What is physics?

According to the Oxford Languages Dictionary https://languages.oup.com/google-dictionary-en/, physics is “the branch of science concerned with the nature and properties of matter and energy. The subject matter of physics, distinguished from that of chemistry and biology, includes mechanics, heat, light and other radiation, sound, electricity, magnetism, and the structure of atoms.”

What do physicists do?

-They teach in secondary schools, universities, and other venues such as teachers’ colleges.

-They do research, both “pure” and applied. (I’m not cazy about the adjective “pure”; it makes it sound like applied physics is impure. But we’re stuck with it.)

According to AI, “Pure and applied physics” refers to two complementary approaches to the study of physics. Pure physics focuses on understanding the fundamental laws of nature, while applied physics focuses on using those laws to develop practical technologies and solve real-world problems.” AI is correct. But there is a caveat: the boundaries are not always clear. “Pure” physics often turns out to produce practial applications. For example, studying the basic structure of atoms led to the laser.

My career consisted of both teaching and research, as well as naming, studying, and reducing science anxiety. See the section on science anxiety.

TEACHING

Physics avoidance” is common for example, in US high schools, sometimes aided and abetted by making it non-required. Of US university students, only one third of one percent are studying physics as their major subject. Even among the STEM (Science Technology, Engineering, and Mathematics) students, only two percent are majoring in physics. In horror films, mad physicists play a prominent role. Examples:

• The Invisible Ray: “A scientist becomes murderous after discovering, and being exposed to the radiation of, a powerful new element called Radium X.”

• Man Made Monster: “A mad scientist turns a man into an electrically-controlled monster to do his bidding.”

• The Fly: “A scientist has a horrific accident when he tries to use his newly invented teleportation device.”

• Monster of Terror: “A young man visits his fiancée’s estate to discover that her wheelchair-bound scientist father has discovered a meteorite that emits mutating radiation rays that have turned the plants in his greenhouse to giants.”

• Last, but surely not least, Stanley Kubrick’s Dr. Strangelove. (“Mein Führer, I can valk!”) Even the good guys, such as Spiderman and the Hulk gained their powers by exposure to radioactivity.

To be fair, Dr. Frankenstein was a biologist. And although it is not related to physics, who can resist The Devil Bat? “A mad scientist develops an aftershave lotion that causes his gigantic bats to kill anyone who wears it.”

Teaching methods:

The traditional method has been the lecture, known variously as “chalk and talk” and ‘the sage on the stage”. It need not be abandoned, but over the last few decades, various teaching strategies have been shown to aid science learning. These include:

• The implementation of teacher–student and student–student interaction in lieu of straight lecturing.

• The design of laboratories to elicit creativity in approaches to problem definition and solution, in lieu of “cookbook” instructions.

• The demonstration of multiple approaches to acquiring scientific knowledge, “Show that the period of a pendulum doesn’t depend on its mass” versus “On what does the period of a pendulum depend?”

• The recommendation of alternative presentations of materials from other textbooks, journals, and popular expositions.

Courses

Check pretty much any university physics syllabus, and it will generally include

• a course for social science and humanities students, alternately called Liberal Arts Physics or more cutely, Physics for Poets.

• several introductory courses for physics majors and others who need it for various requirements, such as chemistry majors and pre-medical/dental aspirants.

• intermediate and advanced courses for physics majors, including specialties such as Pre-engineering and Biophysics.

I taught most of those. Instead of a long description, I will describe my favorite: Liberal Arts Physics, then mention a course for physics students.

Liberal Arts Physics.

It’s one thing to teach majors’ courses, where the students think like us; it’s quite another to teach students who think differently. I employed various techniques. One I call the modified Socratic method. I briefly lectured on the subject at hand. Then I asked a question about the material I just chalked and talked. I didn’t ask for hands. To do so favors the quick and the glib. Instead, I chose a student (preferably one who did not usually shoot their hand up) and asked her or him the question. Then I waited. Either the student would answer in a reasonable time, or coudn’t. If the latter, I followed up with a question whose answer led up to it. If the student still couldn’t answer, I went back further. In my experience, almost all students will reach a point, perhaps several questions back, when they can answer. Then I brought them forward.

