Quantum Mechanics is notoriously difficult, and the subject has raised some deep questions about the natural world. Perhaps the best known example is the Schrodinger's cat thought experiment that poses the following question: does quantum mechanics imply that a cat can be both dead and alive at the same time?
Physics education researchers have found that professors often glance over or sidestep fundamental questions like this, and it's hindering students' understanding. Touching on these interpretive questions not only makes students more excited about physics, but it also leads to a better understanding of the underlying physics principles.
Charles Bailey and his colleagues at the University of Colorado Boulder compared various teaching styles for a modern physics course. Through their research, the team wanted to analyze student perspectives on the measurement problem in quantum mechanics: what does wavefunction collapse mean?
And the measurement problem is perhaps best illustrated by the unfortunate case of Schrodinger's cat:
Consider one cold, calculating physicist who places a cat, a bottle of poison, a Geiger counter to detect radiation, and a decaying radioactive atom in a box. The single atom has a half-life of 53 minutes, meaning that after 53 minutes there is a 50-50 chance that it will emit radioactive particles upon measurement. Before measurement, however, the system remains in a superposition of the decayed state and the undecayed state.
The traditional quantum mechanics interpretation seems to suggest that the superposition follows a chain. The Geiger counter, poison, and ultimately the cat are all in a superposition of states before someone looks inside the box. Quantum mechanics might imply that the cat is both poisoned (dead) and alive at the same time. Counterintuitive indeed!
Other interpretations suggest that the universe branches in these cases, implying that there is a new universe in which the cat lives and another where the cat dies. Both universes are equally real, and there's no universe where the cat is both alive and dead.
But the researchers found that the point is not teaching the "correct" interpretation. Instead, simply allowing students to explore these types of interpretations improved their understanding of the fundamental physics behind quantum mechanics.
The CU researchers looked at four different classes over time that addressed these issues with varying approaches and dedicated class time. They found that explicitly addressing these interpretive questions led students to better understand what quantum probability really means.
At the beginning and end of each semester, Bailey and his team asked students if they agreed or disagreed with the following statement:
The probabilistic nature of quantum mechanics is mostly due to the limitations of our measurement instruments.
Regardless of one's quantum mechanical interpretations, a wide majority of physics professors agree that this statement is incorrect. Quantum probability is not the same as experimental uncertainty.
Bailey and his team found that exposing students to more philosophical questions caused students to disagree with this statement, meaning that they could discern the aforementioned distinction between classical uncertainty and quantum probability.
In addition to better student achievement, this style of teaching also led to more enthusiastic students: After the class, 98% of students thought quantum mechanics was an interesting subject compared to 70% for students in previous classes.
To find out more about this research, take a look at Charles Bailey's dissertation page.
You can also find more information about physics education research at this CU page.