The double-slit experiment, originally performed with light, has also been conducted with particles such as electrons, neutrons, and even larger molecules. While it is true that macroscopic objects like molecules are typically too large to pass through narrow slits, there are techniques that can be employed to study their wave-like behavior.
In the case of the double-slit experiment with molecules, a process called beam collimation is employed to create a well-defined beam of molecules with a narrow velocity spread. This is achieved using various methods such as thermal evaporation, supersonic expansion, or molecular beams produced by chemical reactions. These techniques generate a collimated beam where the molecules travel in a fairly straight line with minimal spread in their velocities.
To perform the experiment, a source emits the collimated beam of molecules towards a barrier containing two slits. The slits are usually very close together, often on the order of nanometers to micrometers in size. The barrier is designed to allow the molecules to pass through the slits and then propagate towards a screen or detector placed behind the barrier.
As the molecules pass through the slits, they undergo diffraction, which is a characteristic wave-like behavior. This diffraction causes the molecules to spread out and interfere with each other as they propagate towards the screen. The interference pattern that emerges on the screen is then recorded or observed to analyze the wave-like properties of the molecules.
It's important to note that the size of the molecules used in these experiments is carefully chosen to ensure that they still exhibit wave-like behavior. While molecules are indeed larger than particles such as electrons, their de Broglie wavelength (which describes the wave-particle duality) can still be significant on the nanometer scale. By carefully selecting the molecular species and controlling the experimental parameters, scientists can observe interference patterns, similar to those observed in the double-slit experiment with light or smaller particles.
The ability to observe wave-like behavior in larger molecules helps bridge the gap between the quantum world of atoms and the macroscopic world we experience in everyday life, further highlighting the fascinating nature of quantum mechanics.