Feynman said, “You know what? I had not thought of it but I think you are right.”
“You can imagine how thrilled and elated I was upon receiving this imprimatur from Feynman,” Srivastava, now 83 and still active in research, told ThePrint in an interview over email and the phone.
Since that meeting, Srivastava has solved the mystery of cosmic rays originating from the centre of the Milky Way galaxy, discovered new phenomena about black holes, and devised a technique that can revolutionise cancer care. He has not only taken inspiration from physicists such as Feynman and nuclear physics pioneer Ernest Rutherford, but also the father of evolution, Charles Darwin, and science fiction writer Isaac Asimov.
Born in Gorakhpur in 1941, he was a prodigy who completed high school at 12, his B.Sc. by 16, and M.Sc. by 18. He then secured a Ph.D. in physics from Indiana University at 23. By 24, he was a postdoctoral fellow and instructor at University of California and then moved to Northeastern University as an assistant professor. He is now professor emeritus.
Srivastava has thrice been on the Nobel Prize Nominating Committee, solicited by the Royal Swedish Academy. He is also a fellow of the American Physical Society. He has written numerous papers on cosmology, black holes and particle physics and, at the same time, tried to apply nuclear physics for real-world solutions.
Most recently, he has led research teams that have published papers on two diverse subjects. One of them adds to existing knowledge about the phenomena on the surface of a black hole. The other paper proposes a novel method for generation of medical radioisotopes, a class of chemicals that are becoming increasingly important in diagnosis and treatment of conditions including cancer.
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A special technique to make radionuclides
A personal loss motivated Srivastava to conduct research in nuclear medicine. His niece, Professor Meenakshi Narain, whom he described as a “brilliant physicist” at Brown University, passed away due to cancer.
“I was her mentor. She would come to Boston for treatment. And even though it was very painful for both of us, I used to say, ‘Both of us are nuclear physicists. We should be able to discuss the matter objectively’,” Srivastava recalled.
“I would talk to her about cosmology and nuclear physics. Towards the end, she used to ask me to write little notes which she could share with her students.”
In radionuclide therapy, radioisotopes or radionuclides are administered to cancer cells to kill them. These radioactive substances can be produced through nuclear fission (breakdown of the nucleus), neutron activation, or with the help of cyclotrons that accelerate charged particles (usually protons) that are then used to bombard target materials at high speed and produce radionuclides.
Leading a team of scientists from Italy, Switzerland, and the US, Srivastava proposed a novel method for the generation of medical radioisotopes using electron accelerators rather than proton accelerators. Their results were published in 2021 in the journal Exploratory Biotechnology Research, and separately by the World Scientific in 2021 as ‘Proceedings of the 19th Lomonosov Conference, Moscow State University.’
Existing procedures using nuclear reactors and proton accelerators can also generate radioisotopes, but Srivastava’s finding is a game-changer because electron accelerators are already present in most cancer hospitals. Most alternative methods require nuclear reactors, many of which have been shut down around the world.
Electron accelerators are used for radiation therapy using beams such as X-rays. Srivastava, John Swain, Allan Widom, Georges de Montmollin, Pierre-Alain Tercier, Olivier Pisaturo, and Frederic Mieville repurposed these to allow the devices to make radioisotopes.
This allows for local production, saving time and money. It would also ensure greater efficiency of radionuclides because nuclear medicines are time-sensitive and have short half-lives, and spending hours to have them flown from different places drastically reduces their potency.
“Imagine that an oncologist at a hospital needs to procure a certain amount of a radioisotope to inject into a cancer patient as a cure,” Srivastava explained. “The first way is that the doctor can order it to an outside company which produces the radioisotope locally, where the company is located, and thus, the nuclear medicine has to be transported to the hospital. This requires transport and expense.”
“The second way is to use a proton accelerator, which may be present at the hospital, and can locally produce the radioisotope. Thus, after the radioisotope is separated from its nucleus, the doctor can use it very soon after its production. The problem is that most oncological hospitals do not have a proton accelerator. So this method is not an option for them,” Srivastava said.
Proton accelerators are not only costly and potentially unsafe but also work at very high energies, occupy a lot of space, and require specialised expertise. Electron accelerators, meanwhile, do not come with these drawbacks.
Moreover, while the effect of radioisotopes produced using electron accelerators would wear off in a week because of the short half-lives of the nuclear medicines, those produced using proton accelerators or nuclear reactors may leave an unwanted radioactive element in the patient’s body for over a month—which can be fatal.
Srivastava and his team generated ⁶⁴Cu (Copper-64), ⁶²Cu (Copper-62), ¹⁸F (Fluorine-18), and ¹¹C (Carbon-11), all of which have short half-lives. These are used in medical imagery, with Fluorine-18 being the most sought-after radioisotope.
It began with a small hospital experiment
It took Srivastava and his team six years—from 2015 to 2021—to devise this technique. They worked at the radiation oncology department of the Swiss Fribourg hospital.
“We worked with Pierre-Alain Tercier of the radiation oncology division. He had training in nuclear physics before he became a doctor. That is why he was able to immediately understand our goal. I told him, ‘Buy some copper pieces, put them in front of your machine and see what you get’,” Srivastava said.
The researchers irradiated a sample of pure copper using a 22 mega electron volt electron accelerator and observed that two copper radioisotopes were produced. Their measured half-lives were found to be within two percent of their expected values, indicating that the experiment was a success. Similarly, they produced Fluorine-18 and Carbon-11.
