(I feel like stating the obvious...
)
"whatever begins to exist must have a cause for it's existence".
I think that's overly complicated.
"whatever" = any/every
"begins to exist" = action
"cause for it's existence" = cause of an action
Or in simple words: Every action must have a cause.
But what would the cause be? You cause something to happen by enacting it - ie: with an action.
So: Every action is caused by an action.
And to reverse that and put it into rather familiar terms:
Every action has an equal and opposite reaction.
Newton's First Law, I think?
But anyway, the whole "you can't get something from nothing", in strict terms, is (to me) so blatantly true that anyone asking for proof of it is just being ridiculous.
Sure, there will be plenty of times when it
appears to be false - when things seem to come from nothing - but all that means is that we couldn't detect the cause.
As for the inevitable yet redundant religious debate: Anyone thinking the statement can prove or disprove the existance of a god is being a fool.
God might or might not exist. The statement being true doesn't prove that either way. If the statement was false, it still wouldn't prove it either way.
As for what the smallest unit of existance is - it is whatever the most powerful microscope in existance can detect.