Einstein said his happiest day of thought was free fall when he cannot distinguish free fall with still.
But can we?
Two objects free fall together will stay together but fall sequentially will fall apart further and further. This distance growth can be measured using other free fall objects such as light although need a correction but qualitatively no problem to confirm. Or sound which is fixed with the air. Two objects stay still will keep distance stationary. So space can be fixed no need to expand or shrink over time in both cases.
Mathematically, people in space can measure if it is Euclidean space or non-Euclidean space using local space as a reference point.
Jixin
Even if air is so thin that it does not drag or react with the falling object, it is unfair to change the space between each air molecule just to meet to perspective of the falling object.
A man and an apple are both in an elevator that free-falls in a gravitational field.
If both are at the same altitude at the beginning, indeed, the man cannot tell if they are in outer space or free-falling in a short period of time.
However, when approaching the center of the attraction, the distance between the apple and the man gets closer due to the centric geometry of the gravitational field, which always points to the center of the mass, i.e., the gravity field line is not parallel along the falling path.
If the apple is above the man along the field line, the apple will flow towards the ceiling of the elevator because the speed of the elevator and the speed of the apple is a function of time over the falling. The elevator, the apple, and the man's mass centers cannot be at the same distance from the attractor center. Thus, they separate from each other over time due to the different speeds of each over time, even though they have the same initial speed.
So the equivalence Einstein assumed is temporary and only works for an extremely short time, i.e., transient.
Also we know that still in outer space is not still, but obitaling the sun and the galaxy center, and other centers. But at least that still will maintain for a long time, say millions of years within measurement error.