For over a century, quantum physics has revealed that light behaves like both a wave and a particle. Recent research from the Massachusetts Institute of Technology (MIT) delved deeper into this idea. Their experiment demonstrated that light can be either a particle (photon) or a wave, but never both at the same time.
The debate around the nature of light isn’t new. It stretches back to the 17th century with figures like Isaac Newton and Christiaan Huygens. Newton proposed that light must consist of particles to explain phenomena like sharp mirror images, while Huygens argued for its wave-like behaviors, including diffraction and refraction.
In 1801, physicist Thomas Young conducted the famous double-slit experiment. He projected light through two slits, expecting to see two discrete spots if light were purely particles. Instead, he observed alternating light and dark patterns on a screen. This indicated that light waves were interacting, creating interference patterns.
Fast-forward a century, and Max Planck introduced the concept of “quanta,” confirming that light is indeed made of particles called photons. Albert Einstein expanded on this, showing that photons can also exhibit wave-like traits. This dual nature is termed wave-particle duality.
Yet, there’s a catch. The uncertainty principle states we cannot observe a photon acting as both a wave and a particle simultaneously. Niels Bohr referred to this concept as “complementarity,” emphasizing that these properties can never truly be measured at once.
Einstein challenged this principle. He suggested a measurement method during Young’s double-slit experiment, asserting that we could observe a photon both as a particle while moving through a slit and as a wave during interactions. Bohr disagreed, arguing that any attempt at dual measurement would erase the interference pattern, leading to just two bright spots.
History has favored Bohr’s perspective, but doubts persisted. Many questioned whether experimental setups might obscure simultaneous observations of light as both a wave and a particle.
To test this, the MIT team, led by physicists Wolfgang Ketterle and Vitaly Fedoseev, simplified the double-slit experiment. They used 10,000 individual atoms, cooled to just above absolute zero. Each atom acted like a tiny slit, allowing photons to scatter in different directions. Over multiple trials, they created similar diffraction patterns as seen in Young’s original experiment.
Ketterle noted that what they achieved could be seen as a new twist on the double-slit experiment. “These single atoms are like the smallest slits you could possibly build,” he explained.
The results supported Bohr’s argument. When photon measurement increased, the diffraction pattern weakened, confirming that measuring light as particles diminished its wave-like behavior.
Notably, the experimental apparatus didn’t interfere with outcomes. The researchers could turn off the lasers holding the atoms in place and make measurements quickly. The findings remained consistent: we cannot discern light’s particle and wave nature simultaneously.
This research deepens our understanding of quantum physics. As Ketterle observed, even Einstein and Bohr likely couldn’t have envisioned conducting such an experiment with single atoms and photons. It underscores the fascinating complexity of our universe, where elements exist in states of probability, and the characteristics we observe arise from the complex interplay of many particles.
This study was published in the journal Physical Review Letters.
