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OLLI lectures Fall 2016Horst D Wahl

(hwahl@fsu.edu)

lecture 3, 25 Oct 2016

Hot Topics in Physics

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Outline of 2nd class Recap Present paradigm, cont’d

Particles, cont’d Cosmos

Neutrinos (maybe??)

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Recap Quantum theoryWave-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 stateo Cannot predict outcome of measurement, only probability for a

given outcome

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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”

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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 Bosonso γ (electromagnetic force)o W±, Z (weak, electromagnetic)o g gluons (strong force)

Higgs boson spontaneous symmetry

breaking of SU(2) mass

“Standard Model” of Particle Physics

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From Contemporary Physics Education Project http://www.cpepweb.org/particles.html

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Particles of Standard Model

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Particles of the Standard Model

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Contemporary Physics Education Project

http://www.cpepphysics.org/

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“every-day” matter

Proton

d u

d

νe

Neutron

e

u d

u

Electron Electron Neutrino

γ

Photon

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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

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Beta decay

d u

d

NeutronProton

u d

u

e

Electron νe

Anti-electron Neutrino

W −

Mean lifetime of a free neutron ~ 10.3 minutes

Mean lifetime of a free proton > 1032 years!Question: Why doesn’t the neutron in the deuteron decay? Hint: deuteron mass = 1875.6 MeV/c2

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Quantum Field Theory

Energy and matter are equivalent (E = mc2)

“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

t

Vacuum FluctuationInvolving top quarks

. .

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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

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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

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Study of high energy interactions -- going back in time

(13.8

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pp physics at the LHC correspondsto conditions around here

HI physics at the LHC correspondsto conditions around here

19LHC Physics Highlights

Pbar p physics at the Tevatron correspondsto conditions around here

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“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

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“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

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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

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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 theoryo 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?

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Unsolved mysteries..

http://www.cpepphysics.org/images/Unsolved.jpg

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Unsolved mysteries..

http://www.cpepphysics.org/images/Unsolved.jpg

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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,…)

http://www.universeadventure.org/

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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 1920-1924 Hubble:

Andromeda “Nebula” is outside the galaxy, and is itself a kind of galaxy.

1929 Hubble: the universe expands.

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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) rs=2GM/c2 (the Schwarzschild radius) Meaning of rs: if all mass M is compressed within

rs then the light can not escape ⇒ black hole. Example: the rs 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

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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.

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Beginning of Time: Big Bang Big Bang theory with inflationMost widely accepted cosmological theoryStarts with “Big Bang”, i.e. abrupt appearance of

expanding space time (13.798±0.037)Gy ago inflationary epoch: t ≈ 10-36 to 10-32, space expands by

huge factor 1027 to size of a grapefruitAfter 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

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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). (https://www.wikiwand.com/en/Big_Bang )

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Other cosmological theories

Cyclic theory (Big Bang – Big Crunch):Every Ty (1012 years), expansion changes to

contraction ⇒universe shrinks, becomes infinitesimally small, then a new Big BangCycles of Big Bang and Big Crunch continue

forever Eternal inflation: Spacetime infinite in space and in past and

future timeOur Big Bang and universe is just one of many

…..

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Chronology of the Universe Very early universe (1st ps):

Planck epoch (before tP = 10-43 s)o None of present theories apply, all forces unified

Grand unification epoch (From Planck epoch until inflation):o 3 forces unified – electronuclear forceo We hardly know anything about this

Early Universe (first 380000 years): From quark epoch to photon epoch:

o Emergence of familiar forces and particleso 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,..

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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 http://map.gsfc.nasa.gov/media/020622/index.html

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Hubble deep field view

http://hubblesite.org/newscenter/archive/releases/2014/27/image/a/format/xlarge_web/

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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 380 000 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)

https://map.gsfc.nasa.gov/media/121238/ilc_9yr_moll2048.png

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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 380 000 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)

http://www.esa.int/spaceinimages/Images/2013/03/Planck_CMB

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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

http://sci.esa.int/science-e-media/img/63/Planck_power_spectrum_orig.jpg

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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 energyo acts as a sort of an anti-gravity. o distinct from dark matter, o responsible for the present-day

acceleration of the universal expansion.

http://map.gsfc.nasa.gov/media/080998/index.html

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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%. (http://sci.esa.int/planck/51557-planck-new-cosmic-recipe/ )The 'before Planck' figure is based on the WMAP 9-year data release presented by Hinshaw et al., (2012).

44http://particleadventure.org/images/history-universe-2013.jpg

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http://particleadventure.org/images/history-of-the-universe-2015.jpg