Here Comes The Sun

Here Comes The Sun,
by Bill McKibben

I recently finished Bill McKibben’s excellent book Here Comes The Sun (McKibben and I are about the same age, so we both like the Beetles reference. The page just before the Table of Contents has a single line of text: “And I say, it’s all right.”). The subtitle is “A Last Chance for the Climate and a Fresh Change for Civilization.” It’s one of the most optimistic climate change books I have read.  After summarizing his past angst-ridden pronouncements on global warming, McKibben writes in the introduction to Here Comes The Sun “And yet, right now, really for the first time, I can see a path forward. A path lit by the sun.”

The heart of his argument is that now, finally, wind power and especially solar power have gotten so cheap that the change to green energy will be not only virtuous but also economically advantageous. In his book, McKibben addresses four questions that are often asked by green energy skeptics. I’ll look at them one by one.

Can We Afford it?

McKibben writes

Sometime in those 10 years [between 2014 and 2024] we passed some invisible line where producing energy pointing a sheet of glass at the sun became the cheapest way to produce power, and catching the breeze the second cheapest... As the energy investor Rob Carlson put it recently, continuing to burn fossil fuel is a “self-imposed financial penalty” that will “ultimately degrade America's long-term global competitiveness.”

The gist of his argument is that with fossil fuels, you have to pay for the fuel each and every time you use it to get energy. Year after year you keep paying for coal or oil or gas. With solar and wind energy, you pay once to set up the technology and then the fuel (the sun and wind) is free. FREE! FOREVER! (Or at least for the lifetime of the solar panel or wind turbine.)  I’m an cheapskate and I love free stuff. And you save the planet as a bonus. As McKibben points out, one problem is that energy becomes so cheap that energy companies can’t make money supplying it. What a wonderful problem to have.

But Can the Poor World Afford It? 

It turns out that the developing world is leapfrogging straight to solar power, skipping the centralized fossil fuel phase. Why?

The switch is being driven by the desire for reliable and affordable power. 

McKibben compares it to how cell phones allowed poor countries to skip the expensive land line infrastructure and go straight to mobile communication. Countries in Africa and the Middle East are right now putting up solar panels, with the process starting at the grass roots rather than from the top down. Who do they buy their solar panels from? China. 

But Is There Enough Stuff?

McKibben thinks the concerns about having enough raw materials such as lithium to build the solar panels, wind turbines, and batteries is a legitimate problem, but probably not an insurmountable one. 

Yes, you have to mine lithium to build a battery. But once you've mined it, that lithium sits patiently in the battery doing its job for a decade or two (after which, as we will see, it can be recycled). If you mine coal, on the other hand, you immediately set it on fire—that's the point of coal. And then it’s gone. And then you have to go mine some more.

He says we should compare the risks and cost of mining and recycling green energy materials to the much greater risks of mining and dealing with the left over from fossil fuels, such as coal ash.

Do We Have Enough Land?

The land needed for solar and wind is surprisingly small, especially compared to that taken up by fossil fuels. McKibben quotes an estimate that oil and gas wells, coal mines, pipelines, power plants, and the like take up about 1.3% of America’s land. Green energy will require far less. McKibben compares a solar array to a corn field.

Converting some of these [corn] fields to solar panels makes enormous ecological sense. That's because one way to look at a field of corn (or any other crop) is that it’s already an array of solar panels.  A plant is a way to convert sunshine into energy through photosynthesis... Somewhere between 1 and 3 percent of the sunlight falling on a leaf actually becomes energy. The photovoltaic panel works considerably better [20, and possibly some day up to 40, percent]...

You could supply all the energy the US currently uses by covering 30 million acres with solar panels. How much land do we currently devote to growing corn ethanol [not the corn we eat, but the corn we use to help fuel our cars]? About 30 million acres. 

The biggest threat is not a lack of land, but the not-in-my-backyard attitude so common in the USA. 

Because this is a blog about my textbook Intermediate Physics for Medicine and Biology, let’s do one of those estimation problems that Russ Hobbie and I encourage. The solar constant is 1390 W/m². That’s how much light energy from the sun per square meter that reaches the earth (or, at least, the top of our atmosphere). The cross-sectional area of our planet that intercepts this light is πR², where R is the earth’s radius (6.4 × 10⁶ m²). That gives 1.8 × 10¹⁷ W, or 180,000 TW (the “T” is for tera, or 10¹²). Humanity’s worldwide average power consumption is about 18 TW. So, we only need 0.01% of the solar energy available. Granted, some of that sunlight is reflected or absorbed by the atmosphere, some is incident on the ocean, and no solar panel is 100% efficient. Still, the land area needed for solar and wind farms, while not small, is reasonable. 

