What made Louie think that life and death began with a spark of light?

Louie read about the research of a team from Northwestern University. They had recorded a zinc flash at the moment that a sperm fertilized an egg. A rush of calcium at that moment caused zinc to be released from the egg. As the zinc burst out, it attached itself to small, fluorescent molecules: a spark of light that was picked up by camera microscopes. After reading that, he remembered sitting with terminal patients as they died, and they talked about a tunnel with a light at the end. That make Louise think that life and death began with a spark of light.