Several lines of evidence also suggest that a rapid cosmic inflation of the Universe occurred very early in its history (roughly 10 seconds after its creation). Recent observations also suggest that the cosmological constant ("Λ") is not zero, and that the net mass-energy content of the Universe is dominated by a dark energy and dark matter that have not been characterized scientifically. They differ in their gravitational effects. Dark matter gravitates as ordinary matter does, and thus slows the expansion of the Universe; by contrast, dark energy serves to accelerate the Universe's expansion.