For cosmologists, the key question was whether DES’s new cosmic pie chart based on galaxy surveys would differ from estimates of dark energy and dark matter inferred from Planck’s map of the cosmic microwave background.
Lambda-CDM is in many ways a simple model that starts with Albert Einstein’s general theory of relativity, then bolts on dark energy and dark matter.
According to Lambda-CDM, dark energy is the “Cosmological constant,” represented by the Greek symbol lambda in Einstein’s theory; it’s the energy that infuses space itself, when you get rid of everything else.
New dark energy arises in the newly formed spatial fabric, so that the density of dark energy always remains constant, even as the total amount of it relative to dark matter increases over time, causing the expansion of the universe to speed up.
The leading alternative theory envisions dark energy as a field that pervades space, similar to the “Inflaton field” that most cosmologists think drove the explosive inflation of the universe during the Big Bang.
The slowly diluting energy of the inflaton field would have exerted a negative pressure that expanded space, and Frieman and others have argued that dark energy might be a similar field that is dynamically evolving today.
Frieman doesn’t discount the possibility of discovering that dark energy is an evolving quantum field, which would invite a deeper understanding by going beyond Einstein’s theory and tying cosmology to quantum physics.