May the Weak Force Be With You

We couldn’t live without the weak force, the least understood and underappreciated natural force.

David Armstrong wants to educate people about the weak force. In a press release from the College of William and Mary, Joseph McClain introduces us to the physicist who thinks people should appreciate a property of the universe without which life could not exist.

Armstrong came to William & Mary in 1994. Now, as Chancellor Professor of Physics, divides his time between Small Hall and the Jefferson Lab, where he collaborates on a number of particle-physics experiments, most of which involve the weak force. When Armstrong talks about his work to people who don’t speak physics, he starts by explaining that the weak force is one of the four fundamental interactions that keep the universe running.

Without the weak force, the sun and life would be impossible.

“Two of them are familiar to most of us,” Armstrong said. “Gravity: it keeps the planets in orbit around the sun and keeps us affixed to the Earth. Electricity and magnetism: We’ve learned since Maxwell that they’re two aspects of the same force. We’re familiar with those, and electromagnetism is what’s responsible for the electrons staying in orbit around the nucleus. Basically, all of chemistry arises from electricity and magnetism.”

Less familiar to the lay public, he said, are the two nuclear forces. The strong force holds together the protons and neutrons (and their constituent quarks) in the nucleus. The last, and least familiar, of the fundamental interactions is the weak force, responsible for certain kinds of radioactive decay.

“Unlike those other interactions, I can’t give you an example of something that’s held together by the weak force,” Armstrong said. “But the weak force is incredibly important, because life wouldn’t exist without it.”

How so? What has the weak force done for you lately? Well, it gives you sunlight. It also gives you medical imaging.

He pointed out that the fusion process in the sun, whereby hydrogen atoms glom onto one another to become helium, is an example of the weak force in action. A critical step in that reaction chain takes place through the weak force, so in fact the weak force drives the sun’s nuclear furnace.

“If the weak interaction were significantly stronger than it is, then the sun would have burned out years ago,” he said. “If the weak interaction were weaker, then the sun wouldn’t have ignited.”

“Certain kinds of radioactive decay, which are often useful in things like medical imaging, take place through the weak interaction,” he explained.

Physics aficionados can read more about the weak force in the article. One of the weird characteristics of the weak force, he explains, is that it violates a symmetry of nature called parity. “And, for scientists, the odd-one-out parity status of the weak force gives Armstrong and other physicists an entry point into the pursuit of new physics, beyond the Standard Model.”

This implies that the “Standard Model” is not a complete account of matter and energy. So yes, young physics student, there is more to discover. The rest of us can be thankful that we have a beautiful star, the sun, giving us a remarkably constant flow of energy to the Earth.

Paul wrote, “God chose what is weak in the world to shame the strong” (I Corinthians 1:27). Isn’t it just like God to amaze modern physicists with something they call “weak” that turns out to be critical for life?

To be dazzled by little-known facts that make life possible, read Michael Denton’s new book Children of Light. He shares the remarkable coincidences between the sun and earth that allow for the existence of large, complex creatures like humans. It almost looks designed, doesn’t it? In a podcast on ID the Future, Denton is at a loss for words to explain how astonishing the fine-tuning in the laws of physics are for our benefit.