Practice Tests
IELTS Reading (AC) Task 1 #201

A. Quantum entanglement is one of the most bizarre and counterintuitive phenomena in quantum mechanics, famously described by Albert Einstein as "spooky action at a distance." It occurs when two or more quantum particles, such as photons or electrons, become linked in such a way that their fates are intertwined, no matter how far apart they are separated. Measuring a property of one particle, such as its spin or polarisation, instantaneously influences the corresponding property of the other entangled particle.

B. The core of this mystery is that before a measurement is made, the properties of the entangled particles are not predetermined; they exist in a probabilistic state of superposition. For example, an entangled pair of electrons could have one with a "spin up" and the other with a "spin down." We don''t know which is which until we measure one. But the moment we measure the first electron and find it has spin up, we instantly know that the other, even if it is light-years away, must have spin down.

C. This instantaneous connection appears to violate the principle that nothing can travel faster than the speed of light. However, entanglement does not allow for faster-than-light communication. This is because the outcome of the measurement on the first particle is random; we cannot control it to send a specific message to the person measuring the second particle. We only see the correlation after we compare our results, which requires communication at or below the speed of light.

D. Once a purely theoretical curiosity, quantum entanglement is now a key resource in the development of new technologies. It is the fundamental principle behind quantum computing, where entangled qubits can perform complex calculations that are impossible for classical computers. It is also being used to develop ultra-secure communication systems based on quantum cryptography, where any attempt to eavesdrop on the communication would instantly break the entanglement and be detected.