Science
in Christian PerspectiveScience
in Christian Perspective
From JASA 9 (September 1957): 8-11.
In the course of preparing talks which would have both a scientific and a theological content, the author has found in the phenomena of solid-state luminescence a number of effects which illustrate spiritual truths in a striking manner. It must of course be emphasized that the effects to be discussed in this paper are simply illustrations of spiritual truths, and have no direct connection with the truths whatsoever.
An appreciation of these illustrations must be based on an elementary grasp of the mechanism of solid-state luminescence. We shall first therefore very briefly outline the pertinent information concerning luminescence for those who may not be familiar with it. Then we shall show how the basic phenomena of luminescence may be used to stage a pageant, as it were, with each of the phenomena illustrating a spiritual truth, and at the same time maintaining a consistent picture on both the scientific and the theological level.
A luminescent material (frequently called a phosphor) is a material which is capable of transforming invisible radiation, which it absorbs, into visible radiation, which it emits. Luminescence differs from incandescence in that the latter involves the utilization of high thermal energies to excite electrons at random throughout a material, whereas the former involves the conversion of absorbed radiation into emitted radiation at particular special sites in the material where electron excitation and de-excitation to produce emission occur exclusively. Thus incandescence involves heating the material and the emission spectrum obtained is characteristic of the temperature of heating, but not of the material; luminescence involves no heating and the emission spectrum is characteristic of the material.
Luminescent materials are in essence very simple. Ordinary table salt, for example, can be a luminescent material if treated in the proper way. The best luminescent materials consist of a highly purified major constituent with the properly chosen minor or impurity constituent (present in proportions of 1 to 1000 parts per million), which provides the sensitive special sites where luminescence can occur. These sites are frequently called luminescence centers.
Let us consider a typical luminescent material like zinc sulfide. Pure zinc sulfide (pure, that is, to the limit of spectroscopic detection) containing essentially only zinc and sulfur atoms, is practically non-luminescent. Small proportions of silver incorporated in this zinc sulfide, however, produce a material which emits blue light when excited by ultraviolet, electrons, or nuclear particles (that is, by any excitation of sufficient energy to excite or ionize luminescence centers). Copper impurity produces a material emitting green light, and manganese impurity produces a material emitting orange light. The color of the emission is a characteristic both of the impurity and of the material into which it is incorporated. The impurity disturbs its neighboring atoms in the crystal, producing localized regions where electrons can be excited to higher energy states and can then return to their ground state at a later time, giving up a portion of their energy as light when they return.
After the exciting radiation is turned off, the luminescence emission will decay to essentially zero in time ranging from microseconds to days or even longer. The actual decay time depends on the lifetime of excited electrons in metastable states before returning to the ground state of the luminescence center. There are two general types of metastable states: (1) the electron is not freed from the center but remains in a metastable excited state of the center; (2) the electron is freed from the center and may be temporarily captured at other places in the material called trapping centers, which are able to bold the electron for a length of time until the electron is freed again from the trapping center by using thermal energy present in the crystal vibrations.
In luminescent materials in which the electrons are free to move about through the crystal between the process of excitation and the process of emission, it is possible that the electron may be captured by other centers than the luminescence centers, which are able to dissipate the electron's energy as heat rather than as light. These poison centers are in competition with the luminescence centers for the free electrons and they reduce the over-all luminescence efficiency by transforming the energy of some of the electrons into useless thermal energy rather than permitting it to be converted into visible radiation. Impurities such as iron, cobalt, or nickel act as poison centers in zinc sulfide. They can have a severely deleterious effect on the quality of the luminescent material if present in only the smallest proportion: 1 part per million or less.
