BLOGS

Excited helium nuclei inflate like balloons, offering physicists a chance to study the strong nuclear force which binds the nucleus’s protons and neutrons. Kristina Armitage/Quanta Magazine

Topics: Modern Physics, Nobel Prize, Particle Physics, Quantum Mechanics, Steven Weinberg, Theoretical Physics

A new measurement of the strong nuclear force, which binds protons and neutrons together, confirms previous hints of an uncomfortable truth: We still don’t have a solid theoretical grasp of even the simplest nuclear systems.

To test the strong nuclear force, physicists turned to the helium-4 nucleus, which has two protons and two neutrons. When helium nuclei are excited, they grow like an inflating balloon until one of the protons pops off. Surprisingly, in a recent experiment, helium nuclei didn’t swell according to plan: They ballooned more than expected before they burst. A measurement describing that expansion, called the form factor, is twice as large as theoretical predictions.

“The theory should work,” said Sonia Bacca, a theoretical physicist at the Johannes Gutenberg University of Mainz and an author of the paper describing the discrepancy, which was published in Physical Review Letters. “We’re puzzled.”

For many years, physicists didn’t understand how to use the strong force to understand the stickiness of protons and neutrons. One problem was the bizarre nature of the strong force — it grows stronger with increasing distance rather than slowly dying off. This feature prevented them from using their usual calculation tricks. When particle physicists want to understand a particular system, they typically parcel out a force into more manageable approximate contributions, order those contributions from most important to least important, then simply ignore the less important contributions. With the strong force, they couldn’t do that.

Then in 1990, Steven Weinberg found a way to connect the world of quarks and gluons to sticky nuclei. The trick was to use an effective field theory — a theory that is only as detailed as it needs to be to describe nature at a particular size (or energy) scale. To describe the behavior of a nucleus, you don’t need to know about quarks and gluons. Instead, at these scales, a new effective force emerges — the strong nuclear force transmitted between nucleons by the exchange of pions.

A New Experiment Casts Doubt on the Leading Theory of the Nucleus, Katie McCormick, Quanta Magazine

Living on: data taken by the now-defunct CDF experiment has revealed a surprising mass for the W boson. (Courtesy: Fermilab)

Topics: Fermilab, High Energy Physics, Modern Physics, Particle Physics, Steven Weinberg

The most precise measurement to date of the mass of the W boson has yielded a result seven standard deviations away from that predicted by the Standard Model of particle physics. The stunning result was obtained by a painstaking analysis of data taken at the Fermilab Tevatron collider in the US before it closed in 2011. The particle physics community must now study the results carefully to work out whether it is an incredible statistical fluke, an unknown experimental error, a flaw in the Standard Model, or a genuine indication of physics beyond the Standard Model.

The W boson is one of the most intriguing particles described by the Standard Model. Together with the neutral Z boson, the charged W boson mediates the weak interaction, which causes beta decay and several other important processes in particle physics. The weak interaction has long intrigued scientists searching for physics beyond the Standard Model, partly because it is the only force known to violate charge-parity symmetry. If particles in a process are exchanged for their antiparticles and the spatial coordinates are inverted, the weak interaction in this mirror image process is not always identical. This puzzle is not explained in the Standard Model.

W boson mass measurement surprises physicists, Tim Wogan, Physics World

My autographed copy from Dr. Weinberg.

Topics: History, Nobel Laureate, Nobel Prize, Steven Weinberg

AUSTIN, Texas — Nobel laureate Steven Weinberg, a professor of physics and astronomy at The University of Texas at Austin, has died. He was 88.

One of the most celebrated scientists of his generation, Weinberg was best known for helping to develop a critical part of the Standard Model of particle physics, which significantly advanced humanity’s understanding of how everything in the universe — its various particles and the forces that govern them — relate. A faculty member for nearly four decades at UT Austin, he was a beloved teacher and researcher, revered not only by the scientists who marveled at his concise and elegant theories but also by science enthusiasts everywhere who read his books and sought him out at public appearances and lectures.

