Gravity Gravity ( g ) is one of the four main forces within the standard model of particle physics . Gravity has been historically defined as the mass between two objects . ( ) Gravity phenomena have a direct relationship to field density . ( ) Gravity is defined throughout the universe by a gravitational constant , which sets the relative strength of the force . The have the ability to change the gravitational constant of the universe , and thereby redefine gravity . ( ) Effects of gravity . While often considered an apocryphal story , the " invention " of physics , and a new era in the understanding of gravity was born the day the apple fell on Isaac Newton ' s head , thanks to the jostling of an apple tree by Quinn . ( ; ) Spock once used a reference based on this " discovery " in a statement describing the behavior of James T . Kirk , stating , " " If I let go of a hammer on a planet that has a positive gravity , I need not see it fall to know that it has in fact fallen . " " ( ) While climbing El Capitan , Spock , using gravity boot s , tells Kirk that he believes he doesn ' t understand the gravity of the situation . But Kirk tells him that " Gravity is foremost on my mind . " ( ) During a scan of Aldean DNA , Doctor Beverly Crusher was able to confirm that gravitational variations were not responsible for the Aldeans ' sterility . ( ) Earth normal . An M class planet is defined by having a gravity that is approximately equal to Earth ' s sea level . ( ) Gravity found to be similar to Earth was often described as " Earth - normal . " ( ) Other planets , such as Talos IV , had a gravity of 0 . 9 " g " , which was ten percent " lighter " than the gravity found on Earth . ( ) Contrarily , Exo III had a gravity of 1 . 1 " g " , which was ten percent " heavier " than Earth ' s . ( ) The gravity aboard the hulk of an abandoned insectoid ship was within two points of Earth - normal . ( ) Adaptations to gravity . Typically , the effects of gravity fluctuations on humanoid s that are adapted to an " Earth - normal " gravity can cause them to get symptoms of nausea . ( ) The manipulation of gravity , via means of artificial gravity , has been a scientific breakthrough for many species , dating back billions of years . ( ) Earth began employing artificial gravity technology as early as the 22nd century . ( ) On more than one occasion , the gravity aboard the fell to 0 . 8 " g " . ( ) While this was not typical aboard Earth or Federation starships , in the early days of space travel , freighter captain s enjoyed manipulating gravity to make their crew s light on their feet . ( ) Captain Mayweather of the kept the ship ' s gravity at a level of 0 . 8 " g " . ( ) While training a crew of former Maquis , Tuvok increased the gravity on certain deck s aboard the by ten percent during their exercise run . ( ) Some lifeform s could manipulate gravity by their own will , such as the dikironium cloud creature , which was capable of using gravity as a propulsive force . ( ) Other species were capable of living in a variable - gravity environment , such as Bevvox , a bioplasmic lifeform . ( ) The Elaysian s were a humanoid species whose planet had a gravity much lower than that of Earth , and were unable to function fully in Earth - normal gravity . ( ) Experiments with gravity . During the mid - 23rd century , a means was devised , called the slingshot effect , that made use of a star or planet ' s gravity as a mode of time travel . ( ) The Manheim Effect was created by Paul Manheim , based on a theory regarding the manipulation of both time and gravity . ( ) Nathaniel Teros was a scientist who did extensive work with low gravity species , namely through neuromuscular adaptation . ( )