The problem of distant starlight
According to the “young-earth creationist” (YEC) view of origins, the first chapters of the Bible strictly demand that the universe was created less than 10,000 years ago. Within the YEC movement it is commonly believed that a recent creation is in good agreement with all available evidence (when interpreted alongside a literal reading of Genesis). In contrast, BioLogos emphasizes that there are multiple independent lines of evidence that directly contradict such a young age of the Universe. The proposal of Jason Lisle, an astrophysicist working with Answers in Genesis, entails a response to the line of evidence related to distant starlight.
One of the more visible evidences which seems to challenge the YEC position can be seen on the sky on any cloudless night spent on the countryside, far away from the light pollution of the cities. It stretches across the firmament as a band of diffuse light which the Ancient Greeks suitably named “the milky circle” (γαλαξiας κuκλος or galaksias kuklos, hence our term: galaxy). Little did the Ancients know that this Milky Way would later be measured to span a distance of 1,000,000,000,000,000,000,000 meters. Do not worry if you cannot grasp this number (nobody can, really). It is more to give you an idea of what astronomical distances “look” like. To wrap their heads around such numbers, astronomers have started thinking in units of light-years: the distance a ray of light can travel in one year. According to Einstein’s theory of relativity, the speed of light is the highest speed possible. Using the speed of light that scientists measured, it would take a ray of light 100,000 years to traverse our galaxy (We will get back to the speed-of-light measurement issues later).
When you look at the Milky Way, you are basically looking at the side of our disk-shaped galaxy. Our galaxy contains about a hundred billion (!) stars. And our galaxy is just one out of billions in the observable universe. Astronomers have pointed the Hubble Space Telescope at regions of the sky that had appeared to be empty before. Looking “deeply” enough, they found huge collections of galaxies much like our Milky Way. Distances have been reliably measured beyond 40,000 times the size of our own galaxy. This is an awfully long (and according to standard physics, impossible) distance for light to cross within a mere 6,000 years. And yet we see light constantly arriving at Earth from these distant regions.
If the YEC position is scientifically viable, a satisfying solution should exist to the distant starlight problem. Of course, the first line of defense is to cast doubt on the measurement methods (e.g., see this YEC news article regarding the use of Cepheid variable stars). That approach has not worked out well because many different distance measurements independently converge on the current “cosmic distance ladder”. Such convergence has lead YECs to recognize that this matter should not be taken lightly (pun intended). It has been proposed that light could have been created “en route”, which entails that God placed all those rays of light already well on their way towards Earth. However, Lisle and others have rejected this proposal because it would imply that God is a deceiver. Back in 1994, Dr. Russell Humphreys proposed a so-called “white hole cosmology” to explain distant starlight. However, it seems this theory has met its own demise under pressure of both theoretical errors and falsified predictions. While Lisle seems to have acknowledged the severe difficulties facing that theory, YEC ministries like the Institute for Creation Research (ICR) still subscribe to it. It’s a longstanding discussion which is not the focus of this series.
It is clear that this situation has left the YEC movement with a dire need for a fresh approach that is more convincing, both theoretically and observationally. A trained astrophysicist would be the most likely source of such a solution. This is where Lisle comes in. After finishing his PhD in solar astrophysics at the (secular) University of Colorado, Lisle went on to become one of the leading scientific minds in the YEC movement. He became an expert voice on the problem of distant starlight for major YEC apologetics ministries such as ICR and Answers in Genesis (AiG). In 2010, Lisle published a long-awaited article containing the details of a solution at which he had been hinting for years: the Anisotropic Synchrony Convention (ASC). Say what? Well, let’s go about this topic slowly.
An extremely short primer on Special Relativity
Synchronization has to do with the concept of time in Einstein’s theory of Special Relativity (SR). Now, explaining SR would be a whole semester worth of study in itself, but I’ll do my best to give you a very basic understanding. SR involves a mind-flip relative to our standard way of thinking about time and space. For everyday life purposes we all fare pretty well by thinking in terms of absolute time and absolute space. This is what physicists call Newtonian or “classical” physics. In classical physics, all speed measurements depend on our own movement speed. For example, a train carriage stands still for the passenger inside, but moves for those waiting on the station. In SR, we need to flip this classical mentality around. SR is based on one main premise: the speed of light is the same for every observer (independent of location and speed). The speed of light is exactly the same whether measured by someone waiting on Earth or someone flying a spaceship. Now, how does one perform such a measurement? Imagine that every observer has a single clock. Someone can determine the speed of light by measuring the time it takes for a ray of light to travel away, bounce off a mirror and travel back (i.e., back and forth or “two-way”). In classical physics, space and time were absolute, so measurement outcomes would change with the speed of the observer. However, in SR, only the two-way speed of light is absolute and to keep it absolute, time and space need to be stretched. This results in all kinds of strange predictions that contradict our common-sensical way of looking at the physical world: different observers experience time and space differently. A common SR textbook problem concerns the question of trying to fit a 20 feet ladder in a 10 feet barn: “How fast do you have to run while holding the ladder so that there is a moment at which the ladder is fully contained in the barn?” There is an actual quantitative answer to this question based on something called Lorentz Contraction. I do not expect you to be able to perform any calculation at this point, but it serves to give you a flavor of the weirdness of SR.
