As we close out the year and look ahead to the next, we take this opportunity to reflect on the groundbreaking research findings that emerged from Caltech in 2023. From furthering humanity's knowledge of and response to viruses, to refining the use of autonomous technologies, to leveraging advanced instrumentation to bring greater clarity on our universe and our place within it, Caltech continues to powerfully and meaningfully shape understanding of and interaction with the world. Here are some highlights.
Shaking and Quaking Earth and Moon
New insights into earthquake physics that could improve early warning systems emerged from the use of existing underground fiber-optic cables, while a study of earthquake swarms on the eastern side of the Sierra Nevada mountains in California led researchers to conclude that the Long Valley caldera, the remains of a volcanic eruption occurring 760,000 years ago, is simply settling from the effects of the ancient event and not heading toward another one.
Far more distant quakes—on the Moon—were examined using data from seismometers placed by Apollo astronauts on the lunar surface five decades ago. With the help of machine learning, researchers showed that the Moon shakes more often and more predictably than Earth, principally because of the extreme swings of temperature experienced by its atmosphere-less surface. Along with these "thermal" moonquakes, regular moonquakes were found to occur each morning, caused by vibrations of the abandoned Apollo 17 lunar lander structure as it expands and contracts with changes in surface temperature.
The theory that the Moon itself is the result of a collision between Earth and another planetary body—called Theia—gained support from Caltech researchers, while a modeling study suggested our solar system's inner planets and the moons of the outer planets, as well as numberless "super-Earths" scattered across the universe, may all be the result of a single mechanism of rocky planet formation that takes place in a narrow band around stars or planets, where competing forces turn vapor into solids.
Surveying the Cosmos and Finding Exoplanets, Two-Faced Stars, and Gravitational Waves
Thanks to spectral emission data obtained by the Caltech-led Keck Cosmic Web Imager, located at the W. M. Keck Observatory atop Maunakea on the island of Hawai'i, we are able to view the cosmic web, streams of gas-feeding galaxies that are faint and therefore difficult to visualize, with greater precision than ever before. Caltech teams unveiled a hot gas giant planet about the size of our Jupiter, located some 12,000 light years away, that is being devoured by its sun (just as our Sun will consume Mercury, Venus, and probably Earth, in 5 billion years). Also discovered was a highly unusual white dwarf star that shows two very different faces to Earth-based telescopes as it rotates on its axis every 15 minutes, one composed primarily of hydrogen and the other of helium.
The Nanohertz Observatory for Gravitational Waves (NANOGrav), using data from radio telescopes that monitor dead stars known as pulsars, provided Caltech astronomers with increased confidence that in addition to the supermassive events that produce gravitational waves that can be detected by LIGO (the Laser Interferometer Gravitational-wave Observatory located in Hanford, Washington, and Livingston, Louisiana), there is a background hum, or slow-rolling sea of gravitational waves throughout the universe. For its part, LIGO extended its observations beyond the quantum limit using a technology called "squeezing" that allows quantum noise to be manipulated to improve detection and analysis of incoming gravitational waves.
Much closer to home, the basement of the Cahill Center for Astronomy and Astrophysics on the Caltech campus has served throughout 2023 as the site for testing the instrumentation of the SPHEREx (Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer) space telescope, scheduled for launch in 2025. SPHEREx will map the entire sky at infrared wavelengths.
Understanding Ourselves Through Modern Science and Ancient Documents
Sodium is a key nutrient for humans, but there can be a fine line between consuming too little or far too much. This year, Caltech biologists pinpointed the areas of the brain that give us an appetite for salt when we need it and the ability to tolerate high levels of salt in food and water. They also used machine learning to gain insight into the unique neural mechanisms of anger and our perception of beauty in art.
Despite their promise and interrogatory power, new technologies cannot probe the behavior of people who lived centuries ago. To that end, a Caltech historian developed a method to learn more about the ordinary people of early medieval Europe using documents collected by ecclesiastical authorities of the time that record economic transactions, marriages, divorces, inheritances, disputes, and more.
Improving Human Health Through AI, Wearable Sensors, and Artificial Embryos
In 2023, Caltech researchers continued their quest to improve modern medicine and the human condition through a variety of methods, including artificial intelligence (AI), computer models, wearable sensors, cutting-edge imaging technology, and more.
