The field of modern cosmology is the study of the universe and its most important properties, answering questions such as, What is our universe made of? How does it behave? and How did it get to its present state? Two concepts which come up regularly in helping cosmologists to answer these questions are known as
dark matter and
dark energy. And although we often hear about these ideas in the news or in popular science fiction, it's reasonable to ask: What do we actually
know about dark matter and dark energy? How should a Christian think about these concepts, and do they conflict with the description of God's creation of the universe described in the opening chapters of Genesis? Before I try to answer these questions, let me briefly describe what dark matter and dark energy are, and then present some of the primary evidence for their existence.
Dark matter was first predicted in 1933 by a cosmologist named Fritz Zwicky who was trying to understand the motions of galaxies through space. Since the force of gravity causes things to move (e.g., think of dropping an apple), an object's motion through space can be related to the gravitational force that it feels: the stronger the gravitational force, the stronger the effects on the object's motion. In studying how galaxies move in groups, Zwicky found that there was not enough gravitational force between the individual galaxies in the group to explain the overall motions of each galaxy. In order to explain the motions he actually observed, Zwicky needed to find a way to make the gravitational force between the galaxies
stronger than it initially appeared to be. To do this, he first noticed that the gravitational force could be made stronger if he made the galaxies "heavier" by imagining that each galaxy contained more material than just the stars which were visible to his telescopes. This extra material would therefore have to be invisible — meaning that it could not emit visible light the way stars do — and so it came to be known as "dark matter." This dark matter, Zwicky suggested, would make the galaxies heavier, and thereby add the extra gravitational force that was needed to explain the galactic motions he had observed. Since then, Zwicky's conclusions have come to be regarded as a standard part of how we understand our universe: dark matter is generally believed to be present in and around almost every galaxy, even though today we still do not actually know what dark matter
is.
The presence of dark matter can also be inferred from the properties of our own galaxy's motions. If one measures the orbital speed of stars in our galaxy, and how this orbital speed depends on the stars' distances from the galaxy's center, it is possible to use law of gravity to predict how much mass must be contained within those stars' orbits. Interestingly, once scientists actually calculated the predicted mass, and compared it with the total mass of all visible stars in the same region, they again found that the predictions were much larger than the total visible mass, implying that there must be a lot more mass in the same region which is
not visible. Precise numerical calculations based on the most recent cosmological data have estimated that this dark matter is about 5 times as heavy as "normal," visible matter, like stars. Thus, although we still do not know what dark matter is, it nevertheless has a good basis in observation and is very likely (in my opinion) to exist.
Despite having a similar name, dark energy is quite different from dark matter. To understand the primary evidence for dark energy, one first needs to understand something about how astronomers measure distances to cosmological objects, like galaxies. One of the most popular methods uses the concept of a "standard candle," which is an object which has a known brightness that we can calculate. If we can calculate how bright an object
really is, and measure how bright it
appears to be in the night sky, we can use this to estimate how far away the object is. Standard candles are therefore extremely useful for estimating distances in cosmology.
The other bit of background one needs in order to appreciate the significance of dark energy is the realization that
the universe is expanding. This means that almost all galaxies are receding from our own galaxy, and the farther away a galaxy is, the faster it is receding from us. All of this can be written down in precise mathematical form, and it is possible to determine (after working through the math) whether the universe's expansion has been constant throughout its lifetime, or whether it has dramatically sped up (or slowed down) at some point in the past.
Let me illustrate this idea with an analogy. Suppose that you are watching a car drive away from you, and that you know exactly how bright the car's taillights are. As the car drives away, the taillights appear to get dimmer (because they are getting farther away), and you manage to figure out a mathematical equation to relate the car's distance to how bright its taillights appear, and use this to calculate the car's distance from you. Now imagine doing this once every 5 seconds (say). What would happen when you measured the car's distance? If the car were driving at a
constant speed, the distance would change by the
same amount every 5 seconds: 100 feet, 200 feet, 300 feet — a constant increment of 100 feet every 5 seconds — and so on. Now imagine that the car is
accelerating; what would you expect to see? You would start observing larger and larger changes in distance: say, 100 feet, 250 feet, 500 feet, and so on. In short, you would be using only the brightness of the car's taillights (and your clever mathematical equation) to measure the car's speed and acceleration.
This is exactly the same sort of thing that cosmologists have measured with respect to the universe's expansion, and the conclusion has been that the universe is in fact
speeding up. Now, in the analogy above, the acceleration of the car could be explained by the fact that the driver might be pressing on the gas pedal, leading to more energy (and therefore motion) being produced by the car's engine. Cosmologists, on the other hand, have no such "gas pedal" to explain the universe's expansion, so instead they have posited an otherwise unknown "dark energy" to do the explanatory work. The "dark" part, in this case, only indicates that we do not know what the energy
is or where it comes from; it really has nothing to do with the energy being "dark," i.e., invisible to our telescopes.
So how do the concepts of dark matter and dark energy line up with the creation account given in Genesis? In fact,
neither concept poses any significant difficulty for a literal, six-day understanding of God's creation. First, dark matter is simply a theoretical concept invented to resolve some otherwise difficult problems in cosmology. This sort of thing happens regularly in science, and normally with great success. Although the true nature of dark matter is not yet well-understood, I suspect that the next few decades will help to clarify it quite a bit, and it should pose no problem for Christians who understand Genesis to describe the literal account of how God created the universe. The notion of dark matter does nothing to undermine our understanding of how God described His own creative activities in Scripture.
Although dark energy also poses no real difficulties to a literal reading of Genesis, its relationship to Genesis is slightly more complicated. The most obvious connection involves how the idea of dark energy came about in the first place: the prediction of dark energy originated from the expectation that the universe has been expanding since its creation in the Big Bang. If the universe was not actually formed in the Big Bang, however, then it is simply unclear how the apparent acceleration of the universe's expansion should be interpreted. Dark energy may or may not exist; the Big Bang theory indicates that something like it should exist, while the Genesis account is simply agnostic about its existence. In other words, if dark energy
were discovered directly, although it would certainly
fit with an account of the universe's history which denied the literal understanding of Genesis, it is far from clear that the evidence
itself would contradict the Biblical account. Thus, dark energy should likewise not be understood as a hindrance to accepting the Biblical record, even though exactly how the two would fit together is still an open question in creationist research.
Both dark matter and dark energy are theoretical concepts which have been posited by modern cosmologists to help resolve various problems or tensions in the current standard model of the universe. At the time of writing, there has still been no decisive verdict as to which of these, if either, actually exist. Fortunately, whether or not dark matter and dark energy reflect genuine aspects of God's creation, their potential existence poses no threat to the Christian's understanding of Scripture and creation. They are, rather, just one more opportunity for us to worship the Creator.