Hot Topics in Physics. OLLI lectures Fall 2016 Horst D Wahl lecture 3, 25 Oct 2016

Transcription

1 1 Hot Topics in Physics OLLI lectures Fall 2016 Horst D Wahl (hwahl@fsu.edu) lecture 3, 25 Oct 2016

2 2 Outline of 2 nd class Recap Present paradigm, cont d Particles, cont d Cosmos Neutrinos (maybe??)

3 3 Recap Quantum theory Wave-particle duality: o waves can behave like particles, particles can behave like waves o What we find depends on what question we ask Physical systems o described by state vectors o Physical observables represented by operators which act on state vectors (wave functions) o incompatible observables uncertainty relation Measurement o requires interaction changes the state o Cannot predict outcome of measurement, only probability for a given outcome

4 4 Recap (2) Particles: All the matter that we know is made of elementary constituents (particles): o Quarks, gluons, electrons Interaction between particles described by Standard Model of Particle Physics

5 5 Standard Model of Particle Physics A theoretical model of interactions of elementary particles, based on quantum field theory Symmetry: SU(3) x SU(2) x U(1) Matter particles Quarks: up, down, charm, strange, top, bottom Leptons: electron, muon, tau, + their neutrinos Force particles Gauge Bosons o γ (electromagnetic force) o W ±, Z (weak, electromagnetic) o g gluons (strong force) Higgs boson spontaneous symmetry breaking of SU(2) mass

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7 From Contemporary Physics Education Project 7

8 Particles of Standard Model 8

9 Particles of the Standard Model 9

10 Contemporary Physics Education Project 10

11 11 every-day matter Proton Neutron u u d Photon d d u γ Electron e Electron Neutrino ν e

12 Gravitational interaction Binds matter on large scales Weak interaction Causes radioactivity Electromagnetic interaction Binds electrons and nuclei to form atoms Binds atoms to form molecules etc. Strong interaction Binds quarks to form hadrons (protons, ) Binds protons and neutrons to form nuclei 12

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14 14 Beta decay Mean lifetime of a free neutron ~ 10.3 minutes Neutron d u d W Proton u d u Mean lifetime of a free proton > years! Question: Why doesn t the neutron in the deuteron decay? Hint: deuteron mass = MeV/c 2 Electron e Anti-electron Neutrino ν e

15 15 Quantum Field Theory Energy and matter are equivalent (E = mc 2 ) t.. Vacuum Fluctuation Involving top quarks Virtual particles A particle-antiparticle pair can pop out of empty space ( the vacuum ) And then vanish back into it Consequence: structure of the universe depends on particles that don t exist in the usual sense (but did when the Universe was very young and hot) One of the aims of particle physics: understand those particles, even though they do not appear visibly in our everyday experience We do not see these particles in everyday life We must recreate the state of the early hot universe to make them t

16 16 field or particle? All fields have small packets of energy associated with them --- field quanta Quantum of electromagnetic field = photon (γ) Quanta are excitations of field -- can become real if field kicked hard enough Field quanta are particles that carry forces Elementary particles interact by exchange of field quanta e - e - γ e - e - Interaction of 2 electrons by the exchange of a photon; photon is the quantum of the electromagnetic field

17 17 The world around us Most of what s around us is made of very few particles: electrons, protons, neutrons (e, u, d) this is because our world lives at very low energy all other particles were created at high energies during very early stages of our universe can recreate some of them (albeit for very short time) in our laboratories (high energy accelerators and colliders) this allows us to study their nature, test the standard model, and discover direct or indirect signals for new physics

18 18 Study of high energy interactions -- going back in time (13.8

19 pp physics at the LHC corresponds to conditions around here Pbar p physics at the Tevatron corresponds to conditions around here HI physics at the LHC corresponds to conditions around here LHC Physics Highlights 19 19

20 20 Standard Model of Particle Physics Quantum field theory Particles are excitations of the fields (electron field, quark field, ) Interactions are mediated by quanta of gauge fields Gauge fields and form of interactions are determined by symmetry of the Lagrangian of the theory, where symmetry means invariance under certain transformations ( gauge transformations ) invariance under gauge transformations leads to theories with massless particles Higgs field provides mechanism to break symmetry so as to allow particles to have mass while still preserving nice features of the theory