The Final Word

When I can, I like to give authors the final word in my blog posts. So, here is how McKibben ends Here Comes The Sun

I end this book saddened, too, of course—saddened by all that happened in the last 40 years, and by all that we haven’t done. But I also end it exhilarated. Convinced that we’ve been given one last chance. Not to stop global warming (too late for that) but perhaps to stop it short of the place where it makes civilization impossible. And a chance to restart that civilization on saner ground, once we’ve extinguished the fires that now both power and threaten it.

I’ve changed my mind. I’m gonna give George Harrison the final word.

Sun, sun, sun, here it comes.  

 

“Here Comes The Sun,” by the Beatles

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

   

Bill McKibben on Here Comes The Sun

https://www.youtube.com/watch?v=AADsgqz4nU4 

Mark Hallett (1943–2025)

Mark Hallett,
from the NIH Record.

Readers of this blog may remember neurologist Mark Hallett, who I featured three years ago in a post about his retirement from the National Institutes of Health. Today, I must share some sad news: Hallett died of brain cancer on November 2, 2025.

Mark Hallett was a pioneer in using transcranial magnetic stimulation to study the brain. In Intermediate Physics for Medicine and Biology, Russ Hobbie and I describe magnetic stimulation.

8.7 Magnetic Stimulation

Since a changing magnetic field generates an induced electric field, it is possible to stimulate nerve or muscle cells without using electrodes. The advantage is that for a given induced current deep within the brain, the currents in the scalp that are induced by the magnetic field are far less than the currents that would be required for electrical stimulation. Therefore transcranial magnetic stimulation (TMS) is relatively painless. It is also safe (Rossi et al. 2009). 

Magnetic stimulation can be used to diagnose central nervous system diseases that slow the conduction velocity in motor nerves without changing the conduction velocity in sensory nerves (Hallett and Cohen 1989). It could be used to monitor motor nerves during spinal cord surgery, and to map motor brain function. Because TMS is noninvasive and nearly painless, it can be used to study learning and plasticity (changes in brain organization over time; Wassermann et al. 2008). Recently, researchers have suggested that repetitive TMS might be useful for treating disorders such as depression (O’Reardon et al. 2007) and Alzheimer’s disease (Freitas et al. 2011).

Mark Hallett,
from the NIH Record.

Here is what I wrote about Hallett in a review of my experience with magnetic stimulation.

One of my first tasks at NIH was to meet with two medical doctors in the National Institute of Neurological Disorders and Stroke—Mark Hallett and Leo Cohen—who had recently begun using magnetic stimulation. Hallett obtained his medical degree from Harvard and was chief of the Human Motor Control Section, housed in NIH’s famous clinical center. He is a leading figure in neurophysiology, specifically in magnetic stimulation research, and is often asked to publish tutorials about magnetic stimulation in leading journals. Hallett once told me that he began college as a physics major but switched to a pre-med program after a year or two. Cohen earned his MD from the University of Buenos Aires in Argentina. In the late 1980s, he worked in Hallett’s section, but eventually became the head of his own Human Cortical Physiology Section at NIH. Together Hallett and Cohen were doing groundbreaking research in magnetic stimulation but lacked the technical expertise in physics required to do things like calculate the electric fields produced by different coils…

Hallett and Cohen obtained a magnetic stimulator at NIH in the late 1980s. They described magnetic stimulation and its potential uses in the Journal of the American Medical Association [Magnetism: A new method forstimulation of nerve and brain. JAMA, 262, 538–541, 1989.], where they highlighted how assessment of central conduction times using magnetic stimulation could be useful for diagnosing diseases, such as multiple sclerosis, and also how the method could be suitable for monitoring the integrity of the spinal cord during surgery. They emphasized that although methods existed to measure the conduction time in the brain for sensory fibers, stimulation of the brain was needed to measure conduction times in central motor fibers.

Not entirely realizing the explosion of research I was lucky enough to be wading into, I started collaborating with Hallett and Cohen to calculate the electric fields produced during magnetic stimulation... Our first work together was a technical paper comparing the electric and magnetic fields produced by a variety of coils with different shapes… Hallett and Cohen were most interested in the electric field induced during transcranial magnetic stimulation, so my next task was to use a three-sphere model to calculate the electric field in the brain...

