Does Anyone Actually Know What Dark Energy Is?

With this composite image, made using data from the Hubble Space Telescope Chandra X-Ray Observatory, researchers have discovered clues to increase our knowledge of dark matter. This image is a powerful collision of clusters. These clusters show formations of dark matter, where it separated from the ordinary matter. (NASA)

Dark matter, dark energy, and black holes. They’re often mentioned in the same breath, but do we really know how they’re linked? Or what we’re talking about at all? Because of the dearth of information related to dark matter and energy, most of the astrophysics field is purely theoretical. Yet, there are some accepted truths and a recent paper from Cornell researchers is looking to confirm one of them.

The Universe is growing at a continuously accelerating rate. While this is not news—that groundbreaking discovery was made in 1998—it’s an incredibly profound notion scientists have been attempting to unpack in the almost two decades since. After nearly 20 years, though, we still don’t know what causes the expansion of our Universe. Scientists have attributed that growth to dark energy… yet don’t know exactly what it is or how it works. That said, there are some theories. The video below discusses them in detail: think of it as “Intro to Dark Matter and Energy.”

As mentioned above, a recent paper from a group of Cornell astrophysicists seeks to confirm the origin of dark energy. The paper supports Einstein’s theory of a “cosmological constant” and the researchers attribute dark energy to “frozen” neutrinos, a type of subatomic particle. The paper argues that as parts of the Universe cool off, a process that takes millions of years, neutrinos “freeze” in their place. These frozen neutrinos would naturally appear to astrophysicists to be dark energy.

In order to better explain their theory, the Cornell group created a simple analogy. Simpson, Jiminez, Pena-Garay, and Verde argue:

“The underlying phenomenology of this freezing process is founded in classical mechanics. A cyclist who is pedaling uphill might begin to struggle against an increasingly steep gradient. Yet no matter how feeble the rider’s power output becomes, they can always maintain a constant pedaling rate, simply by selecting an appropriately high gear. They can never roll backwards.”

Their findings are generating excitement in the field, with astrophysicist Ethan Siegel declaring this “very clever” theory is important because it can be tested and verified. Still confused? Read the paper itself here.