Once upon a time, there were some really smart people who liked to talk about science. They decided to have a special meeting called the "Fifth Solvay Conference".
This meeting was a place where lots of important scientists from around the world could get together and talk about very complicated things. They wanted to figure out how to understand the very, very small things that make up our world, like atoms and particles.
At the conference, they talked about things like radiation and how it works, how light and energy act like waves, and lots of other things that might be hard for a 5-year-old to understand.
Some of these scientists were like the superheroes of the science world. They had names like Albert Einstein and Marie Curie. They had really cool ideas that helped us to understand our world better.
At the end of the conference, all the scientists got together for a big photo. It was pretty amazing seeing all these brilliant minds in one place, just like going to a superhero team-up!