title: Detection of gravity through nonequilibrium mechanisms.
abstract: Using the principles of physics, could we set a fundamental lower limit for the size of a cell that can respond to gravity?  Pollard (1965) tried to obtain such a limit assuming a gravity sensing mechanism that could be described as a system in thermodynamic equilibrium.  In this chapter, a dynamic gravity sensing mechanism that is not in thermodynamic equilibrium is considered.  It is shown that under some conditions nonequilibrium systems can be more sensitive than equilibrium systems.  The dynamic mechanism described here is able to respond to gravity by virtue of its ability to perform a process similar to "signal averaging" used in electronic detection of weak signals.  Through this process, a system is able to respond to a small systematic force embedded in a larger but randomly fluctuating force.
authors.affiliation: Department of Chemistry, Wake Forest University, Winston-Salem, NC 27109.
authors.forename: D K
authors.initials: DK
authors.lastname: Kondepudi
mesh_terms: D002465:Cell Movement; D002468:Cell Physiological Phenomena; D048429:Cell Size; D055598:Chemical Phenomena; D002621:Chemistry; D006112:Gravitation; D018466:Gravity Sensing; D008954:Models, Biological; D011336:Probability; D015398:Signal Transduction; D013816:Thermodynamics