FROM THE VERY SMALL TO THE VERY LARGE

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FROM THE VERY SMALL TO THE VERY LARGE

• PARTICLE PHYSICS AND THE COSMOS

Michael Dine July 2004
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Questions from Professor Browns Lecture

• 1.  How big is the universe?2.  What is the
  large-scale geometry of the universe?3.  Why is
  the universe accelerating?4.  What is dark
  matter?5.  Why are protons indestructable?6. 
  Why are quarks confined?7.  Why is the charge of
  the proton the same as the charge of the
  electron?

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New York Times April, 2003

• Reports a debate among cosmologists about the Big
  Bang.
• lll1.html

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Dr. Tyson, who introduced himself as the
Frederick P. Rose director of the Hayden
Planetarium, had invited five "distinguished"
cosmologists into his lair for a
roasting disguised as a debate about the Big
Bang. It was part of series in honor of the late
and prolific author Isaac Asimov (540 books
written or edited). What turned out to be at
issue was less the Big Bang than
cosmologists' pretensions that they now know
something about the universe, a subject about
which "the public feels some sense of ownership,"
Dr. Tyson said. "Imagine you're in a living
room," he told the audience. "You're
eavesdropping on scientists as they argue
about things for which there is very little data."
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Dr. James Peebles, recently retired from
Princeton, whom he called "the godfather" Dr.
Alan Guth from the Massachusetts Institute of
Technology, author of the leading theory of the
Big Bang, known as inflation, which posits a
spurt of a kind of anti-gravity at the beginning
of time and Dr. Paul Steinhardt, also of
Princeton, who has recently been pushing an
alternative genesis involving colliding universes.
Rounding out the field were Dr. Lee Smolin, a
gravitational theorist at the Perimeter Institute
for Theoretical Physics in Waterloo, Ontario,
whom Dr. Tyson described as "always good for an
idea completely out of left field - he's here to
stir the pot" and Dr. David Spergel, a
Princeton astrophysicist.
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But Dr. Smolin said the 20th-century revolution
was not complete. His work involves trying to
reconcile Einstein's general relativity, which
explains gravity as the "curvature" of
space-time, with quantum mechanics, the strange
laws that describe the behavior of atoms.
"Quantum mechanics and gravity don't talk to
each other," he said, and until they do in a
theory of so-called quantum gravity, science
lacks a fundamental theory of the world. The
modern analog of Newton's Principia, which
codified the previous view of physics in 1687,
"is still ahead of us, not behind us," he said.
Although he is not a cosmologist, it was fitting
for him to be there, he said, because "all the
problems those guys don't solve wind up with us."
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Today, you are listening to someone seemingly
more out in left field -- a particle
physicist. Particle physics seeks to determine
the laws of nature at a microscopic really
submicroscopic, level. What does this have to
do with the Big Bang?
EVERYTHING!
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• With due respect to the New York Times, articles
  like
• this give a very misleading impression.
• We know
• There was a Big Bang
• This even occurred about 13 Billion Years Ago
• We can describe the history of the universe,
• starting at t3minutes
• There is now a huge amount of data and a picture
• with great detail.

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• There are lots of things we dont know. With due
  respect to Lee Smolin, the correct address for
  these questions is Particle Physics.
• What is the dark matter?
• Why does the universe contain matter at all?
• What is the dark energy?
• What is responsible for inflation?
• What happened at t0?
• We cant answer any of these questions without
  resolving mysteries of particle physics. We need
  to know that laws of nature which operate at the
  smallest distances we can presently imagine. This
  will be the subject of this talk.

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What is particle physics?

• Particle physics is just that the study of
  particles. What
• are the proton and neutron? What are they made
  of? What
• about the electron? How do all of these
  particles interact with
• each other? The tools mainly big machines,
  called particle
• accelerators.
• Why bother?
• Its fun.
• Learning about the elementary particles, we
  learn what are
• the laws of nature which operate at very
  small distance
• scales.

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More questions

• Why does studying the behavior of small
  particles tell us something about the fundamental
  laws of nature.? And dont we already know all of
  the laws? And why do we care, anyway?
• Why do we need big machines in order to study
  small particles?

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Physical Law

• Newton Fma FG M1M1/R2
• Probably the most famous physical laws.
  UNIVERSAL

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Newton could use his laws to explain the motion
of the planets, the moon. Haley comets.
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Explained Keplers Laws Planets move in
elliptical Orbits, with the sun at one focus.
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Electricity and MagnetismFaraday
Conducted experiments which showed that a
changing electric field produces a magnetic
field and vice versa, and that a changing
magnetic field induces current (generators)
Electricity and magnetism aspects of one related
set of phenomena ELECTROMAGNETISM.
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Electricity and MagnetismMaxwell
Wrote down the laws of electricity and
magnetism Maxwells equations. Light, radio
waves (Maxwell predicted), and other radiation
all part of the same set of phenomena.
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HERTZ RADIO WAVES
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So two sets of laws. These describe most of the
phenomena of our day to day experience gravity,
light, electricity, magnetism With these,
scientists of the late 19th century understood
the motion of the planets in great detail, and
made great technical progress. They started, as
well (somewhat inadvertently) to explore the
world of atoms. The end of the 19th century saw
the discovery of the first elementary particle,
by Thompson the electron.
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EINSTEIN
Excited by Maxwells equations and also puzzled.
There seemed to be a maximal speed at which light
could travel. Puzzled, also by the problem of
the photoelectric effect the emission of
electrons by light. Also wondered about the
existence of atoms. Were they real, or just a
trick to understand the periodic table?

