| definition |
In cosmology, a hypothetical new 'element,' distinct from any normal matter (either
baryonic or not) or radiation, intended to explain the observed ever accelerating
expansion of the Universe. Quintessence can have several types and differs from the
cosmological constant in that it can vary in space and time. In modern physics, the
four known "elements" are the baryons (proton, neutron, etc.), the leptons (neutrinos,
electrons, etc.), the photon, and the hypothetical non-baryonic matter, which is thought
to be 80% of the total matter in the Universe. The quintessence field is a possibility
which can be confirmed or disproved by measurements of the dark energy value at different
redshifts. In some models, the quintessence is fine-tuned to explain both the cosmological
constant problem and the inflation in the very early Universe.
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