Cherish Those Junior Moments

When old people forget names, they apologize for having a “senior moment”. And when innovation by young people is dismissed by the “adults in the room”, the youngsters face a “junior moment”. One might naively suggest that somewhere in between these two moments lies the sweet spot for being taken seriously as “not too young and not too old”, what is professionally known as the status of an “expert”.

But in my experience, professional life is worth living for its junior moments. They hold the promise for a reboot in our thinking, not appreciated by “experts”. Once you lose interest in the thrill of junior moments, you turn professionally into “dead wood”.

The transition to “dead wood” is a matter of choice, not of biological age. I know of many old scientists who are innovative risk-takers, and a larger number of fledgling scientists who walk narrowly within the beaten path because of the peace-of-mind it brings.

Next month I will be attending a conference honoring my sixtieth birthday, organized by my former students, postdocs and collaborators in astrophysics over the past four decades. I very much hope to celebrate junior moments on that occasion. Let me mention a few examples.

By the year 2000, astronomers had identified a correlation between the mass of black holes at the centers of galaxies and the luminosity of the spheroid of stars that surrounds them. It appeared to me that any such correlation is probably the result of the black hole saturating at a mass where its powerful energy output expels the gas reservoir that feeds it, similarly to a baby shoving the food off the table once the calories consumed makes it too energetic. The self-inhibition of the black hole growth depends on the depth of the gravitational potential well that keeps the gas feeding it, similarly to the depth of a bowl confining the food in the baby analogy. This depth can be gauged through the velocity dispersion of stars. At a 2000 conference in Leiden in the Netherlands, I proposed plotting the correlation between black hole masses and the velocity dispersion of stars in their host spheroid of stars. This proposal was immediately dismissed as uninteresting or impractical by experts at the conference. Upon returning to Harvard, I attended two lectures by candidates in an assistant professor search of our department, Laura Ferrarese and Karl Gebhardt, who both presented a correlation between black hole mass and spheroid luminosity in their job talks. In my separate meetings with each of them, I suggested that they plot the correlation with velocity dispersion instead. Two months later I received an independent email from each of them, informing me that the correlation with velocity dispersion is tight and that they are about to submit an exciting paper along with their research groups on the subject. This later became the hottest result in this field for over a decade and the two teams fought fiercely among themselves for the credit of being first to derive the by now well-established correlation between black hole mass and velocity dispersion.

A couple of years later, I was on sabbatical at Princeton and recognized that imaging the motion of a “lightbulb” just outside the Innermost Stable Circular Orbit in the highly curved spacetime of a black hole could establish a new test of Einstein’s theory of gravity. I conjectured that such a light bulb could be realized naturally through a “hot spot” in an accretion disk of gas, heated through reconnection of magnetic field lines that cross each other, similarly to the flares occurring on the surface of the Sun. When I suggested this simple-minded idea to young “experts”, they dismissed the notion of a “hot spot” as unrealistic given the turbulent dynamics of gas near a black hole. They argued that any “hot spot” will quickly dissipate through turbulence or be sheared away by the rotating gas. Based on my earlier experience with the black hole correlation idea, I decided not to give up and upon my return to Harvard, I suggested this idea as a research project to a young postdoctoral fellow, Avery Broderick, who just arrived at our newly established Institute for Theory and Computation. In the subsequent few years, Avery and I wrote a series of papers on the observable consequences (light curves, time- dependent images and polarization maps) of a simple-minded “hot spot” moving around the largest black hole in the sky, Sgr A*. This black hole resides at the center of the Milky Way galaxy and weighs four million Suns. We also made the first predictions for the image of the black hole in the giant elliptical galaxy M87, which was observed a decade later by the Event Horizon Telescope (EHT). Our predictions, summarized in an extended Scientific American article in 2009, laid the theoretical foundation for the EHT image. Four years ago, a team of astronomers at the Max Planck Institute for Extraterrestrial Physics in Germany, led by Reinhard Genzel and spearheaded by Frank Eisenhauer, announced the observational discovery of hot spots moving in a circle on the sky for three flares near the ISCO of Sgr A*. Their observational data, confirming my theoretical idea from 1.5 decades earlier, was obtained with the GRAVITY instrument on the Very Large Telescope Interferometer in Chile.

Another junior moment from three years ago occurred when my student, Amir Siraj, and I discovered the first interstellar meteor in the CNEOS public catalog, dating back to an impact by a meter-scale object near Papua New Guinea on January 8, 2014. When our paper was written in March 2019, meteor experts blocked its publication for three years, arguing that our conclusion cannot be trusted since scientists have no access to the uncertainties in the government data that underlined the CNEOS catalog. Last month, the Office of US Space Command confirmed to NASA the validity of our conclusion about the interstellar origin of CNEOS 2014–01–08 at the 99.999% confidence. This makes CNEOS 2014–01–08 the first major interstellar object discovered in the solar system, predating `Oumuamua by almost four years. The newly released light curve of its fireball implies that it was tougher than iron meteorites.

A week ago, I came up with a novel idea for confirming the never-detected “memory effect” from gravitational waves, using the Moon-Earth system as the detector. Distinguished physicists who for decades specialized in Lunar Ranging and other tests of Einstein’s gravity in the Solar System, like Eric Adelberger, Irwin Shapiro or Rai Weiss, were all impressed and inspired by the innovative idea. But younger arXiv moderators chose to block its public posting, arguing that the manuscript is too short. Since another post of mine - about the maximum possible flux from a cosmological source as a test of new physics, was also blocked by the same argument, I came up with the solution of combining the two into a single manuscript. This avoided the gatekeepers restriction and made my two innovative ideas visible to the scientific community.

As long as one keeps innovating, these junior moments never stop.

In conclusion, if the organizers of my birthday conference will ask me to blow out 61 candles on a cake and make a wish, I have a single wish in mind … that these junior moments will never stop.


Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He chairs the advisory board for the Breakthrough Starshot project, and is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021.



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Avi Loeb

Avi Loeb is the Frank B. Baird Jr Professor of Science and Institute director at Harvard University and is the bestselling author of “Extraterrestrial”.