2. Virtual particles
Quantum mechanism is something unexceptional and is hard to understand. It helps in the interaction of virtual particles with the ordinary particles.
This theory greatly depends upon the visual particles. The theory provides information regarding the small amount of matter which appears for a small time interval and then disappears. The presence and disappearance of the matter releases energy as the particles are transformed into energy.
The physicists explain that the space creates energy through this way and poses negative pressure on the universe which leads to its expansion.
It is one of the hypothetical theories that have been developed about the dark energy. The hypothesis is developed on the basis of expansion of the universe.
The Quintessence was first presented into papers by Rahul Dave, Paul Steinhardt and Robert R. Cardwell. According to some physicists, it is the fifth fundamental force. It is also reported to be the latest theory that is different from the cosmological theory as it is dynamic in nature and the cosmological constant does not change.
The fundamental of this theory is that the quintessence varies with location and time and thus the energy density decreases with time.