According to the principles of quantum mechanics, when two particles are entangled, their quantum states become correlated in such a way that the measurement of one particle can instantaneously affect the state of the other, regardless of the distance between them. This phenomenon is known as quantum entanglement.
In your scenario, if Alice observes her entangled particle and causes its quantum state to collapse, the state of Bob's associated entangled particle will also be instantaneously affected. This means that Bob's particle will also undergo a collapse of its quantum state, and its properties will be determined by the measurement outcome on Alice's particle.
However, it is important to note that Bob cannot be made aware of the specific measurement outcome on his particle without making his own observation or measurement. The collapse of the quantum state does not transmit information about the measurement outcome to Bob directly. The collapse merely establishes a correlation between the entangled particles, but the specific outcome obtained by Alice remains unknown to Bob until he performs his own measurement or observation on his particle.
This feature of quantum entanglement is known as the "no-communication theorem." It states that entanglement cannot be used to transmit information faster than the speed of light. The outcomes of measurements on entangled particles may be correlated, but this correlation cannot be exploited to communicate information between observers without conventional means of communication.
In summary, when Alice observes her entangled particle and causes a collapse of its state, Bob's associated particle will also collapse accordingly. However, Bob cannot determine the specific outcome of Alice's measurement without making his own measurement or observation, and the principles of quantum mechanics prevent the use of entanglement to transmit information instantaneously.