Quantum riddles

Inside a chamber of vacuum chilled to near-absolute zero, two nanodiamonds – each so tiny that about 200,000 would fit on the full stop at the end of this sentence – may one day probe a question that has gripped physicists for a century. Using lasers, sensors, and electromagnetic fields, scientists hope to measure the feeble gravitational tugs between the diamonds and answer the question: does gravity obey the laws of quantum mechanics?

The nanodiamond experiments, first proposed eight years ago and anticipated to take place no earlier than the mid-2040s, will represent a fresh attempt to confront a deeper mystery linked to quantum mechanics, the set of rules that govern the subatomic world – the behaviour of photons and particles such as electrons and protons. Despite its triumphs in explaining the infinitesimal realm and real-world applications – from electronics and smartphones to magnetic resonance imaging – quantum mechanics comes with consequences that have baffled physicists for decades. Some even wear the mystery as a badge of honour. Many physicists point to Nobel laureate Richard Feynman's remark in a 1964 talk that he could "safely say that nobody understands quantum mechanics", a declaration that rings largely true even in 2025.

Quantum mechanics emerged in the early 20th century when physicists such as Max Planck, Niels Bohr, and Werner Heisenberg began reimagining the subatomic world. Its rules diverge sharply from classical mechanics – the predictable motions that govern apples and aircraft or pulleys and planets. In the quantum domain, particles act like waves, exist in two states at once, and influence each other across vast distances – phenomena proven by rigorous mathematics and repeated experiments.