Caryn: Didn't PhD Creationist Relativists like Russell Humphreys ("Starlight & Time") and Gerald Schroeder ("Genesis & the Big Bang") show that a 10,000 year universe is not incompatible with a 10 billion year one, just as Relativity compels us all to accept Geocentricity to be an equally viable model of reality?!

Not so far as I can tell. Schroeder does not use literal days. He thinks that the word "day" in Genesis is meaningless. In his story, the first "day" starts 15.75 billion years ago, and runs to 7.75 billion years ago. The remaining "days" are successively shorter, the 6th being 500,000,000 years long. See "How to Make 6 Days Last 13 Billion Years".

Humphreys is a physicist, but not a "relativist", for what it's worth (his specialty is nuclear physics & engineering, though he should be able to teach himself relativity well enough). His thesis in "Starlight and Time" explicitly violates the laws of physics, by having the universe expand outwards from a black hole. He relies on this shortcoming, so as to give meaning to the phrase that God "stretched out the heavans" (or some such, I can't recallt the exact quote). As far as I am concerned, this is a fatal weakness, for it requires the presumption of direct devine intervention to explicitly violate the laws of physics. That might be perfectly consistent with a creationist notion of the miraculous, but I don't accept anything with built in miracles as "scientific", and neither do the vast majority of scientists.

Donnie: Has anyone ever estimated how much of the Sun (or rather, the nebula that produced the Solar System) was primordial material, how much was contributed by 1st-generation stars, how much by 2nd-generation stars, and so on? Or is there any distinction between first- and subsequent-generation material?

There is no distinction between first and subsequent generation material, so that distinction is impossible. What we do know is that the sun is a main sequence star that is fusing hydrogen into helium. Anything heavier than helium in the sun cannot have been made in the sun (mostly), but must have been processed through at least one previous generation of stars.

Now, I say "mostly" because the sun is hot enough to derive about 2% of its output energy from the "CNO bi-cycle", a catalytic cycle of fusion that can leave behind extra carbon, nitrogen & oxygen. But that effect is quite small, and it's a good bet that more than 99% of the C,N, & O that we see in the sun came from those earlier stars, and not the suns own CNO cycle.

See "Solar Fusion & Neutrinos".

Curtmudgeon: First, Tim, thanx for classifying stellar evolution as a theory. So many people forget that little detail, or the actual definition of the word theory. Anyway, as support for your theory, you'll be happy to give two or three examples of stars that have evolved exactly according to that theory, with documentation, won't you? Thought not.

Indeed, stellar evolution is a theory. However, are you really sure that you yourself are aware of what a "theory" really is? Do you know the difference between the words hypothesis and theory?

A "guess", as you might say, is an "hypothesis" in the jargon of science. It can be anything, and it can come from anywhere; it can be a suggestion from your kid, it can be suggested by reams of data, or it can be generated by too much coffee at 3AM. After all, it's just a guess.

But, suppose we test that guess and see if it's right? Suppose it passes that test, and we test it again? Suposse we test that "hypothesis" a zillion times, and each time the test result implies that the hypothesis is true. What happens then? Our hypothesis becomes a theory.

Yuppers, when scientists say "theory", they are talking about something which is accepted as either true, or very likely to be true, based on some kind of documented experience.

So I call stellar evolution a theory becasue it is based on strong, documented evidence, and well accepted basic physics. To dismiss the whole notion on some semantic displeasure over the word theory is disingenuous, and just plain naive.

Will I support my theory by giving an examole of a single star, seen to evolve throughout the whole life cycle? No, as we both know it's quite impossible. However, I will maintain that it is also quite irrelevant.

I will support the theory of stellar evolution through two pathways. First, just plain physics. I already gave reference to appropriate text books on the subject, where the physics and application thereof is given in detail. Now, to quote myself from the first post: "I figure, if anyone wants to hang around and debate the age of the universe, they should be obliged to explain why astrophysical ages are all wrong.". Now, if you are going to personally claim that the physical theory of stellar evolution is physically invalid, then you are personally responsible for describing the relevant physics, from valid sources (such as the books I cite), and explaining the mistakes. If you can't do that, yourself, personally, then you are in no position to argue that the theory is scientifically flawed.

