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  • If you were to take any everyday object, say a coffee cup, and break it in half,

  • then in half again, and keep carrying on, where would you end up?

  • Could you keep on going forever?

  • Or would you find a set of indivisible building blocks out of which everything is made?

  • Physicists have found the latter- that matter is made of fundamental particles, the smallest things in the universe.

  • Particles interact with each other according to a theory called theStandard Model”.

  • The Standard Model is a remarkably elegant encapsulation

  • of the strange quantum world of indivisible, infinitely small particles.

  • It also covers the forces that govern how particles move,

  • interact, and bind together to give shape to the world around us.

  • So how does it work?

  • Zooming in on the fragments of the cup,

  • we see molecules, made of atoms bound up together.

  • A molecule is the smallest unit of any chemical compound.

  • An atom is the smallest unit of any element in the periodic table.

  • But the atom is not the smallest unit of matter.

  • Experiments found that each atom has a tiny, dense nucleus,

  • surrounded by a cloud of even tinier electrons.

  • The electron is, as far as we know,

  • one of the fundamental, indivisible building blocks of the universe.

  • It was the first Standard Model particle ever discovered.

  • Electrons are bound to an atom's nucleus by electromagnetism.

  • They attract each other by exchanging particles called photons,

  • which are quanta of light that carry the electromagnetic force,

  • one of the fundamental forces of the Standard Model.

  • The nucleus has more secrets to reveal, as it contains protons and neutrons.

  • Though once thought to be fundamental particles on their own, in 1968

  • physicists found that protons and neutrons are actually made of quarks,

  • which are indivisible.

  • A proton contains twoupquarks and onedownquark.

  • A neutron contains two down quarks and one up.

  • The nucleus is held together by the strong force,

  • another fundamental force of the Standard Model.

  • Just as photons carry the electromagnetic force,

  • particles called gluons carry the strong force.

  • Electrons, together with up and down quarks,

  • seem to be all we need to build atoms and therefore describe normal matter.

  • However, high energy experiments reveal that there are actually six quarks

  • down & up, strange & charm, and bottom & top

  • - and they come in a wide range of masses.

  • The same was found for electrons,

  • which have heavier siblings called the muon and the tau.

  • Why are there three (and only three) different versions of each of these particles?

  • This remains a mystery.

  • These heavy particles are only produced, for very brief moments, in high energy collisions, and are not seen in everyday life.

  • This is because they decay very quickly into the lighter particles.

  • Such decays involve the exchange of force-carrying particles,

  • called the W and Z, whichunlike the photonhave mass.

  • They carry the weak force, the final force of the Standard Model.

  • This same force allows protons and neutrons to transform into each other,

  • a vital part of the fusion interactions that drive the Sun.

  • To observe the W and Z directly,

  • we needed the high energy collisions provided by particle accelerators.

  • There's another kind of Standard Model particle, called neutrinos.

  • These only interact with other particles through the weak force.

  • Trillions of neutrinos, many generated by the sun, fly through us every second.

  • Measurements of weak interactions found that there are different kinds of neutrinos

  • associated with the electron, muon, and tau.

  • All these particles also have antimatter versions,

  • which have the opposite charge but are otherwise identical.

  • Matter and antimatter particles are produced in pairs in high-energy collisions,

  • and they annihilate each other when they meet.

  • The final particle of the Standard Model is the Higgs boson

  • – a quantum ripple in the background energy field of the universe.

  • Interacting with this field is how all the fundamental matter particles acquire mass, according to the Standard Model.

  • The ATLAS Experiment on the Large Hadron Collider is studying the Standard Model in-depth.

  • By taking precise measurements of the particles and forces that make up the universe,

  • ATLAS physicists can look for answers to mysteries not explained by the Standard Model.

  • For example, how does gravity fit in?

  • What is the real relationship between force carriers and matter particles?

  • How can we describeDark Matter”,

  • which makes up most of the mass in the universe but remains unaccounted for?

  • While the Standard Model provides a beautiful explanation for the world around us,

  • there is still a universe's worth of mysteries left to explore.

If you were to take any everyday object, say a coffee cup, and break it in half,

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B2 US TED-Ed standard model standard model universe particle

What's the smallest thing in the universe? - Jonathan Butterworth

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    April Lu posted on 2018/11/27
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