“What Scientific Evidence Proves that God Created and Designed the Universe?” is the title of The John Ankerberg special series to be aired later this month. One of the principal goals of our blog is to encourage respect for science as an apologetic tool. Several diverse groups will benefit from the program content. One group is the community of faith. Others include secularists whose belief in God may range from weak to non-existent.
Let’s consider Christian believers first. We might ask if such “scientific evidence” is necessary for Christians, since we may assume they have already been convinced of God’s existence and His creative acts. We must enlarge on this assumption and make a strong case that even the mature and confident Christian needs regular affirmation and support for belief in the reality of God. In our experience, consider how satisfying it is to receive additional evidence supporting and reaffirming the beliefs and activities we have embraced. Speaking on a personal level, since my retirement, the opportunity to use additional quality time to research new scientific discoveries has reinforced and enriched my enjoyment of the divinely created world and my confidence in the reality of God. This spills over into greater awareness of meaning and purpose in areas other than science. Scientific evidence pointing to the existence of God has multiplied many-fold during the lifetimes of the people able to read this post or listen to a television series.
Scientific support for design, order, and coherency in our physical world is related to evidential apologetics. There are two other major types of apologetics which also substantiate belief in God, namely, classical (philosophical) and pre-suppositional apologetics. There is an important role for each type of apologetics in support of our faith. I encourage each reader to affirm and strengthen his faith by making a study of each and every apologetic approach. This is established by a verse from the New Testament, Jude 3, which, in many translations, speaks of contending for the faith (belief system). In every translation I checked, urgency was the defining emotion. Eugene Peterson’s The Message translation says: “Dear friends, I’ve dropped everything to write you about this life of salvation that we have in common. I have to write insisting—begging!—that you fight with everything you have in you for this faith entrusted to us as a gift to guard and cherish.”
Wednesday, January 7, 2009
Friday, January 2, 2009
Opportunity Knocks
During January and February, the John Ankerberg Show will begin two science series that will help fill a vital instructional niche on the topics of creation and origins. Virtually everyone on the faith/worldview spectrum should take note. This includes believers and non-believers, theists and non-theists, churched and non-churched. The programs will appeal to a range of people, from those certain of their belief system, to skeptics, agnostics, and atheists. The two series deal with fundamental questions concerning our belief in God’s existence as a loving, caring Designer, as well as how and when He acted to produce our cosmos and the living things which inhabit it. As with all past John Ankerberg Show discussions on science, the presentations are supported by the very latest and best evidence available, analyzed by outstanding scholars.
It has been my personal campaign to encourage church leaders to include the exciting discoveries of science in their lineup of educational offerings as an apologetic instrument for strengthening faith in God as the Creator. Science-linked instruction in our churches is not able to offer proof for the existence of God, as proof is most commonly understood. No such proof exists. Even professionals in science would not characterize their findings in this manner. Scientist Owen Gingrich makes the point that Isaac Newton had no proof that the earth moved, or that the sun was the center of the planetary system. Such assumptions, however, provided explanation and enabled the process of prediction. People believed the proposal because of its coherency, not because of the proof it provided. Demonstration of stellar parallax (indicating the earth was revolving around the sun) and Foucault’s pendulum experiment (showing that the earth was rotating) provided coherency to the proposals, but not actual proof. Those discoveries, surprisingly, did not produce sudden acceptance of heliocentric (sun-centered) cosmology, according to Gingrich.
In a church setting where science topics are discussed, there are multiple opportunities to acquire a coherent view of the world which could bolster belief in God. Essentially, such offerings would be studies in “natural theology,” incorporating knowledge in many different fields in order to make sense of a world authored by God. Many church leaders experience discomfort with the topic of science; their sense of security and confidence is stronger in areas of Christian doctrine. This is the best reason not to miss the upcoming John Ankerberg Show presentations by outstanding Christian science professionals. Our parishioners, particularly our young people, have a profound need for apologetic instruction based on quality, scholarly science.
