May 13, 2003Lynn Cominsky - Cosmology A3501 Professor Lynn Cominsky Department of Physics and...

May 13, 2003 Lynn Cominsky - Cosmology A350

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Professor Lynn CominskyDepartment of Physics and Astronomy

Class web page: http://glast.sonoma.edu/~lynnc/courses/a350/

Best way to reach me: [email protected]

FINAL: May 27 5-7 PM

Astronomy 350Cosmology - Review


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Solar System

Relative sizes and order of planets

Sun Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto


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Solar system formation

Protoplanetary Nebula hypothesis: Fragment of interstellar cloud separates Central region of this fragment collapses to form

solar nebula, with thin disk of solids and thicker disk of gas surrounding it

Disk of gas rotates and fragments around dust nuclei– each fragment spins faster as it collapses (to conserve angular momentum)

Accretion and collisions build up the mass of the fragments into planetesimals

Planetesimals coalesce to form larger bodies


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Solar System Formation

Formation of the SunSolar nebula central bulge collapsed to

form protosunContraction raised core temperatureWhen temperature reaches 106 K, nuclear

burning can startSolar winds could have blown away

remaining nearby gas and dust, clearing out the inner solar system


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Planets around other stars

Over 100 planets around other stars are known


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Formation of other solar systems

Most extra-solar planets that have been discovered have “hot Jupiters” – very close to star compared to our system

Most are also found in elliptical orbits vs. circular orbits in our solar system

It is hard to explain elliptical orbits in solar systems of any age.

Close orbits can be explained by the initial formation of the planet further away, then a migration in towards the star.


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Classifying Stars

Hertzsprung-Russell diagram


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Properties of Stars

Temperature (degrees K) - color of star light. All stars with the same blackbody temperature are the same color. Specific spectral lines appear for each temperature range classification. Astronomers name temperature ranges in decreasing order as:

Surface gravity - measured from the shapes of the stellar absorption lines. Distinguishes classes of stars: supergiants, giants, main sequence stars and white dwarfs.

O B A F G K M


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Main Sequence Stars

Stars spend most of their lives on the “main sequence” where they burn hydrogen in nuclear reactions in their cores

Burning rate is higher for more massive stars - hence their lifetimes on the main sequence are much shorter and they are rather rare

Red dwarf stars are the most common as they burn hydrogen slowly and live the longest

Often called dwarfs (but not the same as White Dwarfs) because they are smaller than giants or supergiants

Our sun is considered a G2V star. It has been on the main sequence for about 4.5 billion years, with another ~5 billion to go


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How stars die

Stars that are below about 8 Mo form red giants at the end of their lives on the main sequence

Red giants evolve into white dwarfs, often accompanied by planetary nebulae

More massive stars form red supergiants Red supergiants undergo supernova

explosions, often leaving behind a stellar core which is a neutron star, or perhaps a black hole


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White Dwarfs, Neutron Stars and Black Holes

White dwarfs are the size of the Earth and about 1 Mo

Neutron stars are 10 km in radius and about 1.4 Mo

One teaspoon of NS material weighs 100 million tons!

After supernova, if cores are larger than 3 Mo , a black hole will be formed


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Properties of Black Holes

Black holes have been observed in several different sizes Stellar mass: > 3 –15 Mo Intermediate mass: 100-1000s Mo Supermassive: 106 – 109 Mo

BHs do not have magnetic fields, so they do not emit pulsations (as do neutron stars)

BHs do not have a surface, so materials cannot undergo nuclear burning

BHs can be found in binary systems, where they accrete matter from their companions


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Black Hole Structure

Schwarzschild radius defines the event horizon

Rsch = 2GM/c2

Singularity is “clothed” inside the event horizon

Cosmic censorship prevails (you cannot see inside the event horizon) Schwarzschild BH


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Signatures of Black Holes

Frame Dragging: Rotating bodies drag space and time around themselves as they rotate – like a spinning object stuck in molasses

Gravitational Waves: waves of gravity that travel at the speed of light, produced by colliding stars, black holes, or asymmetric spinning objects. Also produced by the Big Bang