There are two ostensible difficulties with this method. First is the time consumed. Second is the possibility of provoking the student’s anxiety. For the first, the time used acts as a review of the subject for the other students, some of whom are unsure of the various answers. For the second, it is the teacher’s obligation to make clear that this is the case, and to assure the student—and all the others—that the procedure will be used randomly on all of them. Finally, the teacher should praise the student as they answer each of the questions in the process.

I also used in-class group exercises in lieu of labs, which are not usually part of the liberal arts physics course. For example, when we were studying circular motion, I divided the class into groups; one set of groups examine how a clothes washer works; the other set, a clothes dryer.

Freshman Physics Projects.

For freshman physics students we instituted group projects. These were semester-long, several hours a week. Students selected projects and chose an instructor as adviser. Here are some examples:

High friction surfaces

Dynamics of motion in vertical circles

Seismological models in the laboratory

Friction on ice

Analysis of pianos

Investigation of wind turbines and solar cells

At the conclusion of the course, each group made a presentation to faculty and any students who wish to attend. These were twelve minutes long: ten for presentation, two for questions and comments. (The amounts were fexible.) Each of the group members presented part of the report. Grading by the advisors was for each individual student and for the group as a whole. Our freshman project course was just one of many examples of group project work. It and similar group methods have been shown to be pedagogically effective. One of the greatest virtues of group project work is that also it levels the playing field, especially for females and less confident students.

Much more can be said about pedagogy, but this shall suffice. You can find more in Helge Kastrup’s and my book, Fear of Physics https://iopscience.iop.org/book/mono/978-0-7503-4866-9

GRAPHIC

RESEARCH

Here I describe some reseacrch projects in which I was involved.

Physics of the eye: the double flash effect

In 1980, my Loyola colleague, Professor of Psychology Richard Bowen discovered that if you shine a bright light over a brief time into the eye and follow it with another, you will see the second one flickering, despite the fact that the light iself doesn’t. From this we concluded that the flickering is generated in the eye. You might have seen oscillating pulses on a cardiac machine in a hospital. They are the flicker response to a pulse from the heart. You might also have see a square pulse analogous in shape to our inital bright light–hopefully not: that’s called flatlining.

Rich asked me if physics could help in understanding the phenomenon. Since the bright square-shaped “inducing” pulse” causes flicker of the “response pulse”, suppose we make the inducer flicker and see what the response does. I proposed that we try a non-square inducing pulse and see what happens to the to the flicker. Are there inducer frequencies that produce brighter and/or more flickers? We found the answer to be yes. This was an example of an effect called resonance, which occures in many phenomena. It’s what you get when you tune in a radio station. At certain frequencies of the inducer, we saw the flicker light intensity become higher and generally produce more flickers. This occurred at more than one inducer frequency – more complicted that the single-renonance effect. Let’s turn to a musical instrument for an analogy. For any but the flute, which produces a single fundamental, there appear ultraharmonics: overtones. Its name gives the information: in addition to the fundamental, higher frequencies appear: those tell you what the instrument is. But there are also lower frequencies appearing: so-called subharmonics or undertones (really–that’s the word). Here is an example. https://www.youtube.com/watch?v=i5CSUHpK4QM&t=147). And both over-and undertones of flickers were what we saw. Altogether, we saw three resonances: the “fundamental”, one overtone, and one undertone. The fundamental resonance appeared at a somewhat different frequency than that predicted by the simple one-resonance physical model; one overtone (the ultraharmonic) appeared at three times that frequency and one undertone (the subharmonic) at 1/3 of it. Another Loyola colleague, mathematician Rich Lucas and I, examined these effects and found that they were described by a formula called the Duffing Equation. (https://en.wikipedia.org/wiki/Duffing_equation if you’re interested.)

We don’t know the biology of the eye : that’s not our expertise. But the mathematics and physics we do. Perhaps someday it will all be explained by the biology.

Physics of the atmosphere

Fog

By Carl Sandburg

The fog comes

on little cat feet.

It sits looking

over harbor and city

on silent haunches

and then moves on.

