The strange world of contemporary physics…
PHIL 160: Lecture 2
I. Two of Lederman’s analogies and what
they suggest.
II. What can the evidence be for objects,
events, and processes that are
unobservable?
III. Preview of Gould reading.
Lederman’s analogies
“The pyramid of science”
Dependent upon
.
.
.
Biology
Chemistry
Physics
Causal
Mathematics
The “library of matter”
What are the most basic elements The universe as the library
of a library? What are its most basic
Books? No they are complex elements?
objects (“cut-able”) that are The forces of nature are the
made up of other (simpler, grammar, spelling, and
smaller) things algorithm
Words? They are also complex Analogous to 0 and 1, the
(cut-able) and can be broken subatomic particles, quarks
down into 26 letters… and leptons, are currently
Which can in turn be broken believed to be the “atomic”
down into just 0 and 1… (un-cut-able) elements of
If it makes no sense to take apart the universe
the 0 and the 1, we’ve found
the “atomic” components of
the library
Lederman’s 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… let’s start with the last..
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.
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
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.
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 Lederman’s 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.
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…
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 physics:
What 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
The Standard Model
Fermilab
The Tevatron
Was the world’s 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
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.
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!
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.
So what is Lederman’s 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…
So what is Lederman’s 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…”
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
…
New slide: now added
“One afternoon while you’re 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!
“That’s not unlike what particle physicists do for a
living.”
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!
Sheldon Glashow’s 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.”
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.
Natural selection
Darwin’s “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.