Creation Science
Age of the Universe
Stellar Evolution

High Resolution Solar Spectrum from the 150 foot Solar Tower Telescope at Mt. Wilson Observatory

Young-Earth creationists hold that the entire universe, and not just the Earth, is 10,000 years old or less. They hold to this position despite the fact that it stands in stark contrast to virtually everything learned in a wide variety of scientific disciplines. Geophysics, astrophysics, cosmology, they all show that the Earth is billions of years old, and the stars & universe are even older.

Stellar evolution is one of the most extensive disciplines of study in astrophysics; it is the study of the life cycles of stars. Like biological evolution, which deals with the evolution over time of populations of stars, so does stellar evolution deal with populations. But, unlike its biological counterpart, in which only populations and not individual creatures evolve, in stellar evolution, it is the individual star which evolves. Each star passes through distinct stages in its lifetime, and these stages can be predicted and modeled by applying the principles of physics. It certainly is no easy task, but it is comprehensible nevertheless.

But of course, young-Earth creationists cannot tolerate or allow such concepts, for stellar evolution in the standard form takes a long time, well in excess of the paltry few thousand years the young-Earthers will allow. One of the founders and leaders of the modern young-Earth movement, Henry M. Morris, tells us what he thinks about stellar evolution ...

"Furthermore, they say, we can still see stellar evolution taking place in the heavens. We can see stars, galaxies, and planets in various stages of this cosmic evolutionary process.

No we can't! The heavens and the earth were "finished." All of God's heavenly "works were finished from the foundation of the world" (Hebrews 4:3). As long as people have been looking at the stars, they have never seen a single star evolve. We do occasionally see stars disintegrate, but that's not evolution! The tragedy is that so many leaders of Christian colleges, publications, churches, and para-church organizations are blindly following these latter-day apologists for modern scientism.

Perhaps the greatest anomaly in this situation is the incredibly weak scientific case for the whole scenario of cosmic evolution. There can be no "experiments" or "observations" of stars evolving, in the very nature of the case, so it cannot be scientific, though it may be naturalistic - all based on mathematical manipulations, computer simulations, and atheistic or pantheistic philosophies."

Henry Morris in Creation by Inflation and Quantum Fluctuation
Back to Genesis 129a, August 1999. The italicized emphasis is from Morris.

This is much the same as Morris has said from the beginning, so I see no need for repetitive quotes from the past. Other creationist sources repeat essentially the same line of reasoning, namely that since we have not actually seen a star actually evolve right before our very noses, then we cannot assume that they evolve at all. Indeed, Morris explicitly says that it cannot even be science, and he is not alone in this opinion amongst young-Earth creationists.

Morris' denial that the study of stellar evolution is even science at all can only seem bizarre to anyone who has actually done science, or ever learned what it is. Thousands of stellar astrophysicists, in almost every country in the world, will be greatly surprised to discover that what they do is not even science. Perhaps it is curious that only Morris seems to have spotted this essential defect in the discipline, but it is the message that really counts, and not the messenger. And so we should explore the questions. Is the study of stellar evolution science? And if it is, is it good science?

Is it Science?

Let's handle the easy one first. Morris' intent & meaning are fairly obvious I think, that science requires "experiment" and "observation", and since we do not directly observe stellar evolution in real time, and do not repeat it in a laboratory experiment, then it cannot be science. But this ony means that Morris has yet to learn what science is. He is wrong on two major points.

First, he is wrong about how "experiment" and "observation" work in science. It is not necessary to duplicate a phenomenon in order to scientifically study it. It is only necessary to make an hypothesis about the phenomenon, and to test the hypothesis. That's where "experiment" and "observation" come into play, in the testing of an hypothesis, not in the duplication of the phenomenon. In this case, the phenomenon is "stellar evolution"; we don't need too see it in real time, we only need to be able to test hypotheses about it. So the fact that we don't actually see stars evolve in front of our nose does not exclude the study of stellar evolution from the halls of science. This should not come as a surprise. In a courtroom we can convince ourselves (or more importantly a jury) that a crime has occurred, and an individual is guilty, yet the entire scenario is a past event that can never be duplicated. Yet we are sure we know who did it & why. That same kind of general process leads us to be able to understand past events in science just as well.

The other major mistake is in understanding what an "experiment" is. Most of us associate "experiment" with some scientist wearing a white lab coat, black horn rimmed glasses, and swirling some strange colored gunk in a flask. But the mathematical manipulations and computer simulations that Morris takes so lightly (a curious response from an experienced civil engineer, whose own discipline of hydraulics & fluid mechanics lives and breathes on mathematical manipulations & computer simulations) constitute the "experiments" that Morris is looking for. By applying the fundamentals of stellar physics and letting the clock tick, we can see a star evolve, in real time, in front of our noses, in the computer. So, in this sense overlooked by Morris, we do in fact see stars evolve.

There can be no doubt but that the study of stellar evolution is science, and that Henry Morris is wrong. But is it good science? That takes a slightly longer time to reach the affirmative answer.

Is it Good Science?

The observational key to understanding stellar evolution is the ubiquitous Hertzsprung-Russell Diagram, commonly known as the "HR diagram", and also referred to as a "color magnitude" diagram by astronomers.

Figure 1
HR Diagram for Globular Cluster M5

Figure 1 above shows a color - magnitude diagram for globular cluster M5. Typical globular clusters sport anywhere from 100,000 to 1,000,000 stars. M5 is one of the larger globulars, and so probably has as many as 1,000,000 stars in it. Each point in the diagram above represents a single star. The horizontal ("x") axis follows the difference of the "B band" magnitude minus the "V band" magnitude; magnitudes are logarithmic, and a smaller number means a greater brightness. The magnitude difference gives the relative color of the star, with bluer stars on the left, and redder stars on the right (which is the standard convention for HR diagrams). The vertical ("y") axis is the magnitude, or brightness of the star. Bright stars are at the top, and dim stars at the bottom (also the standard convention). So stars in the lower right will be relatively dim & red, while stars in the upper left will be relatively blue & bright.

