1)The sky is dark! (Olber’s
Paradox)
If the Universe were infinite in space and time, every line of sight would eventually
end on a star. Even if it were very far away and faint, that would
be made up for by having more of them in a smaller patch of sky. The sky should have
the same brightness as the Sun (or at least an M star!). This resolved by
the fact that the Universe started a finite amount of time ago (the expansion
helps too
with the redshift).