Quintessence (physics) in the context of "Fifth force"

Current observations suggest that the expansion of the universe will continue forever. The prevailing theory is that the universe will cool as it expands, eventually becoming too cold to sustain life. For this reason, this future scenario popularly called "Heat Death" is also known as the "Big Chill" or "Big Freeze". Some of the other popular theories include the Big Rip, Big Crunch, and the Big Bounce.

If dark energy—represented by the cosmological constant, a constant energy density filling space homogeneously, or scalar fields, such as quintessence or moduli, dynamic quantities whose energy density can vary in time and space—accelerates the expansion of the universe, then the space between clusters of galaxies will grow at an increasing rate. Redshift will stretch ancient ambient photons (including gamma rays) to undetectably long wavelengths and low energies. Stars are expected to form normally for 10 to 10 (1–100 trillion) years, but eventually the supply of gas needed for star formation will be exhausted. As existing stars run out of fuel and cease to shine, the universe will slowly and inexorably grow darker. According to theories that predict proton decay, the stellar remnants left behind will disappear, leaving behind only black holes, which themselves eventually disappear as they emit Hawking radiation. Ultimately, if the universe reaches thermodynamic equilibrium, a state in which the temperature approaches a uniform value, no further work will be possible, resulting in a final heat death of the universe.

Christof Wetterich (born April 12, 1952) is a German theoretical physicist. He is a professor of theoretical physics at the Heidelberg University. He is known for his work on the Seesaw mechanism in grand unification theory (GUT), quintessence, the Wetterich equation for the functional renormalization group (FRG) and asymptotic safety in quantum gravity.

Robert R. Caldwell is an American theoretical physicist and professor of physics and astronomy at Dartmouth College. His research interests include cosmology and gravitation. He is known primarily for his work on theories of cosmic acceleration, in particular dark energy, quintessence, and the Big Rip scenario.

He coined the term phantom dark energy.