Believe it or not, the extreme mega-ellipsis is not the worst thing about this example.
I’ll prove this is nonsense: Right now, as I type this post, I’m trying to grasp that number… and my head hasn’t collapsed into even relatively ordinary degenerate matter, much less a black hole.
Beginning a sentence with There exists sounds awkward. I see it a lot these days, and I suspect it’s someone’s idea of how to avoid the oh-so-evil Because Passive Voice (although it isn’t!) use of is. Fun fact: replacing is with exists doesn’t mean you’ve got a zingy and exciting verb now; you just have one that draws inappropriate attention to itself without changing the essential meaning.
Called as is also awkward and nonstandard. Change to either called or known as. (You could also rewrite the sentence, as I plan to do, so you don’t need either.)
Also, why is entropy (which is not supposed to be capitalized) enclosed in double quotation marks as if it’s not, like, regular entropy but more like freaky entropy?
What is it supposed to mean, “your brain will exceed the maximum limit it can hold”? Maximum of what? Also, you should delete either maximum or limit; you don’t need both.
Replace the ampersand (&) with and. Then add a comma after and.
If for some unfathomable reason you must write this nonsense, this is how to do it:
Graham’s Number is so big that if you try to grasp it, the entropy of your brain will exceed its possible limits, and your head will collapse into a black hole. Strange…