It actually sits perfectly still on its haunches for a pretty long time before it moves on. How do we know? From lidar. Taking its name from radar: radio detection and ranging, lidar is light detection and ranging. A radio wavelength of an FM station at 100 million Hertz (your radio reads “100”) moving at the speed of light: 300 million meters per second, is 300/100: Three meters. Lidar detects much shorter wavelengths than radar: it requires the use of a laser. Lidar wavelengths are in the visible and infrared: The wavelength of green light is of order five 10 millionths of a meter. It can therefore probe much smaller objects. Radar and lidar work the same way: the simplest design consists of a transmitter and a detector at the same place. A pulse is sent out; it collides with and scatters back from an object to the detector. The total round trip time gives the distance to the object. For radar it could be an airplane. For lidar it can be something much smaller, such as a fog droplet.

I was part of a group that studied fog by lidar, using a pulsed ruby laser as the transmitter and the telescope at Northwestern University’s Lindheimer Astrophysical Research Center (LARC) as the detector. We fired a ruby-colored pulse into a fog and found that the backscattered signal to the teleoscope from the fog was unchanged over a period of hours, which we had not expected. I also undertook to analyze the “distribution function” of fog droplets; i.e., how many of each size there might be. I chose reasonable guesses for the smallest and the largest droplets. Their radii are on the order of micrometers: millionths of a meter. Droplets of that size scatter light, making it hard to drive in fog. Not so for rain, whose droplets are much larger, and less susceptible to light scattering.

GRAPHIC OF LARC.

Physics of the atom

When we look at a rainbow or through a prism, we see light as a continuous spectrum. Why this was so was unclear. So physicists looked for a simpler system, as is their wont. That was a single gas, such as hydrogen. It emitted a line spectrum; that is, only certain wavelenghts showed up when it was heated, as in Figure__. But that too, despite being simpler, was not understood. Enter Niels Bohr, a youg Danish physicist, who provided an answer in 1913– by breaking the rules of classical physics. Electrons circling the nucleus were like planets circling the Sun. If a planet dropped from one orbit to another, energy would be given off. Thus so an electron. But here’s the difference. Planets can take any orbit they like. If the same were true about electron, the the energy given off could be anything–a continuous spectrum! Bohr got around this by postulating–contra classical physics- that the electrons, unlike the planets, were constrained to certain orbits. Thus the light energy given off when an electron dropped from one energy level to a lower one could only have certain values; viz., a line spectrum. The color of the line was determined by the size of the quantum leap in energy, as in Figure__.

GRAPHIC OF HYDROGEN SPECTRUM

GRAPHIC OF BOHR PICTURE OF HYDROGEN

GRAPHIC OF HYDROGEN ENERGY LEVELS

Over the next few years, Bohr’s model was modified; for example, the orbits were shown to be elliptical rather than circular. But then came a model of the atom that overthrew Bohr’s, relegating it to the sobriquet “The old quantum mechanics”. The new quantum mechanics, which we have to this day, is based on the premise that an electron (and any other particle) is also a wave. The breakthrough was provided by Erwin Schrodinger (he of feline fame), with his famous equation linking wave and particle properties. To give two concrete examples, if you look through a screen door at a streetlight, it will appear to have alternating light and dark sections; this is proof of the wave nature of light. On the other hand,when an elevator door reopens as you leap in, that’s because you are interrupting an invisible beam of light, which triggers a crcuit which reopens the door. That beam can only be explained by light being made up of particles.

So far, so good. But now things get a little more complicated. Let’s stick with the Bohr model for convenience.The first element in the periodic table is hydrogen. Hydrogen gas in its simplest form consists of two particles: a heavy, positively charged nucleus and a light, negatively charged electron circling it, as in Figure__.

The next element is helium, which in its simplest forrm is a nucleus twice as heavy and twice as charged as hydrogen’s, with two electrons circling it. (A tangential word about two important properties of helium. First, it is used in balloons, because is is lighter than air and thus floats. Second, if you breathe it, you can sound like Donald Duck.)

