How quantum entanglement works

Quantum entanglement is a physical phenomenon in which two particles remain connected over long distances so that the actions performed on one particle also have an effect on the second particle. If it sounds mind-boggling, it’s because it is. Albert Einstein, who first discussed the idea of quantum entanglement in a joint paper with Boris Podolsky and Nathan Rosen, dubbed the phenomenon “spooky action at a distance” because it implies faster than light communication, which his theory of relativity ruled out.

The particles in the entangled pair form an inseparable whole and one cannot be fully described without the other. However, entanglement is broken when particles interact with the environment, such as when a measurement is made. The paradox of quantum entanglement lies in the fact that a measurement of either one of the entangled particles collapses the entire system before the result of one measurement can be transmitted to the other particle.

As a thought experiment, we can imagine that two separate particles are sent in opposite directions, separated by thousands of miles, one in Washington and one in London. In quantum entanglement, these two particles remain connected in spite of the distance, so if we were to spin one particle in Washington clock-wise, the second one in London would instantly spin anti-clockwise.

Quantum entanglement only applies to small particles such as atoms and electrons, not too large objects such as animals or buildings. Although scientists initially believed that the phenomenon only applied to minuscule particles, recent experiments have shown that it can also happen between slightly larger objects that are visible to the naked eye – such as vibrating aluminum sheets measuring 15 micrometers in diameter.

Scientists don’t know yet what exactly links the two particles and Einstein called the phenomenon impossible because it implied that objects could be influenced by something else other than their own surroundings, but scientists were able to prove that it is possible.

One study published in the journal Science reports the experiment of physicist Jian-Wei Pan from the University of Science and Technology of China in Shanghai, who together with his team produced a pair of entangled particles on a satellite which orbits 300 miles above the atmosphere, then beamed these particles to two labs on earth that were 750 miles apart. This experiment broke two records: one – it was the first time someone ever produced entangled particles in space, and 2 – this was the biggest distance that linked particles could maintain. Before it, the biggest distance was 86 miles. This distance was achieved because on Earth, in order to send two entangled particles in different directions, you need diver optic cables to transmit them. Since fibers absorb light, the connection is weakened after every mile. But in the vacuum of space, there is no light to be absorbed, and so the entangled particles will maintain their connection for longer.

The implications of experiments such as this one – and of the phenomenon itself – are huge. Scientists believe that quantum entanglement could have applications in computing and cryptography and that it could help us create ultra-precise clocks. At the same time, by challenging our understanding of causality, locality, and realism, quantum entanglement raises both scientific and philosophical debates, breaking the rules of standard physics.