Pondering the infinitely large and small, … there’s the neutrino. Grok this:
“The sun is emitting neutrinos like mad, so that about a hundred trillion of them pass through your body every second , …” — Carroll, Sean (2016-05-10). The Big Picture: On the Origins of Life, Meaning, and the Universe Itself (p. 177). Penguin Publishing Group. Kindle Edition.
[Wikipedia] “About 65 billion (6.5×10^10) solar neutrinos per second pass through every square centimeter perpendicular to the direction of the Sun in the region of the Earth.”
So, I got out a ruler and drew a square on a piece of paper, each side 1 centimeter long. Which looked like less surface area than the nail on my little finger. Imagine seeing 65 billion things passing through that space. Like crazy invisible “hail ” everywhere. All the time.
And an amazing property: currently the neutrino’s speed is effectively the speed of light (within measurement error) and likely has non-zero mass! — maybe one millionth that of the electron . And it comes in flavors. And maybe neutrinos do not interact with each other, just like photons.
As far as size, that’s spooky: “… , it does not have a size in the same sense as everyday objects.”
The saga continues with the Big Bang model and research on the cosmic microwave background; also the Standard Model of particle physics. Chasing the ghost particle.
 Neutrino mass inferred from “the experimentally established phenomenon of neutrino oscillation.”
3-7-2017 Supernova 1987A: “This was the first time neutrinos known to be emitted from a supernova had been observed directly, which marked the beginning of neutrino astronomy. The observations were consistent with theoretical supernova models in which 99% of the energy of the collapse is radiated away in the form of neutrinos.”