The matter of choosing one’s Synchrony Convention
Remember that SR only pins down the two-way speed of light, denoted with the constant c ≈ 300,000 kilometers per second. This is useful because this quantity can be measured with a single clock (this clock just waits until the ray of light comes back). However, what if, for example, you want to make an appointment to do sports with someone very very far away, separately but simultaneously? Together you will need to decide on some kind of rule to synchronize both of your clocks at different points in space. This choice is called a “Synchrony Convention”. Einstein would advise you to do this such that your one-way speed of light is also constant, always equal to c. This means that it takes a ray of light as much time to go towards your friend as it takes to return to you. If the light leaves you at 1:00PM and arrives back at 3:00PM, we set the clock of your friend such that it reads 2:00PM when the ray of light bounced off his mirror. In Einstein’s convention, the speed of light is the same in directions away from and towards any observer. Einstein’s convention is denoted with the term “isotropic” because this word literally means “the same in every direction”.
Now comes the trick. Instead, one can choose the synchronization of clocks in such a way that the clock of your friend reads 3:00PM at the moment of reflection. Since on your own clock, the light signal left at 1:00PM and came back at 3:00PM, it seems like the ray of light took two hours to arrive at your friend, but zero hours to come back. This means the measured one-way speed of light is two times slower in directions away from you and infinite in directions towards you. This is allowed within SR, since synchronization is essentially a matter of convention. This convention is called “anisotropic” because the speed of light now depends on the direction with respect to the observer. This is why Lisle appropriately uses the term Anisotropic Synchrony Convention (ASC). The procedure of synchronization is visualized in the animation below, which also illustrates the difference between the two synchronization conventions.
Let’s suppose that we follow Lisle’s lead in rejecting the proposal that starlight was created in transit. Then, the ASC describes a possibly young universe and the standard convention describes a necessarily old universe, while leaving the physical system unchanged. So, did we stumble upon the means of unification between standard and young-earth creationist cosmology? Unfortunately, not quite. One of these two ways is more truthful to the actual physics that underlie our universe. Einstein chose a constant one-way speed of light. How exactly did he motivate this choice? He has been famously quoted for saying, “God does not gamble.” Well, Einstein certainly did not allow himself to make any gamble here, either. He firmly based his framework on our knowledge of the fundamental nature of light waves, which goes back to Maxwell’s work on electromagnetism. I’ll take you through it step by step.1
Introducing electric and magnetic fields
How does light travel? The best answer we currently have comes from James Maxwell, a devout Christian physicist from the 19th century. Initially, Maxwell was not focusing on the question of light. He was trying to understand how electric fields interact with magnetic fields. Not everybody will be familiar with the concept of these fields, so I hope that the physics-minded among you will forgive me for shortly going over some basics. An electric field may be visualized as a collection of arrows that indicate in which direction a positive charge would be pushed if it were placed in the field. Magnetic fields are trickier to understand. For our purposes, it suffices to say that magnetic fields (1) arise from moving charges and (2) bend the movement direction of charges. I purposefully say bend because magnetic forces only act perpendicular to the motion of charges. This notion of perpendicularity will return later on. As these notions are sufficient for the purpose of our discussion, we will not study these fields in additional depth.
A primer on Maxwell’s theory of Electromagnetism
With this extremely concise understanding of these two fields, we can proceed with our treatment of their interaction: electromagnetism. Electric and magnetic fields have an intriguing reciprocal relationship: (1) changes in electric fields cause magnetic fields and (2) changes in magnetic fields cause electric fields. These relationships were defined in Maxwell’s equations. Now, imagine an empty universe with only a single perturbation in its electric field. The magnetic field will respond by changing. Replying immediately to that, the electric field will also change. Essentially, the magnetic and electric fields will start dancing around each other. Moving across space, they “pull” each other forth: an electromagnetic wave. A visualization of this phenomenon can be seen in the figure below.
