What are Christopher’s beliefs about death, heaven, and the afterlife?

In Chapter 61, we learn that Christopher doesn't believe in Heaven, and that he believes only old people believe in Heaven. Christopher later asks Reverend Peters, who sometimes visits his school, what he thinks of heaven. He then pressures the minister to tell him where in the universe heaven is...... Reverend Peters responds that Heaven is beyond the universe. After getting his answer, Christopher immediately demonstrates that the Reverend's answer isn't mathematically or physically possible.

Christopher also notes that when people die, they are put in the ground, after which, they decompose into smaller and smaller components—molecules and atoms—some of which are used by plants to grow. His mother, on the other hand, was cremated, so she turned into gas and ash. The gas logically went up into the air..... but he isn’t sure about the ash. He wasn't at her funeral.