“If God is everywhere, how can anything else exist outside of Him? For example, how can God and Satan occupy the same space?”
God is everywhere, but that is not the same thing as saying He is everything. God is not a physical being. He is not part of this universe. God is spirit. Physical laws only apply to what is physical. If God chooses to reveal Himself in a physical body (as He did with Jesus – John 1:1,14, Isaiah 7:14, Matthew 1:20-23, 1 Timothy 3:16), that body can only be in one place at a time. When Jesus was physically present in Jerusalem, He couldn’t physically be in Galilee at the same time. But His physical manifestion does not replace His spiritual nature. His Spirit is still present everywhere.
However, even in the physical world, some things can occupy the same place at the same time. Right now you have many different, independent radio signals occupying the same space as your body. They are not a part of you and you can’t detect them with your five senses. But if you have a radio inside you, you can tune them in one at a time and listen. They exist inside you whether you have a radio or not. God and Satan can co-exist like one radio signal can occupy the same space as another radio signal. This is only an analogy. God isn’t electromagnetic wave, for that is still part of the physical universe. But there is a better analogy…
The universe is God’s creation. He is not naturally part of it. I look at it like a book author existing outside the contents of his book. In one sense, a human author is all-powerful and all-present to the world of his story. He is in complete control of it. He wrote the whole thing and knows it from start to finish. Nothing can happen in his story outside of his own knowledge and will. The story has a timeline, but the author is not part of that timeline. From the beginning to the end, the author sees the story as a timeless present. In a sense, he is present in the story because he can change anything he desires anywhere in the story… and none of his story characters can stop him. If he places a character in what appears to be a hopeless crisis, the author can write a way out of the crisis, even a miraculous way. (This is a key feature in most good books and movies. The writer develops one or more difficult or hopeless situations, and also writes a solution to each crisis. This brings praise to the writer.)
God is in a sense the author of the story of the universe, but He has gone above and beyond what human authors have done. He has inserted Himself into His own story, and has given His human characters the ability to interact with Him and free-will in choosing to accept or reject Him. He has even let us know many things in advance before they happen, such as the birth, death, and resurrection of Jesus, the formation of the state of Israel in 1948, or how we’re destroying ourselves in the last days. He has also told us the final outcome of the story. Detailed knowledge of all these things would be impossible if God did not exist.