Is this all we can say? Surely not. Maxwell would not be called a physicist if he had not examined his equations to study this phenomenon further. His famous equations can be studied in vacuum (i.e., without charges) to understand what behavior electric and magnetic fields produce together. This treatment results in the traditional form of the wave equation for both the electric and the magnetic field. The resulting wave equations then completely characterize the behavior of these waves. For example, they show that the electric and magnetic field waves travel perfectly perpendicular to each other, as can be seen in the animation (this property is no coincidence, remember the perpendicularity described earlier). But, much more importantly, one specific term in the wave equation defines how fast the wave travels (v stands for ‘velocity’):
At this point, the job was relatively easy for Maxwell. He simply plugged in the measured values of the physical constants ε0 and μ0 (both come from electromagnetism) to obtain the velocity, about 3.1×108 m/s. He was familiar enough with experimental results in physics to realize that this result corresponded very well with the speed of light according to the available measurements at his time. This led him to propose that, in fact, light itself is an electromagnetic wave. This means that, earlier, when we imagined the electric and magnetic fields dancing with each other, we actually witnessed the birth of a ray of light in our mind’s eye. At this point, I am tempted to say, “And there was light. God saw that the light was good.”
Coming full circle
So now, let us come back to where we started. Maxwell’s equations led to the idea that light consists of electromagnetic waves and that these always travel at the same speed in vacuum. To these findings, Einstein applied the idea that the laws of physics are observer-independent. This gave rise to his assumption of a universally constant speed of light. In turn, this led to his famous framework of Special Relativity (which we introduced in the previous post). Now, Special Relativity still leaves space for the choice of a synchronization convention. In light of our current discussion, we now understand what drove Einstein to assume a constant one-way speed of light: it agrees with the electromagnetic nature of light. Electromagnetic waves have a finite, constant speed. In contrast, Lisle’s proposal assumes a non-constant speed and, moreover, an infinite speed in directions towards an observer. While this way of synchronizing is technically allowed, it does not respect the physical nature of light as Einstein’s choice does.
A Railway Analogy
To understand what went “wrong” here, suppose that the local railway company wants to boast that it operates at travelling speeds that are virtually infinite into the city. However, their trains suffer from physical limitations and have a maximum speed of about 50 miles per hour. To overcome this quandary, the railway company decides to change the synchronization convention of the clocks on all of its stations. The clocks are synchronized in such a way that trains into the city seem to arrive instantaneously, while trains out of the city travel at half the speed (say 25 miles per hour). With such amazing advertisements, it does not take long before somebody starts a lawsuit against this company (especially since we are talking about the US here). In its own defense, the company might say that this way of synchronizing clocks is technically allowed, just like the standard convention. The judge is taken somewhat off guard by this unusual proposal and decides to consult with expert physicists on the issue. Their advice entails that the accuracy of the advertised claims should be determined using the synchronization which is truthful to the physical limitations of trains (i.e., the standard convention). The judge decides to follow this piece of advice and the railway company loses the lawsuit.
Of course, our example is subject to simplifications. For example, in ASC every “station” has its own synchronization (such that the speed is infinite towards every observer regardless of his or her location). Also, for lightwaves the physical limitations are derived from Maxwell’s theory while those of trains are measured directly. These differences do not change the point of our analogy that physical limitations should be taken into account when discussing speeds.
The comprehensibility of God’s Creation
Some may view God as some kind of engineer who has put together an extremely complex machine (called the universe) and then decided to step back to watch its development. All kinds of variations can be added to this picture, such as God predicting intended outcomes beforehand or throwing in miracles now and then. However, this description bypasses an essential aspect of God’s providence that occurs “behind the scenes” every moment. By his divine will, he is continuously upholding physical order within his own Creation. He is keeping it all together, moment by moment. What comes to mind are Paul’s words on Jesus in Colossians 1:17, “He is before all things, and in him all things hold together.” The Christian doctrine of creation is not just about the initial “spark”, but about a continuous act of divine providence (as discussed by Jim Stump in another post here on BioLogos). The resulting regularities are what make our world understandable. Nature appears to function according to a coherent set of physical laws. No matter what faith one has, everybody can marvel at this property. As Einstein put it, “the eternal mystery of the world is its comprehensibility.”
In the physics that underlie the created order, God provides us with a framework for comprehension. He himself chooses to maintain it every single moment. The previous post clarified that the standard synchrony convention of Einstein respects the physical nature of light (finite, constant speed), whereas the ASC does not. Therefore, while the ASC may potentially solve a single interpretive issue related to Genesis 1, it does so at the expense of the God-ordained regularities of nature.
At this point, let’s return to the railway analogy. Our imaginary railway company set the station clocks in such a way that all the trains seemed to arrive instantly in a certain city, say New York, no matter from which station they departed. So, imagine passengers sitting on a train, checking the clocks on all of the stations. They stepped in at 3 o’clock. Halfway towards the Big Apple, there is a short stop at an intermediate station. To their surprise, it’s also 3 o’clock there. Some extra passengers get on and the train departs. Finally, they arrive in New York City at… 3 o’clock. The passengers who got on the train halfway measured the same traveling time as those who made the full journey. But in physical reality, those passengers who got on the train halfway experienced only half the traveling time of the other travelers. What all these passengers have in common is that they arrived in New York at the same time.