The Ankerberg website lists outlets where the program is broadcast.
It has been my personal campaign to encourage church leaders to include the exciting discoveries of science in their lineup of educational offerings as an apologetic instrument for strengthening faith in God as the Creator. Science-linked instruction in our churches is not able to offer proof for the existence of God, as proof is most commonly understood. No such proof exists. Even professionals in science would not characterize their findings in this manner. Scientist Owen Gingrich makes the point that Isaac Newton had no proof that the earth moved, or that the sun was the center of the planetary system. Such assumptions, however, provided explanation and enabled the process of prediction. People believed the proposal because of its coherency, not because of the proof it provided. Demonstration of stellar parallax (indicating the earth was revolving around the sun) and Foucault’s pendulum experiment (showing that the earth was rotating) provided coherency to the proposals, but not actual proof. Those discoveries, surprisingly, did not produce sudden acceptance of heliocentric (sun-centered) cosmology, according to Gingrich.
In a church setting where science topics are discussed, there are multiple opportunities to acquire a coherent view of the world which could bolster belief in God. Essentially, such offerings would be studies in “natural theology,” incorporating knowledge in many different fields in order to make sense of a world authored by God. Many church leaders experience discomfort with the topic of science; their sense of security and confidence is stronger in areas of Christian doctrine. This is the best reason not to miss the upcoming John Ankerberg Show presentations by outstanding Christian science professionals. Our parishioners, particularly our young people, have a profound need for apologetic instruction based on quality, scholarly science.
The Ankerberg website lists outlets where the program is broadcast.
Friday, December 26, 2008
James Clerk Maxwell
James Clerk Maxwell (1831-1879) is an anomaly among scientists. Charles Darwin was Maxwell’s contemporary, but the similarity in their work and worldviews ends there. While many scientists in the early years of the Scientific Revolution, beginning with the 17th century, were unashamed Christians who did not hesitate to express their faith, by the mid-19th century that picture had changed. Enlightenment thinking, with its positive liberating effects on the human spirit, gave many people, scientists included, a sense of self-sufficiency and self-empowerment. At the risk of oversimplifying things, their “need” for and acknowledgement of God as an integral part of their view of natural reality, was diminished. This new outlook nurtured and strengthened the conclusions of naturalistic scientists. The germination of Darwin’s broad evolutionary proposals found fertile ground. James Clerk Maxwell stands apart as exceptional.
Maxwell’s theory of electromagnetism incorporated and unified the pioneering discoveries of electricity and magnetism from the previous 50 years. He discovered that visible light was an electromagnetic wave. He taught that many different electromagnetic wavelengths, longer and shorter than those of visible light, should be possible and anticipated their discovery. The complete range of wavelengths, from long to short, became known as the electromagnetic spectrum. Shortly after Maxwell’s death, radio waves and X-rays were demonstrated. Application of knowledge of the electromagnetic spectrum is a landmark advance in science. Without such application, our 21st century lives would be very different. Albert Einstein pronounced Maxwell’s work “the most profound and the most fruitful that physics has experienced since the time of Newton.”
The story of James Clerk Maxwell is one of unparalleled inspiration. As a young man he was gifted with curiosity and creativity. He never relinquished respect for the spiritual truths of his parents’ Presbyterian and Anglican traditions. Later, at age 22, he experienced what has been called an “evangelical” conversion. Thereafter, he never shied from expressing his deeply held Christian faith. There was never a hint of “God-of-the-gaps” explanations for any scientific principle he ever discovered. In addition to his cornerstone theory of electromagnetism which sets him apart, he investigated many other topics, including the nature of Saturn’s rings, color photography, viscosity of gases, and theory of heat.
