Introduction to Modern Physics

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Introduction to Modern Physics
A (mainly) historical perspective on - atomic
physics - nuclear physics - particle physics
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Start of Modern Physics
Electron discovery 1897 Atomic
Physics Nuclear Physics Particle
Physics STANDARD MODEL ?? Theory of Everything
??
A modest goal !
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A lesson from history!!
At the end of the 19th century CLASSICAL
PHYSICS Mechanics Newton 1687 Electromagnetism
Maxwell 1848 Plusa few loose ends!! The End
of Physics ??
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Thenattempt to predict Blackbody Radiation
DISASTER !!
Electromagnetic radiation
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Electromagnetic Radiation
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Electromagnetic Radiation
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c ? f
Frequency vibrations/second
Speed of light 3 x 108 meter/second or 30cm (1
foot) per nanosecond
Wavelength (meter)
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Theories of Blackbody Radiation
Classical disaster !
Quantum solution
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Plancks Quantum Theory
I(?,T) ?-5 / (ehc/?kT - 1)
The oscillators in the walls can only have
certain energies NOT continuous!
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About the same time the electron was
discovered.
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So about 100 years ago people believed in the
existence of atoms - electron is part
of an atom? - atoms emit radiation
strangely? - what else is in an atom?
- atoms emit electromagnetic waves?
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Then 1905 !! Einsteins Miraculous Year - to
be celebrated this year as the Year of Physics
http//www.wyp2005.org/
http//www.einsteinyear.org/
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Example
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The Photoelectric Effect
Light tiny particles!
Wave theory takes too long to get enough
energy to eject electrons Particle theory energy
is concentrated in packets -gt efficiently ejects
electrons!
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An application of the photoelectric effect
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So matter contains electrons and light can be
emitted in chunks so what does this tell us
about atoms??
Possible models of the atom
Which one is correct?
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The Rutherford Experiment
Electric potential V(r) 1/r
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The correct model of the atom
but beware of simple images!
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Probability of finding electrons in a hydrogen
atom
Results from quantum theory
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Atomic signatures
Rarefied gas
Only discrete lines!
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How atomic light emmision works
A photon!
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But why dont all our atoms collapse??!!
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if waves can be particles, perhaps particles
can be waves
? h/mv
SELF DESTRUCTS!
OK !
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Electrons as waves an application
A GEM foil
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1920s Full description of atomic behavior -gt
Quantum Mechanics
Weird stuff!!
Ghosts!??
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so things get fuzzy at the atomic/quantum
level in fact we can no longer be certain of
anything!
?x ? (wavelength)
?p h/?
(?x) (?p) h
Heisenbergs Uncertainty Principle
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On to the Nucleus 1930s
Existence of protons Rutherford/neutral atoms
1932 Chadwick discovers the neutron
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Note the relative scales!
Nucleus baseball
Atom city
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Nucleus
Atomic mass number
A
X
Nuclide
Z
Atomic number
e.g. Uranium-235
235
U
92
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A N Z
so normally N gt Z
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The most important graph in all of science
Why there are stable nuclei
Why the Sun shines
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Why dont nuclei fall apart??
Two Protons


Repel

No charge
No charge
No charge
No charge
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So there MUST be a NEW FORCE
The Strong Nuclear Force
Pions Gluons more later!
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Nuclei can also decay
Alpha decay e.g.
Alpha particle
Beta decay n -gt p e ?
Gamma decay e.g.
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Applications of Nuclear Physics
Fission
limitless energy ??
Fusion
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Applications of Nuclear Physics
e
e- -gt 2?
PET
MRI
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Or
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But still open questions remain Whats
inside a proton/neutron? What causes Beta
decay? What other elementary particles
exist? What other forces exist? Why is
the proton mass 1800x the electron mass?
Where does mass come from?
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Introduction to High Energy Physics Research (or
how to chase quarks and get paid for it)
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Structure of Matter
Matter
Molecule
Atom
Nucleus
Quark
Baryon
(Hadron)
u
10-14m
cm
10-10m
10-15m
10-9m
lt10-19m
protons, neutrons, mesons, etc. p,W,L...
top, bottom, charm, strange, up, down
Chemistry
Atomic Physics
Nuclear Physics
Electron
Mass
(Lepton)
proton 1 GeV/c2
lt10-18m
High Energy Physics
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How do we DO Particle Physics
Use collisions of elementary particles!
?
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Definition Study of matter and forces at the
most fundamental level Why HEP? Investment in
basic research has always returned major economic
dividends. 50 GNP related to modern
physics - must keep up flow of new knowledge
or economy/society will stagnate.
?
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History of Particle Physics
Nuclear Physics
Atomic Physics
Quantum Mechanics
Relativity
Particle Physics
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Ingredients -gt discovering particles e, p,
n, ?? ?? ?? ?? ?? -gt understanding properties
of interactions Electromagnetic ? e
scattering Weak nuclear neutron decay
Strong nuclear proton-antiproton scattering
(Gravity ??) -gt Finding -gt Combining forces
e.m. weak ? strong ?? gravity ???
patterns
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How do we do particle physics?
Theory
Experiment
Phenomenology
A constant interplay of ideas/experiment
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Start of Modern Physics
Electron discovery 1897 Atomic
Physics Nuclear Physics Particle
Physics STANDARD MODEL ?? Theory of Everything
??
A modest goal !
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What do we know now (2004)?
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A question of Scales Planck scale 10-35
Quarks ? 10-19 m Nucleus 10-14 m
Atom 10-10 m You
1.5m Collider detector 10 m
Accelerator 104 m
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Early Particle timeline
I am born
My career starts!
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The recent particle timeline
Revolution!
What next??
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Pacific Ocean
I280 Junipero Sierra Freeway
2-mile accelerator
Part of Stanford University
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The Mark I detector where the charm quark was
discovered and a Nobel Prize was won
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Fermilab - Chicago
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We have seen that the Standard Model covers a
wide range of phenomena and explains them
well. BUT - no means of generating mass -
matter asymmetry - dark matter - how is
electroweak symmetry broken? - are quarks
composite?
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Famous scientist as the Higgs
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Supersymmetry
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Do all forces become one at high energy??
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UTA and Particle Physics