A common young earth argument for a young earth is that the velocity of light has been decreasing exponentially since the creation of the universe.1 One of the most significant implications of a rapidly decaying speed of light is that the universe could actually appear to be much older than it really is. This is because, in the past, the speed light would have been much faster, meaning that light would have traveled much farther, making the universe appear old even though it were young. This page will examine the problems associated with the theory, both in terms of how the universe works, and the data used to support this claim.
Theoretical problems abound with the idea that the velocity of light might be changing with time. Einstein's famous theory of general relativity is the most serious challenge. To remind you, the theory is reproduced below:
E = mc2
where E = energy, m = mass, and c = velocity of light
Although still called a "theory," Einstein's equation has survived the tests of nearly a century of observational confirmation.2 The equation above shows that any change in the velocity of light results in huge changes in either the amount of energy or mass in the universe. For example, a modest 2-fold decrease in the velocity of light would result in a 4-fold decrease in the amount of matter, or amount of energy in the universe. There is no evidence that any of these kind of changes are occurring in our universe.
 Figure 1. Velocity of light for 193 values for the years beginning in 1675.3 |
Not only are there theoretical problems with the decay of the speed of light,
but the data used to support this concept is less than convincing.3
Figure 1 (right) shows the data from 193 studies beginning in 1675. The only
thing notable about the data is how constant the speed of light has been using
these 193 uncorrected values. It can be seen that the deviation from the linear
regression is largest in the past (which would be expected, given the primitive
nature of the early experiments). Very little deviation from the regression
line can be seen for values reported during the last 100 years. The
"R2" value reported on Figure 1 is a measure of the kind of
linear relationship represented by the data. An R2 value of 1.0
indicates a perfect linear relationship between the two variables (in this case,
between the date and the value of C). A value of 0.0 indicates that there is no
relationship between the two variables. In Figure 1, the R2 value of
0.0005 indicates that there is no significant relationship between the velocity
of light and time.
 Figure 2. Velocity of light for 120 selected values for the years from 1727 to 1983.3 |
Not being content with these numbers, young earth creationists selected and
corrected the values to produce the figure seen to the left (Figure 2). Some of
the best values were eliminated because they did "not come under the
proposed hypothesis." These numbers included the values that were
determined using laser measurements and the atomic clock.
 Figure 3. Velocity of light for 114 of 120 selected values for the years from 1800 to 1983.4 |
Looking at the above figure, one notes that the slope of the line is largely
determined by a few points done in the 1700's, at a time when methods were crude
and very susceptible to large errors. A plot eliminating the first 6 values from
figure 2 (all those before 1800), produces the plot seen in Figure 3 (right). As
can be seen, the values recorded from 1840 to 1983 have not significantly
changed over that period of time.
A constant speed of light is a problem to young-earth creationism, since the nature of the creation (i.e., the large distances between galaxies) requires either an old universe (required for light from the oldest galaxies to travel to earth) or one that was made to deceive people into thinking it was old. An exponentially decreasing speed of light solves both problems, since the large distances between galaxies could be explained by a much faster speed of light in the past, and God would not have had to create the universe with "appearance of age." However, the young earth hypothesis that the velocity of light has been decreasing with time is contradicted by both theoretical and observational conflicts.
Last updated 05/29/01