The uncertainty principle in quantum mechanics shows that an observer cannot accurately measure an object’s position and momentum at the same time, which forces us to reconsider the meaning and nature of what it means to “see” an object.
The uncertainty principle of quantum mechanics forces us to rethink what it means to “see” an object. This principle reveals a characterization of the quantum world that is fundamentally different from our everyday experience of ‘observation’. In everyday life, we think we can accurately measure the position and motion of objects, but in the quantum world, uncertainty is inevitable.
To see a book, light reflected from it must reach our eyes. In other words, to see something is to perceive photons emitted or bounced off an object. These photons are like invisible, square windows that allow us to perceive reality. But this process is not just a passive transmission of information; it is active in that the act of looking at an object directly affects it.
Photons cause an impact on an object when they hit it and bounce off of it, but why can’t we see a book move while we’re reading it? Because the impact of the light is too small to cause any meaningful movement in the book. It’s the same reason why firing a flash at a flying baseball doesn’t seem to change the baseball’s motion. When photons hit a book or a baseball, there is a disturbance, but the effect is negligible. This is something we intuitively accept in classical physics, but this intuition no longer holds true when we enter the world of elementary particles.
If you want to measure a physical quantity of something, you need to disturb it as little as possible. To reduce measurement error, scientists have carefully designed experiments and used better techniques to reduce these disturbances. They thought that in principle there was no limit to the precision of their measurements. However, physicists have realized that this was wrong when dealing with the world of elementary particles. They realized that the classical concepts of physical quantity measurement no longer have absolute meaning at the subatomic level.
“Looking at an electron” is very different from ‘looking at a book’. If we want to know the state of motion of a particle, we need to know its momentum and position. In this context, momentum is a quantity defined as the product of an object’s mass and its velocity. To know the momentum and position of a particular electron at a particular point in time, we need to measure both physical quantities simultaneously, with as little disturbance to the electron as possible. This process is quantum in nature and requires new concepts that are difficult to understand in terms of classical physics.
In an ideal situation, to “see” an electron, we would shoot light at it, collide with it, and observe the photons that bounce off. If you hit a photon with less momentum, you disturb the electron’s momentum less, and you can measure its momentum fairly accurately. However, because light made up of photons with small momentum has a long wavelength, it is difficult to measure the position of the electron at the moment of observation, which means that the measurement of the position of the photon-electron collision will be inaccurate. To measure the position of the electron more accurately, we need to use light with a shorter wavelength. However, if you use light with a shorter wavelength (photons have a larger momentum), the velocity of the electron that collided with the photon will change dramatically, making the momentum measurement inaccurate. In this way, the uncertainty in the momentum of the electron that the observer can determine and the uncertainty in its position are inversely related, so it turns out that they cannot be reduced at the same time. This is the uncertainty principle.
This uncertainty principle is not just a theoretical limitation of physics. It raises fundamental questions about the way we understand, measure, and perceive reality itself. While classical thinking assumes that an observer can “objectively” determine the state of an object, in the quantum world, the observer’s presence and actions inevitably affect the object. This reminds us that what we ‘see’ is not just an observation, but an interaction.
