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A World Without Rainbows?

by Wayne Anderson

The following article is from Free Inquiry magazine, Volume 21, Number 3.

And God said, This is the token of the covenant which I make between me and you and every living creature that is with you, for perpetual generations: I do set my bow in the cloud, and it shall be for a token of a covenant between me and the earth.  Genesis, chapter 9, verses 12–13

One of the difficulties in adopting a literal interpretation of the Bible is that you can wander off into some pretty strange territory. Take, for example, the Genesis quote above. In it, God promises Noah that he will never again drown the world and seals his promise by creating the rainbow. Interpreted as a just-so story, it is a poetic little myth accounting for a beautiful natural phenomenon. Taken literally, however, it leads Christian fundamentalists into trouble.

For the symbol of God’s promise to mean anything, we must assume that rainbows did not previously exist. The necessary ingredients for a rainbow are light and water droplets suspended in the air, which breaks down the light into different colors. Since rain, a natural occurrence, did not seem to startle Noah or his contemporaries, it seems safe to assume that rain drops existed before the Flood. We know that light already existed from verse 3 of chapter 1 of Genesis, and God’s reference to the “green herb” just before the rainbow covenant implies the presence of color. Therefore the necessary ingredients were already present before the Flood, but they failed to make rainbows. Why?

A rainbow is created when sunlight enters water droplets in the air. The different wavelengths (colors) of the light have slightly different refractive indices in the water. This difference causes each wavelength to bend through a slightly different angle in the drop, thereby dispersing the light into its component colors.

For a rainbow not to be formed, the light must not have been dispersed by the water. But this dispersion is caused by the interaction of the electromagnetic waves of the light with the electrical charges in the atoms of the water, a process governed by the laws of electromagnetism and quantum mechanics. The appearance of a rainbow after the flood implies that God had suddenly altered the fundamental laws of nature. But these laws affect much more than water droplets. They also determine the structure of the atoms. Changing the natural laws would therefore change the atoms, which would in turn affect the light they give off. As is well established by observation, each atom gives off its own unique set of wavelengths of light, called the “spectrum” of the atom. Atomic spectra in pre-rainbow times would have been different from those in the post-rainbow era. Now we have a testable prediction.

The obvious place to look for this effect is in astronomy, because, by viewing the light from ever-more distant stars, we are looking backward in time. Light from sufficiently remote stars was emitted by pre-rainbow atoms and has been traveling through space ever since. Therefore the spectra of those distant atoms should differ markedly from the spectra coming from nearby post-rainbow atoms.

When did the Flood occur? Establishing the date can be a bit dicey, but the ever-resourceful Bishop Ussher put it at 2,349 b.c.e. or 4,348 years ago.1 Since Christian fundamentalists favor his age for the Earth, adopting his Flood date should offend few.

Using Ussher’s calculation, we should find a sharp discontinuity in the appearance of atomic spectra at a distance of 4,348 light years. Light from more distant stars has been traveling for more than 4,348 years and hence came from pre-rainbow atoms, while light from closer stars originated in post-rainbow atoms. Does such a discontinuity exist? Of course not! Even if we try other reasonable dates for the Flood, we never find such a discontinuity.

What does this little exercise tell us about the Bible? Not much, except not to take it literally. Will it convince hardcore Christian fundamentalists? Forget it!


1. This date comes from The Mound Builders by Robert Silverberg (Ohio University Press, 1986), p. 59.

Wayne Anderson teaches physics and astronomy at Sacramento City College. He has written on pseudoscience in Skeptical Inquirer and the New York Times.

[*] Secular Humanism Online Library

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