He was ahead of his time in rejecting the use of bad science to promote a particular interpretation of Genesis scripture, pointing out that ongoing scientific discoveries would enlighten interpretation of scripture. He anticipated the modern discussion of design in the natural world by observing and describing “the ordered uniformity rather than the peculiarity and complexity of nature, as signs of the creator.” In many letters to his wife and others his profound faith was expressed: “Think what God has determined to do to all those who submit themselves to His righteousness and are willing to receive His gift. They are to be conformed to the image of His Son…” His advice to scientists and non-scientists alike was suffused with a Christian worldview: “I think that men of science as well as other men need to learn from Christ, and I think that Christians whose minds are scientific are bound to study science that their view of the glory of God may be as extensive as their being is capable of.”
Most science historians would acknowledge that Maxwell’s contributions to science stand out as perhaps pre-eminent over the centuries from Newton to Einstein. But many writers fail to mention James Clerk Maxwell’s Christian faith. The philosophy of modern secular science is governed by the NOMA principle, in which science and faith are considered non-overlapping, separate realms. After he died, one of his colleagues wrote: “We his contemporaries at college, have seen in him high powers of mind and great capacity and original views, conjoined with deep humility before his God, reverent submission to His will, and hearty belief in the love and atonement of that Divine Savior Who was his portion and comforter in trouble and sickness.” Like Maxwell, most Christians working in 21st century science would not condone separation of the realms as one of their paramount operational principles. Rather, they would endorse the Apostle Paul’s statement in Acts 17:28 as a guiding principle in every aspect of their lives: “In Him we live, and move and have our being.”
Maxwell’s theory of electromagnetism incorporated and unified the pioneering discoveries of electricity and magnetism from the previous 50 years. He discovered that visible light was an electromagnetic wave. He taught that many different electromagnetic wavelengths, longer and shorter than those of visible light, should be possible and anticipated their discovery. The complete range of wavelengths, from long to short, became known as the electromagnetic spectrum. Shortly after Maxwell’s death, radio waves and X-rays were demonstrated. Application of knowledge of the electromagnetic spectrum is a landmark advance in science. Without such application, our 21st century lives would be very different. Albert Einstein pronounced Maxwell’s work “the most profound and the most fruitful that physics has experienced since the time of Newton.”
The story of James Clerk Maxwell is one of unparalleled inspiration. As a young man he was gifted with curiosity and creativity. He never relinquished respect for the spiritual truths of his parents’ Presbyterian and Anglican traditions. Later, at age 22, he experienced what has been called an “evangelical” conversion. Thereafter, he never shied from expressing his deeply held Christian faith. There was never a hint of “God-of-the-gaps” explanations for any scientific principle he ever discovered. In addition to his cornerstone theory of electromagnetism which sets him apart, he investigated many other topics, including the nature of Saturn’s rings, color photography, viscosity of gases, and theory of heat.
He was ahead of his time in rejecting the use of bad science to promote a particular interpretation of Genesis scripture, pointing out that ongoing scientific discoveries would enlighten interpretation of scripture. He anticipated the modern discussion of design in the natural world by observing and describing “the ordered uniformity rather than the peculiarity and complexity of nature, as signs of the creator.” In many letters to his wife and others his profound faith was expressed: “Think what God has determined to do to all those who submit themselves to His righteousness and are willing to receive His gift. They are to be conformed to the image of His Son…” His advice to scientists and non-scientists alike was suffused with a Christian worldview: “I think that men of science as well as other men need to learn from Christ, and I think that Christians whose minds are scientific are bound to study science that their view of the glory of God may be as extensive as their being is capable of.”
Most science historians would acknowledge that Maxwell’s contributions to science stand out as perhaps pre-eminent over the centuries from Newton to Einstein. But many writers fail to mention James Clerk Maxwell’s Christian faith. The philosophy of modern secular science is governed by the NOMA principle, in which science and faith are considered non-overlapping, separate realms. After he died, one of his colleagues wrote: “We his contemporaries at college, have seen in him high powers of mind and great capacity and original views, conjoined with deep humility before his God, reverent submission to His will, and hearty belief in the love and atonement of that Divine Savior Who was his portion and comforter in trouble and sickness.” Like Maxwell, most Christians working in 21st century science would not condone separation of the realms as one of their paramount operational principles. Rather, they would endorse the Apostle Paul’s statement in Acts 17:28 as a guiding principle in every aspect of their lives: “In Him we live, and move and have our being.”