21 21 Gauge Transformations Hermann Weyl (1920): noted scale invariance of electromagnetism tried to unify general relativity and electromagnetism conjectured that Eichinvarianz (scale invariance) may be also a local gauge theory of general relativity did not work out later realized that requiring the Schrödinger equation to be invariant under a local gauge (phase) transformation leads naturally to electromagnetic field and gives the form of the interaction of a charged quantum particle with the e.m. field

22 22 Global and local gauge transformations global transformation: same transformation carried out at all space-time points ( everywhere simultaneously ) local transformation: different transformations at different space-time points globally invariant theories in general not invariant under local transformations in quantum field theory, can restore invariance under local gauge (phase) transformation by introducing new force fields that interact with the original particles of the theory in a way specified by the invariance requirement i.e. in this sense the dynamics of the theory is governed by the symmetry properties can view these force fields as existing in order to permit certain local invariances to be true electroweak interaction theory as well as QCD follow from gauge invariance which is a generalization of the gauge invariance of Maxwell s equations

23 Open questions in particle physics Standard model Has been tested thoroughly, agrees with observations, but there must be something else.. is a good approximation, but becomes inconsistent at very high energies need better theory which contains SM as low energy approximation EW. symmetry breaking mechanism via Higgs Boson is put in by hand Lots of parameters o Masses of charged leptons, neutrinos, quarks, W, Z,.. not predicted by theory o Where do they come from? -- would like theory which predicts all of these parameters from first principles (but maybe not possible?) o Higgs mass calculation has terms quadratic in the masses of the new particles --- difficult to reconcile with low Higgs mass Does not include gravity Some questions: Are there smaller constituents? What is charge? Mass? Flavor? Were forces unified in the early universe? Why is there more matter than antimatter? why is our universe the way it is? o Coincidence? o Theoretical necessity? o Design? 23

24 24 Unsolved mysteries..

25 25 Unsolved mysteries..

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27 27 7. Architecture of the Cosmos GRT, together with particle physics, nuclear physics,.. used as basis for development of quantitative cosmological model standard Big-Bang Model, the Lambda-CDM model explains broad range of phenomena, including the abundance of light elements, the cosmic microwave background, large scale structure and Hubble's Law. Many open questions: Earliest times (<10-43 sec) not yet understood other problems and unsolved questions (e.g. size of cosmological constant, matter vs antimatter, heavy element synthesis, )

28 28 Cosmology In 1919: The known universe only contains the galaxy. Many open questions: o Are there stars / star systems beyond our galaxy? o Is the universe static? o How big is the universe? o Does the universe have a beginning? o What is the material and energy content of the universe? 1920 The great debate : Shapley: The galaxy is vast and includes globular systems and cloud systems of stars. The sun is located at the edge. Curtis: The galaxy is small and the sun is close to the center. Outside there are other galaxies Hubble: Andromeda Nebula is outside the galaxy, and is itself a kind of galaxy Hubble: the universe expands.

29 GRT vs cosmology 1916: Schwarzschild presents the first solution of the field equations. (describes the spherically symmetric gravitational field outside a spherical, uniform and non-rotating mass distribution M) Contains two distances where the solution "does not exist" (singularities): o (1) r=0 (the origin). Here space and time cease to exist. o (2) r s =2GM/c 2 (the Schwarzschild radius) Meaning of r s : if all mass M is compressed within r s then the light can not escape black hole. Example: the r s of the Earth is 9mm Black holes exist -- some very massive (many solar masses); the center of our galaxy contains a massive black hole. Artist s impression of a Black Hole 29

30 30 Big Bang Einstein 1917 Thinks that there are no mass-free solutions (Mach's principle). With the strengthening action of the masses, the universe collapses; introduces an additional term: the cosmological constant Λ, so as to make the universe static. De Sitter shows immediately that there exist mass free solutions. ("That man does not understand his own theory.") Friedman 1922 shows that the original field equations allow expanding solutions. Weyl and Eddington 1923 show that in the de Sitter universe test particles are moving away from each other. Einstein gives the cosmological constant up ("My biggest blunder"). Hubble 1929 shows that the universe expands: beginning of the big bang theory.

