The strange world of contemporary physics

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The strange world of contemporary physics
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PHIL 160 Lecture 2

• Two of Ledermans analogies and what they
  suggest.
• What can the evidence be for objects, events, and
  processes that are unobservable?
• Preview of Gould reading.

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Ledermans analogies

• The pyramid of science
• Dependent upon
• .
• .
• .
• Biology
• Chemistry
• Physics
• Causal
• Mathematics

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The library of matter

• What are the most basic elements of a library?
• Books? No they are complex objects (cut-able)
  that are made up of other (simpler, smaller)
  things
• Words? They are also complex (cut-able) and can
  be broken down into 26 letters
• Which can in turn be broken down into just 0 and
  1
• If it makes no sense to take apart the 0 and the
  1, weve found the atomic components of the
  library

• The universe as the library
• What are its most basic elements?
• The forces of nature are the grammar, spelling,
  and algorithm
• Analogous to 0 and 1, the subatomic particles,
  quarks and leptons, are currently believed to be
  the atomic (un-cut-able) elements of the
  universe

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Ledermans analogies

• What do these analogies reveal about some quite
  basic assumptions that currently underlie or
  motivate researchers in particle physics?
• That the entities and laws studied by particle
  physicists are, respectively, what make up and
  govern all other entities and processes and
  regularities.
• A commitment to simplicity (that just a few
  particles make up everything there is and that
  nature operates on the basis of simple laws)
• That invisible (not able to be directly
  observed) objects are respectable, indeed
  necessary, for (some) theories of physics
• What warrants these assumptions lets start with
  the last..

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Invisible soccer balls and evidence for objects
or processes that cannot be directly observed

• Evidence is at times indirect and involves
  drawing inferences
• Positing the existence of a ball that they could
  not observe, the Twiloins were able to make sense
  of what they could observe.
• Scientists often posit an object (or force or
  process) that cannot be directly observed when
  its existence makes sense of/explains what can be
  observed.

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Invisible soccer balls and evidence for objects
or processes that cannot be directly observed

• Previously unobservable entities posited by
  science
• Molecules
• Genes
• Atoms
• DNA as a double helix

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Drawing inferences

• Deductively valid argument are such that it is
  not possible for their premises to be true and
  their conclusion false.
• Examples
• All men are mortal.
• Socrates is a man.
• Therefore, Socrates is mortal.
• AND
• All men are green.
• Socrates is a man.
• Therefore, Socrates is green.

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Inference to the best explanation

• Unlike deductively valid arguments, the premises
  of arguments of the form inference to the best
  explanation do not guarantee their conclusions .
• They are ampliative they go beyond what is
  contained in the premises.
• So, their conclusions are, at best, probable.
• One way to understand Ledermans arguments for
  the reasonableness of assuming there are
  subatomic particles, such as quarks, is to see it
  as partly involving an inference to the best
  explanation.

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Inference to the best explanation

• The form of an inference to the best explanation
• Accept that hypothesis among the alternatives
  (e.g.,H1, H2, H3 if there are any viable
  alternatives) that best accounts for the evidence
  available (which can take the form of instrument
  readings, observable objects and processes, etc.)
  and is not inconsistent with any known evidence.
• So how is this at work in particle physics

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Fermilab

• Welcome to Fermilab!
• Our mission is to discover what the universe is
  made of and how it works.
• We're asking three simple, challenging questions
  here at the frontier of particle physicsWhat
  is the nature of the universe?What are matter,
  energy, space and time?How did we get here and
  where are we going?
• Fermilab Director Michael S. Witherell

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The Standard Model
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Fermilab

• The Tevatron
• Was the worlds highest-energy particle collider
• 4 miles in circumference and housed in a tunnel
  30 feet below the ring
• Accelerators send particles racing around the
  Tevatron at 99.9999 of the speed of light so
  that the particles complete the four mile course
  nearly 50,000 times a second

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Smashing particles

• Method
• Take speeding subatomic particles and smash them
  together at high energies.
• Send two kinds of particles, protons and
  antiprotons, around the ring in opposite
  directions.
• At two points in the ring, streams of these
  particles (called "beams") flow right into each
  other.
• What follows are millions and millions of
  collisions, at the rate of almost two million
  each second.
• Many kinds of devices record details of the
  debris to identify, based on theory, what kinds
  of particle are being produced in the collisions.