Sunday, December 21, 2008
Seeing the Light
“We don’t really see each other in this classroom. Instead, we only see the light that is reflected from each other.” This riddle-like proposition has always baffled science students when proposed in the classroom. Light is a type of energy which streams toward us from objects as close as the page you are now reading, or as far away as a galaxy a billion light years distant. When our eyes are open, information from billions of light data points streams into our eyes each millisecond. Each time we redirect our line of vision, our eyes receive information from a different set of light data points. Billions of retinal cells then spring into action, instantly transmitting billions of individual electrical messages to vision centers in our brain. The interpretation and meaning of the visual message is then riveted into our consciousness. The term “instant recognition” acquires a more noble meaning when we describe such wondrous events in this way.
Our knowledge of the nature of light has expanded enormously in the past century. Isaac Newton concluded in the 17th century that light was composed of particles. In the next centruies, scientific thinking wavered between two beliefs: either light is composed of particles or light is a wave. Many famous scientists weighed in on the question. Modern thinking endorses a wave/particle duality. Light behaves as if it were a wave and a particle. The discrete particles are called photons--massless packets of energy on a high speed journey.
The expression “seeing the light” means that we now understand what we formerly did not understand. Light is symbolic of knowledge and understanding. Light from the objects in our physical vision is saturated with information about the objects we are observing. We are able to perceive size, shape, color, and motion. These perceptions may help us make predictions and adjust our actions to our advantage. The Bible often uses the term LIGHT to communicate spiritual concepts. For example, “Your word is a lamp to my feet and a light for my path” (Psalm 119:105) and, “The unfolding of your words gives light” (Psalm 119:130 NIV). God’s word is light, a communicator of vital information about Himself, just as physical light streaming into our eyes from physical objects around us carries with it vital information about those objects.
As we study details of light, sound, or any other type of energy, we discover a world of intricacy and order. Research scientists in specialized fields are able to describe light and sound with the precision of mathematical equations. For the non-scientist, skilled professionals are able to communicate the apparent consistency and beauty of facts about these energy types, how they work, how they impact us, and how we apply knowledge of them. It is the opinion of many scientists who are Christians that nature’s orderliness speaks not only of the care God used when He created, but also of His very existence.
Our knowledge of the nature of light has expanded enormously in the past century. Isaac Newton concluded in the 17th century that light was composed of particles. In the next centruies, scientific thinking wavered between two beliefs: either light is composed of particles or light is a wave. Many famous scientists weighed in on the question. Modern thinking endorses a wave/particle duality. Light behaves as if it were a wave and a particle. The discrete particles are called photons--massless packets of energy on a high speed journey.
The expression “seeing the light” means that we now understand what we formerly did not understand. Light is symbolic of knowledge and understanding. Light from the objects in our physical vision is saturated with information about the objects we are observing. We are able to perceive size, shape, color, and motion. These perceptions may help us make predictions and adjust our actions to our advantage. The Bible often uses the term LIGHT to communicate spiritual concepts. For example, “Your word is a lamp to my feet and a light for my path” (Psalm 119:105) and, “The unfolding of your words gives light” (Psalm 119:130 NIV). God’s word is light, a communicator of vital information about Himself, just as physical light streaming into our eyes from physical objects around us carries with it vital information about those objects.
