Whenever anyone used to put question before Buddha-the-Gautama: "When was universe created?" His standard answer was: "It has always been there."
If you consider matter, which is illusory potency of supreme personality of Godhead Shri Krishna, you realize that it's true.
There have been three( and only three entities) quintessential entities always(because there has never been a 'beginning.')
These entities are: Krishna(God/Brahm), Jeevas(Souls) and Maya(matter/universes/illusory-potency).
Krishna is superconscious, Jeevas have tiny consciousness in comparison whereas Maya is inert.
Billions upon billions of universes come into existence when Mahavishnu(an expansion of supreme personality of Godhead Krishna) exhales. These universes come out from pores of his body and when he inhales they merge back into him.
But the illusory potency Maya which was invested in the universes stays same.
Jeevas which come to play and dance in universes do so until those universes merge back into Mahavisnu and then they all go for sleep unless they have attained love for Krishna, in which case only they reach Goloka(or Vaikuntha if devotee is of Vishnu), otherwise they have to rest inside Mahavishnu till next cycle of creation of universes. Then again molecular Mayic play and liberation, or devotion or sleeping again inside Mahavishnu.
But the universes which subside into Mahavishnu don't die, neither they were created in an actual sense.
They have always existed inside him and will always exist inside him.
Such is Krishna's divine play with one fourth of his potencies.
Three fourth of his potencies are in Paravyoma--spiritual sky--which are not known to anyone.
Even Big-Bang model has been replaced by Big-Boom model which suggests the cosmic cycles of expansion and contraction of universes which hint towards eternal nature of created universes.