Where Have You Gone, Physicist Bob Park? Our Nation Turns Its Lonely Eyes to You. Woo, Woo, Woo.

Voodoo Science, by Bob Park, superimposed on
Intermediate Physics for Medicine and Biology.

Bob Park died five years ago this week. He had been in poor health since suffering a stroke in 2013. Park was a physicist and the director of public information at the Washington office of the American Physical Society. He was a leading voice against pseudoscience, both in his weekly column What’s New (which, when in graduate school, I used to look forward to seeing in my email every Friday) and in his books such as Voodoo Science.

I wonder what Park would say if he were alive today? I suspect he would be horrified. But I doubt he would have said that. He was not a whine-and-fuss sort of guy. His tools were humor, irony, and sarcasm. Here is what I imagine What’s New would have looked like this week.

What’s New, by Bob Park

Friday, April 25, 2025

1. VITAMIN A FOR THE MEASLES

The Texas measles outbreak continues. Over 600 cases have now been reported, which is more than for the entire year in 2024. Health and Human Services Secretary Robert F. Kennedy, Jr. encouraged parents to treat their children suffering from measles with vitamin A, and now children are suffering from liver disease because of vitamin A overdosing. Why don’t parents simply ask their pediatrician what to do? Because pediatricians are part of the conspiracy, of course!

2. IF WE IGNORE IT, IT WILL GO AWAY

The Trump administration is trying to undo all the progress fighting climate change that has accumulated over the last few decades. His thinking is: if you ignore climate change, the problem goes away. Besides, it’s all a HOAX! King Canute tried this. He commanded the tide to stop coming in. How do you think that turned out? Physics has a way of winning in the end, whether or not it’s politically popular.  

3. LAB LEAK

The Trump administration has rewritten the covid.gov website to advocate for the lab leak hypothesis for the source of covid-19. Don't worry that the evidence is flimsy! If covid resulted from a lab leak, then it’s the scientists fault. Blame those arrogant liberal elitists like Fauci. But watch out for the next spillover event! (Can I interest anyone in some bird flu?)

4. LYSENKO

Back in the USSR, when Stalin was in charge, a crackpot named Lysenko took control of Russian science. He didn’t believe in modern genetics, regardless of the evidence. Russian agriculture collapsed and millions died. Here in the United States, we have our own version of the Lysenko affair. Trump is Stalin, RFK Jr is Lysenko, and vaccine hesitancy and climate change are genetics. I fear the outcome will be the same, which is bad for science and worse for humanity.

5. HOORAY FOR HARVARD

The NIH (remember that place that used to be the greatest biomedical research institution anywhere, ever?) has stopped funding grants to several universities, including Harvard. HARVARD! Apparently these universities will not cave in to Trump's ideological agenda. What will happen next? Who knows. Maybe Trump will be stopped by the Supreme Court. Maybe the House and Senate will decide they’ve had enough. And maybe, just maybe, it will be the end of American science.

Asimov’s Corollary

Regular readers of this blog know that I am a huge fan of Isaac Asimov. I decided on a career in science in large part from reading Asimov’s books. As a teenager I particularly enjoyed his collections of essays from The Magazine of Fantasy and Science Fiction. He wrote an essay there each month about science: astronomy, physics, chemistry, biology, geology, medicine, and even mathematics. Every time he collected seventeen essays, he would publish them in a book. It would not be an exaggeration to say that I came to be a coauthor on Intermediate Physics for Medicine and Biology largely because of the influence those essay collections had on me when I was young.

Quasar, Quasar, Burning Bright,
by Isaac Asimov.

This week I want to look at one of those essays that is especially germane today. It appears as the final chapter in the book Quasar, Quasar, Burning Bright. The essay is titled “Asimov’s Corollary,” and was first published in the February, 1977 issue of The Magazine of Fantasy and Science Fiction. Now, almost fifty years later, it seems more relevant than ever.  I urge you to get a copy and read it in its entirety. I will quote parts that I think are especially important. 

To help set the stage, let me note a few things.