The second pathway, which links astrophysical theory directly with observation is the Hertszprung Russell Diagram (HRD). The HRD is just a plot of color (x-axis) vs brightness (y-axis). If you look at every star you can find, and plot its color against its brightness, on an HRD, you do not get a random pattern of dots. You do get a highly non random pattern. If you follow my link above, and look at figure 1, you see that the pattern is organized into general reagions, such as the main sequence, the giant branches, and the white dwarfs.

An HRD for a cluster of stars is usually called a color-magnitude diagram (CMD). Figure 3 is a CMD for the globular cluster M5. The labeled regions are explained in the text.

If you make a model of a cluster, and run it through a stellar evolution calculation for X years, tou can create a synthetic model of what the CMD should look like, all derived from the basic physics of stellar evolution. Comparisons show a remarkable agreement between the general, and detailed shape and form, of both modeled & observed CMD's for the same cluster (figure 4 is just one example).

Even small details can be matched, or predicted, by stellar evolution theory. For instance, the well know astrophysicst Erika Böhm-Vitense predicted that there should be a small gap tucked away on the main sequence, where stars would be notably rare compared to the surrounding main sequence, because of the sudden onset of convection in a star's outer layers. It is known, oddly enough, as the Böhm-Vitense gap.

But is there really a Böhm-Vitense gap? It's small & hard to see, but it has been found (The Böhm-Vitense Gap: The Role of Turbulent Convection, F. Dantona et al., Astrophysical Journal 564(2): L93-L96, January 2002; Two Böhm-Vitense Gaps in the Main Sequence of the Hyades, J.H.J. de Bruijne et al., Astrophysical Journal 544(1): L65-L67, November 2000)

In short, the basic physical theory of stellar evolution is able to reproduce, in fine detail, the structure of an observed HRD (or CMD). Hence, we have good reason to assert that the theory really does represent how stars change with time.

Curtmudgeon: Yet we have exactly zero evidence that any star has ever changed states along this so-called sequence.

This too is not quite true. Probably the best example of real time stellar evolution is something known as Sakurai's object (V4334 Sgr). Stellar evolution theory requires the onset of helium fusion to be very sudden, and event called the helium flash. Spectroscopic studies show that Sakurai's Object (discovered, I might add, by an amateur astronomer), originally misidentified as a nova, is a star experiencing helium flash, the first yet recorded.

Most of the events in the life of a star are too slow to be easily observed in a lifetime, but the helium flash is one. Unlike a simple "nova", the observation of a helium flash is the observation of stellar evolution in progress, in real time. The helium flash represents the transition point, where a star at the tip of the red giant branch begins its descent to the horizontal branch. That trip is fast. If, in fact, Sakurai's Object really is a helium flash star, as suspected, then it will soon reappear as a horizontal branch star. There is a campaign on now to look for that event as well.

Curtmudgeon: The idea that there must be some sort of explanation that derives one stellar type from another is strictly an imaginative creation that isn't called for by the known facts.

Absolutely preposterous. The idea that there must be some sort of explanation that derives one stellar type from another is absolutely required by even the simplist notions of physics, and there is no way around that fundamental truth. We know that stars are powered by nuclear fusion, and we know that stars don't have an infinite supply of nuclear fuel, and we know that time passes. Stars must run out of fuel, and that is what pushes stellar evolution along, the transition from one fuel source to another.

On the other hand, the idea that stars must not change with time, is an idea that requires the ignorance of all laws of physics.

The bottom line here is that stellar evolution theory is indeed a very valid physical view of how stars "age" with time. People don't stay the same forever, and there is no good reason to think that stars should either. Stellar evolution theory recreates the observd detailed characteristics of stellar populations, and models the aging process for a star in accordance with the expectations of physics. The ages derived therefrom are derived with fidelity to reality, and not preconceived dogma. The universe is billions of years old, and so are the oldest stars it contains.

<font size=-1>[ This Message was edited by: Tim Thompson on 2002-06-27 22:40 ]</font>