The double-slit experiment actually underlies all of quantum mechanics. It still fascinates researchers today, with its counterintuitive implications for the fundamental nature of light. Originally performed in 1801 by Thomas Young, this experiment wondrously demonstrated the wave-like behavior of light. More than 200 years later, the importance of that experiment has been revived by new research from a cohort of scientists at the Massachusetts Institute of Technology (MIT). Beyond these, they’re probing its quantum fundamentals.
The MIT researchers have revisited Albert Einstein’s 1927 assertion that a photon ought to only go through one of the two slits. Through their investigation, Zhai and Karamatskos shed light on the perplexing behavior of photons and uncover significant implications for the field of quantum mechanics. The study, helmed by Wolfgang Ketterle, involved cooling over 10,000 atoms to nearly absolute zero and manipulating them using laser technology to observe the fundamental principles first set forth by Young and debated by Einstein and other prominent physicists.
A Historical Context
The double-slit experiment was meant to demonstrate the wave nature of light. Young filled the two adjacent slits with light. He then looked at the interference pattern that was produced on a far away screen, demonstrating the wave nature of light. This extraordinary phenomenon perplexed scientists for many decades, especially since it led to profound questions about the nature of reality itself.
In 1927, Albert Einstein disputed much of the accepted science and theories behind this experiment. To get around this, he theorized that an individual photon should only pass through one slit, hence apply an extremely faint pressure to that slit. This claim led to a famous public dispute with Niels Bohr. He countered that attempting to measure which path a photon took would collapse the interference pattern, thus preserving the uncertainty principle that is at the heart of quantum mechanics.
As these two intellectual giants confronted one another, Bohr and Einstein’s back-and-forth revealed the chasm in their views on quantum events. Their fierce dispute still dominates discussions of light’s wave-particle duality today.
The Modern Experiment
MIT’s latest study set out to do exactly that—revisit Einstein’s proposition. To achieve this, they pared the double-slit experiment to its quantum essentials. With Ketterle as a principal investigator, the research group cooled over 10,000 atoms to microkelvin temperatures. Next, they used laser light to trap and isolate each atom. Such an arrangement would be quite similar to Einstein’s imagined image of a spring-suspended slit.
To make their observations, the researchers took the ‘spring’ mechanism out. They wanted to get an idea of how the lack of this underlying architecture would influence the emerging interference pattern in a double-slit setup. Their aim was to make clear Einstein’s prediction that you can detect a photon’s path without destroying its wave-like nature.
By careful experimentation, Ketterle’s group proved Einstein’s theory of being able to trace photon paths. Their findings revealed an unexpected outcome: when they removed the ‘spring’ or stabilizing force, they still observed an interference pattern indicative of wave behavior. This result implied that Einstein’s initial assumptions regarding the interaction between light particles and their environment were not entirely accurate.
Confirming Quantum Theory
The importance of these observations is in their confirmation of quantum theory as described by Bohr. The MIT study further proves that the double-slit experiment continues to be a powerful advocate for quantum mechanics. This is even true when the experiment is stripped down to its simplest elements. That single outcoming interference pattern is key evidence that light has a dual wave/particle nature. This idea is central to the physicist’s approach to physics education today.
Even high school physics classes now regularly teach the double-slit experiment. It’s a wonderful tool to spark students’ imaginations, luring them into the captivating realm of quantum mechanics. Yet its simplicity belies the many powerful principles that it symbolizes. This is what makes it an issue of perennial debate on campus among faculty and students alike.
