Will physics un-gender itself in the new decade?

Black holes are chunks of space from which nothing, no stuff, nor even light can escape, making them invisible by definition. Yet, we know today that they are real, for sure. And “for sure” is why Roger Penrose, Reinhard Genzel and Andrea Ghez were awarded the 2020 Nobel Prize in physics. Black holes were fancied even in the 18th century. English clergyman scholar John Michell and French polymath Pierre-Simon Laplace derived the correct formula between size and mass needed to trap light, using simple Newtonian physics. Consider this: Unless something launches at 40,000 kms/hour from earth, it will fall back and not be able to escape into outer space. If the earth were squeezed, this “escape velocity” would become higher. Squeeze it to the size of a marble, and even light, travelling at a billion km/hour would not escape — the earth would become a black hole!

But unsurprisingly such invisible objects were hard to find. Fast forward to 1915. Einstein discovered a novel way to understand gravity — that anything with mass curves the space around it, more the mass, more the curvature. Other particles with mass that approach it move because of this curvature. Karl Schwarzschild then derived a direct consequence of Einstein’s theory that was uncannily identical to the mass-size relationship for a black hole a la Michell and Laplace. With Chandrasekhar paving the way, Oppenheimer of atomic-bomb fame argued that black holes could form by the collapse of dead stars. Mathematically, however, the curvature of space at collapse became “infinite”, which was disquieting. Even Einstein was unconvinced, and black holes were relegated to being mere mathematical constructs.

The scene transformed in the ’60s with the discovery of quasars, extraordinarily distant pinpoints that each spewed more light than the sum total from the billions of stars in our Milky Way or Andromeda. No star clusters nor exploding stars in concert could fit the bill. Only matter swirling into black holes as heavy as a million Suns, thereby heated to humungous temperatures, could explain quasars. So black holes quasars had to be.

The quasar discovery impelled Penrose, a mathematical physicist, to apply his extraordinary geometric intuition to rescue black holes from the land of mathematical artefacts.

He showed that the complete collapse of dead stars to infinite curvature was inevitable, and that the spherical “surface” of black holes a la Schwarzschild and Oppenheimer, constituted a “horizon of no return” through which the star proceeded to final collapse. Inside this horizon, all directions led to the future with no turning back, until an “end of time” at the centre of the black hole. Although new physics was admittedly needed to fully grapple with this “end of time”, because the horizon “shielded” the central infinity from the observer, the deep disquiet with black holes had ended.

To be sure, however, stars whizzing around a black hole had to be actually seen. In the ’90s Genzel and his team used infrared light to penetrate the dust shroud around the most promising arena, viz., the heart of our Milky Way. A giant black hole was highly likely. But earth’s atmosphere makes stars twinkle, and dance around annoyingly on telescope sensors. The resultant blurring confounds measurements of their speeds. Ghez used the enormous Keck Telescope which could gather lots of light in short exposures, and beat the dancing around, to obtain irrefutable evidence for a black hole. Years on, both teams leapt forward with adaptive optics that corrected twinkling in real time. They got precise elliptical orbits of the stars in the heart of our Milky Way. For sure, a black hole four million times heavier than our Sun sits there — the richly deserved prize-winning discovery.

Right after the announcement, much media comment ensued about Ghez being only the fourth woman to win the physics Nobel. If physics were indeed the “most objective” discipline that it prides itself to be, and if it indeed recognises seekers of truth based purely on the merits of their argument, then the laureate’s gender would be irrelevant. Unfortunately however, as data show, the physics meritocracy is flawed. Also, while the first woman physicist laureate was Maria Skłodowska Curie (1903), the next waited six decades (Maria Goeppert-Mayer, 1963) and the third, another 55 years (Donna Strickland, 2018). Many more have been denied the prize despite their transformational discoveries (Lise Meitner, Chien-Shiung Wu, Vera Rubin, Jocelyn Bell, and India’s Bibha Choudhuri, to name just five). Ghez said, “I grew up hearing the word ‘No’ all the time. You are a girl, you can’t do it… no way you can get…into CalTech…” — ironic but so typical of women physicists’ experiences worldwide. Little wonder that Ghez dedicated her PhD dissertation in 1993 to “…all the women scientists I have known.” Physicists need to internalise that being allowed to follow one’s passion at taxpayers’ expense is a privilege.

All accomplishments are a consequence of that privilege, and from that follows the responsibility to correct the injustices. That responsibility is not a “pressure”, but an honour and opportunity to build a healthier professional climate. That two women in two years got the physics Nobel is doubtless heartening and perhaps a harbinger. But does it symbolise a tipping point? Will the profession un-gender itself in the new decade?

Prajval Shastri is an astrophysicist from Bengaluru whose core research interest is the empirical investigation of giant black holes that are found in the centres of distant galaxies

The views expressed are personal

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