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Foundation
Physics is the fundamental understanding of our Universe
•Observation
•Exploration
•Experimentation
•Interpretation
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Experimental Physics: Basic Research
The world and the Universe which we inhabit is composed
of objects that have mass and are made up of a collection of constituents which are
bound together.
To understand the Universe we do experiments by observing the physical
characteristics of an object or a system.
The system can be
 as small as a proton which is made up of quarks and gluons
 as massive as a black hole with a mass of a billion suns
 a biological system
 as small as an electron or neutrino with no seen structure
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Forces
Every change in a system is due to forces
There are only four forces
•Gravitation - very weak
•Electromagnetic – Everyday force
•Weak – Radioactive decay
•Strong – inside the nucleus
To understand the Universe we have to understand these forces
To understand any object or system we have to use these forces
as our tools for exploration.
BECAUSE WE HAVE TO INTERACT WITH THE OBJECT
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Physics of the Universe
The intellectual thrust of Particle physics, astrophysics and cosmology is to
understand our Universe from
t = 0 to 13.8 billion years
We only have one Universe although some models include speculation about
connections to other Universes
Elementary Particle Physics – Fundamental building blocks and forces
Cosmology – Understanding the history and evolution of the Universe, large
scale structure and phenonoma.
These two disciplines, one at distances of 10-17m and the other to the edge of the
Universe are intimately connected both in physics and experimental techniques.
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The questions
What are the fundamental building blocks?
What is Dark Energy?
Are there extra dimensions?
Are there new laws?
Do all the forces become one?
Why are there so many particles?
What is dark matter?
What are neutrinos telling us?
How did the Universe come to be?
Where did the antimatter go?
What is gravity?
What came before the big bang?
Are there other Universes?
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Overall Framework
Physics is based on experimental observationswhich are incorporated into
theoretical mathematical models which generally make testable extensions
and predictions.
An analogy I use is that we are completing a very large and detailed
painting in which we know a lot detail but much remains to be filled in.
Both high precision in small areas and major discoveries in the whole
picture.
Normally we use as our models and framework the simplest solution that fits all the
experimental observations (no aliens)
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Physical Laws
Physics is the same everywhere in the Universe
Physics has not changed over the age of the Universe
Energy Conservation (Physics is invariant to time)
Momentum conservation (Physics is the same under
space transformation)
Conservation of charge
Conservation of baryon number (protons have a
lifetime > 1034 years)
Symmetry Laws
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Fundamental building blocks
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History of the Universe
10,000,000,001
10,000,000,000
Matter
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Anti-matter
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Matter and Force Particles
Leptons
Strong
Electric Charge
Tau
-1
0
Tau
Neutrino
Muon
-1
0
Muon
Neutrino
0
Electron
Neutrino
Electron
-1
Quarks
Strange
Down
each quark:
-1/3 2/3
Top
-1/3 2/3
Charm
-1/3 2/3
Up
R,
B,
Photon
Quarks
Mesons
Baryons
Nuclei
Atoms
Light
Chemistry
Electronics
Weak
Gravitational
Electric Charge
Bottom
Gluons (8)
Electromagnetic
Bosons
(W,Z)
Graviton ?
Neutron decay
Beta radioactivity
Neutrino interactions
Burning of the sun
Solar system
Galaxies
Black holes
G 3 colours
The particle drawings are simple artistic representations
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Composition of the Universe
Something is providing a
gravitational force in galaxies.
Something is expanding
space
Our current view of the division of energy in the Universe at
the present time
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How do we collect information
We need
The object of interest
Transmission of information
A detector to gather the information
Data analysis
Interpretation of the data
Information can only be carried by particles
Information can be affected in transmission
The detector has specific characteristics and biases
Data analysis can be biased
Interpretations have to include all relevant knowledge
The simplest interpretation is usually favored.
Theories are developed which incorporate experimental results and in general
are predictive of new phenomena
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Techniques
Detector
Probe source
We can use a probe and see what happens to the probe
Rutherford scattering found the nucleus
Using our eyes to look at objects
Using light from distant stars to probe the Universe between the distant
star and earth.
Using lasers for physical and biological systems
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Techniques
We can observe energy emitted by an object either because excess energy has been
put into the object as part of the experiment or because the object naturally has
excess energy.
 Objects in the Universe outside of earth
Nuclear physics
Use of lasers
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Techniques
E = mc2
We can create new systems
High energy collisions make new particles
Florescent biological markers to track biological activity
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Difficulties
Correcting the data for experimental biases
 Light from a distant star is affected by gravitational forces and the
medium such as dust that it passes through.
