The strange world of contemporary physics…The strange world of contemporary physics…

PHIL 160: Lecture 2

I.I. Two of Lederman’s analogies and what Two of Lederman’s analogies and what they suggest.they suggest.

II.II. What can the evidence be for objects, What can the evidence be for objects, events, and processes that are events, and processes that are unobservable?unobservable?

III.III. Preview of Gould reading.Preview of Gould reading.

Lederman’s analogies

““The pyramid of science”The pyramid of science”

Dependent uponDependent upon

..

..

..

BiologyBiology

ChemistryChemistry

PhysicsPhysics

CausalCausal

MathematicsMathematics

The “library of matter”What are What are the most basic the most basic

elementselements of a library? of a library?

Books? No they are complex Books? No they are complex objects (“cut-able”) that are objects (“cut-able”) that are made up of other (simpler, made up of other (simpler, smaller) thingssmaller) things

Words? They are also complex Words? They are also complex (cut-able) and can be broken (cut-able) and can be broken down into 26 letters…down into 26 letters…

Which can in turn be broken Which can in turn be broken down into just 0 and 1…down into just 0 and 1…

If it makes no sense to take apart If it makes no sense to take apart the 0 and the 1, we’ve found the 0 and the 1, we’ve found the “atomic” components of the “atomic” components of the librarythe library

The universe as the libraryThe universe as the library

What are What are its most basic its most basic elements?elements?

The The forces of natureforces of nature are the are the grammar, spelling, and grammar, spelling, and algorithmalgorithm

Analogous to 0 and 1, the Analogous to 0 and 1, the subatomic particles, quarks subatomic particles, quarks and leptonsand leptons, are currently , are currently believed to be the “atomic” believed to be the “atomic” (un-cut-able) elements of (un-cut-able) elements of the universe the universe

Lederman’s analogiesWhat do these analogies reveal about some quite basic What do these analogies reveal about some quite basic

assumptions that currently underlie or motivate assumptions that currently underlie or motivate researchers in particle physics?researchers in particle physics?

That the entities and laws studied by particle physicists are, That the entities and laws studied by particle physicists are, respectively, what make up and govern all other entities respectively, what make up and govern all other entities and processes and regularities.and processes and regularities.

A commitment to simplicity (that just a few particles make A commitment to simplicity (that just a few particles make up everything there is and that nature operates on the up everything there is and that nature operates on the basis of simple laws)basis of simple laws)

That “invisible” (not able to be directly observed) objects are That “invisible” (not able to be directly observed) objects are respectable, indeed necessary, for (some) theories of respectable, indeed necessary, for (some) theories of physicsphysics

What warrants these assumptions… let’s start with the last..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 Evidence is at times indirect and involves drawing inferencesinvolves drawing inferences

Positing the existence of a ball Positing the existence of a ball that they that they could not observecould not observe, the , the Twiloins were able to Twiloins were able to make make sense of what they could sense of what they could observeobserve..

Scientists often posit an object Scientists often posit an object (or force or process) that cannot (or force or process) that cannot be directly observed when its be directly observed when its existence existence makes sense makes sense of/explainsof/explains what what cancan be be observed.observed.

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

Previously unobservable Previously unobservable entities posited by science:entities posited by science:

MoleculesMolecules GenesGenes AtomsAtoms DNA as a double helixDNA as a double helix

Drawing inferences Deductively valid argument are such that it is not Deductively valid argument are such that it is not

possible for their premises to be true and their possible for their premises to be true and their conclusion false. conclusion false.

Examples:Examples:All men are mortal.All men are mortal.Socrates is a man.Socrates is a man.Therefore, Socrates is mortal.Therefore, Socrates is mortal.ANDANDAll men are green.All men are green.Socrates is a man.Socrates is a man.Therefore, Socrates is green.Therefore, Socrates is green.

Inference to the best explanation

Unlike deductively valid arguments, the premises Unlike deductively valid arguments, the premises of arguments of the form “inference to the best of arguments of the form “inference to the best explanation” do not guarantee their conclusions .explanation” do not guarantee their conclusions .

They are ampliative – they go beyond what is They are ampliative – they go beyond what is contained in the premises. contained in the premises.

So, their conclusions are, at best, probable.So, their conclusions are, at best, probable. One way to understand Lederman’s arguments for One way to understand Lederman’s arguments for

the reasonableness of assuming there are the reasonableness of assuming there are subatomic particles, such as quarks, is to see it as subatomic particles, such as quarks, is to see it as partly involving an inference to the best partly involving an inference to the best explanation.explanation.

