From: mk_thisisit
The distinction between the classical world and the quantum world is fundamental to understanding physics . This difference dictates how objects behave and how our observations interact with them .
Defining the Worlds
The Classical World
The classical world is the one we experience daily . It is characterized by large objects, like trams or ping-pong balls, whose behavior is predictable and familiar . In this macroscopic realm, observations have a negligible effect on the object being observed . For example, observing the moon with a telescope or our eyes doesn’t significantly alter its shape or movement, even though it requires illumination .
The Quantum World
The quantum world deals with objects at the atomic and subatomic levels, such as atoms and elementary particles . These objects are “terribly small” . Their behavior is entirely different from what we expect in the classical world . It is a world that is “very alien to us” and one to which humans, despite being composed of it, do not have direct sensory access .
Behavioral Differences
Atoms and other quantum entities do not behave like macroscopic objects . Their existence is governed by different rules . Phenomena that appear “absolutely paradoxical” in the macroscopic world are commonplace in the quantum world .
The Role of Observation
A key difference between the classical and quantum worlds lies in the impact of observation .
- Classical Observation: When observing macroscopic objects, the act of observation “basically have[s] no effect on the object” .
- Quantum Observation: In the quantum world, the act of observation significantly changes our knowledge about the object . It can even change the state of the object itself . For example, to “see” a single electron, one must illuminate it, and this interaction will scatter the photon, thereby disturbing the electron’s movement and state .
“Quantum mechanics is a theory of our observations of the microworld. Everything we know about our world results from our observations… in the case of macroscopic objects the acts of observation… have basically no effect on the object… However, in the case of observation objects it completely changes our knowledge about this object. And this is the difference and it is also said that it changes the state of the object…”
The “Atom” as a Boundary
The phrase “the world is made of atoms” is considered the most important sentence of humanity’s knowledge . Atoms represent the point where the familiar, large-scale world gives way to the vastly different quantum realm . While one can go down to the level of elementary particles beyond atoms, atoms themselves mark the boundary where behavior shifts fundamentally .
This interplay between classical and quantum physics highlights that our everyday experience does not prepare us for the behaviors observed at the smallest scales .