What is Multiverse and does it really exist?

The Question of existence of Multiverse is still a matter of debate in the scientific community, Many Scientists supports this hypothesis including Stephen Hawking, whereas many criticize.

What is Multiverse?

A  hypothetical set of infinite or finite possible universes (including the Universe we live in). it consists of everything that exists : the entirety of space, time, matter, and energy as well as the physical laws and constants that describe them. it is also known as meta-universe. This hypothesis is a matter of debate within the physics community. Physicists disagree about whether the multiverse exists, and whether the multiverse is a proper subject of scientific inquiry.

"Bubble universes" (Source)

Supporters of Multiverse Hypothesis -

 (Click on Scientist's name to read his/her bio.)

Many Scientists including Jim Baggott, David Gross, Paul Steinhardt,George Ellis and Paul Davies have argued that the question of existence of multiverse is philosophical rather than scientific, that the multiverse cannot be a scientific question because it lacks falsifiability, or even that the multiverse hypothesis is harmful or pseudoscientific. (Source)


Author and Cosmologist, Paul Davies In his 2003 NY Times opinion piece, A Brief History of the Multiverse offers a variety of arguments that multiverse theories are non-scientific :

For a start, how is the existence of the other universes to be tested? To be sure, all cosmologists accept that there are some regions of the universe that lie beyond the reach of our telescopes, but somewhere on the slippery slope between that and the idea that there are an infinite number of universes, credibility reaches a limit. As one slips down that slope, more and more must be accepted on faith, and less and less is open to scientific verification. Extreme multiverse explanations are therefore reminiscent of theological discussions. Indeed, invoking an infinity of unseen universes to explain the unusual features of the one we do see is just as ad hoc as invoking an unseen Creator. The multiverse theory may be dressed up in scientific language, but in essence it requires the same leap of faith.
— Paul Davies, A Brief History of the Multiverse

George Ellis,  Taking cosmic inflation as a popular case in point writes that

As skeptical as I am, I think the contemplation of the multiverse is an excellent opportunity to reflect on the nature of science and on the ultimate nature of existence: why we are here… In looking at this concept, we need an open mind, though not too open. It is a delicate path to tread. Parallel universes may or may not exist; the case is unproved. We are going to have to live with that uncertainty. Nothing is wrong with scientifically based philosophical speculation, which is what multiverse proposals are. But we should name it for what it is.
— George Ellis, Scientific American, Does the Multiverse Really Exist?

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