INTRO BY DEB: While much of our work at BioLogos is about presenting the case for evolutionary creation, we also take the time to analyze scientific proposals made by Christians who oppose evolution and an ancient universe. Today we continue a blog series focusing on a proposal from young-earth creationist scientist Jason Lisle to explain how distant starlight could have reached Earth if the universe were created roughly 6,000 years ago. Our guide through the topic is Casper Hesp, a graduate student in astrophysics and a gifted science writer. This series is intended for readers without any background in astronomy who want to learn more about God’s creation and how to think carefully about issues of science and faith.
For any newcomers to this series, I will first recap the conclusions of our previous posts. Distant starlight poses a challenge for young-earth creationism, because if the Earth is only six thousand years old, it’s difficult to explain how we are able to see stars that are millions of light years away. Astrophysicist Jason Lisle (a young-earth creationist) acknowledged the seriousness of this problem and has put forward a novel solution called the Anisotropic Synchrony Convention model (ASC model). This proposal involves a way of synchronizing clocks such that the speed of light is infinite towards every observer (see also our first installment for more details). As such, it is aimed at explaining how light could have reached Earth instantaneously during a six-day Creation event.
There are a number of serious problems with this proposal. We saw in the second post how the ASC as a descriptive convention does not respect the physical nature of light. In the third post, we used that result to arrive at two conclusions regarding the ASC model. Firstly, its plain physical interpretation stretches Creation across billions of years (contradicting the interpretation of Genesis 1 in terms of literal solar days). Secondly, that same interpretation involves placing the Earth at the center of the universe. In the previous post, we started comparing the ASC model itself with our observable universe. We discussed an example of cause and consequence (relativistic jets and their sources) which can stretch 1,000,000 light years across the sky. The ASC model requires the assumption that God created this phenomenon with the mere illusion of a causal relationship. With apparent event histories going back a million years, the ASC model implies that God is intentionally deceiving us. Today, we will explore another, completely independent example of the same problem with the ASC model. This one has to do with galaxies.
Distant galaxies appear to differ from those nearby
Within the observable universe there are billions upon billions of galaxies. Each of them contains up to hundreds of billions of stars. The light coming from these galaxies can tell us an awful lot about them. Among other things, it can inform us about their shapes, the typical age of their stars, whether they are forming new stars, and which elements they contain. It turns out that all of these characteristics of galaxies vary with their distance to us. Compared to galaxies close to the Milky Way, galaxies that are further away typically appear to be (1) bluer in color, (2) lighter in element content, (3) more active in star formation, and (4) “lumpier” in shape.
Don’t worry, we will review those properties below. For now, it is enough to realize that such variation with distance fits well with the standard perspective in which light needs time to travel. Rays of light coming from different distances essentially provide our telescopes with photographs of different time points in the history of our universe. For astronomers it makes sense that the (distribution of) galaxies in the cosmos changed significantly over the billions of years that make up the history of our universe. In this interpretation, distant galaxies can look different than nearby galaxies simply because we observe them as they were billions of years ago (when their light started its long journey towards us). In other words, the light from very distant galaxies comes from the early universe, while the light from nearby galaxies was emitted more recently (within the last few billion years). These objects are the most important empirical constraints for current state-of-the-art cosmological models that aim to describe how the cosmic environment changed over the course of history.
This is where Lisle’s proposal runs into serious problems, because it does not allow for significant changes within a mere 6,000 years. In his ASC model, the light rays of all galaxies in the universe arrived instantaneously on Earth after they were created. Therefore, differences in age cannot be invoked to explain any variation. His model can deal with these systematic differences only by positing either (1) that these differences do not actually exist or (2) that God implemented all of them on the fourth 24-hour day of the Creation week.