31 31 Beginning of Time: Big Bang Big Bang theory with inflation Most widely accepted cosmological theory Starts with Big Bang, i.e. abrupt appearance of expanding space time (13.798±0.037)Gy ago inflationary epoch: t to 10-32, space expands by huge factor to size of a grapefruit After cosmic inflation, expansion continues at decreasing rate Expansion cooling formation of particles, nuclei recombination : at t 380ky formation of atoms (H) Cosmic background radiation (CMB) Accelerated expansion: from t 7 Gy to now

32 Timeline of the metric expansion of space; space (including hypothetical non-observable portions of the universe) is represented at each time by the circular sections. On the left the dramatic expansion occurs in the inflationary epoch, and at the center the expansion accelerates (artist's concept; not to scale). ( ) 32

33 33 Other cosmological theories Cyclic theory (Big Bang Big Crunch): Every Ty (10 12 years), expansion changes to contraction universe shrinks, becomes infinitesimally small, then a new Big Bang Cycles of Big Bang and Big Crunch continue forever Eternal inflation: Spacetime infinite in space and in past and future time Our Big Bang and universe is just one of many..

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36 36 Chronology of the Universe Very early universe (1 st ps): Planck epoch (before t P = s) o None of present theories apply, all forces unified Grand unification epoch (From Planck epoch until inflation): o 3 forces unified electronuclear force o We hardly know anything about this Early Universe (first years): From quark epoch to photon epoch: o Emergence of familiar forces and particles o Ends with formation of atoms CMB Dark Ages (0.38 to 150 My) Universe transparent, but no stars, no galaxies Large structure formation (150My to now until 100Ty?) Stars, galaxies, galaxy clusters,..

37 37 Cosmic History Cosmic Microwave Background (CMB) = oldest light in the universe (380,00 y) patterns imprinted on this light encode the events that happened only a tiny fraction of a second after the Big Bang. In turn, the patterns are the seeds of the development of the structures of galaxies we now see billions of years after the Big Bang. Credit: NASA / WMAP Science Team

38 38 Hubble deep field view

39 CMB -- WMAP The anisotropies of the Cosmic microwave background (CMB) as observed by WMAP. The CMB is a snapshot of the oldest light in our Universe, imprinted on the sky when the Universe was just years old. It shows tiny temperature fluctuations that correspond to regions of slightly different densities, representing the seeds of all future structure: the stars and galaxies of today. (blue hot less dense, red cold denser) 39

40 CMB -- Planck The anisotropies of the Cosmic microwave background (CMB) as observed by Planck. The CMB is a snapshot of the oldest light in our Universe, imprinted on the sky when the Universe was just years old. It shows tiny temperature fluctuations that correspond to regions of slightly different densities, representing the seeds of all future structure: the stars and galaxies of today. (blue hot less dense, red cold denser) 40

41 41 The "angular power spectrum" of the fluctuations in the Planck full-sky map. This shows the relative brightness of the "spots" in the map vs. the size of the spots. Green line = fit with standard model, red dots = Planck measurements

42 42 Content of the Universe contents of the universe: 4.6% atoms: the building blocks of stars and planets. 23% Dark matter: DM is different from atoms, interacts only weakly, does not emit or absorb light. detected only indirectly by its gravity. 72% "dark energy o acts as a sort of an anti-gravity. o distinct from dark matter, o responsible for the present-day acceleration of the universal expansion. a/080998/index.html

43 43 Contents of the universe Planck's high-precision cosmic microwave background map has allowed scientists to extract the most refined values yet of the Universe's ingredients. Normal matter that makes up stars and galaxies contributes just 4.9% of the Universe's mass/energy inventory. Dark matter, which is detected indirectly by its gravitational influence on nearby matter, occupies 26.8%, while dark energy, a mysterious force thought to be responsible for accelerating the expansion of the Universe, accounts for 68.3%. ( ) The 'before Planck' figure is based on the WMAP 9-year data release presented by Hinshaw et al., (2012).

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