Question

why universe is expanding day by day??

Answer 1

milky way example and more components are coming in existence because of cosmic effects

Answer 2

the universe is continually expanding.If fact the rate it which it is expanding seems to be increased.The cause of this increase has given the name dark energy. but we don't really know what it is.

However, on any scal that humans encounter every day, the expansion is far, far too small to be measured. Even on the scale of the Galaxy, hundreds of light years across, the expansion is to small to be noticeable. Only on the scale of galactic clusters is it even noticeable.
this is your ans.