What is the smallest known particle?

Question

what is the smallest known particle known to man? I've heard that it's the atom. It seems that a big part of trying to gain scientific knowledge is knowing what the smallest part of life is.

Answer 1

OH, that's a very good question.  Could be lots of answers.  A cop-out would be to say a photon, it has no mass.  But is that really a particle then?  

I'll vote for the neutrino.  For a long time it was thought to be massless, and now it's known that it does have a very small mass, a few eV.  (yes, energy is a mass, E=mc^2, and that's just how they do it).   Quarks (protons are made of three of them) and leptons (the electron is one of them) are more massive.  There are several types of neutrino, though.

Answer 2

quarks, which make up protons, electrons and neutrons, which in turn make up atoms, which make up molecules, which make up all matter in the universe.

Answer 3

an atom, duh

Answer 4

the greeks thought it was the atom (means indivisible). now we know that atoms are made of protons, neutrons, and electrons. i also heard that each of these might be made up of smaller particles called quarks

Answer 5

Quarks. Is what makes up protons, neutrons, and electrons.. which is what makes up atoms.

Answer 6

It is a Quark...it's what makes up atoms, there are different types of them..

But there are only six and listed below:

Up, Down, Charm, Strange, Top, Bottom

Answer 7

Well, this is a tricky question because when talking about particles, what is the meaning of "size"?  Firstly, the atom is definitely not the smallest particle.  The atom is composed of smaller pieces called electrons, protons and neutrons.  The structure of the atom is kinda like this, the electron is floating around the nucleus which is composed of the heavier protons and neutrons.  But even after getting this small, it has been discovered that even the protons and the neutrons are not fundamental particles.  They too have structure.  They are composed of these things called "quarks" and they are weird and complicated creatures. Oh, and as for the electron, it has no structure and is as far as we know, a fundamental particle (meaning its indivisible). There is also another particle that isn't found in the atom called a "neutrino" and this is even lighter than the electron (which is even lighter than the quarks). And even beyond this, there are force particles, some of which are massless, a good example being the photon, the particle of light. Oh yes, and let us not forget about the evil twin that some of these particles which are collectively called antimatter. Yet even with all this info about relative masses, we haven't determined which is the "smallest" particle. Turns out this question is much more complicated than you probably imagined it to be.

Currently there is something called the Standard Model of Particle Physics.  This is the system under which particle physics is understood, classified and calculated. Turns out that in the standard model of particle physics all particles are treated as points, which are pretty much infinitely small little dots.Though particles are considered to be point-like and therefore all identical in the geometrical sense, there is one thing that can be considered like a "size". To understand this idea I'm about to introduce you to, you first have to understand one of the most fundamental aspects of quantum physics, and that is the all "particles" have both particulate and wavelike properties.  Though particles can "collide" as if they were little balls, the way the behave normally is really more like waves.  The best way to think of "particles" in my opinion (outside of collision and other special cases) is to think of them as filling ALL of space in certain special proportions.  The particles "position" is truly a distributed value and with its "position" being largely at some point A and not so much at some point B (points A and B are just random places).  So like in atom, you can't really say this electron if flying around over here, and this electron is flying around over there, instead you have to say that the electrons distribution is concentrated here, and this other electrons distribution is concentrated there. In this sense, two particles can actually "occupy" the same place (so long as they abide by a special restriction known as the Pauli Exclusion Principle). Very hard to grasp I would believe if this is your first exposure, but with some research you can begin to grasp this beautiful idea.  

Anyways, something interesting a certain french scientist by the name of Louis de Broglie postulated in the mid 1920's was that not only does light exhibit both wavelike and particle properties (a recent and revolutionary idea proved by Einstein in 1905) but that ALL matter exhibits particle and wavelike properties and that the particle-like momentum and wavelike wavelength are directly related.  In other words, he claimed that all particles had a wavelength and provided a way to calculate it (inspired partly by Einstein's E=mc^2). This idea of a wavelike/particle aka "wavicle" property for all matter and energy was later proven experimentally and is a cornerstone of modern physics. Anyhow, the point is, that this wavelength is the closest thing we have right now to a "size" for particles.  However, keep in mind that like I mentioned before, the size of this wavelength depends on the momentum of the particle, meaning that the mass and velocity of the particle will affect how large the wavelength it has (actually, the higher the momentum, the "smaller" the wavelength).  So yea, the "size" of a particle varies among different people who are moving at different speed.  If you were moving right alongside the particle at the same speed it was moving, to you it would look like that particle is stationary, however to someone else the particle might look like it zooming away, and maybe to someone else it could look like its rapidly approaching. The only true and nonsubjective "size" we can ascribe to a particle then would be the "size" it has when its stationary.

Hope that long winded response helped some.