Frame Dragging: Rotating bodies drag space and time around themselves as they rotate – like a spinning object stuck in molasses

Gravitational Waves: waves of gravity that travel at the speed of light, produced by colliding stars, black holes, or asymmetric spinning objects. Also produced by the Big Bang


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Black Holes and Cosmology

BH are a possible endpoint of stellar evolution (from very massive stars)

BH warp space and time around them, thereby affecting the evolution of the galaxies

Central BH in galaxies may be the seeds that formed the galaxies and may be the only things left in the galaxies at the end of time

Central BH in galaxies are signposts that help us find the earliest galaxies


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Shapes of Galaxies Spirals

disk shaped with spiral arms often have bright bulges in center contain interstellar gas, nebulae, star forming

regions, open clusters and globular clusters Barred Spirals

spiral arms emerge from end of bar gas from outer part of galaxy funneled to center

through the bar, forming new stars in bulge Lenticular (“lens-shaped”)

flattened disks of gas and dust no spiral arms


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Shapes of Galaxies Ellipticals

range from spherical to foot-ball shapes lots of old stars and globular clusters star formation is over or just restarting maybe the result of collision and merger of smaller

galaxies Irregulars

lots of gas and new stars forming rather small compared to spirals and ellipticals

Low surface Brightness lots of gas, but few stars can be rather large


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Clusters of Galaxies

Clusters of galaxies are the largest gravitationally bound systems in the universe, with sizes of a few Mpc (a Mpc is about 3 million light-years).

A typical cluster contains hundreds or thousands of galaxies

Most of the mass is in the form of a hot intracluster gas, which is is heated to high temperatures (106-108K or several keV)

Clusters are rare objects: fewer than 1 in 10 galaxies in the universe resides in clusters


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Distances to Galaxy Clusters

Going beyond Cepheid Variables to the next rungs on the Cosmic Distance Ladder

Brightest Cluster Galaxies: The brightest galaxy in a cluster of galaxies has been used as a standard candle.

But: rich clusters with many galaxies will probably have the most luminous galaxies even though these galaxies are very rare, while the brightest galaxy in less rich clusters are probably not as bright


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Large Scale Structure

Most recent surveys are so large that the largest structures (about 100 Mpc) are smaller than the survey size

These surveys measure the distribution of matter in the Universe on scales at or above 10 Mpc

Superclusters are largest structures seen – but they are not gravitationally bound (unlike clusters of galaxies) – they mark the “end of greatness”


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Walls and Voids

Universe looks like soap bubbles in 3D Galaxies occur on the bubble surfaces Superclusters are formed where bubbles merge Walls are made of elongated superclusters – the

largest is the “Great Wall” - about 100 Mpc in length at a distance of 100 Mpc

Voids are about 100 Mpc in diameter – are 90% of space

Clusters of galaxies are bright spots on the walls


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Looking back through space and time

Constellation-X

JWST, FIRST

MAP, Planck

LISA, GLAST

Big Bang inflation

first stars, galaxies,

and black holes

clusters and groups of galaxies

microwavebackground

matter/radiationdecouplingEarly Universe Gap

First Stars Gap


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Distances to Cepheids

Distance to closest Cepheid (Delta Cephei) in our Galaxy can be found using parallax measurements. This determines K in the period-luminosity relation (L = KP1. 3)

Cepheids are very bright stars – they can be seen in other galaxies out to ~10 million light years (with HST)

Since the period of a Cepheid is related to its absolute brightness, if you observe its period and the apparent brightness, you can then derive its distance (to within about 10%)


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Standard Candles

If you have two light sources that you know are the same brightness

The apparent brightness of the distant source will allow you to calculate its distance, compared to the nearby source

This is because the brightness decreases like 1/(distance)2

movie


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Ultimate Time Machine

Doing astronomical observations is like travelling back in time

If an galaxy is 1 million light years away, then the light that you are seeing left that galaxy 1 million years ago, and you are seeing what it looked like long ago

Hubble plotted the distance to a galaxy that he derived by using Cepheid stars as standard candles vs. the speed at which that galaxy is moving away from the observer on Earth – this is known as the Hubble Law


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Hubble LawThe Hubble constant

Ho = 558 km s -1 Mpc -1

is the slope of these graphs

Compared to modern measurements, Hubble’s

results were off by a factor of ten!


