If all matter has wave-like properties, why is it that we don’t observe quantum effects in our daily lives? Consider, for example, the de Broglie wavelength of a 0.15-kg baseball batted at 30 m/s:
At that wavelength, a baseball would need to interact with objects smaller than subatomic particles to show quantum effects.
In summary, because h is so small, the wavelength of matter is also very small for normal-sized objects with even a tiny bit of momentum. Since the wavelength of these objects is much smaller than the size of objects or systems with which it interacts, we ordinarily don’t notice the wave aspect in everyday objects.
However, because wavelength depends on velocity, it can become significant even for macroscopic systems when particle velocities are exceedingly low. This happens at temperatures close to absolute zero (0 Kelvin = -273.15°C), where atoms lose all thermal energy and have only their quantum motion. Massachusetts Institute of Technology researchers recently announced that they were able to cool a dime-sized mirror within one degree of absolute zero.33 Although this temperature is still too high for observing quantum effects, a technique has been developed to get large objects to ultimately show their quantum behavior. Once the mirror can get cold enough—to within a millidegree Kelvin, quantum effects such “quantum entanglement” between the light and the mirror should be observable. This would confirm that very large objects also obey the laws of quantum mechanics, just as molecules do.
This is not a competition of “mine is larger than yours.” The point of these experiments is extremely profound: they demonstrate that quantum behavior is not restricted to the microscopic world. Large, complex macroscopic objects, once thought to be clearly in the domain of classical physics obey the same quantum laws as microscopic particles. This begs the question: is there a limit to the size and complexity of the object that no longer abides by quantum behavior? Probably not!
The outcomes of these experiments have caused an extraordinarily profound impact on physicists’ way of thinking. It showed us that, while our classical view of a single reality may work most of the time, the equations of quantum physics describe a tangible, more fundamental level of reality—one that is absolutely incompatible with our day-to-day experience. If classical physics would suffice to describe the behavior of all objects, then we should expect that a single chunk of matter will go through one slit or the other in a two-slit experiment, and will end up in one of two possible bands on a detector. But that is not what happens. Instead, each particle behaves as if it went through both slits simultaneously, not just in theory, but in experimental actuality!
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