In classical mechanics, the measurement of an object's state typically involves direct interaction with the object. This interaction can perturb the object's state to some extent, although in many cases the disturbance is negligible and can be considered negligible compared to the precision of the measurement. For example, when measuring the position of a ball on a table, we typically use a ruler or a measuring tape that physically touches the ball, causing a slight disturbance in its position due to the contact. However, this disturbance is usually insignificant for macroscopic objects.
In quantum mechanics, the situation is different due to the inherent probabilistic nature of quantum systems and the principle of wave-particle duality. According to the Heisenberg uncertainty principle, there is a fundamental limit to the precision with which certain pairs of physical properties, such as position and momentum, can be simultaneously known. Therefore, the act of measuring one property of a quantum system necessarily introduces uncertainty and can disturb other properties.
In general, it is not possible to measure a quantum system without disturbing it to some degree. This disturbance is often referred to as the "measurement back-action" or the "observer effect." The very act of interacting with a quantum system, such as by shining light on it or detecting particles from it, can alter its state. This is a fundamental characteristic of quantum mechanics.
However, there are certain measurement techniques in quantum mechanics that aim to minimize the disturbance caused by measurements. These techniques, known as "non-demolition measurements," attempt to extract information about a system's properties without significantly altering them. They often involve indirect methods or continuous monitoring of the system over time.
It is important to note that the concept of "measurement" in quantum mechanics is a topic of ongoing debate and interpretation. Different interpretations, such as the Copenhagen interpretation or the many-worlds interpretation, provide different perspectives on the nature of measurement and its consequences.