This blog post explores how quantum mechanics’ Uncertainty Principle redefines the act of ‘seeing’ not as simple observation but as an interaction with the object, and what changes this brings to our perception of reality.
The Uncertainty Principle in quantum mechanics forces us to reconsider the meaning of ‘seeing’ an object. This principle reveals a fundamental difference between the ‘observation’ we experience daily and the nature of the quantum world. In everyday life, we assume we can precisely measure an object’s position and motion, but in the quantum realm, such uncertainty is inevitable.
To see a book, light reflected from it must reach our eyes. In other words, seeing something means perceiving photons emitted or scattered by the object. These photons act like invisible square windows, enabling us to perceive reality. However, this process is not merely a passive transmission of information; it is active in that the very act of observing an object directly influences it.
When a photon collides with and bounces off an object, it imparts a shock to it. So why can’t we see the book moving while we read? It is because the impact light exerts is far too small to cause any meaningful motion in the book. Similarly, even if you flash a camera at a flying baseball, the baseball’s motion appears unchanged. When photons collide with a book or a baseball, disturbance occurs, but the effect is negligible. This is a fact we intuitively accept in classical physics. However, this intuition no longer holds true when we enter the world of elementary particles.
To measure the physical quantity of an object, we must disturb it as little as possible. To reduce measurement errors, scientists carefully designed experiments and employed better techniques to minimize such disturbances. They believed there was, in principle, no limit to how precise measurements could become. Yet, when physicists began to deal with the world of elementary particles, they realized this belief was mistaken. They discovered that the classical concept of measuring physical quantities no longer holds absolute meaning at the subatomic level.
‘Observing an electron’ is vastly different from ‘observing a book’. To determine the state of motion of a particle, we must know its momentum and position. Here, momentum is defined as the product of an object’s mass and its velocity. To determine the momentum and position of a specific electron at a specific moment, we must measure both quantities simultaneously while disturbing the electron as little as possible. This process inherently possesses quantum characteristics and requires new concepts difficult to understand from a classical physics perspective.
Consider an ideal situation: to ‘see’ an electron, we shoot light at it, causing it to collide with the electron, and then observe the scattered photon. Colliding a photon with low momentum disturbs the electron’s momentum less, allowing for a fairly accurate measurement of its momentum. However, light composed of photons with low momentum has a long wavelength, making it difficult to measure the electron’s position at the moment of observation. That is, the measurement of the collision point between the photon and the electron becomes inaccurate. To measure the electron’s position more accurately, light with a shorter wavelength must be used. However, using light with a short wavelength (light with photons of high momentum) causes the electron’s velocity to change dramatically upon collision with the photon, leading to greater inaccuracy in the momentum measurement. Thus, the uncertainty in the electron’s momentum that the observer can determine is inversely proportional to the uncertainty in its position, revealing that both cannot be reduced simultaneously. This is the Uncertainty Principle.
This uncertainty principle is not merely a theoretical limitation within physics. It poses a fundamental question about the very way we understand, measure, and perceive reality. While classical thinking assumes an observer can ‘objectively’ grasp an object’s state, in the quantum world, the observer’s presence and actions inevitably influence the object. This reminds us that ‘seeing’ is not mere observation, but a form of interaction.
