Any difficult search is inevitably described as "like finding a needle in a haystack." But the search for dark energy is just the opposite: We — everything in the universe made of "normal" matter and energy — are the needle, surrounded by the "haystack" of dark energy. To complicate things even more, this search is like trying to find a haystack when you aren't sure if it's a stack or even if it's made of hay.
Similarly, to brush the hay off our vests for a while, dark energy may not be dark and it may not be energy. But astronomers and physicists are convinced that it's there, so they are embarking on several searches.
Since scientists don't know what dark energy is, though, they aren't searching for it directly — at least not yet. Instead, they will study its effect: the accelerating expansion of the universe, which has provided much of the evidence of dark energy's existence. The way in which the universe is accelerating, and changes in the acceleration over time, will help scientists whittle down the list of possible explanations, and may even provide the answer.
The searches will use three basic techniques:
Exploding Stars: Plot the distances and velocities of the exploding stars known as supernovae. More
Sound Waves: Look at the way galaxies are distributed in the early universe to find patterns imprinted in the Big Bang. More
Distortions: Probe the "clumpiness" of the universe at different epochs by studying the shapes of millions of galaxies. More
These studies will probe the universe at different times, from a few hundred thousand years after the Big Bang to the modern epoch, providing a complete picture of how the acceleration has changed over the eons. This information may confirm one of the current theories about the nature of dark matter, or they may suggest an entirely different explanation for the "haystack" of dark energy.