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Hubble Law v = Ho d = cz where

v = velocity from spectral line measurements d = distance to object Ho = Hubble constant in km s-1 Mpc -1 z is the redshift

Space between the galaxies expands while galaxies stay the same size


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Measuring Distance and Time

If the Universe expands at a constant rate

v = Hod and d= vt Solving for t, we find the age of the

Universe:

t = 1/Ho = 9.78 x 109 y h-1

where h = Ho/(100 km s-1 Mpc-1)

Current value for Ho is 70 km s-1 Mpc-1

So the age of the Universe is ~14 x 109 y


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Cosmological parameters

= density of the universe / critical density

hyperbolic geometry

flat or Euclidean

spherical geometry


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Views of the Universe


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Cosmological parameters

In order to find the density of the Universe, you must measure its total amount of matter and energy, including: All the matter we see All the dark matter that we don’t see but we feel All the energy from starlight, background radiation, etc.

The part of the total density/critical density that could be due to matter and/or energy = M

Current measurements : M< 0.3 (WMAP: 0.27)


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Distances to Supernovae

Type Ia supernovae are “standard candles” Occur in a binary system in which a white dwarf star

accretes beyond the 1.4 Mo Chandrasekhar limit and collapses and explodes

Decay time of light curve is correlated to absolute luminosity

Luminosity comes from the radioactive decay of Cobalt and Nickel into Iron

Some Type Ia supernovae are in galaxies with Cepheid variables

Good to 20% as a distance measure


330 0.2 10.80.60.4

Supernovae & Cosmology

M = matter

= cosmological constant

Redshift


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Accelerating Universe

Type 1a SN observations show that the expansion rate of the Universe has not been constant – i.e., that the Hubble constant is not constant

Results from Perlmutter et al. (and also by another group from Harvard, Kirshner et al.) strongly

suggest that if = 0.3, then = 0.7 and there is some type of dark energy which is causing the expansion of the Universe to accelerate

Other results (e.g. WMAP) indicate that total = 1 (the Universe is geometrically flat)


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Acceleration and Deceleration

Evidence from HST supernova observations indicates that the expansion of the Universe is now accelerating, but that it was decelerating in the past as matter formed and gravity dominated


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Dark Matter Evidence

In 1930, Fritz Zwicky discovered that the galaxies in the Coma cluster were moving too fast to remain bound in the cluster according to the Virial Theorem

KPNO image of the Coma cluster of galaxies - almost every object in this picture is a galaxy! Coma is 300 million light years away.


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Hot gas in Galaxy Clusters Measure the mass of light

emitting matter in galaxies in the cluster (stars)

Measure mass of hot gas - it is 3-5 times greater than the mass in stars

Calculate the mass the cluster needs to hold in the hot gas - it is 5 - 10 times more than the mass of the gas plus the mass of the stars!


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Dark Matter Halo

The rotating disks of the spiral galaxies that we see are not stable

Dark matter halos provide enough gravitational force to hold the galaxies together

The halos also maintain the rapid velocities of the outermost stars in the galaxies


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Strong Gravitational Lensing


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Types of Dark Matter Baryonic - ordinary matter: MACHOs, white,

red or brown dwarfs, planets, black holes, neutron stars, gas, and dust

Non-baryonic - neutrinos, WIMPs or other Supersymmetric particles and axions

Cold (CDM) - a form of non-baryonic dark matter with typical mass around 1 GeV/c2 (e.g., WIMPs)

Hot (HDM) - a form of non-baryonic dark matter with individual particle masses not more than 10-100 eV/c2 (e.g., neutrinos)


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HDM vs. CDM models

Supercomputer models of the evolution of the Universe show distinct differences

Rapid motion of HDM particles washes out small scale structure – the Universe would form from the “top down”

CDM particles don’t move very fast and clump to form small structures first – “bottom up”

