a phenomenon that involves heat.
5. Describe a use of nuclear radiation.
6. List some future machines that will result from today's science.
7. What is the proper mispronunciation of "helium nucleus."
8. Describe a heat machine that you used today.
9. For the list of phenomena in question 41 part iii of Chapter 1, classify each phenomenon as motion, heat, or electromagnetism.
10. Measure the period of a pendulum.
11. What was the role of business and government in the scientific progress described in this chapter?
12. Why did it require a couple of centuries of research efforts to understand electromagnetism? How long have we been studying atomic, nuclear, and gravitational phenomena?
13. Should we patent both machines and scientific principles?
14. How have today's science and technology depended on that of past centuries?
15. What portion of the world's population is involved in research in science and technology? How has this portion changed through the centuries?
16. Why do some machines behave in a way that wasn't expected?
17. What is the purpose of knowledge? What is the purpose of machinery? Why do humans pursue these fields?
18. How do science and technology affect our social and cultural ways? Our health has certainly been improved by this research, have our social and cultural ways been "improved?" What portion of our happiness is due to the machines we use or the knowledge we hold? Compare the effects of science and technology on the happiness and the social interactions of people living in Ancient Egypt, an industrialized nation today, the Medieval world, and as gatherer-hunters in today's Brazilian jungle or in ancient America. When and where did we first learn to make newspapers, dishware, pajamas, cigars, wheat bread, and maple syrup?
Suggestions for further reading
A History of Scientific Ideas by Charles Singer, 1959, Barnes and Noble Books New York.
The History of Physics, by Isaac Asimov, 1966, Walker and Co, New York.
Science, Its History and Development Among the World's Cultures, Colin A. Ronan, 1982, Facts on File Publications, New York.
Understanding Physics, Isaac Asimov, 1966 and 1993, Barnes and Noble Books.
Electrostatics, Scientific American March 1972.
The Ubiquitous Atom, Grace and Larry Spruch, 1974, Charles Scribner's Sons, New York.
For descriptions of lots of everyday phenomena see The Flying Circus of Physics With Answers, Jearl Walker, 1977, John Wiley & Sons, New York.
Madame Curie, by Eve Curie, 1937, Pocket Books Inc, New York.
From Quarks to the Cosmos, Tools for Discovery, by Leon M Lederman and David N Schramm, 1995, Scientific American Library. Pbk ISBN 0716760126.
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