• When Asimov mentions “Arthur” he is talking about Arthur C. Clarke, his fellow science fiction writer and good buddy. Along with Robert Heinlein, Asimov and Clarke are considered the “Big Three” in science fiction.
• Asimov loved to talk about himself. You might at first think he’s egotistical, but once you’ve read enough of his works you will realize it’s all a big act…sort of. It is one of the reasons I loved to read his essays.
• By today’s standards Asimov and Clarke sound a bit sexist, assuming all scientists are men. This is, in part, a sign of the times when they lived. I won’t defend their sexism, but I’ll forgive them because of all the good they did and all they taught me.

Asimov writes:

In Arthur’s book Profiles of the Future (Harper & Row, 1962) he advances what he himself calls “Clarke’s Law.” It goes as follows:

When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong…

…Naturally when I read a paragraph like that, knowing Arthur as I do, I begin to wonder if, among all the others, he is thinking of me…

Asimov was an elderly scientist at that time, and was fond of making all sorts of predictions, many of which claimed something was impossible.

Doesn’t Clarke’s Law make me uneasy, then? Don’t I feel as though I am sure to be quoted extensively, and with derision, in some book written a century hence by some successor to Arthur?

No, I don’t. Although I accept Clarke’s Law and think Arthur is right in his suspicion that the forward-looking pioneers of today are the backward-yearning conservatives of tomorrow, I have no worries about myself. I am very selective about the scientific heresies I denounce, for I am guided by what I call Asimov’s Corollary to Clarke’s Law. Here is Asimov’s Corollary:

When, however, the lay public rallies around an idea that is denounced by elderly but distinguished scientists and supports that idea with great fervor and emotion—the distinguished but elderly scientists are then, after all, probably right.

But why should this be?… Human beings have the habit (a bad one, perhaps, but an unavoidable one) of being human; which is to say that they believe in that which comforts them…

Asimov then examines a few cases of people believing things without evidence. He concludes

Then why do people believe? Because they want to. Because the mass desire to believe creates a social pressure that is difficult (and, in most times and places, dangerous) to face down. Because few people have had the chance of being educated into the understanding of what is meant by evidence or into the techniques of arguing rationally.

But mostly because they want to...

When I read this, I think of people claiming (falsely, we know from the evidence) that vaccines cause autism; I think of people claiming (again, falsely) that cell phone radiation causes cancer; and I think of people claiming (still again, falsely) that climate change is a hoax. When I hear these assertions, made passionately and vehemently but with no evidence provided, I think that the elderly scientists (what I would call “the scientific consensus”) is right after all. And while Asimov writes “probably,” I would write “almost certainly.”

I miss you, Isaac Asimov. We need you now more than ever.

 

There is a cult of ignorance. 

https://www.youtube.com/watch?v=oTV1iQyjFFU

 

 Isaac Asimov predicts the future.

https://www.youtube.com/watch?v=cIB1b_8hqB0

Oops!

Finding a mistake in something you wrote is always annoying. When revising the chapter on Atoms and Light for the sixth edition of Intermediate Physics for Medicine and Biology, I found a whopper. It’s on page 402 of the 5th edition, in the section on Blue and Ultraviolet Radiation. Here is the offending sentence:

The minimum erythemal dose at 254 nm is about 6 × 10⁷ J m^-2.

I was trying to add a homework problem to the sixth edition in which I would ask the student to calculate how long it would take to get sunburn for some typical ultraviolet light intensity and I kept getting a ridiculously long time (years) because our value of 6 × 10⁷ is way, way too big. The error goes back to the 3rd edition of IPMB, where you find a reference for that value:

Diffey, B. L. and Farr, P. M. (1991) Quantitative aspects of ultraviolet erythema. Clin Phys Physiol Meas 12:311-325.

The 3rd edition is even more specific, saying the value is in Table 2 in that paper. So, I obtained the article interlibrary loan (kudos to the Oakland University interlibrary loan office, who got the paper for me in about an hour on a Sunday evening). Here is Diffey and Farr’s Table 2. 

The value for minimal erythema at 254 nm is 6 mJ cm^-2, which is equivalent to 60 J m^-2. I think the incorrect value in IPMB arose because of a unit conversion error. There are 1000 millijoules in a joule, not 1000 joules in a millijoule. Such a mistake would cause a factor of one million error, which would result in an erroneous value of 60 × 10⁶ J m^-2, or 6 × 10⁷.

You may have some questions.