CDM HDM


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Standard Big Bang Cosmology

Sometime in the distant past there was nothing – space and time did not exist

Vacuum fluctuations created a singularity that was very hot and dense

The Universe expanded from this singularity As it expanded, it cooled

Photons became quarks Quarks became neutrons and protons Neutrons and protons made atoms Atoms clumped together to make stars and

galaxies


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Big Bang Cosmology

Top three reasons to believe big bang cosmology

1. Big Bang Nucleosynthesis

2. Cosmic Microwave Background

3. Hubble Expansion Inflation solves problems associated with

standard Big Bang cosmology1. Horizon Problem

2. Flatness Problem


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Big Bang Timeline

We are here


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Big Bang Nucleosynthesis

Heavier elements than 4He are produced in the stars and through supernovae

However, enough helium and deuterium cannot be produced in stars to match what is observed – in fact, stars destroy deuterium in their cores, which are too hot for deuterium to survive.

So all the deuterium we see must have been made around three minutes after the big bang, when T~109 K

BBN predicts that 25% of the matter in the Universe should be helium, and about 0.001% should be deterium, which is what we see.

BBN also predicts the correct amounts of 3He and 7Li


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Cosmic Microwave Background

Big Bang theory predicts that the early universe was a very hot place and that as it expands, the gas within it cools.

Thus the universe should be filled with radiation that is literally the remnant heat left over.

Since this radiation has cooled since it was formed by a factor of more than 1000, it is now at a temperature of 2.73 K

Radiation of this temperature radiates in the microwave region of the electromagnetic spectrum – hence the Cosmic Microwave Background


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Universe’s Baby Pictures

Red is warmer

Blue is cooler Credit:

NASA/WMAP


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WMAP measures geometry


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WMAP cosmology

Content of the Universe: 4% Atoms 23% Cold Dark Matter 73% Dark energy

Fast moving neutrinos do not play any major role in the evolution of structure in the universe. They would have prevented the early clumping of gas in the universe, delaying the emergence of the first stars, in conflict with the new WMAP data.


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Cosmological Constant

was introduced by Einstein in his theory of General Relativity, in order to keep the Universe stable – otherwise his equations predicted either expansion or contraction (depending on the density of matter)

In order for the Universe to be geometrically flat (tot=1), but with only 27% matter and dark matter (M=0.27), the other 73% must be a different type of mass-energy that we now call “Dark Energy” (=0.73) and that Einstein called the Cosmological constant,


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Dark Energy Evolution

Dark Energy, however, must have been insignificant not too long ago, otherwise its gravitational influence would have made it almost impossible for ordinary matter to form the stars, galaxies and large-scale structure that we see in the universe today.

It must therefore have a density that decreases much more slowly with time than the (normal and dark) matter density, so it can dominate as the Universe expands


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WMAP supports inflation

Inflation - a VERY rapid expansion in the first 10-35 s of the Universe – predicts: That the density of the universe is close to the

critical density, and thus the geometry of the universe is flat.

That the fluctuations in the primordial density in the early universe had the same amplitude on all physical scales.

That there should be, on average, equal numbers of hot and cold spots in the fluctuations of the cosmic microwave background temperature.

WMAP sees a geometrically flat Universe


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CMB Multipole Measurements

Presence of large peak near l = 200 (1 degree) confirms inflationary expansion

Height of second peak at l = 600 determines relative amounts of baryonic (normal) and non-baryonic (dark) matter

Credit: NASA/WMAP


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Horizon Problem

The Universe looks the same everywhere in the sky that we look, yet using standard Big Bang cosmology, there has not been enough time for light to travel between two points on opposite horizons

So, how did the opposite horizons turn out the same (e.g., the CMBR temperature)?

With inflation, the Universe was much smaller in the beginning (before it inflated), and the horizons were close enough that light and energy could travel between them


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No inflation

At t=10-35 s, the Universe expands from about 1 cm to what we see today

1 cm is much larger than the horizon, which at that time was 3 x 10-25 cm


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With inflation

Space expands from 3 x 10-25 cm to much bigger than the Universe we see today


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Flatness Problem

Why do we see such a flat Universe? ( = 1) Inflation flattens out spacetime the same way

that blowing up a balloon flattens the surface Since the Universe is far bigger than we can

see, the part of it that we can see looks flat


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Composition of the Cosmos


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Today’s Cosmology

= 1.0 from CMB measurements. We live in a flat Universe. This used to mean that the Universe was critically bound – the expansion would gradually coast to a stop.

