The large-scale structure of the universe was set by the tiniest of forces—quantum fluctuations—during the incredibly brief period of rapid expansion that occurred just after the Big Bang. These initial moments, the only period in which both quantum and gravitational dynamics have ever significantly interacted, created a gravitational noise still visible in the primordial light that astronomers call the cosmic microwave background (CMB). In “The Unlikely Primeval Sky” (pages 352–359), Craig Hogan explores our current understanding of the CMB and the information that can be derived from it, including the fact that our cosmos is strangely smooth and surprisingly flat compared to the vast majority of likely universes. Is this a fluke, or a call for new physics? (Cover art by Illustris Collaboration.)

When HIV enters a cell, its genome (white strand, top right corner) incorporates into the cell’s genome in the nucleus. As the cell activates its genes, the virus’s genes turn on too. The cell then transcribes the viral RNA (yellow squiggles), which moves through the cell and is used to synthesize the virus’s proteins (red). As the viral RNA and proteins accumulate at the cell’s membrane, the immature viral particles bud off, taking with them pieces of the membrane and its proteins (magenta). Viral enzymes finish processing the proteins to create the HIV capsid (the protein shell that encloses the virus’s genome) leading to a fully mature virus particle. In “A Revolutionary Drug to Treat and Prevent HIV Infection” (pages 288–295), author John Raul Somoza describes the process of developing a new drug, lenacapavir, that interferes with capsid assembly and movement. (Cover illustration by David S. Goodsell, B-HIVE Center, RCSB Protein Data Bank and Scripps Research. doi:10.2210/rcsb_pdb/goodsell-gallery-047)

Unseen animals can often still be heard. That’s part of the impetus behind the growing field of ecoacoustics, which aims to measure entire soundscapes in different habitats as a way of gauging an ecosystem’s health over time. Becky E. Heath and her colleagues have been particularly interested in studying the tropical rainforests of Malaysian Borneo, as shown on the cover. But first, as Heath details in “The Ecoacoustics of Forests” (pages 224–231), they have to be able to make reliable, high-quality, directional recordings. Heath and her colleagues have been working on a spatial recording device, shown at center, which incorporates multiple microphones that each can pinpoint the direction from which a sound originates. The microphones also operate without any recording delays that would cause error in calculations of sound distance or direction. Working with animal sound databases and machine learning technologies, Heath and her team have shown that their recordings can be used to estimate species abundance in different areas. (Cover art by Beatriz Ortiz.)

Sculptor Ellen Jewett brings together zoology, botany, ecological principles, and surrealism to explore human concepts of nature as familiar and comforting but also alien and indifferent. In “Creatures Both Serene and Deeply Strange” (pages 150–155), Jewett describes to contributing editor Sandra J. Ackerman her process of creating the plants and animals in her works through meticulous research and the techniques of medical illustration. Vulpes Anima (Soul Fox), created in 2024, depicts intricate relationships among a variety of life forms, both predatory and vulnerable. Using natural, local, and recycled materials wherever possible, Jewett invites human viewers to think more about conservation and our connections with the nonhuman world. (Cover image courtesy of Ellen Jewett.)

The hippocampus is crucial to memory, which is essential to consciousness. This artist’s depiction focuses on a portion of the seahorse-shaped organ. Though not anatomically accurate, it hints at real forms, such as the dentate gyrus (lower left), an adaptive neural circuit vital to learning, memory, and emotional regulation. A thready, high-speed axon network links the circuit to the CA3 layer, a subunit packed with neural connections. CA3 aids in encoding episodic memories and spatial information, and helps us reconstruct memories from partial cues. In “Consciousness: The Road to Reductionism” (pages 96–103), Alan J. McComas gives a historical tour of the key brain areas behind consciousness. He also explains that this organic machine often decides to act, remember, and direct our attention before we are consciously aware of those choices. (Cover art by Greg Dunn.)

Few things in life are more satisfying yet elusive than a live musical performance. For nearly a century and a half, audio engineers have designed equipment to recapture the concert hall experience, without ever fully succeeding. In “The Science of Hi-Fi Audio” (pages 32–39), John G. Beerends and Richard Van Everdingen explain that part of the problem is human subjectivity. Beerends has helped develop precise standards for quantifying the perceived quality of spoken words, but no such standards exist for music because people vary so much in their individual responses. There is also the challenge of sonic immersion: Stereo systems produce too little, while home theater setups produce too much. Beerends and Van Everdingen have collaborated on a novel loudspeaker that addresses both issues, producing immersive sound that mimics the qualities of a concert hall, while allowing listeners to adjust that sound to their own preferences. (Cover illustration by Michael Morgenstern.)