The light of the world

[Guest post: The following is an extended version of an article prepared for publication in print by Dr. Ján Morovič, which is reproduced here with the author’s permission.]

By pronouncing “Let there be light.” (Genesis 1:3), God spoke it into being and when he became incarnate in the person of Jesus, he identified himself with it by proclaiming: “I am the light of the world. Whoever follows me will not walk in darkness, but will have the light of life.” (John 8:12). Jesus even attributed that same nature to us, when turning to the crowd who had just heard him preach the beatitudes, and saying: “You are the light of the world.” (Matthew 5:14-15). Light was also the sign by which Jesus’ divinity was manifested to Peter, James and John on Mount Tabor, an event about which Matthew wrote: “[H]e was transfigured before them; his face shone like the sun and his clothes became white as light.” (17:2). Finally, completing the arc started in Genesis, the New Testament ends by foretelling – in its last chapter – a definitive victory of light, where those gathered around God at the end of time are described as follows: “Night will be no more, nor will they need light from lamp or sun, for the Lord God shall give them light, and they shall reign forever and ever.” (Revelation 22:5).

Not only is light singled out in Scripture, and existentially identified with God and his sons and daughters, but it is also presented as the means by which understanding comes about. St. Paul exhorts the first Christians in Ephesus to “[l]ive as children of light” (5:8) and emphasizes the tight link between light and vision: “But all things become visible when they are exposed by the light, for everything that becomes visible is light. […] Watch carefully then how you live, not as foolish persons but as wise.” (5:13,15).

Such an understanding of light is, in fact, very close to how contemporary science defines it: as “radiation […] considered from the point of view of its ability to excite the human visual system” (CIE, 2011). Light is fundamentally about the effect of matter on human sensory perception. The only thing that makes the range of electromagnetic radiation with wavelengths between around 400 and 700 nanometers be light is that our eyes are lined with cells in which oxidation takes place when such radiation is incident on them. This, in turn, triggers an electrical signal that passes through an interconnected sequence of neural layers, leading to the back of the brain, where such signals are further processed in dramatically complex and varied ways that lead to our visual experiences.

The evolution of vision, which originated during the lower Cambrian period 508 million years ago (Parker, 2009) in the photoreceptor proteins of single-cell organisms, has reached a remarkable degree of sensitivity to light in humans. For a start, our eyes go to extraordinary lengths to detect light. A single photon incident on a photoreceptive rod cell in a human retina triggers a signal, and even though it takes five to nine photons landing on such a cell for at least 100 milliseconds for the signal to make it past the visual system’s noise suppression, reach the brain and result in conscious perception (Hecht et al., 1942), the staggering degree of the eye’s sensitivity becomes clear when these numbers are put into perspective: a single candle emits 5 million billion (i.e., 5×10¹⁵ - a quadrillion!) photons during such a 100 millisecond period. Put differently, a single candle could be seen in complete darkness from a distance of 30 miles between two mountaintops.

As if this wasn’t enough, our eyes go further still. Instead of simply relaying signals from the array of light-sensitive cells that line their backs, such signals are first combined so that the relationships of a signal from one cell with those from cells around it are amplified. This center-surround mechanism (Wandell, 1995) means that the boundaries between differently-colored regions in our environment are emphasized. Further down the neural pathway from the eyes to the brain, in the lateral geniculate nucleus, the signals from cells sensitive to different ranges of radiation wavelengths are again processed and differences between opponent colors: red-green, yellow-blue and black-white are also enhanced (de Valois et al., 1966). As a result, the signal that originates in the light-sensitive cells of our eyes is enhanced both for spatial and color discrimination, even before it is reaches and is processed and interpreted by the brain and leads to a conscious experience.

What does all of the above mean though, and how can we even begin to reflect on Scripture and the findings of contemporary science side-by-side? Even though Scripture is not and does not claim to be science, and, e.g., the Genesis account of creation is better thought of as symbolical (like the Catechism of the Catholic Church teaches (§337)) or as myth, this does not mean that it “refer[s] to fictitious-fabulous content, but simply to an archaic way of expressing deeper content.” (John Paul II, 2011). The truth revealed in Scripture, the truth sought by empirical and scientific means and even the truth expressed in art are not distinct truths though, and instead present different modes of knowledge of the one reality. John Paul II derives this position from the principle of non-contradiction, whereby truth cannot contradict truth. Hence, the truth, which

“God reveals to us in Jesus Christ, is not opposed to the truths which philosophy perceives. On the contrary, the two modes of knowledge lead to truth in all its fullness. The unity of truth is a fundamental premise of human reasoning, as the principle of non-contradiction makes clear. Revelation renders this unity certain, showing that the God of creation is also the God of salvation history. It is the one and the same God who establishes and guarantees the intelligibility and reasonableness of the natural order of things upon which scientists confidently depend, and who reveals himself as the Father of our Lord Jesus Christ.” (John Paul II, 1998)

During this Year of Light, proclaimed by the United Nations for 2015, we can look at the insights about it both from Scripture and science, and form a picture that is richer than either of them would provide by themselves. Instead of considering these two modes of knowledge as competing with each other, or requiring each other for justification, they stand on their own feet and complement each other. With respect to light, science shows us its fundamentally relational nature - both because of its very definition pointing to the relationship between humans and the world around us, and because of how human vision is tuned to the perception of relationships among the matter that acts upon it. Science also underscores the importance that light has for life, by showing the extraordinary sensitivity that has evolved to it. Scripture, in turn, identifies light with God, with those who follow him, and with the destiny of creation, and it points to light as a means for attaining wisdom and persistence in living as God’s children.

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References
CIE (2011) CIE S 017/E:2011 ILV: International Lighting Vocabulary, CIE, Vienna, Austria
De Valois R. L., Abramov I., Jacobs G. H. (1966) Analysis of Response Patterns of LGN Cells, Journal of the Optical Society of America, 56:966–977.
Hecht S., Schlaer S., Pirenne M. H. (1942) Energy, Quanta and vision, Journal of the Optical Society of America, 38:196-208.
John Paul II (2011) Man and Woman He Created Them, Pauline Books and Media
John Paul II (1998) Fides et Ratio, Encyclical Letter, §34
Parker, A. R. (2009) On the origin of optics, Optics & Laser Technology 43(2):323–329.
Wandell B. A. (1995) Foundations of Vision, Sinauer Associates, Sunderland, MA. [UPDATE on 2nd July 2015: An abridged version of this post has now been published in New City Magazine.]