Inference to the best explanation

The form of an inference to the best explanation:The form of an inference to the best explanation: Accept that hypothesis among the alternatives Accept that hypothesis among the alternatives

(e.g.,H(e.g.,H11, H, H22, H, H33… if there are any viable … if there are any viable alternatives) alternatives) that best accounts for the evidence that best accounts for the evidence availableavailable (which can take the form of instrument (which can take the form of instrument readings, observable objects and processes, etc.) readings, observable objects and processes, etc.) and is not inconsistent with any known evidence.and is not inconsistent with any known evidence.

So how is this at work in particle physics… So how is this at work in particle physics…

FermilabFermilab

Welcome to Fermilab!Welcome to Fermilab!

Our mission is to discover what the universe is Our mission is to discover what the universe is made of and how it works.made of and how it works.

We're asking three simple, challenging questions We're asking three simple, challenging questions here at the frontier of particle physics:here at the frontier of particle physics:

What is the nature of the universe?What is the nature of the universe?

What are matter, energy, space and time?What are matter, energy, space and time?

How did we get here and where are we going?How did we get here and where are we going?

Fermilab Director Michael S. WitherellFermilab Director Michael S. Witherell

The Standard ModelThe Standard Model

FermilabFermilab

The TevatronThe TevatronWas the world’s highest-energy Was the world’s highest-energy

particle colliderparticle collider4 miles in circumference and 4 miles in circumference and

housed in a tunnel 30 feet housed in a tunnel 30 feet below the ringbelow the ring

Accelerators send particles racing Accelerators send particles racing around the Tevatron at around the Tevatron at 99.9999% of the speed of light 99.9999% of the speed of light so that the particles complete so that the particles complete the four mile course nearly the four mile course nearly 50,000 times a second50,000 times a second

Smashing particlesSmashing particles

Method: Method: Take speeding subatomic particles and smash them Take speeding subatomic particles and smash them

together at high energies. together at high energies. Send two kinds of particles, protons and antiprotons, Send two kinds of particles, protons and antiprotons,

around the ring in opposite directions.around the ring in opposite directions.At two points in the ring, streams of these particles (called At two points in the ring, streams of these particles (called

"beams") flow right into each other."beams") flow right into each other.What follows are What follows are millions and millions of collisionsmillions and millions of collisions, at the , at the

rate of almost two million each second. rate of almost two million each second. Many kinds of devicesMany kinds of devices record details of the debris record details of the debris to to

identify, based on theory, what kinds of particleidentify, based on theory, what kinds of particle are are being produced in the collisions.being produced in the collisions.

Smashing particlesSmashing particles

Using the Tevatron, Fermilab Using the Tevatron, Fermilab scientists have confirmed:scientists have confirmed:

The bottom quark (1977)The bottom quark (1977)

The top quark (1995)The top quark (1995)

The tau neutrino (2000)The tau neutrino (2000)

““We collide particles in the We collide particles in the hope of seeing something hope of seeing something never seen before.”never seen before.”

But But predictedpredicted by theory! by theory!

The detectorsThe detectors

The CDF Collider Detector.The CDF Collider Detector.

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

So what is Lederman’s evidence?So what is Lederman’s evidence?

““My evidence for atoms and quarks is as good as the My evidence for atoms and quarks is as good as the evidence [the TV provides that the Pope exists].evidence [the TV provides that the Pope exists].

““What is that evidence? Tracks of particles in a What is that evidence? Tracks of particles in a bubble" chamber. In the Fermilab accelerator, the bubble" chamber. In the Fermilab accelerator, the “debris” from a collision between a proton and an “debris” from a collision between a proton and an antiproton is captured by a 3 story, 60 million antiproton is captured by a 3 story, 60 million dollar detector.dollar detector.

““Here, the “evidence” – the “seeing” – is tens of Here, the “evidence” – the “seeing” – is tens of thousands of sensors that develop an electrical thousands of sensors that develop an electrical impulse when a particle passes…impulse when a particle passes…

So what is Lederman’s evidence?So what is Lederman’s evidence?

““All of these impulses are fed by through hundreds All of these impulses are fed by through hundreds of thousands of wires to electronic data processors.of thousands of wires to electronic data processors.

““Ultimately, a record is made on spools of magnetic Ultimately, a record is made on spools of magnetic tape, encoded by zeroes and ones.tape, encoded by zeroes and ones.

