-
-
---------------------------- - 2367 - Particle Physics - the Standard Model
-
- The world we know and love is made of molecules, and molecules are made of atoms. Chemist Dmitri Mendeleev figured that out in the 1860s and organized all atoms into the elements and into the periodic table that grew to 118 different chemical elements.
-
- By 1932, scientists knew that all those atoms are made of just three particles: neutrons, protons and electrons. The neutrons and protons are bound together tightly into the nucleus. The electrons, thousands of times lighter, orbit around the nucleus at speeds approaching that of light.
-
- But, How are they held together? The negatively charged electrons and positively charged protons are bound together by electromagnetism. But the protons are all bound together in the nucleus and their positive charges should be pushing them powerfully apart.
-
- What binds these protons and neutrons together?
-
- We started out with only four particles, protons, neutrons, electrons, and photons. Four grew to five when Anderson measured electrons with positive charges. These became positrons that were striking the Earth from outer space.
-
- Dirac had predicted these first anti-matter particles. Five became six when the pion, which Yukawa predicted would hold the nucleus together, was found.
-
- Then came the muon, 200 times heavier than the electron.
-
- By the 1960s there were hundreds of “fundamental” particles in place of the well-organized periodic table. There were long lists of baryons (heavy particles like protons and neutrons), mesons (like Yukawa’s pions) and leptons (light particles like the electron, and the elusive neutrinos). But, all these particles had no organization and no guiding principles.
-
- Finally Quarks were discovered. They come in six varieties called flavors, up, down, strange, charm, bottom and top. In 1964, Gell-Mann and Zweig described how to mix and match any three quarks to get a baryon. Protons are two ups and a down quark bound together; neutrons are two downs and an up.
-
- Choose one quark and one antiquark to get a meson. A pion is an up or a down quark bound to an anti-up or an anti-down. All the material of our daily lives is made of just up and down quarks and anti-quarks and electrons. How simple is that?
-
- How are quarks bound together? They are tied to one another so tightly that you never ever find a quark or anti-quark on its own. The theory of that binding, and the particles called gluons that are responsible, is called quantum chromodynamics. It’s a vital piece of the Standard Model, but mathematically difficult, even posing an unsolved problem of basic mathematics.
-
- The other aspect of the Standard Model is “A Model of Leptons.” , a 1967 paper by Steven Weinberg that pulled together quantum mechanics with the vital pieces of knowledge of how particles interact and organized the two into a single theory.
-
- It incorporated the familiar electromagnetism, joined it with what physicists called “the weak force” that causes certain radioactive decays, and explained that they were different aspects of the same force. It incorporated the Higgs mechanism for giving mass to fundamental particles.
-
- Since then, the Standard Model has predicted the results of experiment after experiment, including the discovery of several varieties of quarks and of the W and Z bosons, which are heavy particles that are for weak interactions, what the photon is for electromagnetism.
-
- The possibility that neutrinos aren’t massless was overlooked in the 1960s, but became part of the Standard Model in the 1990s.
-
- Discovering the Higgs boson in 2012 is something that was long predicted by the Standard Model. It was another crucial victory for the Standard Model.
-
- Science was concerned that the Standard Model was still incomplete. They were concerned that it didn’t adequately embody the expectations of simplicity. They were worried about its mathematical self-consistency. They wanted to eventually bring the force of gravity into the fold.
-
- Physicists have made numerous proposals for theories beyond the Standard Model. These bear exciting names Grand Unified Theories, Supersymmetry, Technicolor, and String Theory.
-
- However, these beyond-the-Standard-Model theories have not yet successfully predicted any new experimental phenomenon or any experimental discrepancy with the Standard Model. We’re working on it.
-
- After decades of theories and experiments the Standard Model is worthy of celebration as the Absolutely Amazing Theory of Almost Everything.
-
- See Review - 2313 - Reducing our whole world down to 6 particles. Then it asks 10 questions that the Standard Model still does not answer.
-
- Other review articles on Particle Physics can be found in these Reviews:
-
- 2290 - The universe of fundamental particles.
-
- 2240 - Particle physics and quantum fields.
-
- 2018 - A lesson in particle physics. Includes listing of 7 more reviews on the subject.
-
- 1921 - Particle physics in the year 2016
-
- 1883 - Fundamental particles and the 5th force carrier.
-
- 1868 - What do neutron lifetimes have to do with it? Includes a list of 16 more reviews.
-
- 1848 - Particle physics, a history lesson. Includes 7 biographies of famous physicists, from Max Planck to Carl Anderson
-
- 1799 - A primer on particle physics.
-
- 1693 - Playing around with particle physics.
-
- 1512 - Getting familiar with the Standard Model.
-
- 973 - Physics in a nutshell.
-
- 811 - The large Hadron Collider.
-
- 631 - Mass, momentum and inertia?
-
- May 16, 2019.
----------------------------------------------------------------------------------------
----- Comments appreciated and Pass it on to whomever is interested. ----
--- Some reviews are at: -------------- http://jdetrick.blogspot.com -----
-- email feedback, corrections, request for copies or Index of all reviews
--- to: ------ jamesdetrick@comcast.net ------ “Jim Detrick” -----------
- https://plus.google.com/u/0/ -- www.facebook.com -- www.twitter.com
--------------------- Thursday, May 16, 2019 -------------------------
-----------------------------------------------------------------------------------------
No comments:
Post a Comment