The biggest questions in science

Physicists believe that at the tiniest scales, space emerges from quanta. What might these building blocks look like?

An elusive substance that permeates the universe exerts many detectable gravitational influences yet eludes direct detection.

Scientists are beginning to unravel a mystery that has long vexed philosophers.

Untangling the origins of organisms will require experiments at the tiniest scales and observations at the vastest.

By reaching down into the quantum world, scientists are hoping to gain more control over matter and energy.

The reach of the scientific method is constrained by the limitations of our tools and the intrinsic impenetrability of some of nature’s deepest questions.

The evolutionary origin of the enzyme-catalysed Krebs cycle is unclear. Here, the authors identify non-enzymatic intermediates that replicate key elements of the cycle, suggesting that inorganic catalysts may have driven the origin of metabolic processes.

Current mineral-based theories do not fully address how enzymes emerged from prebiotic catalysts. Now, iron–sulfur clusters can be synthesized by UV-light-mediated photolysis of organic thiols and photooxidation of ferrous ions. Iron–sulfur peptides may have formed easily on early Earth, facilitating the emergence of iron–sulfur-cluster-dependent metabolism.

Several brain regions and physiological processes have been proposed to constitute the neural correlates of consciousness. In this Review, Koch and colleagues discuss studies that distinguish the neural correlates of consciousness from other neural processes that precede, accompany or follow it, and suggest that the neural correlates of consciousness are localized to posterior cortical regions.

Uncovering the neural basis of consciousness is a major challenge to neuroscience. In this Perspective, Tononi and colleagues describe the integrated information theory of consciousness and how it might be used to answer outstanding questions about the nature of consciousness.

Hawking radiation is observed emanating from an analogue black hole, with measurements of the entanglement between the pairs of particles inside and outside the hole offering tantalizing insights into the field of black hole thermodynamics.

An experiment to estimate when stars began to form in the Universe suggests that gas temperatures just before stars appeared had fallen well below predicted limits, and that dark matter is not as shadowy as was thought.

Dark matter could decay into conventional particles leaving behind specific signatures in the gamma rays and cosmic rays. Astronomical observations are used to search for these elusive dark matter footprints.

Topology and collective phenomena give quantum materials emergent functions that provide a platform for developing next-generation quantum technologies, as surveyed in this Review.

This Review surveys the electronic properties of quantum materials through the prism of the electron wavefunction, and examines how its entanglement and topology give rise to a rich variety of quantum states and phases.

Interfacing spin quantum memories with photons requires the controlled creation of defect centre—nanocavity systems. Here the authors demonstrate direct, maskless creation of single silicon vacancy centres in diamond nanostructures, and report linewidths comparable to naturally occurring centres

The key to exploiting quantum materials for applications is the control of their properties. This Review discusses strategies to externally modify their properties on demand.

The leading proposals for converting noise-resilient quantum devices from memories to processors are compared, paying attention to the relative resource demands of each.

Quantum communications will be used to transmit entanglement and secure keys, but it is important to estimate their optimal transfer rates. Here the authors compute the fundamental limit of repeaterless quantum communications for the most relevant practical scenario.