A
quintessence scalar field is like a field of springs covering every
point in space, with each spring stretched to a different length, ... For Einstein's cosmological constant, each spring would
be the same length and motionless.

A quintessence scalar field is like a field of springs covering every point in space, with each spring stretched to a different length, ... For Einstein's cosmological constant, each spring would be the same length and motionless.

The cosmological constant
was a vacuum energy (the energy of empty space) that kept gravity from
pulling the universe in on itself, ... A problem with the
cosmological constant is that it is constant, with the same
energy density, pressure, and equation of state over time. Dark energy,
however, had to be negligible in the universe's earliest stages;
otherwise the galaxies and all their stars would never have formed.

The cosmological constant was a vacuum energy (the energy of empty space) that kept gravity from pulling the universe in on itself, ... A problem with the cosmological constant is that it is constant, with the same energy density, pressure, and equation of state over time. Dark energy, however, had to be negligible in the universe's earliest stages; otherwise the galaxies and all their stars would never have formed.

If the results from measurements such as those that could be
made with SNAP lie outside the thawing or freezing scenarios, then we
may have to look beyond quintessence, perhaps to even more exotic
physics, such as a modification of Einstein's General Theory of
Relativity to explain dark energy.

Because dark energy makes up about 70 percent of the content
of the universe, it dominates over the matter content. That means dark
energy will govern expansion and, ultimately, determine the fate of the
universe.