1. The strange world of contemporary physics…

2. 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.

3. Lederman’s analogies “The pyramid of science” Dependent upon...BiologyChemistryPhysics Causal CausalMathematics

4. 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, we’ve 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

5. 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..

6. 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.

7. 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

8. 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.

9. 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.

10. Inference to the best explanation  The form of an inference to the best explanation:  Accept that hypothesis among the alternatives (e.g.,H 1, H 2, H 3 … 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…

11. 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

12. The Standard Model

13. 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

14. 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.

15. 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!

16. 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.

17. 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…

18. 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…”

19. 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 …

20. 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.”

21. 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!

22. 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.”

23. 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.

24. 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.