Please wait to see the images move. There are 2 great forces in space. The negative force and the positive force. The negative force contacts the positive force by electric charge, which formed thunder between the 2 forces. Thunder between the 2 forces generates large amount of energy.
Energy causes space to expand.
Billions of years later, our universe will shrink again to its original size. Then it becomes a black hole. Expanding universe is a hot universe. Shrinking universe is a cold universe, which is a black hole. Shrinking universe becomes cold and awaits one day to be hit by the thunder again.