According to this theory, The universe is supposed to be expanding and contracting alternatively i.e. pulsating. At present, the universe is expanding.
According to pulsating theory, it is possible that at a certain time, the expansion of the universe may be stopped by the gravitational pull and it may contract again.
After it has been contracted to a certain size, explosion again occurs and the universe will start expanding. The alternate expansion and contraction of the universe give rise to Pulsating Universe.