Nothing
A few months ago I was involved in a group discussion where a question was asked. "What is nothing?" The consensus: Nobody knows. However, I think "nothing" CAN be defined. At least from our perspective, which is all we have to work with, for now. Let's explore the topic.
Waves can model all phenomena we perceive. Our reality is built from an interpretation of waves, visible light being an obvious example; heat and sound follow suit. Press your finger on the back of your hand, that is an amplitude. Repeat the process, that is a frequency. I will let you explore for yourself how smell and taste are interpretations of waves.
Consider a wave 
with an amplitude measured from an arbitrary baseline.
Now, superimpose the trough and peak. 
What is left? Baseline. Nothing?
So, can we accept a definition of "nothing" as The product of equally opposite waves? What does that entail? Nothing can come from something, and something CAN come from nothing.
Existence
A definition of existence could be drawn from similar reasoning. Something exists if it possesses the ability to affect something else. By this logic, ideas exist alongside physical objects. The ideas within our consciousness have an impact on the physical world. The opposite is also true.
The idea of God has had a profound effect on our world. In this respect, does God exist?
Just some things to think about. I'm sure he's not watching you. (He doesn't have eyes, lol)