Let us apply this to the ASC model. It has all rays of light departing from all over the universe and arriving at Earth at approximately the same time, during the fourth solar day of Creation. However, in physical terms (constant speed of light), those rays of light coming from the Sun took about 8 minutes and those from the next nearest star Alpha Centauri took about 5 years, while those emanating from the center of our galaxy (Sagittarius A*) took about 26,000 years (!). To keep their time of arrival the same on the physical level, God would have needed to create Sagittarius A* almost 26,000 years before he created Alpha Centauri. That star would have been created almost 5 years before the Sun. As distances to objects become larger, the moment of their creation gets pushed back further in time to allow their light to arrive simultaneously with that of the Sun. It results in a scenario in which God created the universe gradually, starting with the objects farthest away from Earth and proceeding inward with the speed of light. Along the way of this journey centered on Earth, more and more light rays or “passengers” are being picked up from a variety of objects. But all of them arrive on Earth exactly on the fourth solar day of the existence of the Earth. This process can be compared to that of a cosmic 3D-printer which prints the universe starting with the outside “shell”, and then moving inward until it reaches the Earth at its center. If you are having trouble with visualizing this, below I have produced a small animation. The dot in the middle is the future location of the Earth, while the globe around it delineates the volume which remains to be filled with created objects.
The revival of geocentrism
I can imagine that this leaves you with more questions than answers regarding the ASC model. So, let us carefully summarize our results. While the ASC model may seem to provide a neat account of Creation within the ASC, it gives rise to a rather peculiar story on the physical level (assuming a constant speed of light). On that level, there are at least two remarkable features.
- The process corresponding with the fourth solar day of Creation in the ASC model is effectively spread out over a period of billions of years for the observable universe. This does not align at all with a literal solar day as commonly perceived. It defeats the original purpose for which the ASC model was constructed: namely, to uphold the “plain reading” of Genesis 1 in terms of literal solar days. The ASC model, when interpreted in terms of plain physics, contradicts the very reading that it aims to defend.
- As can be seen from the animation above, the ASC model results in the revival of a geocentric view of the universe. It renders the whole universe as having been created inwardly and geocentrically. This is reminiscent of the times when even respected theologians like John Calvin believed that the Scriptures demand that people adhere to a geocentric worldview (see, for example, this BioLogos blog post by Wyatt Houtz). While we all thought that humanity had put the issue of geocentrism to rest centuries ago, the ASC model indirectly brings it back to life in a different form.
Now, could God have created the universe in this particular way? Of course he could. If he desired so, he could also have created the heavens to revolve around Earth. He could even have created everything with the appearance of age. But the models that have prevailed over the course of time are the ones that make the most sense of God’s created order. The scientific method favors models that produce coherent and parsimonious descriptions of Creation. This principle is called Ockham’s razor, after the English Franciscan friar to whom it was attributed: William of Ockham (1285-1347). One formulation of this principle is as follows, “Everything should be kept as simple as possible, but no simpler.” Now, geocentrism has already lost in popularity due to this criterion and hence, in extension, this places pressure on the viability of the ASC model.
You must have noticed the spectacular image shown above. The purple haze shows the radio emission of relativistic jets belonging to the galaxy Centaurus A. Here the object is projected in its actual size as it would be seen on the sky if its light were visible to the human eye. This stunning example spans 1,000,000 (!!!) light years across the sky, and many more jets such as these can be found. (If you’re wondering about that shining globe on the left, that’s the full Moon.)
But what causes those jets exactly? At the center of this huge flare of Centaurus A (at the small dot in the middle with a higher intensity) lies an object 55 million times heavier than our Sun. It’s a black hole! Black holes are objects so dense that even light can’t escape from them. They don’t usually emit any light themselves, but the matter around them does. Black holes pull huge amounts of gas towards themselves (mainly hydrogen atoms). As a result, the temperature around the black hole increases. Due to the heat, the hydrogen atoms start to separate into free charged particles (protons and electrons). As the gas is being pulled inward, it starts spinning quickly around the center (much like a ballerina pulls her arms towards her body to increase the speed of her pirouette). Consequently, each black hole possesses a very dense, hot, rotating disk of free charged particles. This is what they call the accretion disk, because it consists of the matter that is being collected by (or accreted onto) the black hole.
Hopefully, moving charges will remind you of something we discussed earlier, namely, that these charges are the necessary ingredient for creating magnetic fields. The charges in the accretion disk are moving at incredible speeds and are gathered in large numbers. This and other effects produce extremely strong magnetic fields near black holes, even the strongest we know of, especially in the regions above and below the disk (at the “poles”). Although astrophysicists don’t fully understand how it works, these changing magnetic fields near the poles can start to function like some sort of cosmic launching platform. Any matter that ends up near the poles will then be propelled into space at speeds of the same order as the speed of light (~0.5c for this example). Since this can happen at both poles of the black hole, objects can have two jets in opposite directions ranging across humongous distances. In the image shown above, astronomers happened to observe such a phenomenon stretching across the sky. These jets are moving perpendicular to our line of sight. In case you’re having trouble to visualize the launch of such jets, I have produced the small simplified animation shown below. The blue cones are the jets, while the green ellipse shows the disk on its side.