The first thing to notice is that the stars, on this plot of color ("x") vs brightness ("y"), are not randomly scattered around; they form a very distinct pattern. That pattern exists because physics does not allow a star to have just any old color & brightness, but allows only colors and magnitudes associated with specific physical states. The labeled areas of the diagram have specific names as follows:

A Main Sequence
B Red Giant Branch
C Helium Flash Zone
D Horizontal Branch
E Schwarzschild Gap
F White Dwarf Zonze (off diagram)

It is extremely important at this point to keep in mind that this is observational data, the plotted brightnesses & colors of real stars. But this diagram is duplicated in detail by stellar evolution models, Morris' "mathematical manipulations" and "computer simulations". Input the laws of physics and a mathematical model of the stars structure and mass, recreate a cluster in the computer, and you recreate the color magnitude diagram, including all of the features that are labeled here (and many more that are not labled but well known to astronomers, such as the main sequence turn-off point [above and to the left of the letter "A"] and the "clump" at the red end of the Horizontal Branch, and the difference between the "red giant" and "asymptotic giant" branches, that is not so clear in this diagram). If stars don't evolve, and all models of stellar evolution are wrong, then it certainly must be miraculous to say the least, that computer simulations of stellar evolution recreate observed HR diagrams with fidelity. This looks like not only science, but good science as well.

The basic scenario is that stars begin as "protostars", to the left of the main sequence, and then evolve to the left until they reach the main sequence. Once a star reaches the main sequence it moves slowly up and to the left, getting slightly brighter and bluer as it ages. During this time the star is fusing hydrogen into helium in its core. But when the star runs out of hydrogen in the core, it begins to fuse hydrogen into helium in a shell that surrounds the core. That makes the star unstable, and it evolves off to the right and up, from the main sequence, to the red giant branch. But the helium product of hydrogen fusion forms a new core, and when it gets hot enough, the helium in the core will quite suddenly "ignite", and the star enters a new phase where it is converting hydrogen into helium in the shell around the core, and helium into carbon and oxygen in the core. That ignition of helium is called the "helium flash", and happens when the star gets around area "C" in the diagram. The star then descends rapidly onto the horizontal branch (where exactly depends on the ratio of hydrogen and helium to heavier elements in the star). But eventually the helium core is exhausted just as the hydrogen core was, and the star now begins to fuse helium into carbon & oxygen in an inner shell around the core, and hydrogen into helium in an outer shell around that. Once again the star is unstable, and ascend almost back up the red giant branch, to the asymptotic giant branch (just to the left of the red giant branch, they are not easily distinguishable in this diagram; the heavy dark clump aboove the letter "B" are red giants, the few scattered points above them are asymptotic branch giants, on their second trip up to gianthood). On the asymptotic branch, stars move through all of the stages where heavy elements up to iron are synthesized by nuclear fusion; these stages of stellar evolution go by much too fast for the outer layers of the star to respond, so the changes internally make no difference at the surface. At that point stars that don't become supernovae, move off to the left, out of the range of the diagram, becoming very blue and very bright, with strong stellar winds that form planetary nebulae, and eventually leave behind small, massive white dwarf stars, that reside below this diagram, where the arrow next to "F" points. That's stellar evolution in a nutshell. There are no built in biases or preconceptions. You create a physical model, and then turn it loose to do as it pleases. The result is a computerized model of stellar evolution that just happens to coincide beautifully with stars as they are observed in nature.

How far along a star will get, in the story of stellar evolution, depends on its mass. All stars spend most of their lifetimes on the main sequence. A star like our sun will sit on the main sequence, slowly brightening, for about 1010 years. A small, minimum mass (about 0.08 solar masses) red dwarf star will sit on the main sequence for about 1014 years (that's 100 trillion years, for those of you keeping score). But massive stars, say 5 solar masses, will hang around the main sequence for no more than 100,000,000 years, and drastically less for very massive star, like 20 solar masses or more. Our sun will become a red giant, but is not massive enough to make the second trip, up the asymptotic branch. It will cool down to a helium white dwarf (a white dwarf with a helium core; white dwarfs can have cores of helium, carbon, or iron). Exotic, supermassive stars like Eta Carinae, which is over 100 solar masses, can never be main sequence stars at all. They are intrinsically unstable, and may even be too massive to supernova; the instability may blow away essentially all of the star's mass as a stellar wind.

All of this is a congruence between stellar evolution modeling on a computer, and observations of stars, especially in clusters. To say that stellar evolution is not science is, to be blunt, pathetic. There is an enormous literature in stellar evolution that describes the science in excruciating detail. My favorite reference is the book Stellar Interiors: Physical Principles, Structure and Evolution, by C.J. Hansen & S.D. Kawaler, Springer 1994 [ISBN 3-540-94138-X], but there are many worthwhile sources no doubt. The 3 volume set Introduction to Stellar Astrophysics by Erika Bohn-Vitense, Cambridge university press, 1989-1992 covers stellar evolution specifically in volume 3. Donald D. Clayton's book Principles of Stellar Evolution and Nucleosynthesis, McGraw-Hill, 1968 is the classic. Every profession has one book that's on everybody's bookshelves, and Clayton's is definitely one of those books for anyone in the nucleosynthesis business.

Appendix - Relevant Websites

Tim Thompson