You should not be surprised to encounter those who do not believe in Christ, or in anything. The pages of scripture have frequent references to people who do not believe. In fact, the Israelites had a lot of people who ignored the faith of their fathers, the exodus, the covenant, etc.
You should simply take this in stride. If you don’t have an answer, that is fine, too. That may not be a lesson for anybody else, but it can be a lesson for you if you keep after it.
Scripture teaches us that we should believe, in order that we can understand.
If we knew everything at the level of scientific knowledge, then we wouldn’t need faith. But, the Bible, from the beginning, demands faith. We believe in things that science is not capable of proving.
One of the things about the universe (and beyond) is just “infinity.” How can anybody understand that? Visualize two points and a line through them that just goes on forever, beyond our visible universe and then maybe forever throughout all the other alleged parallel universes. There is no end to that line, no boundary, in either direction, This will never be understood.
It’s incomprehensible to me that all the visible universe was once packed into a space the size of an atom.
Remember, we are “salt” and “light” for the world. That’s all we need to know for now.