Detecting the “God Particle”: July 4, 2012
In 1964, theoretical physicists predicted the existence of a particle we now call the Higgs boson. Its existence would help explain why particles—unlike photons—have mass. In 2012, scientists at CERN finally made the long-awaited observation of the elusive Higgs boson. The ATLAS and CMS collaborations independently detected a particle with Higgs-like properties using the Large Hadron Collider. As expected, the particle weighed in at 125 gigaelectronvolts. The confirmation came almost 50 years after its prediction, for which theorists François Englert and Peter Higgs were awarded the physics Nobel Prize in 2013. The experimental discovery of this particle is strong evidence for the existence of a Higgs field, which, in combination with the Higgs boson, “gives” other particles mass by transferring energy to them through a process known as the Higgs effect. This allows massive particles to interact gravitationally. Without it, particles would fly around freely at the speed of light and never interact.

First Discovery of Naturally Occurring Topological Insulators: 2013
Topological insulators are special materials that can conduct electricity on the surface but are insulating on the inside. These materials allow for the manipulation of electron spin and therefore have potential applications in “spintronic” devices that rely on electron spin instead of charge, as well as quantum computers that encode information in spin-based qubits instead of bits. They are a recent discovery, predicted in 1987 and synthesized for the first time in 2007. At that time it wasn’t clear that naturally occurring topological insulators existed. But after kawazulite was found in a Czech goldmine and processed into nanoflakes in the lab, scientists at Germany’s Max Planck Institute found that the mineral—made of bismuth, tellurium, selenium, and sulfur—behaves as a natural topological insulator. This is exciting not just because it is naturally occurring, but also because it may be a better candidate for some applications than synthetic topological materials due to its near-perfect crystal structure.

Gravitational Waves Shake Things Up: February 11, 2016
Einstein’s theory of general relativity was corroborated once again when the LIGO and Virgo collaborations announced the first detection of gravitational waves. These ripples in space-time were detected on September 14, 2015, at the LIGO detectors in Livingston, Louisiana, and Hanford, Washington, and announced in February the following year. Scientists traced the source of the waves to the Southern Hemisphere. They were probably generated by the interaction of two black holes, estimated to be around 29 and 36 solar masses. The black holes likely circled each other, releasing energy through ripples in space-time before eventually collapsing into each other and releasing a tremendous amount of energy. This is the signal LIGO picked up. Scientists have since turned the signal into an audio recording, enabling you to “hear” the collision of the black holes. This work opens the world to a new form of observational astronomy through gravitational waves, helping to usher in the era of multimessenger astronomy—an approach that coordinates and integrates observational data collected by different types of instruments to create a more holistic picture.

Cassini Space Probe Sends Its Last Message: September 15, 2017
The world said goodbye to the Cassini spacecraft as it plunged into Saturn’s cloudy atmosphere in the fall of 2017, turning into a meteor from the high pressure and heat. Although it started with 6,900 pounds of fuel, Cassini crashed into Saturn with less than 90 pounds left. Over nearly 20 years, the spacecraft relayed important findings about Saturn and its surrounding moons to us here on Earth. Not only did Cassini discover six new moons, it also discovered hydrocarbon-containing lakes on Titan, water jets spraying from Enceladus, and the possibility of a large saltwater ocean under the ice of Enceladus. The water jets revealed the presence of hydrogen gas produced through chemical and thermal interactions, which on Earth creates an ideal environment for microbial life. Cassini was sent to its death to protect these potentially life-harboring moons from contamination, ensuring that the moons of Saturn will be a location of interest for scientists in the future.

Likely Source of High-Energy “Ghost Particles” Identified:
July 12, 2018
Neutrinos are often called “ghost particles” because they are nearly massless particles with no charge and rarely interact with matter. There are millions of neutrinos passing through you every day. Most of the neutrinos scientists have detected are relatively low energy and are produced by the sun, supernovae, and collisions between cosmic rays and particles in the Earth’s atmosphere. Astronomers have also detected a few surprisingly high-energy neutrinos from unknown sources. On September 22, 2017, the IceCube detector in Antarctica observed a neutrino with an energy of 300 trillion electronvolts. The project immediately asked multiple telescopes to look at the patch of sky where the neutrino came from to see if they could identify a likely source for the high-energy particle. Those observations suggest that the neutrino was produced in a galaxy four million light-years away, with a rapidly spinning supermassive black hole at the center—otherwise known as a “blazar.” This collaborative effort is an amazing example of what is possible with multimessenger astronomy.

The First Picture of a Black Hole—Or at Least the Matter It’s Ripping Apart: April 10, 2019
Captured by the Event Horizon Telescope, an array of eight ground-based radio telescopes around the world, the first-ever image of a black hole and its accretion disk shows the center of Messier 87, an elliptical galaxy 55 million light-years from Earth. The supermassive black hole located at the center, weighing in at 6.5 billion solar masses, casts a shadow on its surrounding accretion disk, shown in bright orange. Similar to how the sun bends nearby starlight during a solar eclipse, this image shows that there are objects massive enough to warp the fabric of space-time so that even light cannot escape. The image supports Einstein’s theory of general relativity and also allowed scientists to measure the Schwarzschild radius of the black hole and calculate its mass. The result agreed with existing estimates from a more established method based on orbiting stars. This suggests that the image-based technique is a valid method of mass determination.

Honorable Mentions
The past decade has been filled with innovative and important developments in physics and astronomy. Many not included in the above list still deserve to be mentioned. For example, in 2014, Aephraim Steinberg and his colleagues at the University of Toronto demonstrated that quantum information can be compressed. They were able to take the information stored in three identical quantum bits, or qubits, and represent it in two nonidentical qubits. This is an important step on the path to creating efficient quantum computers, because classical data compression methods don’t work on quantum information.

In 2015, the successful landing and recovery of Falcon 9 flight 20 by SpaceX marked significant progress toward reusable rockets. It was the first time that the first stage of a multistage rocket successfully returned to Earth and landed upright. SpaceX went on to relaunch the first stage in March 2017 and expressed a goal of eventually reusing rockets more than once in 24 hours.

Finally, this decade delivered an exciting science experience for many people across America. On August 21, 2017, a total solar eclipse spanned the width of the entire continental United States—something that hadn’t happened for 99 years. The path of totality crossed 14 states, and all parts of the country had views of at least partial totality. The next event of this kind will take place in April 2024, when the path of totality will cross 12 states.

Did we leave out any developments that you think were among the most noteworthy of the 2010s? Share your thoughts by emailing sps [at] aip.org.