We mentioned above that electrons temporarily held in trapping centers can be released by acquiring sufficient thermal energy from the crystal vibrations. Alternatively such trapped electrons can be freed by absorbing the required energy from light of the proper wavelength; usually this wavelength lies in the red or infrared portions of the spectrum. If infrared radiation is allowed to fall on a luminescent material which has been excited and which is relatively free of poison centers, the sudden release of trapped electrons with their return to their ground state, producing emission, causes a sudden increase in brightness; this effect is called infrared stimulation of luminescence. On the other hand, in materials with poison centers, it is possible for the infrared to act in such a way that effectively the electrons freed from traps are captured by the poison centers rather than by the luminescence centers. The result is a sudden decrease in emission intensity; this effect is called infrared quenching of luminescence,
Thus we
have, very briefly set the stage for our pageant. It is now necessary for us to
introduce the cast and proceed with our illustrations of spiritual truth.
*Research solid-state physicist at the RCA Laboratories, Princeton, N.J.
Dramatis
Personae
The Natural
Man
Material without luminescence centers, either with or
without poison centers
The Study and Preaching of the Word Exciting radiation; e.g.,
ultraviolet
The New
Man
Material with luminescence
centers
Fruit of the Christian Life
Luminescence emission
Sins
Poison centers
Backsliding: Loss of
Communion Decay of
emission
Spiritual
Strength
Trapped electrons
Times of
Adversity
Infrared
When ultraviolet falls on a material without luminescence centers, regardless of whether poison centers are present or not, there is no appropriation of the ultraviolet to produce luminescence emission.
[The universal invitation of the Gospel goes forth to all men through the preaching, reading and study of God's Word. But unless the heart of man has been prepared by the Holy Spirit, the invitation falls on deaf ears. Sin blinds the spiritual heart of natural man. Even the natural man who stands in the world's righteousness, free from obvious sin, does not have within himself the power to appropriate the invitation of salvation for himself-to take for himself the "whosoever" of the promise.]
When luminescence centers have been properly incorporated within a material, the material can appropriate the ultraviolet to produce visible emission originating at those very centers.
[The Holy Spirit acts in accord with the purpose of God, to give the new birth to God's elect. He forms a new creation within man so that the invitation of the Gospel and the study of the Word are received with joy and turned into service to God. It is the new nature, acting in opposition to the old nature which still remains, which is the source for all Christian service to the glory of God.]
Different luminescent materials have different emissions, varying in both color and intensity from material to material. Materials with a high proportion of poison centers present will have a much lower brightness than they would have if the poison centers were absent. For all materials the emission intensity increases as the excitation intensity increases.
[The Holy Spirit gives different gifts to different men. All who receive the new birth receive salvation, now and forever, but they are endowed in various ways for particular places in the work of the Kingdom. Such endowments vary both as to type and as to the degree of ability, but regardless of this, each man's service grows in both quality and quantity as his communion with God and his knowledge and application of the Word increase. just as surely, the presence of sin in his life will detract from his service and testimony; as long as the sin remains unrepented and unconfessed, he will fall short of the place in God's service which he should be filling.]
If the ultraviolet is turned off, the luminescence emission will decay until finally there will be no emission left. If the previous exposure to the ultraviolet has been short, or if the ultraviolet intensity is weak, or if the material does not have many trapping centers, the decay will be fast. If the material has many trapping centers and has been excited for a long time by high intensity ultraviolet, the decay will be slow and appreciable brightness can persist for some length of time. But, in either case, the emission intensity starts to decrease when the ultraviolet is turned off and continues to decrease until there is nothing left.
[Maintenance of a healthy Christian life of confidence and service requires unbroken feeding on the Word of God and communion with God in prayer. If regular meditation and study of the Word is discontinued, the quality of that Christian's life will start to decay. If the Christian has only a superficial knowledge of the Word and has not built up any reserves of spiritual strength within himself, it will not be long before his Christian testimony has completely disappeared. If the Christian has for a long time been a consecrated student of God's Word and has developed a reservoir of spiritual strength upon which to call in time of need, some semblance of testimony and service may persist for a long time. But, in either case, the quality of Christian service starts to drop as soon as separation from the Word is caused, and will continue to drop to nothing unless the Christian turns again to God in repentance and follows the guidance of the Holy Spirit back into a healthy spiritual life.]