Here’s the problem: the structure of the hydrogen gas can be obtained by exact calcuation. The spectrum of helium and all the other elements can only be obtained approximately. This has nothing to do with quantum physics. It turns out, and was proved mathematically centuries ago, that the “two-body problem” is the only one that can be solved exactly. And hydrogen gas is the only case of this for the elements. So physicists have constructed elaborate schemes to get good approximate results for the others; i.e., those that match experiment–in our case, spectra. The one I worked with is called Self Consistent Field Theory. (By “field” we mean what is commonly called “force field”, like, say, the gravitaional field of the Earth, or in the case of atoms, the elecromagnetic field: the field of electricity and magnetism combined.) Imagine an atom with a few electrons, and one in a larger orbit than all the rest. What does it see? It sees the nucleus surrounded by a sort of cloud of the other others. Sodium is an example. It has a nucleus of charge +11, and circling it, eleven electrons, each of charge -1, as in the figure. The eleventh electron is at a considerably larger orbit than the others. (Chemists call this the valence electron.) So the eleventh one sees a “quasi-nucleus” (for want of a better term) of approximate charge +1. But that’s like hydrogen. So it can be solved exactly. Well, not so fast. That cloud isn’t really a cloud, it’s ten electrons zipping along in their orbits around the nucleus. Counting the nucleus and the valence electron, that’s a 12-body problem! So now the self-consistency kicks in. The problem as, we said, can only be solved numerically. (When I started in the late 60’s, the input consisted of stacks of cards. Now I could do it on my Mac.) So we start with the valence-electron-quasi-nucleus cloud model and do a hydrogen-like calculation. But then we have to do it for all the other electrons. The lucky valence electron sees an approximately spherical cloud between it and the nucleus. Each of the others, however, is embedded in a cloud that surrounds it. The computer then calculates the approximate orbit of each of the electrons in turn. It does it repeatedly, until the latest iteration gives the same answer as the one before it. A good way to think of it is that at the end, each electron contributes to the field just what it gets from the field. The criterion for judging if a step is better than the one before it is that the energy of the whole system should be lowered. That’s a general rule, not restricted to quantum physics. Balls roll downhill. And keep in mind: All of these calculations are not actually dealing with electrons as pure particles; they also have wave properties, as we saw.

GRAPHIC of sodium

I got into this business serendipitously. I was working on my Ph.D. in experimental physics (in which I later realized I was a disaster). The money of my then-adviser ran out, and I was left high and dry. So I threw myself at the feet of Art Freeman, then chair of the Northwestern physics department. Art, a theoretical physicist, changed my life: He said “Would you like to work for me?” That’s where I learned self-consistent field theory, with which I spent a great part of my research life. I owe my career to Art, who passed away a few years ago at age 88. We became much more than teacher-student. He was my son’s godfather and a witness to signing of my wedding document.

Here are some of the research problems I worked on. NB. All of my work was done with colleagues!

How bright is a star really? Transition probabililties.

Ordinary stars are mostly hydrogen. So we might expect to see spectral lines due to the transition of an electron from one energy level to a lower one, as in Figure__. Astrophycists have determined what the intrinsic brighness of each of the stars would be. You would think that these values would tell you how far away the star is. Not quite. In addition to the size of the energy jump, there is a probability of its likeliness of making that jump. That has to be factored in. We call that the “transition probability”. That’s what we can calculate using self-consistent field theory, and that was the subject of my Ph.D. dissertation. I did it for carbon, nitrogen, and oxygen. Why? Because astrohysicists have found some in stars, albeit in much lower quantity than hydrogen. So there it stood. But now came another problem: their spectra were mostly at wavelengths in the ultraviolet range. (Think sunburn.) The Earth’s atmosphere blocks most of that out. The only way to use my results would be for measurements made outside the Earth’s atmosphere. So my results were relegated to obscure journals from 1971–until the early 1990’s, when a colleague came to me, excitedly announcing that my work was now being cited. In a word (well, two words): Hubble Telescope! Not exactly the text on my T-shirt: “I BECAME A PHYSICIST FOR THE FAME AND THE MONEY”, but gratifying nonetheless, to have made a contribution to knowledge about the stars.

Sneaking a peek at the nucleus. Muonic atoms.

Look again at the figure of the Bohr atom for hydrogen in Figure__. Other atoms look about the same: a heavy compact nucleus and lightweight electrons revolving around it from considerable distance, again like the solar system. How much can we know about the structure of the nucleus if the only possiblel probes, the electrons, are so far away? Well one way to find out is to see if we can find electron-like objects that can get closer in. We can. They are called muons. They have the same charge as electrons: -1,, but are 207 times its mass. Doing the math (I won’t), that puts them 207 times closer to the nucleus than electrons. With them, we can probe features of the nuckeus that would otherwise be invisible to us. One such is its internal magnetism. Without going into detail, that’s what we did.