Given that the first option has been explored and rejected on scientific grounds (see footnote 2 below for details), the ASC model can only be salvaged by invoking the second option, namely that God ordered the universe like a dart board (with the Milky Way located exactly on the bull’s eye) for reasons as of yet completely obscure to us. It should be clear that this geocentric option is unsatisfying, especially if more insightful explanations exist. As scientists, we cannot invoke God merely to keep our models from falling apart. Otherwise God’s creative work as a whole would be marked by incoherence such that scientific exploration is impossible (see also our previous post for a discussion on the principle of intelligibility). So let us ask the following question regarding the observed differences between galaxies far away and close by: Compared to the ASC model, how insightful is the explanation provided in the context of standard cosmology? The rest of this post will be devoted to an exploratory introduction, giving a partial answer to this question.
The mere observation that important galaxy properties vary systematically with distance is problematic for the ASC model. In contrast, in “mainstream” astronomy these properties fit well into the larger picture of cosmic history. Actually, our current understanding of galactic evolution not only allows for the presence of variation, but also explains why the variation is present. At the end of this post, I would like you to walk away with a rudimentary understanding of what underlies the differences between the galaxies. Since most of the light of galaxies is produced by the little lamps we call stars, understanding those will be essential for grasping the galaxies. Our small crash course on galaxy evolution will be mostly constrained to that topic.
The birth of stars: Collapsing clouds
During the birth of our universe, only the lightest elements were formed, mostly hydrogen and helium. After the universe had cooled down enough, those initial elements formed huge clouds of cosmic gas and dust. Parts of these collapsed under their own gravity. This is how the very first stars were born. In fact, we still observe signs of new stars being born every day, such as in the awe-inspiring image of the Eagle Nebula shown at the top of this page. The light of a newly formed star (in the middle, on the left) is heating these pillars of gas and dust, while star formation is taking place inside of them. One of the most peculiar aspects of Lisle’s paradigm is that he staunchly rejects the possibility of star formation through natural processes. For him, every single star is the product of a supernatural act of creation.
However, there is an entire field of scientists who are experts in the phenomenon of star formation. How can a star be born from such a collapsing cloud? As more mass travels inward due to gravity, the center of the cloud becomes denser and hotter. At some point during the collapse, the pressure in the center becomes high enough for the fusion of hydrogen atoms into helium (nuclear fusion). The energy (light) released by the fusion then starts pushing the matter outwards (counteracting the gravitational pressure). Eventually, a stability is reached and the collapse comes to a halt completely as a new star is born. As such, every star is characterized by a balance between gravity (pulls inward) and nuclear fusion (pushes outward). More massive stars allow faster fusion rates, making the massive stars shorter-lived but able to shine hotter and bluer. Part of the light produced by nuclear fusion manages to escape the star. That’s the part we can observe here on earth.
The life and death of a star
Why does every baby star thrive on the fusion of hydrogen and not on other elements? Hydrogen is the lightest element in the universe. The smaller the weight of an atom, the better it lends itself to fusion into heavier atoms (i.e., lower pressure is required, more energy is released). Most stars spend the largest part of their lifetimes burning hydrogen and become slightly colder and fainter as their hydrogen resources shrink. Their light starts out being relatively blue and reddens as its temperature drops. The presence of heavier elements (“contamination”) in the core of a star reduces the efficiency of hydrogen fusion, effectively reducing the temperature of the star and reddening the light it emits. Finally, the emitted light is filtered through the outer layers of the stars. Because specific elements absorb light at specific wavelengths (called “absorption lines”), this filtering can give us specific information about their element contents.
After most of the hydrogen in the core of a star has been depleted (converted into helium), the core can collapse further until the pressure is high enough for the fusion of the next lightest stable element (helium). If the star has enough mass, this cycle can continue towards heavier elements all the way up until iron. After that, the fusion of atoms cannot release any extra energy and there’s nothing left to keep the gravity at bay. A runaway process ensues as all the matter is rapidly pulled inward. This continues until there’s literally no space left for the atoms to move around in anymore. All of the collapsing matter bounces off this hard “atomic wall,” the backlash of which produces an extremely powerful shockwave. This excess of energy allows for the production of elements heavier than iron (e.g., gold). Stars that “die” in this way are called supernovae, they literally go out with a bang. The explosion effectively injects the star’s fusion products into the surrounding space, allowing those heavier elements to become part of newly formed stars. The core is left behind in the form of a white dwarf star. This completes the lifecycle of a star. It implies that all atoms heavier than helium (with the exception of trace amounts of lithium) were essentially the by-products of the lifecycles of stars. These same elements were the crucial building blocks of life on earth (most notably: carbon, oxygen, and nitrogen). We might rephrase the words God spoke to Adam in Genesis 3:19 as follows: “For you are stardust, and to stardust you shall return.”
