The idea that each atom contains smaller universes is not a scientifically supported concept. It falls within the realm of speculative or philosophical speculation rather than established scientific understanding.
In our current understanding of the universe, the term "universe" refers to the entirety of all space, time, matter, and energy that exists. It encompasses galaxies, stars, planets, and everything we can observe through scientific methods. The size of the observable universe is estimated to be about 93 billion light-years in diameter, based on our best cosmological measurements.
It's important to note that the concept of size becomes more complex when discussing the universe as a whole. The universe may be infinite in extent, or it could have a finite but unbounded spatial geometry, meaning that it has no edge or boundary. The exact nature and size of the universe beyond our observable horizon are still the subject of ongoing scientific investigation and debate.
However, the notion that smaller universes exist within individual atoms is not supported by scientific evidence or mainstream scientific theories. It's essential to distinguish between scientific understanding and speculative ideas when discussing such concepts.