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[[Matter]], and therefore everything seen, is made out of fundamental particles of nature.  These fundamental particles are hadrons and leptons, the hadrons being further subdivided into baryons and mesons.  Hadrons include the proton and neutron and leptons include the electron, muon and tau as well as the corresponding neutrinos.  For simplicity, the overwhelming majority of matter in the universe is comprised of protons, neutrons and electrons.   

[[Matter]], and therefore everything seen, is made out of fundamental particles of nature.  These fundamental particles are hadrons and leptons, the hadrons being further subdivided into baryons and mesons.  Hadrons include the proton and neutron and leptons include the electron, [[muon]] and tau as well as the corresponding neutrinos.  For simplicity, the overwhelming majority of matter in the universe is comprised of protons, neutrons and electrons.   

These particles have been mysterious for quite some time: although [[physicist]]s knew they existed, they knew very little about them. In [[physics]], you can say you "know" something when, among other proprieties, you can predict and describe the way it behaves. You know that a [[stone]] will fall if it's not held properly. [[Physicist]]s can describe how it falls and predict exactly where it will touch the [[ground]] using mathematical formulas.

These particles have been mysterious for quite some time: although [[physicist]]s knew they existed, they knew very little about them. In [[physics]], you can say you "know" something when, among other proprieties, you can predict and describe the way it behaves. You know that a [[stone]] will fall if it's not held properly. [[Physicist]]s can describe how it falls and predict exactly where it will touch the [[ground]] using mathematical formulas.