Caltech researchers and colleagues presented a new way to use AI to help surgeons evaluate and develop their performance, while Caltech medical engineers further enhanced the capabilities of wearable sweat sensors, which can now monitor estrogen and C-reactive protein (a marker for inflammation) levels, and developed a "smart" bandage that promises to improve chronic wound care by monitoring indications of inflammation or bacterial infection.
An embryo-like model made from stem cells that mimics the second week of human embryo development may soon offer new insights into why some pregnancies fail, where certain defects and diseases emerge, and also help scientists figure out how to develop synthetic human organs for transplant.
At smaller scales, Caltech researchers investigated the mechanisms by which a particular type of bacteriophage (a tiny virus that targets bacterial cells) called φX174 escapes its bacterial host and successfully infects and destroys additional bacterial cells. This work could lead to new treatments for bacterial infections that are resistant to existing antibiotics colleagues. Researchers developed a new molecule-imaging apparatus to visualize materials at the single-molecule level, and devised a new drug delivery platform using ultrasound and gas vesicles that shows promise for targeting chemotherapy more directly against cancer cells.
On the COVID-19 front, Caltech researchers developed a more sensitive at-home COVID-19 antigen test with a technology that can be utilized to design tests for other pathogens, and combined the two different techniques used in current COVID-19 vaccines—mRNA technology and protein nanoparticle technology—to make a potent hybrid vaccine. In other work, biologists presented new insight into the biological processes of the human immunodeficiency virus (HIV) at the atomic scale.
Heat Waves, Air Pollution, and Solar Power from Space, Oh My!
Caltech continues to investigate the drivers behind climate change and to develop alternative sources of energy. Since 2014, California state law has required cutting methane emissions, but a Caltech study found those emissions are decreasing in the Los Angeles area much more slowly than utility companies have estimated. In other work, researchers showed that LA County's recent record-breaking heat waves hit low-income areas harder than more affluent ones, and developed new techniques for understanding the chemistry involved in the naturally occurring conversion of volatile organic compounds into aerosols that will allow scientists to better predict the impact of aerosols on the environment and on human health.
On the green energy front, in January 2023, the Caltech Space Solar Power Project (SSPP) launched an instrument into orbit around Earth that harvests solar power and wirelessly transmits it to Earth. In the spring, this instrument, the Space Solar Power Demonstrator (SSPD) was the first to successfully receive solar power and transmit it to Earth, where it was detected by a receiver on the rooftop of the Gordon and Betty Moore Laboratory of Engineering on Caltech's campus.
Evolving Optics, Color-Changing Plastics, and Mighty Morphin' Robots
Caltech scientists and engineers identified, engineered, and designed a series of new devices and materials that have the potential to reshape our world, including the creation of polymers that change color when stress is applied to them, making the location of strain visible; metals 3D printed at the nanoscale with messy atomic arrangements that surprisingly make them three-to-five times stronger than similarly sized materials with more orderly structures; and 3D-printed nanoscale optical devices that are so small they could direct different colors of light to individual pixels in a camera's image.
On a larger scale, Caltech engineers created M4, the Multi-Modal Mobility Morphobot, a bioinspired robot that is capable of eight different types of motion (including flying, rolling, and walking) and can sense upcoming terrain and select the most effective form of locomotion.
Quantum Sound, Quantum Microscopes, Quantum Erasers, and a New Center for Quantum Research
Caltech expanded its presence as a premier hub of quantum research with the summer groundbreaking of the Dr. Allen and Charlotte Ginsburg Center for Quantum Precision Measurement. The center will serve as an interdisciplinary home for precision measurement, quantum information, and the detection of gravitational waves, or ripples in space-time.
In other news concerning the quantum realm, a new method was revealed for converting electrical quantum states into sound and back again, allowing devices to store sound (which, like light, is both a particle and a wave) for future quantum computers. Other researchers doubled the resolution of microscopes through quantum entanglement, in which the respective states of two particles are linked to one another even when they are not close to one another. Entanglement is central to this year's development of "quantum erasers" that can remove certain types of errors in quantum computers.
Slithering, Swimming, and Spinning—Animal Motion by the Numbers
Finally, as phenomena in the natural world are mapped mathematically, surprising consonances are uncovered, including the discovery that when very different animals—such as snakes, single-celled organisms, and sting rays—move by changing their shape, a single mathematical algorithm can successfully describe their motion.