• Who did it? Although Russ Hobbie made the initial mistake (he was sole author on the 3rd edition), I read this number when teaching from our book, and when preparing the 4th edition and then again when preparing the 5th edition and never batted an eye. Apparently 60 MJ of UV light causing a person to have only a mild reddening of the skin didn’t bother me at all. I always tell my students to “THINK BEFORE YOU CALCULATE!” but I didn’t. 
• If it was in the book, how could it be wrong? Don’t believe everything you read. Just because something is written in a textbook doesn’t make it true. Authors try their best to get everything right, but sometimes they make mistakes. Read critically and thoughtfully. (I’m giving this advice to myself here, more than to you, dear reader). 
• What’s erythema? Erythema is redness of the skin. In our context, it is a the initial stages of a sunburn.
  
• What is the “minimum erythemal dose”? Here’s what Diffey and Farr say: “The erythemal response of the skin to ultraviolet radiation is usually inferred from the minimal erythemal dose (MED). This value is determined by exposing adjacent areas of skin to increasing doses of radiation (usually employing a geometrical series of dose increments) and recording the lowest dose of radiation to achieve erythema at a specified time, usually 24 hours, after irradiation. The visual detection of erythema is subjective and is affected by unrelated factors such as viewing geometry, intensity and spectral composition of ambient illumination, colour of unexposed surrounding skin… and the experience and visual acuity of the observer.” So, it’s the dose where you say “Gosh, my skin is slightly red, I must have gotten a little too much sun today,” and then go about your business with hardly another thought. 
• Why did Russ and I give the value for 254 nm? We mean that the ultraviolet radiation has a wavelength of 254 nm, which puts it in the UVC range (100–280 nm). UVC light can certainly cause damage and sunburn, but almost no UVC gets through the earth’s atmosphere to reach our bodies. Most sun tans and sunburns are caused by UVB, which is in a narrow band of wavelengths from 280–315 nm. Wavelengths much shorter are removed by the atmosphere, and the photons for wavelengths much longer do not have enough energy to do significant damage. The wavelength in the above Table 2 that’s most appropriate for this discussion is 300 nm. So, looking at Table 2, perhaps a better value for the minimum erythemal dose would be 24 mJ cm^-2 or 240 J m^-2. In the sixth edition of IPMB, we will use 200 J m^-2 as our typical value (unless we change our minds…when it comes to revising a textbook, it ain’t over till it’s over). Warning: this value depends on factors such as your complexion, so don’t take it too seriously. It’s a ballpark estimate. Everyone is a bit different. 
• Well, just how much UVB are we exposed to? We can estimate that from Figure 14.28 in IPMB. In the range from about 295 to 315 nm, the average value of the spectral dose is about 10 mW m^-2 nm^-1. If we multiply by a 20 nm range, we get 200 mW m^-2, or about 0.2 W m^-2. That value is for the sun straight overhead (noon near the equator with a clear sky). It’s consistent with other values I have found. 
• How is all this related to the “UV index” that the weather forecaster talks about? The UV index is a linear scale (not logarithmic like the decibel scale for hearing), and to calculate it you multiply the intensity in W m^-2 by 40. So, the value of 0.2 W m^-2 that I quoted earlier corresponds to a UV index of 8. Here in southeast Michigan we can reach a UV index of 8 at noon on a cloudless summer day. In January we are at a UV index of about 2. Latitude and time of the year make a big difference, as does time of the day (in the morning and evening, sunlight comes in at an angle and must therefore pass through more atmosphere than at noon). 
• So, how long can I stay in the sun before getting sunburn? On the beach in Hawaii during the summer at noon you can reach a UV index of about 12, so the intensity is 0.3 W m^-2, which means 0.3 joules per second per square meter. If your minimum erythemal dose is 200 J m^-2, then (0.3 J m^-2 s^-1) t = 200 J m^-2, so t = 667 seconds or 11 minutes. That’s the minimum dose. I bet you could go a half hour before suffering from something you would call a serious sunburn. But if you stay out all afternoon surfing at Waikiki, it could be a problem. 
• Can’t I protect myself with sunscreen? Yes, the sun protection factor (SPF) is the factor by which the intensity actually reaching your skin is reduced by the sunscreen. If you put on SPF 30 sunscreen there in Hawaii, your time for a minimum erythemal dose goes up from 11 minutes to five and a half hours. Maybe you can get away with all day, since the UV index will be lower in the morning and evening, extending your time. Just make sure it doesn’t get washed off in the water. You may have to reapply it often.
  

