They move around like they have no mass because they use gravity propulsion- They ‘feel’ like they are standing still, and the world is moving around them.
As I understand it, in some theories when you drop a rock, the rock isn’t falling towards the Earth. Instead, the rock remains stationary and the Earth moves up to meet the rock.
So, the idea that a ship remains stationary and the universe moves around it is theoretically possible.
Doesn’t make any sense to me. But then a lot of advanced theories don’t make sense to me.
My thought is that they are 4-dimensional and phase in-and-out of our 3 dimensions as desired.
The reason this is my supposition, is as follows: The retired Israeli director of space assets and operations, is on record saying that we are in communication with the aliens and that they do not want the public to know about them "until mankind understands what space and spaceships are."
Sounds 4-dimensional to me!