Final answer:
In quantum mechanics, measurement affects the quantum system by triggering it to take a specific quantum state, a concept founded on the Heisenberg uncertainty principle. Before measurement, a system is not in a specific state but has many possibilities, and the act of measuring affects which outcome is realized.
Step-by-step explanation:
In quantum mechanics, measurement plays a crucial role by affecting the system being measured. This interaction between measurement and system is encapsulated within the Heisenberg uncertainty principle. This principle states that certain pairs of physical properties, like position and momentum, cannot both be measured precisely at the same time. The act of measuring one of these quantities can alter the other, therefore limiting the precision with which both can be known.
Quantum theory understands particles as wave packets, which implies inherent limitations on the simultaneous measurement of a particle's position and momentum. During measurement, a quantum system is affected and will 'choose' one of its possible quantum states—this is known as 'wave function collapse'. Thus, option 3 is correct: Measurement can trigger a system to take one of its allowed quantum states.
It is important to note that prior to measurement, we cannot say that the system was in a specific state among its possibilities. Measurements in quantum mechanics do not reveal pre-existing states but are integral in creating the specific outcome from many possibilities, as is illustrated in experiments such as the double-slit experiment or in the practical applications of quantum computing.