Let me apologize one more time for the bogus value of minimal erythemal dose in the 5th edition of IPMB. I feel bad about it. I sure hope no one used it to justify spending lots of time in a tanning booth. I call those things “cancer booths.” Stay away from them. 

I'll be proofreading the 6th edition of IPMB extra carefully. My motto will be: THINK BEFORE YOU WRITE!

Tomie De Paola

Sound,
written by Lisa Miller,
illustrated by Tomie De Paola

Children’s book author Tomie De Paola died five years ago last Sunday. I fondly recall reading De Paola’s books to my daughters Stephanie and Kathy when they were growing up. But how could Tomie De Paola possibly intersect with Intermediate Physics for Medicine and Biology? Well, you might be surprised! The first book that De Paola illustrated was Sound, written by Lisa Miller. It was part of the “Science is What and Why” series published by Coward–McCann, Inc.

Each book in the Science is What and Why series introduces fundamentals of physical science using a simple, attractive approach specifically designed for young boys and girls. Straightforward, lively language and distinguished illustrations which are a practical extension of the text present scientific facts as fascinating and exciting as the realm of the imagination.

As Gene Surdutovich and I work on the 6th edition of IPMB, I think we should strive for “straightforward, lively language and distinguished illustrations.”

De Paola’s drawings in Sound have much more charm than the figures in Chapter 13 of IPMB, which is about Sound and Ultrasound. Yet, his book covers topics that Russ Hobbie and I also discuss, such as the wavelength, frequency, and amplitude of a sound wave, and echos. I can’t help but think of De Paola as a kindred soul.

Sound appeared early in De Paola’s career; it was published in 1965. He continued illustrating books about science (I need to read The Popcorn Book), but he is best known for his children’s stories. Many of his books were autobiographical. I loved reading The Art Lesson and Tom with my girls. Although I’m not particularly religious, I thought his best work was The Clown of God.

Now, with my first grandchild due this summer, I’m looking forward to rereading many of De Paola’s books. I can’t wait.

 

Meet Tomie dePaola

https://www.youtube.com/watch?v=3_XINGTzl5U

Tomie De Paola on the television show Barney, another favorite of my daughters. 

https://www.youtube.com/watch?v=s01_ikK_SrQ

 


Tomie De Paola: Why Reading is Important 

https://www.youtube.com/watch?v=7epT0qUaaX4&t=16s

 

 

The Art Lesson 

https://www.youtube.com/watch?v=9TUQ4F27HMo 

 

Tom by Tomie de Paola 

https://www.youtube.com/watch?v=doFJAxHX5yw

 

The Clown Of God by Tomie De Paola 

https://www.youtube.com/watch?v=Gnwlzj1xdmM

The Rest of the Story 5

Bill grew up in Schenectady, New York, the youngest of four children. While a child he became interested in science because of his fascination with telescopes. He was smart; he graduated from high school at the age of 15, and then attended Schenectady’s Union College, finishing in just three years. By the age of 22 he had graduated with an M.D. from the Albany Medical College. Many of his friends didn’t realize how bright Bill was, because he was so modest and friendly, and had such a wonderful sense of humor.

Bill became an active duty medical officer posted at the U.S. Naval Hospital in Newport, Rhode Island. After a fellowship in neurology at the University of Minnesota, he joined the new medical school at UCLA. He was much loved as a medical doctor and a mentor, but he disliked many of the invasive procedures that he had to perform as a clinical neurologist.

In 1959, Bill had an idea how to noninvasively image the brain using multiple x-ray beams in different directions. After two years of effort he had a working prototype, applied for a patent, and published an article about this work. But when he approached a leading x-ray manufacturer, the company president couldn’t image there would ever be a market for such a device. Frustrated, Bill turned his attention to other things.