“The passing of Steven Weinberg is a loss for The University of Texas and for society. Professor Weinberg unlocked the mysteries of the universe for millions of people, enriching humanity’s concept of nature and our relationship to the world,” said Jay Hartzell, president of The University of Texas at Austin. “From his students to science enthusiasts, from astrophysicists to public decision-makers, he made an enormous difference in our understanding. In short, he changed the world.”

UT Austin Mourns Death of World-Renowned Physicist Steven Weinberg, UT News

I'm sure the University of Texas, the New York Times, US News & World Report among many others will do more justice than a blog post from a doctoral student in Nanoengineering.

Photo at a banquet for the National Society of Black Physicists (NSBP), and National Society of Hispanic Physicists (NSHP) joint meeting, September 22, 2011, University of Texas, Austin.

His passing made me take stock of the popular books by physicists in my library (a short list): "The Collapsing Universe" (Asimov); "Ideas, and Opinions," "Relativity: The Special, and the General Theory" (Einstein); "Surely, You're Joking Mr. Feynman," "Six Easy Pieces," "QED: The Strange Theory of Light, and Matter," (Feynman); "Gravity" (Hartle); "Stephen Hawking's Universe," "A Brief History of Time," "The Universe in a Nutshell," (Hawking), "The God Particle: If the Universe is the Answer, What is the Question?" (Lederman); Warped Passages: Unravelling the Mysteries of the Universe's Hidden Dimensions" (Randall); "The Black Hole Wars: My Battle With Stephen Hawking To Make The World Safe for Quantum Mechanics" (Susskind); "Black Holes, & Time Warps: Einstein's Outrageous Legacy" (Thorne), following in alphabetical order by author, lastly Professor Steven Weinberg. Some of my humble ruminations of him:

The above is from a Joint Conference between the National Society of Black Physicists and the National Society of Hispanic Physicists in Austin, Texas on September 22, 2011. The photo above as I recall is from the now-defunct Blackberry mobile phone, so please forgive the image quality and pixel density. In my mind, a parallel remembered photo: Einstein lecturing African American physics students at Lincoln University. I cannot say he was going for a double entendre. I remember in the parking lot before I left, holding tightly the steering wheel of the rental, feeling goosebumps, and catching my breath.

I met Dr. Weinberg and thanked him for signing my only copy of "The First Three Minutes" when I was a graduate student in Astrophysics at the University of Texas (I have a hardcover copy; the most recent prints are paperback or Kindle). I was quite astonished that he remembered me. I filed my request sheepishly through his Administrative Assistant, but he did remember my request, and me specifically.

These were my first thoughts when a friend posted the UT News article on Facebook. Her husband had been a student of Dr. Weinberg, and a physics colleague for almost four decades. I called him to give my personal condolences. We both agreed it was the passing of an age that may never be repeated again. With each passing day, each quote by Dr. Carl Sagan in "A Demon-Haunted World" is becoming prophesy.

Though my friend is an accomplished scientist himself, he always felt intimidated by his mentor's presence. He and Professor Weinberg tentatively made a date to resume their lunch meetings, subsumed by the pandemic, until life or the cessation of life inevitably happens. The body wears out, and Entropy eventually has the last say. In the end, our positive impact is our epitaph, it is how we will be remembered.

*****

It is the loss of a giant in an age ruled by madness. I got to shake hands with Professor Steven Weinberg at the National Society of Black Physicists (NSBP), and the National Society of Hispanic Physicists (NSHP) when they held a joint meeting in Austin, Texas, September 22, 2011.

I have both “The First Three Minutes” (he graciously autographed), and “To Explain the World.”

His passing should make us all more determined to do just that in a world now ruled by gaslighting, and in the words of Carl Sagan, “thirty-second sound bites” (if they’re even that long). We should shine his passion for scientific inquiry as lights in “this present darkness.”

I think he’d want us to remember him that way.

At least that’s how I’m consoling myself through the tears.