In 1998, physicist Paul Steinhardt and his colleagues coined a term that would describe a mysterious field of what they believed to be dark energy, or a “fifth essence.” They called it “quintessence.” Based upon an earlier idea proposed by Fermilab physicist Chris Hill and colleague Josh Freeman, quintessence suggested that, like the cosmological constant of Einstein’s vision, this essence fills all of “empty” space with a form of matter-energy that is changeable in strength. Some parts of space might have a thicker quintessence, others a thin “layer,” creating a field of invisible essence that has no direction, like a vector field, only magnitude, like a scalar field. Described as kinetic energy by Tom Siegfried in Strange Matters, the strength of this field would be measured by how quickly it approaches the zero point. Because quintessence is believed to exert negative pressure, it is said to be a slow rolling scalar field, one that does not change too quickly over a period of time. Whether or not quintessence is the dark energy so eagerly sought by physicists will decide the fate of the universe itself, because of its relationship to expansion. The presence of a negative energy in space would possibly stop the expansion
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