I was anxious to test the prediction of where excitation occurs along a peripheral nerve during magnetic stimulation [that Peter Basser and I had made]. The ideal experiment would be to dissect a nerve, place it in a dish filled with saline, and then stimulate it. However, Hallett and Cohen were focused mainly on clinical applications, so we tested the prediction in humans. The experiment was performed by Marcela Panizza, an Italian medical doctor, and her husband Jan Nilsson, a biomedical engineer originally from Denmark but working with Panizza in Italy. Panizza and Nilsson would often visit NIH to collaborate with Hallett and Cohen. In the experiment, the median nerve was stimulated at the forearm and the motor response was recorded using electrodesattached to the thumb... [They showed that] that magnetic stimulation did not occur where the electric field was largest, but instead where its spatial derivative was largest.

The research at NIH was assisted by an outstanding group of young scientists who worked with Hallett and Cohen. For example, the Brazilian neurologist Joaquim Brasil-Neto examined how the orientation of the electricfield influenced the stimulation threshold... Peter Fuhr analyzed how the latency of motor-evoked potentials depended on the position of thestimulating coil relative to the head... Eric Wassermann—a medical doctor who trained with Hallett and was editor of the Oxford Handbook of Transcranial Stimulation—wrote a review of safety issues... One of the most serious safety hazards was discovered by Alvaro Pascual-Leone, a Spanish MD/PhD who trained at NIH in the 1990s. Pascual-Leone and his colleagues wanted to record the electroencephalogram (EEG) during and immediately following rapid rate transcranial magnetic stimulation, so they stimulated with silver EEG recording electrodes placed over the scalp. One patient suffered a burn under an electrode.

Hallett was one of my most important collaborators throughout my career. In fact, if you look at Google Scholar to examine my most influential articles (those with over 100 citations each), Hallett was my most common coauthor (13), followed closely by Leo Cohen (11), then my PhD advisor John Wikswo (8), and finally my good friend from NIH Peter Basser (6), who also collaborated with Hallett. One could argue that no other scientist except Wikswo had such an impact on my career.

Hallett was a giant in his field of neurology. He will be missed by many, including me.

Oral History 2013: Stanley Fahn Interviews Mark Hallett

https://www.youtube.com/watch?v=eR-D9bLWKhQ 

The Pardee and Riley Experiment and the Discovery of mRNA

Today I want to discuss an experiment that led to the discovery of messenger RNA (mRNA). Why did I choose to focus on one specific experiment? First, because of its importance in the history of molecular biology. Second, the experiment highlights the use of radioisotopes like those Russ Hobbie and I describe in Chapter 17 of Intermediate Physics for Medicine and Biology. Third, the recent development and of mRNA vaccines for Covid and other diseases makes this a good time to review how our knowledge of mRNA was established.  

A crucial experiment was performed by Arthur Pardee and Monica Riley at the University of California, Berkeley, and published in 1960. Let me provide some context and set the stage. The structure of DNA had been discovered by Watson and Crick in 1953. By 1960, scientists knew that individual genes in DNA coded for individual proteins. The question was how the genetic information got from DNA to the protein. RNA was suspected to be involved, in part because ribosomes—the stable cellular macromolecules where DNA was produced—are made from RNA. Were the ribosomes the messenger, or was there something else? Many key experiments in biology, like the one by Pardee and Riley, are performed using a simple model system: E coli bacteria. Another important tool of early modern biology was radioisotopes, a product of modern physics from the first half of the twentieth century that was essential for biology during the second half of the century. 

Since I’m neither a molecular biologist nor a historian of science, I’ll let Horace Freeland Judson—author of one of my favorite history of science books, The Eight Day of Creation: The Makers of the Revolution in Biology—tell you about Pardee and Riley’s work.

