For nearly a hundred years, scientists have known that the universe is expanding. This expansion was proposed in the Big Bang theory (the most widely accepted model as to how the universe formed). However, until around 1925, scientists were unsure of the validity of the idea that are universe was growing in size. At this time, Edwin Hubble figured out that, contrary to the popular belief, the universe was not static. Instead, it was expanding, and it had been since the Big Bang. 

The most logical assumption was to believe that since the explosion had occurred billions of years ago, the rate of expansion would have slowed down considerably. Gravity would counteract the forces that generated this expansion. This idea led to the theory of a “Big Crunch” where the forces of gravity overpower the forces of expansion and the universe collapses in on itself. However, there’s one big problem. The rate of expansion isn’t decreasing

Data shows us that the universe is actually speeding up in its rate of expansion. But how is this possible? First, let’s look at how this data was collected. 

One of the methods used analyzes the lightwaves from distant stars. As these waves travel across vast distances, they loose some energy, meaning the length of each wave becomes longer. When this happens, it becomes more redshifted. On the other hand, shorter waves appear to the blue shifted. We know that waves loose energy over long distances. So objects that are closer will appear blue shifted and objects farther away will appear redshifted. 

The light from stars appears red shifted to our telescopes. That much makes sense. The universe is expanding, so the light waves should loose energy by the time they reach us, making their light seem redshifted. However, the thing that continues to puzzle scientists is the increasing rate of expansion. Comparatively, stars are becoming more and more redshifted at faster rates. This means that they are moving away from us at faster and faster speeds. 

If we account for the major forces that we know of in our universe, it shouldn’t be enough to speed up the rate of expansion. If anything, it should be slowing down. This led scientists to the conclusion that there must be another force at work. This force, now called dark energy, is held responsible for the rate of expansion. 

Dark energy (along with dark matter) make up the majority of our universe, however, we know very little about them and their properties. The mystery of these forces continue to baffle scientists, but new discoveries and technological advancements continue to assist the collection of more data, helping us to understand this critical aspect of the cosmos.