 All detectors are not perfect and corrections need to be made
Errors occur
 in the transmission of the information
In the detector
In the amount of data collected
Subtraction of backgrounds to obtain the signal
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Interpretation
Conclusions are drawn as to the meaning of the data and the physics it
reveals
It is very important to understand
 What assumptions have been made
Is the analysis unbiased
 The dependence on other experimental results
 Does the data warrant the conclusions.
 What do the conclusions predict
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Technology and devices
Forefront physics is also the forefront of technology
New devices to measure more precisely
New devices to increase data by many factors of 10
New devices required to explore new physics
Forefront technology either developed for basic research or for
commercialization leads to widespread use of new technology in all branches
of science, engineering and industry and new devices for everyday use
Lasers
Medical imaging
The World Wide Web
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Solar System
http://janus.astro.umd.edu/javadir/orbits/ssv.html
http://www.nineplanets.org/overview.html
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Planet orbits
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The Milky Way
The Milky Way
The Milky Way is a gravitationally bound collection of roughly a hundred billion stars.
Our Sun is one of these stars and is located roughly 24,000 light years (or 8000
parsecs) from the center.
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Units of distance
Light Year: the distance that light travels in one year (9.46 x 10^17 cm).
Parsec (pc): 3.26 light years (or 3.086 x 10^18 cm).; also kiloparsec (kpc) = 1000
parsecs and megaparsec (Mpc) = 1,000,000 parsecs.
Astronomical Unit (AU): the average separation of the earth and the sun (1.496 x
10^13 cm).
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Distances
Some Representative Distances:
The Solar System is about 80 Astronomical Units in diameter.
The nearest star (other than the sun) is 4.3 light years away.
Our Galaxy (the Milky Way) is about 100,000
light years in diameter.
Diameter of local cluster of galaxies: about 1 Megaparsec.
Distance to M87 in the Virgo cluster: 50 million light years.
Distance to most distant object seen in the universe: about
18 billion light years (18 x 10^9 light years).
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Spiral Galaxy
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Typical Spiral Galaxy
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Size of the Milky Way
Not shown is the halo which is a spherical region, centered
on the nucleus, with a radius of about 50000 light years.
This halo contains very old stars, produced early on when
the galaxy was still forming. Most of these stars are in
vast collections called globular clusters
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Milky Way Spectra
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Sloan digital sky survey
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Galaxies and voids
This false-color optical map, covering about 4300 square degrees, or 10 percent of the sky,
This false-color optical map, covering about 4300 square degrees, or 10 percent of the sky, shows the distribution in space of
distribution in space of some 2 million galaxies.
someshows
2 millionthe
galaxies.
The image suggests that galaxies dot the surface of giant interconnected bubbles surrounding
immense voids of empty space
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The Universe within 1 billion Light Years
Number of superclusters = 80
Number of galaxy groups = 160 000
Number of large galaxies = 3 million
Number of dwarf galaxies = 30 million
Number of stars = 500 million billion
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Voids
• Voids are the dominant feature and have a typical
diameter of ~ 30Mpc.
• Voids are very underdense region, δρ/ρ~0.95
• Up to 40% of volume of the universe is occupied by voids
• The largest void observed, Bootes void, has a diameter of
about 124Mpc.
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Composition of the Universe
Our current view of the division of energy in the
Universe at the present time
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Extra solar planets
http://planetquest.jpl.nasa.gov
Kepler
Spitzer
Hubble
The challenges.
Planets don't produce any light of their own, except when young.
Enormous distance from us. Lost in the blinding glare of their parent stars.
Detection
• Wobbling of parent star
• Variation in light from parent star “Transit Method”
• Frequency shift of light from planet as it’s velocity changes “Doppler”
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Red shift, looking back in time
The Universe expanded very rapidly in a fraction of
a second. Now imagine the Universe 13 billion years
ago. All parts of the Universe were in the same state
of the beginning of star formation and emitting light.
As the light travels toward us at velocity c space is
expanding so the distance the light has to travel
increases so there is a point that emitted light 13
billion years which has just reached us.
c
s
This light is red shifted because of the expansion of space c = fλ
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Velocity versus distance
light
v
 We observe that the light from distant objects is
shifted to longer wavelengths, that is toward the red.
This shift is due to the expansion of space since the
light was emitted
The red shift is used to determine velocities
HYDROGEN SPECTRUM
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v/c = ((z+1)2 -1)/((z + 1)2 +1)
Z = Δλ/λ
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