Is God shooting straight with us?
At this point, we can return once again to Lisle’s proposal. He proposed that all objects such as galaxies were created mature—instantaneously, and fully formed. So our own galaxy would have been created approximately in its current state, complete with spiral arms and stars at different points in their development. After Creation, light needs about 100,000 years to traverse our galaxy. Since light travels at the fastest speed possible, this is the minimal time needed for regions to “connect” causally. For stable systems such as most galaxies one might choose to be lenient towards such an assumption.
However, take another look at the jets in the image above. It’s definitely not a stable system. We see some discrete “blurps” in the jets, as if the output has been changing in the past. Even light (traveling at the fastest speed possible) did not have time enough to “connect” these regions with each other within 6,000 years. In the ASC model, such relativistic jets (including their discrete blobs) were created midflight. This would give us human beings only the illusion of a causal relationship between the source (the medium near the black hole) and the astrophysical jet itself. This illusion would include a fictional history of variable input from the source near the black hole. Even today, distinct parts of this particular jet would only be causally connected with very small surrounding regions (only about 0.5 percent of the whole jet length).
Lisle rejected the proposal of light being created in transit based on the principle of intelligibility. His argument was that we would expect God to provide some way to understand his Creation. Otherwise, it would not be worth the effort of trying to make sense of everything at all anymore. The fact that Lisle and other young-earth creationists have rejected the idea of light being created in transit is what originally led to the need of a solution to the distant starlight problem. However, we have seen in this post that Lisle’s proposal suffers from exactly the same problem which it aimed to avoid. It leads to a picture of the universe wherein God produced sequences of imaginary events in relativistic jets. This would revive the idea of God creating “appearance of age,” overruling any attempts to understand Creation coherently. It leads to the Omphalos hypothesis, which holds that God created nature with all the telltale marks of a distant past which it never had. Young-earth creationists such as Lisle have aimed to distance themselves from this hypothesis because it contradicts the principle of intelligibility. However, as we’ve seen here, assuming the mature creation of relativistic jets revives the Omphalos hypothesis.
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. 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 our scope. 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).
Introducing the Cosmic Microwave Background
Our universe is literally bathing in light, what scientists call the Cosmic Microwave Background (CMB). These light rays (photons) are so low in energy that they are invisible to the naked eye. To get an idea of how numerous they are, consider that every cubic centimeter is filled with about 400 of them. And every single second, as many as 20 trillion of these photons pass through the tip of your finger alone. The word microwave refers to the typical wavelength of this light (~2 mm). Its intensity curve across wavelengths follows a very distinctive shape (see the image below).
The CMB was discovered accidentally by radio astronomers Penzias and Wilson in 1965. They were trying to measure radio signals bouncing off of weather balloons. However, their measurements were disturbed by background noise which appeared to be coming from all directions. After going over their equipment many times, they excluded the possibility of any technical faults. It puzzled them greatly. Then, by mere chance, Penzias got to know that a group of astrophysicists over at Princeton had been making preparations to look for cosmic radiation as a remnant of the Big Bang. This specific theoretical prediction concerning the “afterglow” of the Big Bang had already been made 17 years earlier, in the year 1948.
It was at this point that Penzias and Wilson started to come to terms with the significance of their discovery. Their observations were within the exact predicted range aimed for by the Princeton astrophysicists (more about that below). To compare the explanatory power of the young-universe paradigm with that of “mainstream” modern cosmology, we will first look at the place of the CMB in a young universe. It appears the CMB cannot be accounted for in way that leaves young-universe models unscathed.
The (Lack of) Place for the CMB in a Young Universe
How might a young-universe model, such as the ASC model, deal with omnipresent radiation coming from all directions? This is a tough job, given the size of the observable universe (billions of light years) and a time restriction of about 10,000 years. In fact, no one has managed (or attempted) to give a physical description which might explain all the features of the CMB in a young universe.
Of course, a young-universe model could simply include a clause saying that the universe was initially created already filled with these light rays. A young-universe proponent might argue that this feature could be an integral part of creating a fully mature universe. Unfortunately, that assertion would still leave all those light rays without any physical source. All of the trillions of CMB light particles that are passing through us every second would have been created already “on their way” towards us. This argument is essentially saying that God created light in transit (with only an illusory connection to a physical cause). However, that same argument has been rejected completely by young-earth ministries such as Creation Ministries International. They have generally argued it would render Creation unintelligible. The rejection of this idea led to the necessity of new solutions to the distant starlight problem, which motivated Lisle to construct his ASC model. After investing so much effort in circumventing the light-en-route issue, it would be disconcerting if one were to reintroduce it by filling the universe with sourceless radiation. This point cannot be overemphasized.
