The most popular Physics Today articles of 2020

This year’s most-read articles on Physics Today‘s website reflect the important issues we grappled with in 2020. Among the topics covered in the pieces on our top 10 list: confronting racism in the physical sciences and exploring the many impacts of the global pandemic.

1. Graduate departments move away from GREs (published online 9 July)

In response to the COVID-19 pandemic, many physics and astronomy graduate programs, including those at Harvard, Cornell, and Caltech, temporarily dropped the requirement for applicants to submit scores on the general GRE and the GRE physics subject test. Access and cost were the major reasons behind those decisions, considering the closing of testing centers and job losses in the economic downturn. As Dalmeet Singh Chawla reported, concerns over equity had already driven some schools to disregard GRE test scores in the graduate application process. Some department leaders surmise that the pandemic-driven policy changes will further illustrate that bypassing test scores aids in recruiting talented, diverse groups of students.

2. Helium shortage has ended, at least for now (published online 5 June)

“The coronavirus pandemic may have deflated uncounted birthday celebrations,” wrote editor David Kramer, “but that’s been good news for physicists and chemists who need an assured supply of helium.” With helium demand for party balloons and industrial processes down due to the pandemic, the global helium supply crunch of the past few years abruptly ended. The increased availability aided researchers whose labs depend on the gas for superconducting magnets and other purposes—yet helium’s cost remained surprisingly high.

3. Commentary: Disentangling anti-Blackness from physics (published online 20 July)

University of California, Berkeley, physicist Charles D. Brown II’s commentary about anti-Black racism in the physics community is one of PT‘s most widely shared articles of all time on social media. It is also one of the most important. Brown detailed the racism he has faced as an undergraduate, graduate, and now postdoc. He cited statistics on the paucity of Black people in physics and walked readers through studies that explored the impacts of racial bias and microaggressions. “Black physicists at all levels, undergraduate through faculty, face bias and racism that form powerful barriers to their careers and make it exceptionally difficult to persist, let alone thrive,” he wrote. Brown concluded with a list of several concrete steps that are needed to address the underrepresentation of Black physicists.

Three months later, Brown co-organized #BlackInPhysics Week, an effort dedicated to “celebrating Black physicists, amplifying their voices, and making Black role models more visible, thus revealing a more complete picture of what a physicist looks like.” As part of that effort, PT and Physics World published a series of seven essays that addressed different aspects of being a Black physicist. In advance of the week, editor Toni Feder interviewed 14 Black physicists about their work and their experiences in the physical sciences community.

4. Gravitational-lensing measurements push Hubble-constant discrepancy past 5-sigma (March 2020 issue, page 14)

Over the last few decades, astronomers have applied two approaches to measuring the value of the Hubble constant, a measure of the present rate of the universe’s expansion. By analyzing the cosmic microwave background radiation with probes such as the European Space Agency’s Planck, researchers have homed in on a value of 67.4 ± 0.5 km/s/Mpc. The alternative method, which measures the distances to various astronomical objects and their recessional velocities, has closed in on a value of 74.0 ± 1.4 km/s/Mpc. In March editor Johanna L. Miller reported on a new Hubble constant determination based on a third method: analyzing quasars whose light undergoes gravitational lensing by a massive foreground galaxy. The result, 73.3 + 1.7 − 1.8 km/s/Mpc, agrees well with the distance/velocity method and deepens the mystery as to whether a systematic error or new physics is behind the discrepancies among the various Hubble constant measurements.

5. An atomic physics perspective on the kilogram’s new definition (May 2020 issue, page 32)

Last year the General Conference on Weights and Measures introduced new definitions for some of the SI fundamental units. The most noteworthy change was to the kilogram, whose mass is now defined not by a chunk of metal in France but by a fixed frequency standard. In May physicists Wolfgang Ketterle and Alan Jamison explained how the new kilogram definition is intricately tied to atomic physics.

6. World’s physics instruments turn their focus to COVID-19 (May 2020 issue, page 22)

Although many labs suspended basic research in March due to the pandemic, some physical science facilities remained open to conduct research on the novel coronavirus. In May editor David Kramer examined the crystallography and cryoelectron microscopy work at light sources around the world to determine the structure of the virus.

7. Hubble‘s 30-year legacy (published online 1 April)

The Hubble Space Telescope was shuttled into orbit on 24 April 1990. Over the ensuing 30-plus years, the telescope has made hundreds of thousands of observations that have captured awe-inspiring images and led to many important discoveries.

To commemorate the telescope’s three decades in space, PT published a sky map filled with all the locations the workhorse instrument has scoured. Versions of the map, which was created for PT by astronomer and data visualization designer Nadieh Bremer, appeared online and on the center spread of the April 2020 magazine. Another infographic (part of it shown above) categorized the cosmic objects that astronomers have studied with Hubble‘s help.

8. Negative carbon dioxide emissions (January 2020 issue, page 44)

Combating climate change may require not only cutting carbon dioxide emissions but also removing greenhouse gas from the atmosphere. In the January cover story, editor David Kramer explored the potential of negative emissions technologies such as reforestation, improved forest management, bioenergy with carbon capture and storage, and direct air capture.

9. Academics to stage Strike for Black Lives, ShutDownSTEM on 10 June (published online 8 June)

Less than three weeks after the killing of George Floyd in Minneapolis, thousands of academics canceled their classes, meetings, and other normal business on 10 June to dedicate themselves to protecting the lives of Black people. The Strike for Black Lives was the idea of physicists Chanda Prescod-Weinstein and Brian Nord. Along with physicist Brittany Kamai of the #ShutDownSTEM initiative and other organizers from the physical sciences community, they encouraged academics to go beyond holding seminars about diversity and take swift action through efforts such as participating in a protest or calling government leaders. Organizations including the American Association for the Advancement of Science, the American Institute of Physics (which publishes Physics Today), and arXiv also participated in the day of action.

10. Does new physics lurk inside living matter? (August 2020 issue, page 34)

“Asked whether physics can explain life, most physicists would answer yes,” wrote Arizona State physicist Paul Davies. “The more pertinent question, however, is whether known physics is up to the job, or whether something fundamentally new is required.” In his August feature article, Davies explained the importance of the concept of information in understanding living things and how information might serve as a bridge between physics and biology. He also explored whether known physics can explain forms of life both known and unknown.