Finding out what constitutes dark energy is an intrinsically difficult task because of the fact that its source is completely unknown, as well the fact that it doesn’t, y’know, emit any light. But researchers at NASA aren’t just going to roll over and let the mystery of dark energy go unsolved; on the contrary, the space agency is doubling down on its efforts to figure out what makes up a whopping 68% of the universe, and its latest endeavor is explained in the clip below.
Although you’ve probably seen hundreds of videos and articles speculating on dark energy, this one is a bit different because it highlights an easy way to understand where the “need” for dark energy comes from in terms of how to explain the physics of the universe. In the clip, the narrator explains that there is a fundamental mismatch between the brightness of white dwarf star supernovae and how much the light we receive from them here on Earth has been redshifted.
As the video explains, researchers have been able to look up into the sky and track down type IA (pronounced “one-a”) supernovae at different cosmological distances. And because the type IA supernovae are all roughly the same magnitude in terms of brightness, one that’s further away than another would obviously become dimmer, which is expected and indeed observed.
The need for dark energy arises when researchers take into account the way the light from type IA supernovae is redshifted upon observation. Redshifting of light occurs as a light source moves away from an observer — as the distance between the light source and the observer increases, the frequency of the lightwaves observed decreases, and therefore moves more toward the red end of the visual light spectrum. (Think of an ambulance’s siren decreasing in pitch as it drives away from you; a siren is, of course, a sound wave moving through air, but the same principle applies.)
Researchers are finding that light observed from type IA supernovae is redshifted more than expected when compared to how dim or bright the supernovae sources are — in other words, supernovae that are further from our observation post (Earth) are, according to how much their light is redshifted, moving away from us faster than those that are closer to us. In fact, there’s a direct correlation: the further away the supernovae are, the faster they’re moving away from us. Which means there’s some kind of energy pushing supernovae (and everything else) away from us faster and faster, but we can’t see it. Things “flying” away from us wouldn’t just happen to pick up speed, something needs to make them go faster.
But even though this is a relatively simple way to understand the need for dark energy in our theoretical puzzle of the physical universe, how is NASA actually doubling down on its goal of figuring out what it is? With the Wide Field Infrared Survey (WFIRST) telescope shown in the video immediately above.
As the video notes, NASA’s WFIRST telescope is going to map a ton of these type IA supernovae, as well as some other sources of EM radiation, to see how they move over cosmic time. This probably won’t give us a direct answer as to what dark energy is, but it will help us to better come up with its properties. As of now, we’re still waiting on an equally succinct NASA video on dark matter, which makes up another 27 percent of the universe….
What do you think of this dark energy explainer video? Are you excited for the launch of WFIRST, which will come some time in the mid 2020s? Let us know your thoughts in the comments!