Science Speaker: Evolving Dark Energy?

Dr. Noah Weaverdyck ’11 is a researcher in cosmology at the Lawrence Berkeley National Laboratory. He’s immersed in building statistical models to analyze data from large-scale surveys of galaxies.

Two of the collaborations he takes part in recently unsealed their surveys and both found evidence that dark energy might *not* be as constant as the simplest models suggest, but rather seems to be weakening as the universe expands.

Weaverdyck is a member of the Dark Energy Survey (DES) collaboration, where he co-leads the Large Scale Structure Systematics analysis team and the Dark Energy Spectroscopic Instrument (DESI) at the Berkeley Lab.

Background: What is the universe made of?

Einstein showed that mass and energy are interchangeable. In terms of this “mass-energy,” our universe seems to consist of around 68% dark energy, 27% dark matter and only 5% normal matter that interacts with light.

Gravity causes mass (both dark and normal) to clump together, forming stars, solar systems and galaxies.

Early in the 20th century, red-shifted light in all directions showed that the universe is expanding. Two groups studying supernovae in the 1990s found that the expansion is accelerating. Unlike gravity, ‘dark energy‘ is pushing mass apart.

We have no direct observations of dark energy. The prevailing model of big bang cosmology, Lambda-CDM, makes a simple assumption that there is a constant dark energy density throughout ’empty’ space.

• Lambda, or Λ, is the symbol for this constant energy density, and also refers to Einstein’s cosmological constant (which implied a repulsive force, if greater than zero)
• CDM stands for Cold Dark Matter