As we study details of light, sound, or any other type of energy, we discover a world of intricacy and order. Research scientists in specialized fields are able to describe light and sound with the precision of mathematical equations. For the non-scientist, skilled professionals are able to communicate the apparent consistency and beauty of facts about these energy types, how they work, how they impact us, and how we apply knowledge of them. It is the opinion of many scientists who are Christians that nature’s orderliness speaks not only of the care God used when He created, but also of His very existence.
Monday, December 15, 2008
Biometric Uniqueness
So you think you’re unique? Modern technology has affirmed what theologians have always known in a spiritual sense: Each of us is unique in the eyes of our Creator. That uniqueness also includes many different physical characteristics. A methodology called biometric verification has expanded far beyond the long-known handwriting analysis and fingerprinting. In the past few decades we have added, among others, voice prints, iris scanning, and DNA as identification tools. The latter two are as close to a sure thing as one could get. The chances of misidentification using them are virtually zero. The first method mentioned, voiceprints, graphically analyzes vocal sounds in a variety of ways. There is a musical quality associated with many of the sounds we hear, so I’ll use musical instruments to illustrate the point.
Consider a plucked violin string. Making our math easy, consider a string which vibrates back and forth 100 times per second. It would produce a sound of 100 hertz, displacing our eardrums 100 times per second. We would hear a “fundamental” pitch of 100 hz. The violin string would also vibrate in two parts, three parts, four parts, and so on. These string sections would produce pitches of 200 hz, 300 hz, and 400 hz, respectively, called overtones. The 200 hz tone is one octave higher, and each successive tone is higher, but by a smaller and smaller musical interval. What do we hear when the string is plucked? We hear only the pitch of 100 hz, but its sound is enriched and made unique by the overtones. Each instrument, when producing a pitch of 100 hz, sounds different from any other instrument because of the differing proportions and intensity of its overtones.
When I learned to play a baritone horn in high school, I quickly discovered that I could play many successive higher notes, without changing the fingering, just by tightening my lips in the mouthpiece. That’s because the entire column of air inside the horn was also vibrating as a half column, a one-third column, a one-fourth column, and so on. I could make the overtones sound alone by altering the mouthpiece conditions. Bugle players have no valves at all in their instruments. They create their melodies using only overtones, but they are limited to a smaller number of playable notes.
How many different human voices can you recognize? Dozens? Hundreds? The vocal cords and voice box of each person you know produce overtones slightly different from anyone else because the thickness, length, and physical quality of each person’s vocal cords are different from anyone else. This results in an endless variety of musical and vocal abilities and characteristics among our acquaintances. In other words, each person’s voice is unique. Beyond the physical processes of sound production, the miracle of the hearing process gives us even greater reason to acknowledge God’s wonders. This is a subject for a future post.
Consider a plucked violin string. Making our math easy, consider a string which vibrates back and forth 100 times per second. It would produce a sound of 100 hertz, displacing our eardrums 100 times per second. We would hear a “fundamental” pitch of 100 hz. The violin string would also vibrate in two parts, three parts, four parts, and so on. These string sections would produce pitches of 200 hz, 300 hz, and 400 hz, respectively, called overtones. The 200 hz tone is one octave higher, and each successive tone is higher, but by a smaller and smaller musical interval. What do we hear when the string is plucked? We hear only the pitch of 100 hz, but its sound is enriched and made unique by the overtones. Each instrument, when producing a pitch of 100 hz, sounds different from any other instrument because of the differing proportions and intensity of its overtones.
When I learned to play a baritone horn in high school, I quickly discovered that I could play many successive higher notes, without changing the fingering, just by tightening my lips in the mouthpiece. That’s because the entire column of air inside the horn was also vibrating as a half column, a one-third column, a one-fourth column, and so on. I could make the overtones sound alone by altering the mouthpiece conditions. Bugle players have no valves at all in their instruments. They create their melodies using only overtones, but they are limited to a smaller number of playable notes.
