Light-Travel Time:

Evidence for an Old Universe

One of the simplest arguments for an earth much older than a few thousand years comes from starlight. Light travels outward from its source at a large but finite rate - 186,000 miles per second, or about 6 trillion miles per year. In fact, astronomers define a distance unit, the light-year, as how far light travels in one year.

THE ARGUMENT

If the universe were only a few thousand years old, we would expect to see no objects more distant than a few thousand light-years away. But, as a matter of fact, we do see objects much further away than this. Most of the stars in our Milky Way galaxy are further, up to nearly 100,000 light-years away. The nearest large galaxy beyond our Milky Way is the Andromeda Galaxy, about 2 million light-years distant. The furthest galaxies we see are several billion light-years from us. And the most distant objects which we can observe, called quasars, range up to 10 billion light-years away (Pasachoff, 1989, chs 5 & 15). Thus the universe is most naturally understood to be greater than 10 billion years old.

This argument depends on several assumptions which we need to consider in order to have some feeling for how compelling the argument is. There are three such assumptions we should consider. Each is a very natural assumption, but it is possible that one or more of these is mistaken. Let us look at each in turn.

ASSUMPTION #1: CONSTANT SPEED OF LIGHT

The first assumption is that the speed of light is constant (or nearly so) throughout space over the history of the universe. If this is not so, then perhaps light travels faster in other places than it does near us, or perhaps it travelled faster in the past than it does now. Notice that this assumption does not require that the speed of light be exactly constant, but only that it not be drastically different elsewhere or at another time. To be able to see objects 10 billion light-years away from us if the universe is only 10 thousand year old, the speed of light must average more than a million times faster elsewhere than it does here, or must have been similarly larger in the past than it is now. There is no observational evidence for anything of this sort.

It is true that Barry Setterfield and others have argued there is evidence for a decrease in the speed of light in the past couple hundred years. But this decrease (which is disputed in any case) amounts to only a few percent at most, so they must assume that the decrease was much faster early in earth's history than it is now in order to bring light here from the most distant objects in just a few thousand years (Norman & Setterfield, 1987).

But if the light speed was only thousands of times faster early in human history than it is now, then Einstein's equation E = mc² means that masses must have been millions of times smaller at that time in order for energy to be conserved. If so, then neither humans nor air would have been heavy enough to keep from floating away from our planet and life would have been impossible. This obviously was not the case, so it does not appear that the speed of light has changed in such a way as to avoid an old universe (Newman, 1991).

ASSUMPTION #2: LARGE DISTANCES

The second assumption is that distance measurements to objects beyond a few thousand light-years are sufficiently accurate to guarantee that these are millions or billions of light-years away and not just thousands.

Distances to relatively close astronomical objects are measured by a geometric technique similar to that used in camera range finders or on artillery range finders such as were used on battleships before the advent of radar. The object is looked at from two different locations, and the difference in apparent position is measured to calculate the distance. The effect can be illustrated by holding up your finger and looking at it against a wall as background first with your left eye and then with your right. Your finger will appear to jump back and forth against the wall. For stars, the two different locations are the position of the planet Earth six months apart (on opposite sides of its orbit), and the shifts even for close stars are very small, a few ten thousandths of a degree. Yet the distances of stars out to perhaps 100 light-years can be measured by this technique.

Distances to objects further away than this are estimated by using statistics derived from the stars within 100 light-years. It is observed that there is a simple relationship between star color and actual brightness, such that blue stars are brighter and red stars dimmer. This is because most stars belong to the grouping called the ``main sequence,'' in which stars are burning their hydrogen into helium, and there is a simple relation between surface temperature (star color) and brightness or luminosity for such stars. This has been demonstrated with computer models for how stars burn. Once the actual brightness of a star is known, its apparent brightness as viewed from the earth is a measure of how far it is away from us. This technique of using main sequence stars not only works for stars closer than 100 light-years, it gives us distances to stars out to a few 100 thousand light-years. Thus there appear to be many stars in our own galaxy that are more than ten thousand light-years away, and the stars in nearby galaxies range up to several 100 thousand light-years away. Beyond this distance it is not possible for us to detect main sequence stars with our telescopes.