Page 2

Bill’s idea for how to image the brain did not go away. Other scientists took up the challenge. Physicist Allan Cormack and engineer Ronald Bracewell each developed detailed mathematical techniques for obtaining an image from beams in different directions. Engineer Godfrey Hounsfield built the first brain scanner in 1971. And the rest is history. Bill’s invention is now known as Computed Tomography (originally called a CAT scan and now referred to as CT for short). It has revolutionized medicine. In 1979, Cormack and Hounsfield won the Nobel Prize in Physiology or Medicine for their contributions to CT. William (“Bill”) Oldendorf did not share the prize, but he shared in the discovery.

William Oldendorf.

And now you know the rest of the story.

Good day! 

_________________________________________________

This blog post was written in the style of Paul Harvey’s The Rest of the Story radio program. You can find four other of my The Rest of the Story posts here, here, here, and here. 

You can learn more about Computed Tomography in Chapter 16 of Intermediate Physics for Medicine and Biology.

William Oldendorf was born March 27, 1925, one hundred years ago yesterday. Happy birthday Bill!

Dipole-Dipole Interaction

One strength of Intermediate Physics for Medicine and Biology is its many homework problems. The problems stress (but perhaps not enough) the ability to make general arguments about how some quantity will depend on a variable. Often getting a calculation exactly right is not as important as just knowing how something varies with something else. For instance, you could spend all day learning how to compute the volume and surface area of complicated objects, but it’s still useful simply to know that volume goes as size cubed and surface area as size squared. Below is a new homework problem that emphasizes the ability to determine a functional form.

Section 6.7

Problem 20½. Consider an electric dipole p a distance r from a small dielectric object. Calculate how the energy of interaction between the dipole and the induced dipole in the dielectric varies with r. Will the dipole be attracted to or repelled from the dielectric? Use the following facts:

1. The energy U of a dipole in an electric field E is U = – p · E,

2. The net dipole induced in a dielectric, p', is proportional to the electric field the dielectric experiences,

3. The electric potential produced by a dipole is given by Eq. 7.30.

Let’s take a closer look at these three facts.

1. When discussing magnetic resonance imaging in Chapter 18 of IPMB, we give the energy U of a magnetic dipole μ in a magnetic field B as U = – μ · B (Eq. 18.3). An analogous relationship holds for an electric dipole in an electric field. The energy is lowest when the dipole and the electric field are in the same direction, and varies as the cosine of the angle between them. I suggest treating the original dipole p as producing the electric field E, and the induced dipole p' as interacting it. 

2. Section 6.7 of IPMB discusses how an electric field polarizes a dielectric. The net dipole p' induced in the dielectric object will depend on the electric field and the objects shape and volume. I don’t want you to have to worry about the details, so the problem simply says that the net dipole is proportional to the electric field. You might get worried and say “wait, the electric field in the dielectric is not uniform!” That’s why I said the dielectric object is small. Assume that it’s small enough compared to the distance to the dipole that the electric field is approximately uniform over the volume of the dielectric. 

3. What is the electric field produced by a dipole? Russ Hobbie and I don’t actually calculate that, but we do give an equation for a dipole’s electrical potential, which falls off as one over the square of the distance. (It may look like the cube of the distance in Eq. 7.13, but there’s a factor of distance in the numerator that cancels one factor of distance cubed in the denominator, so it’s an inverse square falloff.) The electric field is the negative gradient of the potential. Calculating the electric field can be complicated in the general case. I suggest you assume the dipole p points toward the dielectric. Fortunately, the functional dependence of the energy on the distance r does not depend on the dipole direction.

I won’t work out all theentire solution here. When all is said and done, the energy falls off as 1/r⁶, and the dipole is attracted to the dielectric. It doesn’t matter if the dipole originally pointed toward the dielectric or away from it, the force is always attractive.

This result is significant for a couple reasons. First, van der Waals interactions are important in biology. Two dielectrics attract each other with an energy that falls as 1/r⁶. Why is there any interaction at all between two dielectrics? Because random thermal motion can create a fluctuating dipole in one dielectric, which then induces a dipole in a nearby dielectric, causing them to be attracted. These van der Waals forces play a role in how biomolecules interact, such as during protein folding.

From Photon to Neuron:
Light, Imaging, Vision.

