The vast emptiness of the space with no gravitational pull ( unless we are in a proximity of a heavy object) ,the lack of an inherent fixed point to which the direction can be given upon ,the degree of freedom (DOF) of a particle to move freely in 3D space and as well the relativity of motion has to do with the fact that a particle in space ,is infact cannot have a specific direction to move such as “up” /”down” or right/ left.There is no Universal centre/gravity centre with reference to which we can calculate a direction , unlike which is present on Earth,due to latitudes and longitudes.If we consider an observer placed at a distant celestial object,who is observing a particle coming towards it ,the observer may comment the particle is coming down (keeping in mind that the distant celestial object is fixed relative to the motion of the particle) .The observer may also comment ,that the particle is moving left or right .The absence of absolute motion is also the cause for no fixed ‘up’ or ‘down’ or whatsoever.All the celestial objects are moving relative to each other  and thus allows for the fact that space is also expanding with objects either drifting away or moving in opposite to the expansion.While ,we should also consider the fact that , an observer travelling in a space craft reaches in the proximity of a celestial body ,know that going downs means going towards its surface and going down means the vice-versa .But this is also relative to the observer and the inertial design of the space craft .

Thus ,we can conclude that ,a particle in a 3D space cannot move with a designated direction as of up / down or right-left unless there’s another observer to observe it or there is a gravity centre.