We explore the fate of the universe given the possibility that the density associated with ‘ dark energy ’ may decay slowly with time .
Decaying dark energy is modeled by a homogeneous scalar field which couples minimally to gravity and whose potential has at least one local quadratic maximum .
Dark energy decays as the scalar field rolls down its potential , consequently the current acceleration epoch is a transient .
We examine two models of decaying dark energy .
In the first , the dark energy potential is modeled by an analytical form which is generic close to the potential maximum .
The second potential is the cosine , which can become negative as the field evolves , ensuring that a spatially flat universe collapses in the future .
We examine the feasibility of both models using observations of high redshift type Ia supernovae .
A maximum likelihood analysis is used to find allowed regions in the \ { m, \phi _ { 0 } \ } plane ( m is the tachyon mass modulus and \phi _ { 0 } the initial scalar field value ; m \sim H _ { 0 } and \phi _ { 0 } \sim M _ { P } by order of magnitude ) .
For the first model , the time for the potential to drop to half its maximum value is larger than \sim 8 Gyrs .
In the case of the cosine potential , the time left until the universe collapses is always greater than \sim 18 Gyrs ( both estimates are presented for \Omega _ { 0 { m } } = 0.3 , m / H _ { 0 } \sim 1 , H _ { 0 } \simeq 70 km/sec/Mpc , and at the 95.4 % confidence level ) .