Here’s a partial title of one of our papers: “Muonic Hyperfine Anomalies: Large but not Giant”. Never mind what “Hyperfine Anomaly “means; it’s a magnetic feature of the nucleus. Focus on “Large but not Giant”. Why such a title? Because an experimental group had claimed that the effect was huge. Our calculations showed that it was big, but nowhere as big as they claimed. So who was wrong? They were. Why? Because they had their muons in a crystal, they blew the hell out of the crystal when measuring the effect.

Now a word about the politics of science–and don’t let anyone tell you there isn’t any.

First example. There was an international confenence on muonic atoms in Canada. Art Freeman sent me, then in my thirties, to give a paper. I talked with the leader of the experimental group, a lot older and more famous than I, and we agreed to modify our comments to reflect what had been done. I talked first, politely saying the the experimental and theoretical results differed, a far cry from “You screwed up”. He followed–giving a talk extolling their work and never mentioning ours.

Second example. They had published their work in a very prestigious journal. We sent our work showing their error to the same journal. It was rejected. Why? Because journal editors don’t like to get egg on their face. So we published it in another journal, but people who only read the original would never know that the experimental results were proven wrong.

SUSYQM

Most of my research activity from 1995 involved what is called “supersymmetric quantum mechanics”, abbreviated “SUSYQM”. It sounds daunting, and the work was indeed, on the interface of physics and mathematics. But I think I can explain the idea without using either.

First of all, credit where credit is do. The leader of our group was Asim Gangopadyaya, my colleague and friend. The ideas poured out of him–often in the middle of the night. I would sometimes check my email in the morning and receive a message from him sent at four AM. (When does the guy sleep?)

In Figure __ we saw a simple case of energy levels for hydrogen. The difference between states gave the spectrum of hydrogen. We can calculate the energies by solving that old workhorse, the Schrodinger Equation–possible, but tedious. There’s another way, called (you guessed it) supersymmetric quantum mechanics. If you can somehow find the energy of the ground state, you can get all the others. Not only that, from it you can find all the energy levels of related ones, which we call “partners”. Here’s a graph of one and some its partners (Figure__). Notice that the ground state of each is the next state up; i.e., the first excited state of its partner. Here’s a good analogy. Take the four stringed instruments. Tune them so that the differences in pitch are the same for each instrument. Now make the lowest pitch of the cello the same as the second lowest of the bass, the lowest pitch of the viola the same as the second lowest of the cello, and the lowest pitch of the violin the ssame as the second lowest pitch of the viola, as in Figure__. Look familiar? There you have it. If you know the bass, you know all the others.

We found that there are a dozen such systems. One is the hydrogen atom. Another works for diatomic (two-atom) molecules. A third is the quantum version of the harmonic oscillator. (The macroscopic version is a vertical pendulum as in a grandfather clock, or a mass oscillating on a spring, as in Figure___.) The others are for more arcane systems.

Our harmonic oscillator calculations led to another example of scientific politics. Asim found a paper by a prominent physicist in a prominent journal on the “half-harmonic oscillator”: the mass crashing head on into a wall. I looked at the paper and saw that it was wrong. We figured out why, and sent a paper to the same journal. Rejected. So we wrote a second version. Rejected. Finally, we wrote a third version, spelling out all the details. You guessed it: rejected. Asim is a well-spoken, well-mannered fellow. Not so yours truly. I wrote them back, “The minimum requirement of a theory is that it get the right answer.” They wrote back the equivalent of “Never darken our doorstep again.”

Asim and I and another partner, Constantin Rasinariu, wrote two editions of a book: Supersymmetric Quantum Mechanics, An Introduction. I had proposed that instead of our photos on the back cover, we do a centerfold. I even convinced them to photoshop our heads onto muscular bodies in bathing suits. I got Charles Atlas. The other guys chickened out. (BTW, in the book, we put our correct solution for the half-harmonic oscillator.)