For greater distances, use is made of variable stars, one class of which varies with a regular period and has a longer time-span between dim and bright the brighter it actually is. These so-called Cepheid variables may be used to measure distances out to some 10 million light-years. It appears also that the brightest stars in galaxies and the brightest globular star-clusters in galaxies have a maximum brightness, which provides us with distance measurements out to some 100 million light-years. Beyond that distance, it appears that the brightest galaxies in galaxy-clusters has a maximum, and this gives us distance measurements beyond a billion light-years. Thus it appears that we are seeing objects which are more than one billion light-years away, and that the universe is more than one billion years old.

Some have tried to argue that we are not really seeing this far into space. Harold Camping, for instance, argues that only the first method described above for measuring distance is any good, and that all the stars we see are actually only a few light-years further away than the closest ones. But this requires that the very dim stars - which look like they are far away - are actually rather close, and therefore very small. However, Camping has no explanation for how such small stars could hold together (since their masses would produce too little gravity to hold such hot gas) nor how they could burn (since the nuclear reaction which makes stars shine requires a large mass to get hot enough inside). Is it really credible that all the stars, star clusters, galaxies and galaxy clusters we see are small objects only a few light-years away? Camping's argument is just an attempt to avoid the natural conclusion of an old universe without any supporting evidence (Newman, 1982).

Another proposal, using the work of Moon and Spencer, argues that light travels a different route though space than does a meteor or spaceship - that light travels in curves with a radius of 5 light-years rather than in straight lines. Thus the most distant objects we see are really only about 10 light-years away, and that we see multiple images of these to account for all the objects we see. The work of Moon and Spencer in this regard is flawed; see Phillips (1988). Even if it were not, it would not solve the light travel-time problem, as the more distant objects would be images of nearby stars for which the light would have travelled millions of times around the circle and would have taken many millions of years to have done so. In any case, is it really credible that all the stars-clusters, galaxies, and galaxy-clusters we see are just multiple images of less than 100 stars within 10 light-years of us? Again, it looks like this scheme was concocted to avoid the scientific evidence.

ASSUMPTION #3: REAL SOURCES

The third assumption is that the light we observe when we look at the stars at night actually comes from the objects we observe. This again is the natural assumption one would make, though we sometimes see images of people that only come from a drawing which an artist has made.

The commonest attempt to avoid an old universe argues that the light imaging objects more than 10,000 light-years away never left the objects it pictures. The light, they say, was created on the way, since God wanted us to know that these distant objects existed and it would otherwise take billions of years for some of these images to reach us.

This suggestion raises a serious theological problem involving the truthfulness of God. Consider: when we look at our sun, we see what was happening on the sun (movement, rotation rate, sunspots, flares, etc.) as it was about 8 minutes ago when the light we see left the sun. When we look at the next nearest star, we see what was happening about 4 years ago, when the light we see left that star. When we look at a star 8,000 light-years away, we see what it was doing 8,000 years ago. But when we look at a star (say) 12,000 light-years away, we do not see what it was doing 12,000 years ago, because (by this argument) the star didn't exist. Instead we see what it would have been doing if it had existed, but it didn't - fictitious history! Not just "appearance of age," but a full, complex history of events that never happened. And not just for a few isolated objects, but for the vast majority of stars and star-clusters, and for all the galaxies and galaxy-clusters in the universe. To such extremes are we led if we are determined that we must interpret the Bible to teach a young earth, in spite of the evidence God has provided us in nature.

In harmonizing the revelation God has provided us in his Word, the Bible, and in his world, the universe, it seems to me that it is much preferable to spend our efforts on models that do not require us to believe that God has given us fictitious history - either in Scripture or in nature.

Dr. Robert C. Newman

References

Newman, R. 1991. ``An Ancient Historical Test of the Setterfield-Norman Hypothesis.'' Creation Research Society Quarterly 28:77-78.

Newman, R. 1982. ``A Critical Examination of Modern Cosmological Theories.'' IBRI Research Report 15.

Norman, Trevor and Barry Setterfield. 1987. The Atomic Constants, Light and Time. Flinders University. Australia.

Pasachoff, Jay M. 1989. Contemporary Astronomy. 4th ed. Saunders. New York.

Phillips, P. 1988. ``A History and Analysis of the 15.7 Light-Year Universe.'' Perspectives in Science and Christian Faith 40:19-23.