Second, there is a technique to determine the separation between two molecules called fluorescence resonance energy transfer (FRET). The fluorescence of two molecules, the donor and the acceptor, is affected by their dipole-dipole interaction. Because this energy falls off as the sixth power of the distance between them, FRET is very sensitive to distance. You can use this technique as a spectroscopic ruler. It’s not exactly the same as in the problem above, because both the donor and acceptor have permanent dipole moments, instead of one being a dielectric in which a dipole moment is induced. But nevertheless, the 1/r⁶ argument still holds, as long as the dipoles aren’t too close together. You can learn more about FRET in Philip Nelson’s book From Photon to Neuron: Light, Imaging, Vision.

The First Measurement of the Magnetocardiogram

Biomagnetism: The First Sixty Years.

A couple years ago, I published a review article titled “Biomagnetism: The First Sixty Years.” I wrote about that article before in this blog, but I thought it was time for an update. The paper is popular: according to Google Scholar it has been cited 28 times in two years, which is more citations than any other of my publications in the last decade. I remember working on this paper because it was my Covid project. That year I got Covid for the first—and, so far, only—time. I quarantined myself in our upstairs bedroom, wore a mask, and somehow avoided infecting my wife. I remember having little to do except work on my biomagnetism review.

As a treat, I thought I would reproduce one of the initial sections of the article (references removed) about the first measurement of the magnetocardiogram. Russ Hobbie and I talk about the MCG in Chapter 8 of Intermediate Physics for Medicine and Biology. This excerpt goes into more detail about how MCG measurements began. Enjoy!

2.1. The First Measurement of the Magnetocardiogram

In 1963, Gerhard Baule and Richard McFee first measured the magnetic field generated by the human body. Working in a field in Syracuse, New York, they recorded the magnetic field of the heart: the magnetocardiogram (MCG). To sense the signal, they wound two million turns of wire around a dumbbell-shaped ferrite core that responded to the changing magnetic field by electromagnetic induction. The induced voltage in the pickup coil was detected with a low-noise amplifier.

The ferrite core was about one-third of a meter long, so the magnetic field was not measured at a single point above the chest, but instead was averaged over the entire coil. One question repeatedly examined in this review is spatial resolution. Small detectors are often noisy and large detectors integrate over the area, creating a trade-off between spatial resolution and the signal-to-noise ratio.

The heart’s magnetic field is tiny, on the order of 50–100 pT (Figure 1). A picotesla (pT) is less than a millionth of a millionth as strong as the magnetic field in a magnetic resonance imaging machine. The magnetic field of the earth is about 30,000,000 pT (Figure 1), and the only reason it does not obscure the heart’s field is that the earth’s field is static. That is not strictly true. The earth’s field varies slightly over time, which causes geomagnetic noise that tends to mask the magnetocardiogram (Figure 1). Moreover, even a perfectly static geomagnetic field would influence the MCG if the pickup coil slightly vibrated. A key challenge in biomagnetic recordings, and a major theme in this review, is the battle to lower the noise enough so the signal is detectable

Figure 1. Noise sources in biomagnetism.

Most laboratories contain stray magnetic fields from sources such as electronic equipment, elevators, or passing cars (Figure 1). Baule and McFee avoided much of this noise by performing their experiments at a remote location. Even so, they had to filter out the ubiquitous 60 Hz magnetic field arising from electrical power distribution. A magnetic field changing at 60 Hz is a particular nuisance for biomagnetism because the magnetic field typically exists in a frequency band extending from 1 Hz (1 s between heartbeats) to 1000 Hz (1 ms rise time of a nerve or muscle action potential).

One limitation of a metal pickup coil is the thermal currents in the winding due to the random motion of electrons, creating extraneous magnetic fields caused by the measuring device itself. The ultimate source of noise is thermal currents in the body, but fortunately, their magnetic field is minuscule (Figure 1).

Baule and McFee suppressed background noise by subtracting the output of two pickup coils. A distant source of noise gave the same signal in both coils and did not contribute to their difference. One coil was placed over the heart, and the magnetocardiogram was larger there and did not cancel out. The two coils formed a rudimentary type of gradiometer (Figure 2).

The magnetocardiogram resembled the electrocardiogram (ECG) sensed by electrodes attached to the skin. Baule and McFee speculated that the MCG might contain different information than the ECG, another idea that reappears throughout this review. In a followup article, they theoretically calculated the magnetic field produced by the heart. The interplay between theory and experiments is yet one more subject that frequently arises in this article.

Figure 2. Types of gradiometers.

