I personally believe that the dark holes in our universe will fusion until a critical mass is being achieved (some kind of a big crunch). this mass will transform into [(pure energy which is not able to generate gravitiy) <--- I am not sure about this part]. shit happens i don't know what so a new big bang is born... the string theory is a theory that can explain many different universes and this 2nd big bang is going to be one of these different universes with different physical properties.. all this has been happening for alltime. maybe we live in the 515123879488561234568468423112148*10^546541054651624110045561561th universe
and of course there is a multiversum but imo there is no expansion of room and time so no bubbles i think. the distance between one universe and another is fucking great but maybe the gravitation of one universe is immense so this one universe is pulling on our galaxys..

my 5 cents

Energy creates gravitational accelerations, just like mass. And don't forgot gravitational energy is negative.

but energy only exists in our imagination.. i mean there is no existing thing that you can call energy therefore it has no mass and no mass = no gravitiy amiright?

put your hand on a hot stove and see if it exists only in your imagination.

well this is only warmth.. the inner energy makes the atoms swing and interact with the environment.. this is just a result of energy not energy itself

maybe you can paint energy and show it to me

When you come to a street corner and see a car coming, you are really only seeing the light that has bounced off a car. But only the best philosophers would fail to infer the existence of the car from the light that has bounced off of it. Unfortunately these top philosophers have become extinct from failing to look both ways while crossing the street.

god made it.

Chuck Norris.

universe begins how?

It is not said, because noone actually knows. The big band refers to something that happened, which started the process of cosmic creation. For now, the bang itself is an unknown event.