Is there a more insightful way to interpret the CMB? Yes there is. In fact, as described above, Big Bang theorists predicted the existence and exact features of the CMB almost two decades before it was first discovered.
Resolving a dispute of cosmic proportions
The famous Soviet physicist Lev Landau (1908-1968) once said, “Cosmologists are often in error, but never in doubt.” It’s understandable that statements such as these give people the impression that cosmology is more like a belief system than an actual field of scientific inquiry. There were times when things were not as clear-cut as they are today. During the first half of the 20th century, cosmologists were roughly divided into two camps. Those of one camp (including big names such as Albert Einstein) subscribed to Steady State Theory, which involves an eternal universe without beginning or end. The other camp considered the notion of an expanding universe to be more convincing. To decide between these two, theorists have long determined their most important observational differences. Every one of these tests has favored the Big Bang model over alternatives. Of these, we only discuss the CMB today.
Young-earth creationists often claim that cosmology is more like a belief system than like a science. However, that neglects the fact that serious advancements in both theory and technology have been made after Landau’s time. Over the last 50 years, modern cosmology has earned its place among the sciences through rigorous empirical research. As I said in the previous post, the amazing (though not perfect) fit of the current cosmological standard model (Lambda-CDM) is one of the greatest achievements of modern science. In fact, the 2011 Nobel Prize in Physics was awarded to two teams of astronomers whose work accurately established the parameters of the current cosmological standard model (Big Bang). Nevertheless, the myth that cosmology is more like a religion than like a science is still being perpetuated in young-earth circles. This is unfortunate and completely dismisses the scientific work of cosmologists.The prediction of the CMB and its precise properties is an excellent illustration of how the field of cosmology has become the empirical science it is today.
The CMB as a baby picture of the universe
In 1948, the Big Bang model led to the prediction of the CMB by cosmologists. They reasoned that if the cosmos is expanding, there must have been an era in the past when it was too dense for light to travel freely. All matter was so hot and densely packed that protons and electrons were unable to form stable hydrogen atoms. These free charges were constantly interacting with the available light rays. Because of this constant interaction, the light was in balance with the energy of the hot material which filled our baby universe. As the universe kept expanding further, a time came (~300,000 years after the singularity) when the universe was cold enough for protons and electrons to combine and form neutral hydrogen atoms. From that point on, the available light rays could finally start traveling without scattering off free charges all the time. The intense flash of light which was released at that point in cosmic history reflected the properties of the universe back then, extremely hot and almost uniform. Envision this as a baby picture of the universe. The nicest part is that we know when the picture was “taken” because we know at which temperature protons and electrons become able to form stable hydrogen atoms (at ~3000 degrees Kelvin).
Now, over 13 billion years later, the expansion of the universe has stretched out the baby picture by a factor of 1000. This stretching has reduced the temperature by the same factor (~3 degrees Kelvin, close to the temperature predicted in 1948), but all its other properties are still the same. Around 1900, the great physicist Max Planck (1858 – 1947) developed an equation which later turned out to be perfectly applicable to the early universe. Planck’s law describes what light would be radiated by a “perfect emitter”, a source which can be completely described in terms of its temperature. Somewhat counterintuitively, physicists call such a source a “black body”. An old-fashioned light bulb would be an everyday example that approximates a black body. Stars provide a better approximation of the black body spectrum, although still relatively rough. It turns out that the CMB is the most ideal approximation to a perfect black body ever observed in nature. Below is a plot of the CMB light spectrum, comparing the theoretical black body to the actual observation. Actually the main plot includes error bars, but they are so small that they are invisible! I’ve included a double zoomed-in version to give you an idea of how ridiculously small the errors are.
Pebbles in a pond: ripples in the CMB
We’ve just seen how the Big Bang model straightforwardly provided the exact shape and temperature of the CMB, to extraordinary precision. If you consider that to be amazing, then brace yourself, because there’s more. Besides the general shape of the CMB which is the same in all directions, it also has extremely small fluctuations in temperature. This was first measured in 1992 by the COBE project for which the 2006 Nobel Prize in Physics was awarded (see the main image). In some directions, the CMB is just a tiny bit hotter than others (the difference is about 0.0005 degrees Kelvin). Those small differences in density have been interpreted as the earliest “seeds” from which all the galaxies we see in the universe today formed. With a specific set of parameters for a cosmological model, specific predictions can be made concerning the distance between these seeds (measured in degrees on the sky). One analogy that is often used is that of a small pond in which many small pebbles are thrown. If we understand how the ripples travel and interact, we can predict the typical distance between the peaks on the water surface. For the CMB, this theoretical analysis results in a very precise prediction of the typical angular separation of the hot “seeds”. To give you a taste for the specificity of this analysis, see below for a plot of the theoretical prediction (green line) compared to the data points (blue points with error bars) gathered by the recent Planck telescope. Don’t break your head on the particular units, as it’s more meant for illustrative purposes.