<0.3 from extensive observations at various wavelengths. Includes dark matter as well as normal matter and light.

> 0.6 from Type 1a SN observations. Many different theories for “dark energy.” Expansion of the Universe accelerates even though it is flat.


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Multiverses

Universe was originally defined to include everything

However, with inflation, the possibility exists that our “bubble universe” is only one of many such regions that could have formed

The other universes could have very different physical conditions as a result of different ways that the unified symmetry was broken

New universes may be forming with each gamma-ray burst that makes a black hole!


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Leptons

An electron is the most common example of a lepton – particles which appear pointlike

Neutrinos are also leptons There are 3 generations of leptons, each has

a massive particle and an associated neutrino Each lepton also has an anti-lepton (for

example the electron and positron) Heavier leptons decay into lighter leptons

plus neutrinos (but lepton number must be conserved in these decays)


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Types of Leptons

Lepton Charge

Mass (GeV/c2)

Electron neutrino

0 0

Electron -1 0.000511

Muon neutrino

0 0

Muon -1 0.106

Tau neutrino

0 0

Tau -1 175


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Quarks

Experiments have shown that protons and neutrons are made of smaller particles

We call them “quarks”, a phrase coined by Murray Gellman after James Joyce’s “three quarks for Muster Mark”

Every quark has an anti-quark

Modern picture of atom


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Types of Quarks

Flavor Charge Mass (GeV/c2)

Up 2/3 0.003

Down -1/3 0.006

Charm 2/3 1.3

Strange -1/3 0.1

Top 2/3 175

Bottom -1/3 4.3

Quarks come in three generations

All normal matter is made of the lightest 2 quarks


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Force Summary


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Standard Model

6 quarks (and 6 anti-quarks) 6 leptons (and 6 anti-leptons) 4 forces Force carriers (, W+, W-, Zo, 8 gluons, graviton)


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Quantum Electrodynamics

Quantum mechanics describes the laws of motion of sub-atomic particles

Interactions between sub-atomic particles are described by quantum field theories

QED is the quantum field theory which describes electromagnetic interactions at the sub-atomic level

Predictions from QED calculations are accurate to one part in a trillion


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Quantum Chromodynamics

QCD is the quantum field theory which describes the interactions between quarks and gluons

It is difficult to use QCD to make predictions because the gluons carry a color charge and interact with each other

QCD is a non-linear theory which can only be calculated approximately - 10% accuracy for mass of proton – calculations take months of supercomputer time


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Beyond the Standard Model

Standard model describes every particle and interaction that has ever been observed in a laboratory

It has 18 arbitrary constants that are put in “by hand” – where do these come from?

The masses of the W and Z particles are not easily predictable from the Standard Model

The Standard Model also does not predict the pattern of masses and the generational structure – is a new symmetry needed?


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18 Free Parameters

Fundamental electroweak mass scale (1)Strengths of the 3 forces (3)Masses of e-, and (3)Masses of u, c and t quarks (3)Masses of d, s and b quarks (3)Strength of flavor changing weak force (3)Magnitude of CP symmetry breaking (1)Higgs boson mass (1)


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Grand Unification of Forces

Strengths of three forces depend on the energy at which the observations are made

Supersymmetric theories can unify the forces at higher energies than we can observe

strong

weak

electromagnetic 1016 GeV


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Theory of Everything

Mathematical unification of gravity with the other 3 forces (which are governed by quantum mechanics)

Einstein was the first to try (and fail) to develop a ToE – unifying general relativity with quantum mechanics

Supersymmetry + quantum gravity and string theory are two attempts to develop a ToE


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Model Universe/Wrap up

Use materials at hand to model the Universe

Fill out the worksheet

Fill out the assessment quiz – does not count as part of your grade

May 13, 2003Lynn Cominsky - Cosmology A3501 Professor Lynn Cominsky Department of Physics and...

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