Re: What is the smallest existing thing?

Thank you Kol for your question. And a good question it is! Nuclear 
science is pretty recent. In the early 1900s, scientists began to 
discover the inner workings of the atom - the smallest component of 
matter. Protons & neutron in a very dense core with a cloud of electrons 
well outside the core. But that simple explanation was not adequate to 
explain all the data they were observing through experiments.

Currently, the "smallest thing discovered" is wrapped up in a theory 
called 
"The Standard Model".
This model flows from quantum mechanics. Max Planck 
(around 1900) was the first to theorize that, on the microscopic scale, 
energy was not continuous but rather was made of individual packets 
called "quanta".Anyway the Standard Model places the smallest things are 
quarks & leptons. Quarks make up the protons and neutrons. The electron 
is one of the leptons. 
But are these the smallest things? We're not sure. A new 
field of physics speculates that matter and energy may be strings -- 
very, very, very small 1-dimensional objects. The trouble is that the 
size of these strings is so small - it doesn't appear that we can 
actually see them. You see another part of quantum mechanics involves a 
contribution by physicist Werner Heisenberg who finds that on small 
scales - things are not too certain. In fact the Heisenberg Uncertainty 
Principle says that you cannot know a particle's position and momentum 
exactly. These strings are on the order of a Planck length (that is a 
decimal followed by 32 zeros and a 1). We certainly have no way to 
observe such a particle today and being able to even theoretically see 
such a particle is questionable. Is it real? Time will tell. Perhaps 
circumstantial evidence would point to its existance.  http://superstringtheory.com/

So the smallests things: quarks which compose protons and neutrons - for 
the particles we can observe. Theoretically, strings - but so small we 
have no hope of directly observing at present.