How many different human voices can you recognize? Dozens? Hundreds? The vocal cords and voice box of each person you know produce overtones slightly different from anyone else because the thickness, length, and physical quality of each person’s vocal cords are different from anyone else. This results in an endless variety of musical and vocal abilities and characteristics among our acquaintances. In other words, each person’s voice is unique. Beyond the physical processes of sound production, the miracle of the hearing process gives us even greater reason to acknowledge God’s wonders. This is a subject for a future post.
Tuesday, December 9, 2008
If a Tree Falls
An old philosophical riddle asks, “If a tree falls in a forest and no one is around to hear it, does it make a sound?” The debate over this riddle mainly relates to the difference between human perception and the existence (or non-existence) of reality existing outside human perception and awareness. Philosophers have debated similar questions for centuries.
With respect to events triggered by a tree falling in a forest, discoveries since the scientific revolution have enabled researchers to measure, describe, and understand in great detail the physical processes which occur in sound production and transmission. These include the cause of sounds, formation of air compressions and rarefactions, speed of sound, how it is reflected and absorbed, and numerous other events taking place in the sound transmission medium.
In Leviticus 26:36, the Old Testament warned that “the sound of a wind blown leaf” would throw the disobedient Israelites into a panic. In our last post we spoke of a much louder sound, that produced by human vocal cords in normal conversation. Several hundred compression waves--regions of slightly more densely-packed molecules--strike the eardrums of listeners each second. One may wonder how much pressure increase there is in one of these compressions compared with normal, undisturbed air. The answer is a startling, mere one millionth greater pressure than in normal air carrying no sound. That is a 0.0001 % increase, causing our eardrums to be displaced a mere billionth of a centimeter. If our ears were very much more sensitive, we may even be able to hear air molecules in a sound-free room vibrating with their normal kinetic (motion) energy.
The “If a Tree Falls” riddle does not distinguish between the physical events taking place in air and the subjective experience of the listener. The answer depends on whether we are describing physical events in air or subjective experiences in the listener’s mind, or perhaps, both. The physical events could be described as “sound.” Resulting subjective experience is described as “hearing.” The answer also depends on whether we are present in the forest, or located at a great distance where the physical sound cannot reach us. Physical sound is studied by the physical scientist. The subjective effect of sound on the listener is of intense interest to the physiologist or psychologist. But the natural curiosity and sense of wonder of “just ordinary folks” concerning sound and hearing are wonderfully supported by discoveries in both fields.
With respect to events triggered by a tree falling in a forest, discoveries since the scientific revolution have enabled researchers to measure, describe, and understand in great detail the physical processes which occur in sound production and transmission. These include the cause of sounds, formation of air compressions and rarefactions, speed of sound, how it is reflected and absorbed, and numerous other events taking place in the sound transmission medium.
In Leviticus 26:36, the Old Testament warned that “the sound of a wind blown leaf” would throw the disobedient Israelites into a panic. In our last post we spoke of a much louder sound, that produced by human vocal cords in normal conversation. Several hundred compression waves--regions of slightly more densely-packed molecules--strike the eardrums of listeners each second. One may wonder how much pressure increase there is in one of these compressions compared with normal, undisturbed air. The answer is a startling, mere one millionth greater pressure than in normal air carrying no sound. That is a 0.0001 % increase, causing our eardrums to be displaced a mere billionth of a centimeter. If our ears were very much more sensitive, we may even be able to hear air molecules in a sound-free room vibrating with their normal kinetic (motion) energy.
The “If a Tree Falls” riddle does not distinguish between the physical events taking place in air and the subjective experience of the listener. The answer depends on whether we are describing physical events in air or subjective experiences in the listener’s mind, or perhaps, both. The physical events could be described as “sound.” Resulting subjective experience is described as “hearing.” The answer also depends on whether we are present in the forest, or located at a great distance where the physical sound cannot reach us. Physical sound is studied by the physical scientist. The subjective effect of sound on the listener is of intense interest to the physiologist or psychologist. But the natural curiosity and sense of wonder of “just ordinary folks” concerning sound and hearing are wonderfully supported by discoveries in both fields.