The experiment Pardee and Riley had done in Berkeley was new, technically amusing, and persuasive. It amounted to removal of the gene from the cell after it had begun to function. They had grown… bacteria… carrying [a specific gene to produce the protein enzyme beta-galactosidase]… in a broth where the available phosphorus [an important element in DNA] was the radioactive isotope ³²P. The bacteria, with their DNA heavily labeled, were then centrifuged out... [and] resuspended in a nonradioactive broth… [Next] they added glycerol [a type of antifreeze]. Then they took one sample to test for enzyme activity [to check if beta-galactosidase was produced]. They put other samples into small glass ampules, sealed the ampules by fusing the glass at the neck, and lowered them into a vacuum-insulated flask of liquid nitrogen. The bacteria were frozen almost instantly at 196 degrees below zero centigrade. Protected from bursting by the glycerol, the bacteria were not killed, but their vital processes were arrested while the radiophosphorus in the DNA… continued to decay… From day to day, Riley raised ampules of the frozen bacterial suspension from the liquid nitrogen and thawed them… For comparison, they ran the whole [experiment] in parallel without the radioactivity [this was their control].

Before telling you the result, let me digress a bit about phosphorus-32. It’s an unstable isotope that undergoes beta decay to stable sulfur-32. This means the ³²P ejects an electron (and an antineutrino) and transforms to ³²S. In many cases (such as in sodium-24 examined in Fig. 17.9 of IPMB), beta decay occurs to an excited state that then emits gamma rays. But ³²P is “pure” meaning there are no gamma rays, or even different competing beta decay paths. The book MIRD: Radionuclide Data and Decay Schemes by Eckerman and Endo, often cited in IPMB, shows this simple process with this figure and table. 

Note the half-life of ³²P is two weeks, and the average energy of the ejected electron is 695 keV.

What happens when ³²P decays? First, the electron can damage the cells. An electron of this energy has a range of about a millimeter, so that damage would not be localized to an individual bacterium (with a size on the order of 0.001 mm). However, when the ³²P isotope decays, it will recoil, which could eject it from the DNA molecule, causing a strand break. Even if the recoil is not strong enough remove the atom from DNA, there would now be a sulfur atom where a phosphorus atom should be, and these two atoms, being in different columns of the periodic table, will have different chemical properties which surely would disrupt the DNA structure and function. As Judson says

An atom of ³²P decays by emitting a beta particle, which is a high-speed electron, whereupon it is transformed into an atom of sulphur. The transformation, and the recoil of the atom as the electron leaves, breaks the bonds of the backbone of the DNA at that point… Half of those decayed in fourteen days. The [beta-galactosidase] genes were being killed.

So, what was the result? Judson summarizes,

The nonradioactive bacteria sampled before freezing were synthesizing enzyme copiously. So were the radioactive ones before freezing… Thawed after ten days, samples of nonradioactive bacteria synthesized beta-galactosidase just as vigorously as those never frozen. But the bacteria whose [beta-galactosidase] genes had suffered ten days of radioactive decay made the enzyme at less than half the rate they had before. Inactivation of the gene… abolished protein synthesis without delay. Stable intermediates between the gene and its protein—in other words, ribosomes whose RNA carried information to specify the sequence of amino acids—were ruled out. Continual action of the gene was necessary, either directly or by way of an intermediate that was unstable and so had to be steadily renewed.

When Francis Crick and Sydney Breener learned of Pardee and Riley’s results, they combined their knowledge of this experiment with a previous one by Elliot Volkin and Lazarus Astrachan using bacteriophages [a virus that infects bacteria] to hypothesize that a new type of RNA, called messenger RNA, was the unstable intermediary connecting DNA and protein. And the rest is history.

The Pardee and Riley experiment (which made up Monica Riley’s PhD dissertation… wow, what a dissertation topic!) is beautiful and important. It is also relevant today. Why do mRNA vaccines (like the Pfizer and Moderna Covid vaccines) have to be kept so cold when being transported and stored before use? As Pardee and Riley showed, the mRNA is unstable. It will decay quickly if not kept ultra-cold. Can mRNA change the DNA in your cells? No, the mRNA is simply a messenger that transfers the stored genetic information in DNA to the proteins formed on ribosomes. Moreover, one difference between E coli bacteria and human cells is that in humans the DNA is located inside the cell nucleus (bacteria don’t have nuclei) and the ribosomes are in the cytoplasm outside the nucleus. DNA can’t leave the nucleus, and mRNA can only go out of, not into, the nucleus. So an mRNA vaccine will cause human cells to make virus proteins (for the covid vaccine, it will produce the spike protein) that will be detected by your immune system, but the mRNA will only be present a short time before it decays and will not affect your DNA. Finally, the vaccine contains mRNA for only the spike protein, not for the entire virus. So, no actual intact viruses are produced by the vaccine. The spike protein simply activates your immune system, without exposing you to an infection.

Isn’t science great?