All known existing matter, spacetime, the cosmos, and its components considered as a whole. That was easy, wasn't it?
The catch? ***known***
The problem is there is so much unknown, that we are necessarily limited by our own cognizance.
How can we know the unknown?
We can not. We can postulate through mathematic modeling that which should exist. But we don't know if it does actually exist.
Is there a parallel universe?
In science fiction, yes without a doubt. In general relativity theory, no. In quantum physics, yes.
How can they both be true?
There are mathematic modeling and a special theory of relativity. But there are many too many bumps in the math to make it a straightforward model. That is solved by string theory.
String theory smooths out the mathematical inconsistencies that currently exist between quantum mechanics and the theory of relativity.
String theory cont.?
It posits that the entire universe can be explained in terms of really, really small strings that vibrate in 10 or 11 dimensions — meaning dimensions we can't see.
So, a multiverse?
So what, who cares?
Every writer should care! Think of the possibilities. Reverse entropy? Thermodynamics upside down? Space time discontinuum?
Anything you can think of, dream of, or imagine won't even be a speck in a stadium of possibilities.
Why did I post this?
Because it is a thrilling and exciting to be alive in this fragrant and fecund world. If I can excite one other person with the endless possibilities of life , I would be thrilled.