Saturday, December 6, 2008
Sound Principles
Several of the body’s senses rely on energy signals received from locations remote from the body. Sound is one example. Our sense of hearing relies on sound, carried mostly by the medium of air. The Bible speaks of many sound-producing musical instruments, such as trumpets, flutes, harps, and cymbals. It also speaks of the sounds of wind, moving water, rainfall, and thunder, along with less pleasing sounds of chariots in battle and grinding millstones. The sense of hearing is one of God’s greatest gifts to humanity, but the means by which sound travels through the sound-carrying medium is unfamiliar to most.
First, we know that sound does not travel through a vacuum. It needs a medium such as air, although liquids and solids also carry sound. In a soundless room there are trillions of air molecules zigzagging around with kinetic energy, colliding with each other and with the objects in the room. Without a sound producer, however, not much else of interest is happening. The most common producer of sound in air is the vibration of a solid body such as a string, rod, bell, or the human vocal cords of our larynx. What happens in the air when vocal cords or other objects vibrate is fascinating.
The vocal cords of a typical man vibrate back and forth about 120 times per second during speech; the average woman’s cords vibrate 210 times, the average child’s 300 times. Try to envision a vocal cord vibrating outward just once. The surrounding free air molecules are slightly compressed for just an instant, creating a region of slightly greater molecular density. This is called a compression: the air pressure is slightly increased. The compression then starts traveling away while the vocal cord pops back to its original position. A low pressure area is created in this “pop-back” area because the air is slightly thinner. When the cord vibrates outward again, another compression is formed and starts to travel away. If we could visualize the situation we would see many areas of compression separated by areas of rarefaction all traveling away from the vocal cords.
If you have ever stretched a “Slinky” coil toy along the length of a table and given one end a series of quick tweaks, you could see the compressions traveling along the Slinky separated by the rarefactions. Comparing sound production in air to a Slinky is a strong analogy, except that Slinky compression waves are slowpokes compared with sound waves in air. Sound waves travel about 1100 feet per second, or about one mile in five seconds. During this Advent season, the sound of carols produced by voices, bells, and drummer boys will all be the result of air compression waves impacting your eardrums. Enjoy the celebration!
First, we know that sound does not travel through a vacuum. It needs a medium such as air, although liquids and solids also carry sound. In a soundless room there are trillions of air molecules zigzagging around with kinetic energy, colliding with each other and with the objects in the room. Without a sound producer, however, not much else of interest is happening. The most common producer of sound in air is the vibration of a solid body such as a string, rod, bell, or the human vocal cords of our larynx. What happens in the air when vocal cords or other objects vibrate is fascinating.
The vocal cords of a typical man vibrate back and forth about 120 times per second during speech; the average woman’s cords vibrate 210 times, the average child’s 300 times. Try to envision a vocal cord vibrating outward just once. The surrounding free air molecules are slightly compressed for just an instant, creating a region of slightly greater molecular density. This is called a compression: the air pressure is slightly increased. The compression then starts traveling away while the vocal cord pops back to its original position. A low pressure area is created in this “pop-back” area because the air is slightly thinner. When the cord vibrates outward again, another compression is formed and starts to travel away. If we could visualize the situation we would see many areas of compression separated by areas of rarefaction all traveling away from the vocal cords.
If you have ever stretched a “Slinky” coil toy along the length of a table and given one end a series of quick tweaks, you could see the compressions traveling along the Slinky separated by the rarefactions. Comparing sound production in air to a Slinky is a strong analogy, except that Slinky compression waves are slowpokes compared with sound waves in air. Sound waves travel about 1100 feet per second, or about one mile in five seconds. During this Advent season, the sound of carols produced by voices, bells, and drummer boys will all be the result of air compression waves impacting your eardrums. Enjoy the celebration!
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