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.

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.

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.

Scientists have been arguing the question 'how precisely do we need to
measure dark energy in order to know what it is?' ... What
we have done in our paper is suggest precision limits for the
measurements. Fortunately, these limits should be within the range of
the JDEM experiments.

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.