One of the quietest places in the universe is an unremarkable room on the southern coast of the UK. Here, in one of the University of Southampton’s physics labs, overseen by Hendrik Ulbricht, a preposterous amount of effort has gone into eliminating every conceivable disturbance: a 1-tonne slab of granite absorbs all vibrations aside from the faintest tremors, while a pendulum repurposed from a gravitational wave observatory catches the last leftover wobbles and a fridge lowers temperatures to within a whisker of those in the deepest reaches of outer space. All of this is done in the slim hope we might answer a question that has plagued scientists since the advent of quantum mechanics a century ago. In the microscopic quantum realm, reality seems to work differently than in the solid, predictable world we are used to. Hard boundaries melt into one another and objects can become deeply intertwined, or entangled, without physical contact. Quantum objects in what is known as a superposition seemingly inhabit more than one place at a time, at least if we aren’t looking directly at them. But with the smallest of disturbances, entanglement vanishes and superpositions collapse – and the larger an object is, the more likely it is to succumb to certainty. This article is part of a special series celebrating the 100th anniversary of the birth of quantum theory. Read more here. However, over the past few years, scientists have gone from putting tiny things like simple particles into a superposition to getting surprisingly large things into this state, including a sapphire crystal. As these quantum effects get bigger and bigger,…