All of this work was effectively done using that single baby picture of the universe, the CMB. As a final step, we can link it back to what the universe looks like today. The size of the separation between the “seeds” in the CMB can be extrapolated to modern times by taking into account the cosmological expansion. The resulting scale of separation has been shown to correspond with typical present-day distances between galaxy clusters, providing further confirmation. It all connects. The current cosmological standard model combines these and many other findings in coherent ways. Despite having its own shortcomings, this level of elegance is currently surpassing all alternative models by far. There is currently no alternative in sight that might have the potential to integrate all the available findings. This is why most modern-day cosmologists aren’t constantly aiming to overthrow the whole paradigm. Instead, they’re working with the best we have.
The universe has a belly button
We discussed how young-universe models such as Lisle’s ASC model have a tough job in explaining the CMB. One way or another, those models would require postulating the existence and properties of the CMB without any physical explanation. If one would posit that the CMB was “included” in the initial act of creation, this would revive the idea of light being created in transit (without a physical source). That is precisely the premise which Lisle aimed to avoid by constructing his ASC model. He argued that God would be a deceiver if he would create light that gives us the illusion of having been emitted by a source.
Next, we saw that the CMB has, in every way imaginable, the appearance of being a picture of the early universe. Both its overall shape and temperature, as well as its minuscule fluctuations correspond exactly with the predictions of the current Big Bang model. In a way, one could compare the CMB of the universe with the belly button of a human being. It’s a sign of your birth that you always carry with you. The CMB signifies the birth of the universe. Young-universe models either have to argue convincingly against this conclusion or to draw upon the Omphalos hypothesis. As we finish this empirical journey, it should have become abundantly clear that framing cosmology as a belief system, rather than a rigorous science, is a gross mistake. Frankly speaking, that is a myth perpetuated by those who disagree with the conclusions of mainstream cosmology. It completely defies the recent history of this scientific field, which happens to include the 2006 and 2011 Nobel Prizes in Physics.
When we look up at the night sky, we marvel at the countless lights specking the darkness. These lights testify to God’s glory (Psalm 19:1), but they also testify to the universe’s unfathomable size and age. Light from the most distant stars needs billions of years to reach us. In our previous posts, we discussed the attempt of astrophysicist Jason Lisle (a young-earth creationist) to solve this problem for the young-earth creationist paradigm. As we have seen, the proposal suffers from serious issues, both in theory and in practice. However, it is not fair merely to point out faults in a model, because its value can only be understood in comparison to the available alternatives. That’s why, along our way we made sure to make a comparison with the cosmological “standard model”: an expanding universe (Big Bang) with a cosmic history of about 13 billion years. In every case the ASC model has shown major problems while the Big Bang model is an excellent fit to the data.
Before we can conclude our series, there’s still one elephant in the room which needs to be dealt with. In his original article, Lisle not only put forward his proposal for solving the distant starlight problem, but also made the charge that the “standard” cosmological paradigm suffers from a similar issue with light-travel time: the so-called “horizon” problem. This accusation has been endorsed and repeated by other young-earth ministries in subsequent years as a way to play down the distant starlight problem. The horizon problem does indeed exist, and it does have a conceptual link with the distant starlight problem. However, that does not mean it is comparable to the distant starlight problem in terms of severity. If that were true, our whole discussion of distant starlight might be reduced to a case of “the pot calling the kettle black”. Even when we take into account the horizon problem, the standard model integrates the available evidence much better than any model proposed by young-earth creationists.
A problem on the horizon
What exactly is the horizon problem, and how big is it? The current Big Bang model (i.e. the standard model) describes the universe as ever-expanding. If we had a way to reverse (and speed up) the course of time, we could see the universe shrinking. By going over 13 billion years back in time, we would be able to witness the moment when light started traveling freely for the first time. That light is still visible nowadays as the Cosmic Microwave Background (CMB). Travelling another 300,000 years back in time from that point, we would arrive at the point where standard physics breaks down completely: the initial singularity. This is a huge mystery which we will not discuss here.
The observation relevant to our discussion is that the temperature of the CMB is almost exactly the same everywhere. This is true even if we look at opposite sides of the observable universe. If we look eastward on earth, there is a certain limit to how far your eye can see: the horizon. In a similar way, astronomers use the word “horizon” when they talk about the regions in the universe that lie as far away from us as we can possibly observe. The horizon is determined by the distance that light could have traversed since the universe began. If we look at regions on opposite ends of our horizon (cf., east and west), these are located on opposite ends of our observable universe today. If those areas used to be in contact with each other, their temperature could have evened out through physical processes. However, the 300,000-year time-window between the initial singularity and the emission of the CMB is not large enough to “connect” those regions of our baby universe. In other words, those regions were not located within each other’s horizon (hence the name of the problem, see this link for an illustration).
