God is so quiet

[SteveII]

No, there is no logical reason that the physical universe/cosmos/multiverse exists necessarily.

This is simply not true at all.   Quite the opposite, in fact.  The universe existing necessarily is the only logical explanation, IMO. 

Necessarily' means "could not have been otherwise".

correct.

We can all conceive of a state of affairs (a possible world) where nothing at all exists

We could conceive of that world, sure.  But it wouldn’t be nothing.  Nothing cannot “be”, or, “have been” any type of world, or any kind of thing, lol.  Absolute nothingness is a logically incoherent concept, try as we might.  Any “state of affairs” would not be nothing.  It would be some kind of state...with affairs.  ‘Absolute nothing’, is simply an expression of the human mind attempting to comprehend, ‘not any of this’. 

By admitting that we could logically conceive of both a possible world where we have our universe (obviously) and a possible world where it did not exist means precisely that the universe does not 'necessarily' exist. I address 'nothing' below.

Since we can conceive of both possible worlds as being broadly logically possible

We may instinctively attempt to conceive of “nothing” as a way to maintain logical continuity within this ‘cause and effect’ type of experience we’re used to, but “nothing”, described as any kind of thing, is by definition something, not nothing. And, non-existence, by definition, cannot exist.  

Ya’ll get any of that?  😝

In philosophy, 'nothing' (along with nobody, nowhere, none, etc.) are terms of universal negation. All you are doing is playing games with a word that grammatically is a pronoun and making it into a noun. If I had nothing for lunch today, I do not mean that I ate something and it was nothing. If I saw nobody in the office, I do not mean I saw somebody called nobody. 

You are propagating a silly argument that only exists in the world of the atheist echo chamber. Go ahead, find a serious philosopher who has written on the somethingness of nothingness.