How small is the smallest known thing in the universe and could you look at it with a powerful enough microscope?

Question: How small is the smallest known thing in the universe and could you look at it with a powerful enough microscope?
- Keywords:
  size,
  universe
Asked by anon-187172 to Stewart, Miriam, Marton, Laura, Kathryn, David on 13 Nov 2018.
- David Ho answered on 13 Nov 2018:
  
  The lightest particles we know of are called “neutrinos”. These are so light it’s difficult to measure their mass, but we believe it’s between 10^-36 and 10^-39 kilograms. That’s about 0.00000000000000000000000000000000000001 kg!
  
  Neutrinos are far too small to be seen even by the most powerful microscope. They also whip around at very nearly the speed of light, and barely interact with anything — billions pass through you every day without affecting you at all! This makes them really difficult to detect — they are still some of the least well-understood particles today.
- Stewart Martin-Haugh answered on 13 Nov 2018:
  
  The smallest things are called elementary particles. There’s a few different kinds: photons are maybe the most familiar – they transmit light.
  
  What’s really strange about particles is that they seem to have NO SIZE AT ALL: they are 0cm across, so just a point in space. We can see photons, electrons etc in the Large Hadron Collider, which acts a bit like a really big microscope, and as far as we can tell they are indeed points.

Question: How small is the smallest known thing in the universe and could you look at it with a powerful enough microscope?