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Einsteins Extraordinary year 1905

• Photoelectric effect the idea that lights come
  in packets of energy the beginnings of the
  photon concept
• Explanation of the Brownian motion basic to
  physics, chemistry, biology clinched the idea
  that atoms were real.
• Special relativity time and space are relative
  concepts depend on the observer. But the speed
  of light is absolute all observers agree about
  it.

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General Relativity
Now, a deeper understanding of the laws of
electricity and magnetism. But Einstein didnt
know how to reconcile Newtons laws with the
rules of relativity. E.g. in Newtons laws,
action at a distance. Didnt make sense
electricity and magnetism dont work this
way. Einsteins clue the equality of
gravitational and inertial mass. Inertia
something to do with space and time. So gravity?
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Fma FG mM/R2
Gravitation
Inertia
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The equality of gravitational and inertial mass
was first tested in experiments by the Hungarian
scientist Eotvos in the late 1800s
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Einstein and the General Theory of Relativity

• After almost eleven years of struggle, Einstein
  announced his general theory of relativity in
  1916. A theory in which gravity arises as the
  distortion of space and time by energy.
  Proposed three experimental tests
• Bending of light by the sun
• Perihelion of Mercury
• Red Shift

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General Relativity and the Universe
Gravity was unique among the forces in that it is
always attractive. So it acts on things at the
surface of the earth, on the planets, on stars,
and on the universe as a whole. So Einstein and
others tried to apply his theory to the
universe. But the universe is complicated,
varied. How to proceed?
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Einstein Copernicus
Assume the universe is homogeneous and isotropic
no special place or direction.
Einsteins equations have no Static
solutions. The universe expands!
Einstein was very troubled remember that at
that time (c. 1920) Astronomers didnt know about
galaxies!
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Edwin Hubble, who started out as a lazy, rich
kid, became one of the most important of all
astronomers.
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HUBBLE (1921)
Galaxies move away from us at a speed
proportional to their distance
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The Cosmic Microwave Background
In the past, the universe must have been much
hotter Big Bang. Gamow, Peebles if true,
there should be a glow left over from this
huge explosion (but of microwave radiation, not
light). Objects give off a characteristic
spectrum of electromagnetic radiation depending
on their temperature blackbody. The
temperature then was 10,000 degrees today it
would be about 3 degrees Discovered by Penzias
and Wilson (1969). Today thanks to COBE
satellite, the best measured black body spectrum
in nature.
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Artists Rendering of COBE
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COBE measured the temperature of the universe
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More detailed study of the CMBR

• From satellites and earth based (balloon)
  experiments. Most recently the WMAP satellite.

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Detailed information about the universe
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COMPOSITION OF THE UNIVERSE

• From studies of CMBR, of distant Supernova
  explosions, and from Hubble and Ground-Based
  observations we know
• 5 Baryons (protons, neutrons)
• 35 Dark Matter ??? (zero pressure)
• 65 Dark Energy ???? (negative pressure)

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A Confusing Picture Where Do We Stand?

• We have a good understanding of the history of
  the universe, both from observations and well
  understood physical theory, from t180 seconds.
• BUT
• We dont know why there are baryons at all!
• We dont know what constitutes 95 of the energy
  of the universe.
• We know that the universe underwent a period of
  violent expansion (inflation) at about 10-30
  seconds after the big bang. What caused this?

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But weve gotten ahead of our story.

• We started out talking about laws of nature. We
  had Newton, and with him an understanding of the
  planets then Maxwell, and an understanding of
  the electromagnetic spectrum, and now Einstein,
  and we have started to think about the universe
  as a whole. But a lot happened between 1905 and
  these discoveries.

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New particles, new laws

• 1895 discovery of the electron
• 1911 - discovery of the atomic nucleus
• 1920s quantum mechanics
• 1930s the neutron, and understanding of the
  atomic nucleus.
• 1930s discovery of antimatter.

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Rutherfords Discovers the Nucleus
"It was quite the most incredible event that ever
happened to me in my life. It was almost as
incredible as if you had fired a 15-inch shell at
a piece of tissue paper and it came back and hit
you."
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Applications

• Understanding of atoms, quantum mechanics all
  of our modern technological revolution. Also
  important tools for looking at the universe the
  spectrum of light tells us the composition of
  stars, planets.
• Nuclear physics reactors (bombs) also
  understanding of the workings of stars.
• Together, a revolution in astronomy.