““This tape records the hot collisions of proton This tape records the hot collisions of proton against antiproton, which can generate as many as against antiproton, which can generate as many as 70 particles that fly apart into the various sections 70 particles that fly apart into the various sections of the detector.of the detector.

““Science, especially particle physics, gains Science, especially particle physics, gains confidence in its conclusions by duplication…” confidence in its conclusions by duplication…”

New slide: now addedNew slide: now added

Lederman on what he and other particle physicists Lederman on what he and other particle physicists are up to:are up to:

““No subatomic particle is observed directly.No subatomic particle is observed directly.““2 particles collide and spew debris and new matter 2 particles collide and spew debris and new matter

inside the accelerator.inside the accelerator.““Physicists infer the existence of new particles from Physicists infer the existence of new particles from

the fact that they collide with other particles in a the fact that they collide with other particles in a 65 million dollar collision detector.65 million dollar collision detector.

““Think of a bus that drives by your house every day Think of a bus that drives by your house every day ……

New slide: now addedNew slide: now added

““One afternoon while you’re at work, the bus One afternoon while you’re at work, the bus collides with a Subaru.collides with a Subaru.

““The bumper flies off the Subaru and hits your The bumper flies off the Subaru and hits your mailbox, which is hurled through your window.mailbox, which is hurled through your window.

““When you come home, you look at the pattern of When you come home, you look at the pattern of shattered glass and say “Hmmm… A Subaru!shattered glass and say “Hmmm… A Subaru!

““That’s not unlike what particle physicists do for a That’s not unlike what particle physicists do for a living.”living.”

What commitments does Lederman embrace?What commitments does Lederman embrace?

Ontological: concerning what there is…Ontological: concerning what there is… A library of matter, that constitutes a hierarchy, and includes A library of matter, that constitutes a hierarchy, and includes

some one or more “fundamental” kinds of stuff.some one or more “fundamental” kinds of stuff. A simple and elegant universe…A simple and elegant universe…

Epistemological: concerning the possibility, limits, and Epistemological: concerning the possibility, limits, and strengths of our abilities to know…strengths of our abilities to know… Fallibilism, but the strength of inference to the best explanation Fallibilism, but the strength of inference to the best explanation

and that physicists have some significant knowledge and are and that physicists have some significant knowledge and are closing in on answers to others of their most fundamental closing in on answers to others of their most fundamental questions.questions.

Aesthetic: concerning what we find beautiful or pleasingAesthetic: concerning what we find beautiful or pleasing Simplicity! Elegance!Simplicity! Elegance!

Sheldon Glashow’s credoSheldon Glashow’s credo

““We scientists believe that the world is knowable, We scientists believe that the world is knowable, that there are simple rules governing the behavior that there are simple rules governing the behavior of matter and the evolution of the universe. We of matter and the evolution of the universe. We affirm that there are eternal, objective, extra-affirm that there are eternal, objective, extra-historical, socially neutral, external, and universal historical, socially neutral, external, and universal truths, and that the assemblage of these truths is truths, and that the assemblage of these truths is what we call physical science. . . .what we call physical science. . . .

““Any intelligent alien anywhere would have come Any intelligent alien anywhere would have come upon the same logical structure as we have for upon the same logical structure as we have for supernovae…supernovae…

““This statement I cannot prove. This statement I This statement I cannot prove. This statement I cannot justify. This is my faith.”cannot justify. This is my faith.”

Evolutionary theorizingEvolutionary theorizing

The late great Stephen Jay The late great Stephen Jay GouldGould

(1941-2002)(1941-2002)Harvard paleontologist and Harvard paleontologist and

evolutionary theoristevolutionary theoristOne of the strongest defenders One of the strongest defenders

of Darwin and evolutionary of Darwin and evolutionary theorytheory

One of the strongest critics of One of the strongest critics of some aspects of some aspects of evolutionary theory.evolutionary theory.

Natural selectionNatural selection

Darwin’s “great discovery”Darwin’s “great discovery” A A mechanism by which evolution could occurmechanism by which evolution could occur..

What it is…What it is… 1. There is intra-species variation.1. There is intra-species variation. 2. There is a struggle for existence.2. There is a struggle for existence. 3. If some variation provides an advantage (however 3. If some variation provides an advantage (however

small…) in terms of survival and/or reproductive small…) in terms of survival and/or reproductive success, those organisms with it will success, those organisms with it will tendtend toto survive survive better and reproduce more successfully better and reproduce more successfully and tendand tend toto pass on the trait to their offspring. pass on the trait to their offspring.