Science and Religion at the Speed of Light

In the last blog, I promised to demolish the Genesis account of creation without referencing Darwin, evolution, or anything to do with Earth’s geology.  Instead, I’m going to build my case with ironclad facts from the fields of physics and astronomy, facts that have been established over the course of hundreds of years of painstaking inquiry into the nature of physical reality. 

Although no one knew it at the time, Genesis began to unravel the very first time somebody looked at the planet Jupiter through a telescope.  As most of you know, the person in question was Galileo, and the time was the beginning of the 17^th century.  To his great astonishment, Galileo observed four points of light surrounding the giant planet.  Observing them over time, he noted that the positions of the lights changed in ways that made it obvious that they were satellites, orbiting Jupiter in the same way that the planets orbit the Sun.

One of these lights, Jupiter’s moon Io, is so close to Jupiter that it completes a full orbit in only a couple of days, going behind Jupiter for a brief period each time (in astronomy-speak, Jupiter “occults” Io).  Later on in the 17th century, the prominent Danish astronomer Ole Roemer systematically recorded the timing of these occultations over an extended period stretching from 1671 to 1677.   Combining his observations with those of some of his contemporaries, Roemer discovered a remarkably systematic pattern: the time between occultations gets steadily shorter as the Earth’s own orbital motion brings us closer to Jupiter, and then lengthens again as the Earth moves farther away.  Reporting his results to the French Academy of Sciences, Roemer hypothesized that

This… appears to be due to light taking some time to reach us from the satellite; light seems to take about ten to eleven minutes [to cross] a distance equal to the half-diameter of the terrestrial orbit

Clever fellow that he was, Roemer combined this time difference with early estimates of the “half-diameter of the terrestrial orbit” (the distance from the Earth to the Sun, from which he could easily calculate the difference in distance between the Earth and Jupiter when they are closest together compared to when they are furthest apart) to compute the speed of light for the first time (prior to that point, many prominent scientists, Newton included, believed the speed of light was infinite). 

The value Roemer obtained, about 211, 000 kilometers per second, is considerably lower than the currently accepted value of 299,792.458 kilometers per second.  That’s because the radius of the Earth’s orbit wasn’t yet known with any precision in his time.  Still, Roemer’s calculation was in the right ballpark, and the realization that the speed of light had a fixed value, instead of being either immeasurably high or infinite, marked a major advance in the history of science and our understanding of the natural world.  For example, we’ve already seen how fundamental a role the finite speed of light plays in generating time dilation effects.  In subsequent blogs, we’ll discover just how big a nail the speed of light was to drive in the coffin of the biblical story of creation.  But first, we have to identify another important nail, in the form of the distance between the stars and us.  That is the topic of the next blog.