Khoury and Weltman proposed that this substance consists of so-called "chameleons".
One attempt to capture this substance used a ball of cesium inside an aluminium sphere. Khoury and Weltman proposed that this substance consists of so-called "chameleons". One theory of it keeps its density below the radiation density until matter-radiation equality, after which it changes. One phenomenon that verifies the existence of it has a non-zero cross-correlation function between galaxy density and temperature. The existence of this substance drives the equation of state parameter below negative (*) one third. The scale factor is proportional to the exponential of the time times Hubble's constant in universes dominated by it. Evidence for its existence includes CMB anisotropies caused by the late-time integrated Sachs-Wolfe effect. This substance is known to exist due to the negative deceleration parameter found by surveys of Type Ia supernovae. For 10 points, name this substance that comprises about 70% of the energy density of the universe and drives its expansion.
One attempt to capture this substance used a ball of cesium inside an aluminium sphere.
dark energy [accept chameleons before mention]