What does it mean to exist? When we talk about a person existing, we are referring to that person being a material object in the universe.
Concepts are also said to exist. For example, patriotism exists, but you can’t hold it in your hand. For this discussion let’s agree that we are only talking about existence in the material sense.
To be material, that generally means an object has mass. But what is mass? According to Einstein, mass has an equivalence with energy. If we understand energy, we might better understand what mass is. But what is energy?
Energy is defined as a “property of objects.” In other words, it is a concept, such as patriotism, velocity, or honesty. You can’t grab a handful of a concept and put it in your pocket.
So there you have it: To exist, you must have mass. Mass is equivalent to energy. Energy is nothing but a concept. Therefore, you are nothing but a concept, probably in a computer program designed by someone else.
Atheists say God doesn’t exist. I say atheists don’t exist.