The word gravity, from the Latin gravitas, means both weight and heaviness. Gravity is the physical force of attraction between all bodies with mass, be it on a sub-atomic level or on an astronomic scale. Gravity has an infinite extent, and it cannot be absorbed, transformed, or shielded against.

Reduced gravity, microgravity, or zero gravity describe conditions in which the physical force of gravity is limited, diminished, or even (almost) suspended. In these circumstances a body is exposed to a condition of lightness or weightlessness. When a gravitational field is non-uniform, a body in free fall suffers tidal effects. Near a black hole, such tidal effects can become very powerful. Gravity lends weight to all objects and causes the tides, but it can also be used to connote seriousness and depth, or a metaphorical weight or tide.If gravity is another word for seriousness, lightness connotes levity, humour and flippancy. In his collection of lectures, Six Memos for the New Millennium, Italo Calvino remarks, “There is such a thing as a lightness of thoughtfulness, just as we all know there is a lightness of frivolity. In fact, thoughtful lightness can make frivolity seem dull and heavy.”

There are only a few activities providing us with both aspects. Moving on a swing, dancing, making art, caring for a lover can all be both: lightheaded thoughtfulness and lightheaded frivolousness at the same time. Feeling strong enough to part from the ground, but heavy enough to come back again. When the assertion of coming back fails us, we will become very anxious indeed. What if we jump up and do not come back down again?