Physics has evolved through a rigorous adherence to the scientific process — one that continually pits theoretical models against observed experimental results.
According to UCLA physics professor emeritus and former Dean of Physical Sciences Joseph Rudnick, experiments that challenge long established theories can lead to some of the most groundbreaking scientific results. However, Rudnick believes having the confidence to present results that depart from conventional theory can also be incredibly difficult for scientists.
“People become fixated on models or they become wedded to results, and they don’t see everything. If something doesn’t agree with the model, they’ll figure out how to make it agree.” Rudnick also quoted Carl Sagan’s comment that extraordinary claims require extraordinary evidence.
This lesson was taught to Rudnick early in his scientific career by his father, Isadore Rudnick, who was a member of the National Academy of Sciences and also a physics professor at UCLA. Not only were both men faculty members of the physics department at the same time, but Joseph Rudnick also published academic papers alongside his father and currently occupies the very same office his father, who is now deceased, used during his tenure at UCLA.
For Rudnick, one of the most inspirational stories about his father revolves around an experimental finding Isadore made that has connections to the 2016 Nobel Prize in Physics, which was awarded last December in Stockholm, Sweden.
Professors Duncan Haldane, David Thouless and John Kosterlitz won the 2016 Nobel for pioneering theoretical work done on understanding phase transitions in exotic forms of matter, such as superfluids, and Isadore provided significant experimental evidence confirming this theory.
Matter exists in different phases, such as liquid or solid. A superfluid is a particular phase of matter that has several unique and remarkable properties, said Rudnick, explaining his father's work.
Most notably, superfluids have zero viscosity, meaning they can flow with practically no friction.
“Viscosity is what you see in syrup — it’s the property that makes it flow slowly. Superfluids have effectively no viscosity, and this remained unexplained for a long time,” said Rudnick.
In the 1970’s, Isadore Rudnick was examining the properties of extremely thin helium superfluids that were only a few atoms thick. In particular, he was observing the unique way in which certain waves propagated through superfluids, similar to observing how ripples flow through a pond said his son.
Isadore found that there was a critical temperature at which the superfluid suddenly lost its superfluidity and started behaving like a normal fluid. Many of the properties of this apparently discrete transition from superfluidity to fluidity were not consistent with previously observed superfluid phase transitions, and the result was very perplexing to the physics community, said Rudnick.
Some in the scientific community reacted negatively, Rudnick recalled: "You are doing a bad experiment. What you’re seeing is not what you think you’re seeing.”
He emphasized that his father was a very careful experimentalist who prided himself on publishing only results he knew were right, and did not waver from his results.
Video: UCLA professor Isadore Rudnick and his colleague experiments with liquid helium.
Isadore’s result went unexplained for some time until Thouless and Kosterlitz developed a theory for two-dimensional superfluids a few years after Isadore published his results.
Gary Williams, a current physics professor at UCLA and a former colleague of Isadore’s, said the pair’s radical theory departed strongly from current physical convention and claimed that objects known as quantized vortices played a role in the transition of superfluid-to-normal fluid phase.
According to Williams, vortices are fluids that rotate around an axis, and they come in many different forms.
“It could be a tornado. When you pull the stopper out of the sink, a vortex forms as well,” said Williams.
Rudnick said that microscopic vortices are actually present throughout all normal liquids. In superfluids, these vortices can essentially only rotate at what are known as specific, discrete vorticities, and Thouless and Kosterlitz’s theory explained how this property gives rise to the interesting features of superfluids, such as zero viscosity.
The theory was directly applicable to Isadore’s experimental findings on superfluid phase transitions. However, the pair published their theory in the Journal of Physics, and interestingly, Isadore did not hear about their results until several years after their work was published.
In fact, Isadore first became aware of Thouless and Kosterlitz’s theory when a visiting scientist, David Nelson, was giving a presentation about the theory at UCLA, said Rudnick.
“My father was in the audience. When he heard the talk, he went back to his office, pulled out his old lab books and discovered his results were just what the theory predicted,” said Rudnick.
Isadore’s research was a striking verification of Thouless and Kosterliz’s theory.
“It was an important piece of confirming evidence. It demonstrated that Thouless and Kosterliz’s theory was a proper model of physical reality,” said Rudnick. “It was also a vindication of my father’s approach to physics.”
Thouless, Kosterliz and others went on to further extend their theory, which is now having tremendous impact on several areas of physics and is aiding in the development of exotic technologies such as quantum computers.
Isadore’s story, while atypical in science, provides a best-case scenario for how the field should work, said Rudnick.
“It was an experimentalist getting a puzzling, unexplainable result, and theorists working on a model and discovering the model and experiment agree with each other,” said Rudnick.
