The Visitors have harnessed the ability to manipulate gravity.
- Motherships hover indefinitely above major cities
- Shuttles glide effortlessly between the motherships and Earth
- Apples are shown in a demonstration floating
- Seekers have no visible means of propulsion
The vehicles presumably produce their own gravity manipulation. Seekers do as well, unless they are being manipulated by external means. This means that the technology is very small (at least for small objects). Conversely, the apple demonstration shows that, unless there's a device planted within them, the technology exists to manipulate the force of gravity on other objects.
Shuttles appear to require thrust vectoring in addition to gravity repulsion. This implies that the gravity repulsion is solely to provide lift. However, the seeker does not appear to have any airfoils, suggesting that smaller objects, if able to provide their own propulsion, can be moved laterally via gravity manipulation.