Question

How much big is the universe? What are dimentions?Does multiverse really exist?

Answer 1

 From science fiction to science fact, there is a concept that suggests that there could be other universes besides our own, where all the choices you made in this life played out in alternate realities. The concept is known as a "parallel universe," and is a facet of the astronomical theory of the multiverse.

The idea is pervasive in comic books, video games, television and movies. Franchises ranging from "Buffy the Vampire Slayer" to "Star Trek" to "Doctor Who" to "Digemon" use the idea to extend plotlines. (A fuller list of parallel universes in fiction is at the bottom of the article.)

There actually is quite a bit of evidence out there for a multiverse. First, it is useful to understand how our universe is believed to have come to be. 

Answer 2

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universe is expounding day by day so it is nearly impossible to say how big it is.

let me make uh understand what multiverse actually is!!

→ multiverse is the collection of universes .

there is an idea that there is more than one universe hence the collection of universes called multiverse.

$\bf{→ \: my \: idea \: on \: multiverse}$

before I start I just wanna ask a question !

what was there before big bang?

if ur answer is nothing,

then tell me how big bang occurred and there should be a space in which it occured .

for big bang it needs energy and hence my idea is that big bang occurred in multiverse like other universes.