However there is a lot of time for it to happen , you might think several times about what will happen after Kalyug. There aren't a lot of theories for explaining it , but according to Hindu Scriptures as we know about the cycle of yugas , Satyug will start again after Kalyug.
A new universe will be formed with a new world giving life and enormous light all around. The same thing related to the Big Bang theory ( Singularity of Energy inflates into incredibly huge amount of energy giving life to a new universe , the process by which our universe was born.)
After the Big Bang , a huge swarm of gas was formed in the space , it expanded itself, and cooled down. New stars and planets were formed , then our Sun and Earth was formed. Life began from the sea , it evolved itself , forming new lives , animals , birds , then humans.
However the beginning of universe still has a mysterious and unknown process. The Big Bang theory after all , isn't seen by us.