Einstein and Smoluchowski

In Chapter 4 of Intermediate Physics for Medicine and Biology, Russ Hobbie and I discuss the Einstein relationship between diffusion and viscosity. We wrote

The diffusion constant…is closely related to the viscosity, as was first pointed out by Albert Einstein. This is not surprising, since diffusion is caused by the random motion of particles under the bombardment of neighboring atoms, and viscous drag is also caused by the bombardment of neighboring atoms.

All this random bombardment is also related to Brownian motion: the random movement of small particles when they collide with many water molecules.

What is typically referred to as the Einstein relationship is given by our Eq. 4.22,

      D = kT/β,       (4.22)

where D is the diffusion constant, k is Boltzman’s constant, T is the absolute temperature, and β is a factor relating the viscous force to the drift velocity, sometimes called the frictional drag coefficient. Essentially, β is like the reciprocal of the mobility. This equation doesn’t contain the viscosity, but if you use Stokes’ law for β you get

      D = kT/6πηa,     (4.23)

where a is the radius of the particle being considered and η is the coefficient of viscosity.

Russ and I refer to Eq. 4.22 as the Einstein relationship. However, if you look in Howard Berg’s marvelous book Random Walks in Biology, you find this expression is called the Einstein-Smoluchowski relationship. So the natural question is: just who is this Smoluchowski?

To answer that question, I consulted my favorite biography of Einstein, Abraham Pais’s Subtle is the Lord. Pais writes

If Marian Ritter von Smolan-Smoluchowski had been only an outstanding theoretical physicist and not a fine experimentalist as well, he would probably have been the first to publish a quantitative theory of Brownian motion.

Smoluchowski, born to a Polish family, spent his early years in Vienna, where he also received a university education. After finishing his studies in 1894, he worked in several laboratories abroad, and then returned to Vienna, where he became Privatdozent. In 1900 he became professor of theoretical physics in Lemberg (now Lvov), where he stayed until 1913. In that period he did his major work. In 1913 he took over the directorship of the Institute for Experimental Physics at the Jagiellonian University in Cracow. There he died in 1917, victim of a dysentery epidemic.

It is quite remarkable how often Smoluchowski and Einstein simultaneously and independently pursued similar if not identical problems. In 1904 Einstein worked on energy fluctuations, Smoluchowski on particle number fluctuations of an ideal gas. Einstein completed his first paper on Brownian motion in May 1905; Smoluchowski his in July 1906.

So even the great Einstein had competition for many of his ideas. In fact, Smoluchowski nearly derived the relationship first. Pais continues

Smoluchowski began his 1906 paper by referring to Einstein’s two articles of 1905: “The findings [of those papers] agree completely with some results which I had… obtained several years ago and which I consider since then as an important argument for the kinetic nature of this phenomenon.” Then why had he not published earlier? “Although it has not been possible for me till now to undertake an experimental test of the consequences of this point of view, something I originally intended to do, I have decided to publish these considerations…”

Apparently he wanted to get experimental support for his ideas, and by waiting he got scooped.

Both Einstein and Smoluchowski went on to independently study critical opalescence: how the scattering of light passing through a gas increases in the neighborhood of a critical point. Pais concludes

Smoluchowski’s last contribution to this problem [of critical opalescence] was experimental: he wanted to reproduce the blue of the sky in a terrestrial experiment. Preliminary results looked promising, and he announced that more detailed experiments were in progress. He did not live to complete them.

After Smoluchowski’s death, Sommerfeld and Einstein wrote obituaries in praise of a good man and a great scientist. Einstein called him an ingenious man of research and a noble and subtle human being.

My Final Question

Suppose I died tomorrow. When my soul came before that great scientist in the sky, she might say “because of your contributions to Intermediate Physics for Medicine and Biology, I’ll answer one question for you. What is your question?” I can think of many things I would like to know, but the question I’d ask is: “is the linear no-threshold model appropriate at low doses?”

What’s the linear no-threshold model, and why’s it so important? Russ Hobbie and I explain it in Chapter 16 of IPMB.

In dealing with radiation to the population at large, or to populations of radiation workers, the policy of the various regulatory agencies has been to adopt the linear no-threshold (LNT) model to extrapolate from what is known about the excess risk of cancer at moderately high doses and high dose rates to low doses, including those below natural background.