This leaves Big Bang cosmology with two options. Either (1) the universe started out almost perfectly uniform without causal contact between those regions, or (2) the physical picture of Big Bang cosmology is incomplete. The first option closes the door on physical explanations of the uniformity. That’s why cosmologists have generally favored the second option (and have made impressive progress in that, see below). They are interested in understanding the cosmos in physical terms. In a way, the horizon problem is not about the Big Bang model, but about understanding what gave rise to the initial conditions of that model.
Making a mountain out of a molehill
First of all, it’s important to realize that even the least favorable solution to the horizon problem is still much less dramatic than the proposed solutions for the lack of time in young universe models. This can be illustrated by talking about it from a theological perspective. In case of the Big Bang model, we might solve the horizon problem by assuming that God initially created an almost perfectly uniform universe with tiny density differences from which all the galaxies sprang. A bit ad hoc scientifically, but nothing theologically objectionable here. Now compare this with young universe models. These require a special workaround to explain distant starlight and associated time issues. At the very least, a young universe requires the assumption that God initially created it being “mature”. Unfortunately, this maturity includes an impressive collection of phenomena that indicate event histories spanning billions of years. Consider, for example, the presence of fully formed galaxies, many of them still showing the scars of past collisions, relativistic jets, and differences between distant and nearby galaxies. In that case, God would have loaded the initial conditions of Creation with evidence of events that never happened to begin with. Such deception appears to contradict God’s character as revealed to us in the Scriptures. This provides a stark contrast with the most ad-hoc solution to the horizon problem, initial uniformity, which does not require the assumption that God is lying to us through nature. See the table below for an overview.
Towards a physical solution: an inflatable universe
The set of equations that govern the expansion of the universe is fairly straightforward. They describe how the growth of space occurred gradually for the largest part of cosmic history. However, in the very early universe, circumstances could have been different. Respectable theorists think that the universe went through a period of extremely rapid expansion in the very beginning (around the first 10-32 seconds): inflation. The exact particle mechanism is unknown, but postulating such an inflation era solves a number of questions concerning the initial conditions of the Big Bang.2 One of those is the uniformity of the universe. The period of time before inflation could allow for wrinkles in the universe to be straightened out. Inflation is a relatively simple construct that speaks to several problems at the same time. On top of that, some of its predictions regarding the CMB were confirmed observationally. For these reasons, many cosmologists accept it as an elegant solution that outperforms alternatives. Note here that a solution was only needed because the initial conditions of the Big Bang were otherwise considered to be too “special”. There is also a respectable group of theorists who disagree with inflation theory in its current form. It’s work in progress. For the causality problems of young-universe models, on the other hand, there is no working physical solution that explains the initial conditions.
The merit of a model…
At this point, let me emphasize the distinction between the Big Bang model and its initial conditions. While cosmologists are still working on physical explanations of the starting point of the Big Bang (such as inflation theory), that is not the crux of the matter if we’re discussing its merit as a scientific model. The merit of the cosmological standard model (i.e., Big Bang cosmology) is based on its success in describing the development of our universe, given a relatively small set of initial conditions. Completely independent observations have repeatedly favored the Big Bang over alternatives. Further scientific work is still being done to understand the specifics of its starting point.
An interesting parallel might be drawn with evolutionary theory, which is a powerful explanatory tool for understanding how present-day species emerged from past populations. It already integrates the findings of diverse fields such as paleontology and genetics in an elegant manner. The scientific merit of evolutionary theory is derived from its ability to do exactly that. It does not hinge on theories concerning the development of the first life-form (abiogenesis), which is still largely beyond the reach of empirical research. In a similar way, the value of the Big Bang model does not depend on a complete explanation of how its initial conditions arose. Instead, its achievements are understood by appreciating how it manages to describe the development of the universe after the starting point.
We can now formulate an answer to the question posed in the title of this section. Does Big Bang cosmology have a big problem, comparable to the distant starlight problem of young-universe models? Definitely not. It is misguided to place the horizon problem and the distant starlight problem in the same box, despite their conceptual connection. Our limited understanding of the very early universe does not make or break the Big Bang model. The horizon problem results from minor theoretical concerns. Contrastingly, distant starlight is a devastating problem because it directly contradicts the central claim of young-universe models (i.e., that the universe is less than 10,000 years old). On top of that, we have seen that the universe is filled with evidence of event histories stretching across millions and billions of years. Many times over, such evidence gives our universe the appearance of great age; and indeed, that is the conclusion to take home from this series of posts. When we talk about the age of the universe, ignoring this evidence is no light matter.