Now we are ready to harvest rough insights on why distant and nearby galaxies would be expected to differ in the four properties listed before: (1) color, (2) element content, (3) star formation rates, and (4) shape. I hope any trained astronomers reading along with this post will forgive me for the gross generalizations I am making here for the sake of simplicity. Our universe started out as a completely pristine environment (containing almost only hydrogen and helium). The red lining of our story is that, in the early universe, galaxies had a much shorter star formation history. Relatively little time had passed for stars to be formed and to complete their lifecycles. The first point we can take away from this is that the stars of distant galaxies would be expected to be younger on average and, therefore, hotter and bluer compared to those of nearby galaxies. Secondly, the completion of stellar lifecycles is needed for the production and diffusion of heavier elements. In this way, galaxies accumulate heavy elements over time. Because of this, we expect heavy elements to be less abundant in the galaxies of the early universe. A lower abundance of heavy elements would also make distant galaxies bluer compared to nearby galaxies. That’s because contaminations by heavy elements lower the efficiency of the nuclear fusion, making the nearby galaxies redder. Thirdly, in the early universe, the essential ingredient for star formation (hydrogen clouds) was more abundantly available. The hydrogen hadn’t gotten “locked up” yet in other stars. Therefore, distant galaxies are expected to show more signs of star formation. Finally, the presence of those clouds of hydrogen gas and dust is marked by substructures (which we call “lumps”). As such, we can begin to understand why those galaxies are much “lumpier” in shape. Any further discussion here would lead us into domains such as galaxy classification and evolution models. That is beyond the scope of our post. Below you can find a simplified summary of the comparison between distant and nearby galaxies.
|Observables||Distant galaxies||Nearby galaxies|
|Star formation rates||High||Low|
Table 1. A simplified summary of the relevant observables, comparing the averages of distant galaxies (redshift z > 3) and nearby galaxies (redshift z < 3).
Let us come full circle again. In this post, we first pointed out that the galaxies in our universe differ (in terms of color, content, star formation, and shape) depending on their distance to us. Having established this, we evaluated how both the ASC model and the cosmological standard model deal with this pattern. Our aim was to compare them in terms of their explanatory value.
For the ASC model, observed differences between distant and nearby galaxies form a mere nuisance. It has no insightful way to deal with it. The only option appears to be to assert that God intentionally created the universe with patterns in its galaxies which center precisely on our Milky Way (i.e., a geocentric universe). This ad hoc solution provides a stark contrast with the mainstream alternative. In the standard cosmological model, observations of the galaxies are comfortably interpreted as a record of cosmic history over billions of years. In that context we have discussed how four very distinct observables can all be coherently understood on basis of the straightforward physical principles which govern the lifecycles of stars.
Although many details of our cosmic history still need to be sorted out, the overall fit of the standard cosmological model is remarkable. It would not be hyperbolic to say that it is one of the greatest achievements of modern science to date. All of this places even more pressure on the ASC model. In addition to its troubles with dealing with the observations themselves, it also needs to explain why another approach (one which accepts the ancient age of the universe) seems to produce more insightful explanations. Why would God create the universe precisely in such a way that billions of imaginary years need to be assumed to produce a coherent whole? To support the ASC model, one would have to assert that God carefully arranged the cosmos in that misleading way. It is yet another expression of the Omphalos hypothesis, which holds that God created our universe with the mere appearance of age (or rather, history). Our previous post ended with the same conclusion.
So far in this series, we have explored astronomical observations which fit stunningly well into the standard cosmological model, while they require awkward ad hoc solutions within the ASC model. Are there more such examples? Certainly. In the next post we will be looking at the cosmic background radiation that is present everywhere in the universe.