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LOOKING STILL DEEPER

• By the 1940s, much progress, but much not well
  understood
• Photons
• The precise laws underlying the nuclear forces
• To go further theoretical developments
• Experiments probing distances smaller
• than the size of nuclei

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Quantum Electrodynamics

• Feynman, Schwinger, Tomanaga detailed
  understanding of how quantum mechanics and
  electricity and magnetism work together.
  Predictions with awesome precision. E.g. the
  magnetism of the electron explained in terms of
  the electrons charge and mass to one part in
  1012.

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Looking Deeper

• The late 1940s launched the era of large
  particle accelerators. Some of the important
  discoveries (also cosmic rays)
• Particles like the electron, but heavier m t
• Three kinds of neutrino
• Neutrons, protons made up of quarks

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Stanford Linear Accelerator
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HOW DO WE KNOW HOW THESUN SHINES?
ASTRONOMERS AND PHYSICISTS LOOKING AT THE
SURFACE OF THE SUN CAN MEASURE ITS TEMPERATURE
AND FIGURE OUT WHAT ITS MADE OF. THEN THEY
FIGURE OUT HOW THINGS WORK INSIDE. BUT CAN WE
SEE INSIDE?
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Ray Davis and John Bahcall said yes look for
neutrinos produced in the nuclear reactions in
the sun.
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Homestake Gold Mine, South Dakota
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A huge tank of cleaning fluid! Chlorine atoms
hit by neutrinos turn into radioactive argonne.
About once a month, Davis and his crew flushed
out the tank, looked for the radioactivity.
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They did this every month for about 30 years!
They found only ½ as many neutrinos as Bahcall
said there should be. Did this mean We didnt
understand the sun?
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No! We didnt understand the neutrinos!
SNOSudbury Neutrino Observatory
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Where Do We Stand?

• Particle physicists know the laws of nature on
  scales down to one-thousandth the size of an
  atomic nucleus. The Standard Model.
  Experiments at higher energy accelerators at CERN
  (Geneva) and Fermilab (Chicago) are testing our
  understanding at even shorter distances. Expect
  to discover new phenomena.

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PDG Wall Chart
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Back to Our Cosmic Questions

• To answer these questions, we need to know how
  the universe behaved when the temperature was
  extremely high. Temperatureenergy. So we need
  to know about high energies.
• In quantum mechanics, high energiesshort
  distances. We need to know about the laws of
  physics which operate at very short distances.
• With what we know today, we can figure out the
  history of the universe back to about 10-7
  seconds after the big bang!
• BUT THATS NOT GOOD ENOUGH

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• We may soon know the identity of the dark matter.
  This probably requires increasing the energies
  of our accelerators by a factor of 10
• Related to this, we may have some idea where the
  matter in the universe came from
• Other questions may require theoretical as well
  as experimental breakthroughs.

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One possible new phenomenonSupersymmetry

• A new symmetry among the elementary particles.
  Fermions ! bosons bosons ! fermions.
• Theres not time to explain why here, but if this
  idea is right, then it explains what the dark
  matter is!

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This symmetry proposed to solve puzzles of
particle physics, but it turns out that the
photino is automatically a natural candidate
for the dark matter. If it exists with the
conjectured properties, it is produced in just
the right quantity to be the dark matter.
Supersymmetry also provides a natural way to
understand why there are baryons in the
universe at all (a puzzle first posed by
Andrei Sakharov).
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• So a better understanding of the laws of nature
  in the not too
• distant future might answer two of the
  puzzles in our list.
• What about the others?
• Harder But over time, we may have answers. All
  require, as
• Smolin says, an understanding of quantum
  mechanics and
• gravity (general relativity). Particle
  physicists do have a theory
• which reconciles both String Theory. This is
  the subject of
• another talk. But String Theory does have
• Supersymmetry (dark matter, baryogenesis)
• Candidate mechanisms for inflation
• A possible explanation of the dark energy.

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WMAP ORBIT
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3 minutes Synthesis of the Light Elements

• CMBR A fossil from t100,000 years.
• He,Li,De Produced at t3 minutes

p
e
Neutrino reactions stop neutrons decay.
n
n
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Results of Detailed Nucleosynthesis Calculations

• The fraction of the universe made of
  baryonsprotons neutrons
• During last two years, an independent measurement
  from studies of CMBR
• Very impressive agreement!

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April 10, 2003 Thursday Princeton Physics
Department Colloquium, 430 p.m. - Jadwin A-10
Speaker Michael Dine UCSC Title "Bringing
String Theory into Contact With Experiment"
Abstract String theory bears a striking
resemblance to the real world. But making
precise predictions for future experiments is
surprisingly difficult. In this talk, I will
explain the difficulties, and outline the
approaches which are being pursued to developing
a string phenomenology. I will also describe
some of the insights which string theory has
already provided into long-standing puzzles of
particle physics. Host Chiara Nappi Tea in
Room 218 Jadwin Hall, at 4 p.m.