If the excess probability of acquiring a particular disease is αH in a population N [where H is the equivalent dose per person in sieverts and α is a proportionality constant], the average number of extra persons with the disease is

                 m = α N H.         (16.42)

The product NH, expressed in person Sv, is called the collective dose. It is widely used in radiation protection, but it is meaningful only if the LNT assumption is correct. Small doses to very large populations can give fairly large values of m, assuming that the value of α determined at large doses is valid at small doses.”

Let me give you an example of why this question is so consequential. Should our society spend its time and money trying to reduce radon exposure in people’s homes? Radon is a radioactive gas that is produced in the decay chain of uranium. This noble gas can seep into basements, where it may be breathed into the lungs. The decay of radon and its progeny can cause lung cancer. However, the typical yearly dose from radon is very low, about 2 mSv. For an individual the resulting cancer risk is tiny, but if the linear no-threshold model is correct then when multiplied by the population of the United States (over 300,000,000) there can be tens of thousands of cancer deaths each year caused by radon. On the other hand, if a threshold exists below which there is no risk of cancer, then radon probably causes few if any cancer deaths. So, from a public health perspective, the answer to my question about the validity of the linear no-threshold model is crucial.

Other examples are

• The severity of low-dose, widespread exposure to radiation caused by a terrorist attack, such as a small amount of radioactivity dissolved in the water supply of a major city, 
• The hazard caused by low-dose x-ray backscatter scanners used at airports for security, 
• The danger from the release into the Pacific Ocean of minuscule amounts of radioactivity in water leftover from the Fukushima nuclear accident, or 
• The risks associated with storing radioactive waste from nuclear power plants in underground storage facilities.

All these situations have one thing in common: small individual doses to a large number of people. Public health officials need to know whether or not the collective dose is significant, and is it something we should spend our scarce resources trying to minimize.

On that fateful day I fear that even if she answers my last question, I won’t be able share it with you, dear readers (I don’t think they allow blogging down there). We’ll just have to examine the evidence available today.

Quackwatch

One goal of Intermediate Physics for Medicine and Biology is to provide readers with an understanding of the physics underlying biomedicine, so they can recognize and refute pseudoscientific ideas. For instance, in Chapter 9 of IPMB Russ Hobbie and I discuss the physics behind the discredited claim that weak, low frequency electromagnetic fields (ranging in frequency from 60 Hz powerline fields to cell phone radiowaves) are dangerous.

These days, with so much pseudoscience parading as fact, and with the United State’s Secretary of the Department of Health and Human Services being a leading proponent of anti-science nonsense, what we need is something to point out and refute all this quackery. What we need is Quackwatch.org. According Quackwatch’s mission statement, 

Quackwatch is a network of Web sites and mailing lists developed by Stephen Barrett, M.D. and maintained by the Center for Inquiry (CFI). Their primary focus is on quackery-related information that is difficult or impossible to get elsewhere. Dr. Barrett’s activities include:

• Investigating questionable claims

• Answering inquiries about products and services

• Advising quackery victims

• Distributing reliable publications

• Debunking pseudoscientific claims

• Reporting illegal marketing

• Improving the quality of health information on the Internet

• Attacking misleading advertising on the Internet 

For those of you who prefer social media, you can follow Quackwatch on Facebook and Twitter.

Quackwatch was established by Stephen Barrett, a retired medical doctor. These days he’s in his 90’s and deserves a rest after a lifetime of defending science. Unfortunately, there’s no rest for the weary; we need him now more than ever.

Five years ago, Quackwatch become part of the Center for Inquiry, another group that opposes pseudoscience malarkey and that publishes the Skeptical Inquirer magazine. I mention both Quackwatch and the Center for Inquiry in my book Are Electromagnetic Fields Making Me Ill?

Thank you Stephen Barrett for giving the world your wonderful website Quackwatch.org. I wish we all deserved it. 

 

Quackery: A History of Fake Medicine and Cure-alls. CBS Sunday Morning.

https://www.youtube.com/watch?v=G_3K0lFuvHQ

My 50+ Years of Antiquackery Activity with Stephen Barrett and William M. London. Center for Inquiry.

https://www.youtube.com/watch?v=EjYIjBae0wM