Search for 'dark energy' could illuminate origin, evolution, fate of universe

The hundreds of billions of galaxies it contains, each of them home to billions of stars, planets and moons as well as massive star-and-planet-forming clouds of gas and dust, and all of the and other energy we can detect in the form of electromagnetic radiation, such as , gamma rays and X-rays—in short, everything we've ever seen with our telescopes—only amounts to about 5% of all the mass and energy in the .

Along with this so-called normal matter there is also dark matter, which can't be seen, but can be observed by its gravitational effect on normal, visible matter, and makes up another 27% of the universe. Add them together, and they only total 32% of the mass of the universe—so where's the other 68%?

Dark energy.

So what exactly is dark energy? Put simply, it's a mysterious force that's pushing the universe outward and causing it to expand faster as it ages, engaged in a cosmic tug-of-war with dark matter, which is trying to pull the universe together. Beyond that, we don't yet understand what dark energy is, but Penn State astronomers are at the core of a group that's aiming to find out through a unique and ambitious project 16 years in the making: HETDEX, the Hobby-Eberly Telescope Dark Energy Experiment.

The Hobby-Eberly Telescope. Credit: Marty Harris, McDonald Observatory, UT Austin

This pie chart shows rounded values for the three known components of the universe: normal matter, dark matter, and dark energy. Credit: NASA's Goddard Space Flight Center

This diagram shows the changes in the rate of expansion since the universe's birth. The shallower the curve, the faster the rate of expansion. The curve changes noticeably about 7.5 billion years ago, when objects in the universe began flying apart at a faster rate. Astronomers theorize that the faster expansion rate is due to a mysterious force — dark energy — that is pulling galaxies apart. I. Credit: NASA/STScI/Ann Feild

In this representation of the evolution of the universe, the far left depicts the earliest moment we can now probe, when a period of “inflation” produced a burst of exponential growth. The afterglow light (known as the cosmic microwave background) was emitted about 375,000 years after inflation and has traversed the universe largely unimpeded since then. The conditions of earlier times are imprinted on this light, which also forms a backlight for later developments of the universe. Credit: NASA/WMAP Science Team