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Smashing particles

• Using the Tevatron, Fermilab scientists have
  confirmed
• The bottom quark (1977)
• The top quark (1995)
• The tau neutrino (2000)
• We collide particles in the hope of seeing
  something never seen before.
• But predicted by theory!

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The detectors

• The CDF Collider Detector.
• Each detector has about one million individual
  pathways for recording electronic data generated
  by the particle collisions. The signals are
  carried over nearly a thousand miles of wires and
  cables--each one connected by hand and tested
  individually.

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So what is Ledermans evidence?

• My evidence for atoms and quarks is as good as
  the evidence the TV provides that the Pope
  exists.
• What is that evidence? Tracks of particles in a
  bubble" chamber. In the Fermilab accelerator, the
  debris from a collision between a proton and an
  antiproton is captured by a 3 story, 60 million
  dollar detector.
• Here, the evidence the seeing is tens of
  thousands of sensors that develop an electrical
  impulse when a particle passes

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So what is Ledermans evidence?

• All of these impulses are fed by through
  hundreds of thousands of wires to electronic data
  processors.
• Ultimately, a record is made on spools of
  magnetic tape, encoded by zeroes and ones.
• This tape records the hot collisions of proton
  against antiproton, which can generate as many as
  70 particles that fly apart into the various
  sections of the detector.
• Science, especially particle physics, gains
  confidence in its conclusions by duplication

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New slide now added

• Lederman on what he and other particle physicists
  are up to
• No subatomic particle is observed directly.
• 2 particles collide and spew debris and new
  matter inside the accelerator.
• Physicists infer the existence of new particles
  from the fact that they collide with other
  particles in a 65 million dollar collision
  detector.
• Think of a bus that drives by your house every
  day

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New slide now added

• One afternoon while youre at work, the bus
  collides with a Subaru.
• The bumper flies off the Subaru and hits your
  mailbox, which is hurled through your window.
• When you come home, you look at the pattern of
  shattered glass and say Hmmm A Subaru!
• Thats not unlike what particle physicists do
  for a living.

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What commitments does Lederman embrace?

• Ontological concerning what there is
• A library of matter, that constitutes a
  hierarchy, and includes some one or more
  fundamental kinds of stuff.
• A simple and elegant universe
• Epistemological concerning the possibility,
  limits, and strengths of our abilities to know
• Fallibilism, but the strength of inference to the
  best explanation and that physicists have some
  significant knowledge and are closing in on
  answers to others of their most fundamental
  questions.
• Aesthetic concerning what we find beautiful or
  pleasing
• Simplicity! Elegance!

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Sheldon Glashows credo

• We scientists believe that the world is
  knowable, that there are simple rules governing
  the behavior of matter and the evolution of the
  universe. We affirm that there are eternal,
  objective, extra-historical, socially neutral,
  external, and universal truths, and that the
  assemblage of these truths is what we call
  physical science. . . .
• Any intelligent alien anywhere would have come
  upon the same logical structure as we have for
  supernovae
• This statement I cannot prove. This statement I
  cannot justify. This is my faith.

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Evolutionary theorizing

• The late great Stephen Jay Gould
• (1941-2002)
• Harvard paleontologist and evolutionary theorist
• One of the strongest defenders of Darwin and
  evolutionary theory
• One of the strongest critics of some aspects of
  evolutionary theory.

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Natural selection

• Darwins great discovery
• A mechanism by which evolution could occur.
• What it is
• 1. There is intra-species variation.
• 2. There is a struggle for existence.
• 3. If some variation provides an advantage
  (however small) in terms of survival and/or
  reproductive success, those organisms with it
  will tend to survive better and reproduce more
  successfully and tend to pass on the trait to
  their offspring.