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There does arise, however, a strange difficulty. The

interpretation of the galactic line-shift discovered by Hubble as

an expansion (which can hardly be doubted from a theoretical

point of view), leads to an origin of this expansion which lies

"only" about 109 years ago, while physical astronomy makes it

appear likely that the development of individual stars and

systems of stars takes considerably longer. It is in no way known

how this incongruity is to be overcome.

I further want to remark that the theory of expanding space,

together with the empirical data of astronomy, permit no decision

to be reached about the finite or infinite character of

(three-dimensional) space, while the original "static" hypothesis

of space yielded the closure (finiteness) of space.

K = co-ordinate system

x, y = two-dimensional co-ordinates

x, y, z = three-dimensional co-ordinates

x, y, z, t = four-dimensional co-ordinates

t = time

I = distance

v = velocity

F = force

G = gravitational field