When infrared falls on a luminescent material relatively free of poison centers, the sudden increase in electrons freed from trapping centers causes a sudden increase in the emission intensity. But when infrared falls on a luminescent material containing an appreciable proportion of poison centers, the trapping centers are drained free of electrons whose energy is wasted in the form of heat at the poison centers. Such effects ,of infrared stimulation and infrared quenching are particularly noticeable during the decay of emission.
[When adversity comes into the life of a Christian who has been in close communion with God and His Word, and who has built up a reserve of spiritual strength from this communion, the effect of adversity is to call upon those spiritual reserves in order to bring forth even greater service to God. But when adversity comes into the life of a Christian whose communion with God has been weakened by persisting in some favorite sins, the experience of adversity drains away whatever reserves of spiritual strength were present and leaves the Christian in a weaker position than before.]
A fitting Epilogue to the previous drama is provided by considering the entire field of scientific research as an illustration of Christian research in the understanding of the ways of God. This illustration is summarized in the following Table:
Search for knowledge
of
nature
God and His purpose
Develops hypotheses about
nature
God and His purpose
Tests his hypotheses
by
physical
experimentation
study of God's Word
Hypothesis good
if
confirmed by
experiment
confirmed by the Word
Carelessness leads
to
errors in
measurements
errors in interpretation and exegesis
and calculations
Carefulness leads
to
closer understanding of nature closer
understanding of God and His purpose
Being human, both the
scientist and the Christian are limited in the extent to which they can
adequately conceptualize; in developing their understanding they will each be
led to construct hypotheses in their own minds which seem to be good.
They both then desire to know-is my hypothesis really a good one?
The scientist tests his hypothesis by contacting the source of his information
concerning nature; i.e., he performs a physical experiment. If the results
of his experiment agree with those of his hypothesis-his hypothesis can be
accepted as a good tentative one. To establish its reliability further, the
scientist must show that his hypothesis and the results of many different
pertinent experiments continue to agree. In the same way, a Christian tests his
hypothesis about God and His purpose by contacting the source of his information
about God, the Revelation given to men in the Bible for that purpose; i.e., he
studies the Scriptures. He must not be content to confirm his hypothesis with
one or two Scriptural "experiments," but he must demonstrate that the
whole of Scripture, interpreted in the light of Scripture, confirms it.
A careless scientist will overlook vital factors in his experiments or permit preconceived notions to affect the observations he chooses to consider; thus he may reject good hypotheses and cling to poor ones. A careless Christian will overlook vital passages in the Scriptures or will be blinded to unifying interpretations by traditional prejudices; thus he also may miss the good hypotheses and hold to poor ones.
A careful scientist will proceed from questioned hypotheses, to good tentative hypotheses, to accepted theories about nature; in so doing he will bring his understanding of nature ever closer to a reliable description of it. A careful Christian will grow in his understanding of God and His purpose, and by possessing a sound knowledge of the teachings of God, will go on to applying these teachings in his life; in so doing he will grow in sanctification and in useful service to the glory of God.
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Of course there is one very important difference between the two types of this illustration. Nature does not exist between the covers of a book; the scientist's data are always reaching out to reveal new and unforeseen facts about nature. Because of this, all of the scientist's theories, based on his good hypotheses of the past, are only temporary, and may be proven only fair approximations or basically incorrect in concept after all. The data of the Christian, on the other hand, are in essence complete in the Bible, available for objective analysis by the best methods of consecrated scholarship. There may yet be some changes in interpretation on minor issues, but the hypotheses which the Christian proves to be good become his doctrines and they have an eternal validity. They have this eternal validity because they are based on the complete and perfect revelation of God, Who does not change and Who knows the end from the beginning. That is the essential characteristic of the Christian data: that they are not based on the knowledge which man has obtained about God by his experience (as do his scientific data) but rather upon the knowledge which God has given in completeness.