“The first place where I presented my findings was in front of the radiation oncology department of the Swiss Fribourg hospital,” Srivastava said.
Thus, the results confirmed the hypothesis that upon suitable modifications, electron accelerators can be used to produce the required amounts of radionuclides locally, when needed, the study said.
“It has taken us more than 10 years of work and five years to convince the patent-granting authorities to give us the patents,” Srivastava said. “We want the attention of companies like Siemens, General Electric and Varian, and show them that this is a cost-effective, fast and local solution. I intend to talk to people in the governments of different countries who can make such machines.”
The new technique has earned the team five patents, including an international one (February 2020), a Chinese patent (December 2024), one from the European Union (January 2025) and, most recently, an Indian patent (March 2025).
Asked about clinical trials, the professor said that now, with the Indian patent granted, he is hoping for an interview with the Indian health secretary to explain his research.
“A small company, next door to the Swiss Fribourg hospital, which makes chemotherapy medicines, used their method to produce radioisotopes, tested the medicines on animals, and got promising results,” Srivastava added.
Solving a cosmic mystery
The young Indian who attended Feynman’s 60th birthday party and received an imprimatur from his idol went on to become one of the leading professors of quantum physics at the University of Perugia six years later.
At the Italian university, where he taught a course on black holes and quantum theories from 1984 to 2012, Srivastava dug into Albert Einstein’s theory of general relativity, which states that gravity is the curvature of spacetime caused by mass and energy.
“I learnt Einstein’s theory of general relativity from Professor Václav Hlavatý, who, being Jewish, had hidden himself for several years in an unused barn to avoid being sent to an extermination camp during the Second World War,” Srivastava said.
“He had no books or notes with him, so he had to reconstruct everything by himself. Thus, his lectures had unusual clarity and simplicity. Convinced by his example, I have never taken a piece of paper to any of my classes for over five decades.”
Srivastava and Allan Widom, a colleague at Northeastern University, found the solutions to two equations of the theory of general relativity.
“The first concerns the confinement of magnetic fields over cosmic distances by the Einsteinian gravitational field. This provided an understanding of Bode’s law for magnetism,” Srivastava said.
“The second exact solution helped understand the presence of cosmic filamentary structures that exist in the sky.” He has now applied these solutions to particle physics to see if this branch plays an important role in structures described by general relativity, which talk about gravitation. Indeed, his team has found a connection.
In the latest paper on black holes, which appeared online in the gravitation and cosmology section of arXiv in January 2025, and is under review for publication in the journal Universe, Srivastava, along with Orlando Panella, Simone Pacetti and Giorgio Immirzi, have found an interplay between particle physics and general relativity.
The team studied Sagittarius A*, the black hole at the centre of the Milky Way galaxy. Using a concept called the gravitational maximum force principle—which suggests that gravitational force is the strongest and reaches a finite limit when objects are massive and close to each other, and becomes weak with distance—the team proved mathematically that the entire mass of a black hole lies on its surface.
The study said that when all mass is distributed over the horizon surface of a supermassive black hole, which is mostly present at the centre of a galaxy, the distance between nuclear particles, say protons, is reduced to a great extent. “This is when nuclear particle physics kicked in through quantum mechanics,” Srivastava said.
That inter-particle distance can become very small means that the mean energy of the particles can become extremely high, the study says. This is due to Heisenberg’s uncertainty principle, which states that we cannot know both the exact position and momentum (energy) of a particle at the same time, implying that the more precisely we know about one, the less we know about the other.
Srivastava and his team used quantum nuclear theory—which uses quantum mechanics to understand the behaviour of subatomic particles—and calculated that protons on the surface of Sagittarius A* reach energy levels in the peta electron volt (PeV) range, or quadrillion (10¹⁵) electron volts.
Srivastava calls these high-energy nuclear particles on the surface of Sagittarius A* ‘PeVatron’ protons. PeVatron is a source capable of accelerating high-energy particles.
Incidentally, the High-Altitude Water Cherenkov (HAWC) Observatory—a facility located on the edge of the Sierra Negra volcano in Mexico that observes gamma rays and cosmic rays—has detected high-energy photons originating from Sagittarius A*. In September 2024, they published these results, but lacked a theoretical explanation behind the phenomenon, Srivastava said.
He said the HAWC collaboration provided experimental proof that our galactic centre is producing high-energy cosmic rays, while his team explained the theory.
“Thus, we now have theoretical and experimental proof that very high-energy cosmic rays in our galaxy originate from the surface of the massive black hole at the centre of our Milky Way,” he added.
A final breakthrough
Between 1976 and 2016, Widom and Srivastava co-authored several papers in journals, such as Physica Scripta and Proceedings of Science (PoS), exploring energy distribution mechanisms for very high-energy nuclear cosmic ray particles. They hypothesised that compact neutron stars could be generating these high-energy protons.
Widom passed away in 2023.
Srivastava realised the connection between gravity and nuclear particle physics, and deduced that the surface of Sagittarius A* is an ideal mass conductor because all high-energy protons are concentrated on its surface. This solved the mystery of high-energy cosmic rays.
“On the other hand, our team theoretically proved that a proton PeVatron is generated as a result of Einsteinian gravitation concentrating all mass on the surface of a black hole, and nuclear particle physics dictating that the energy between two protons in such configurations must be on the PeVatron scale,” the professor said.
“The proton PeVatron on the surface of Sagittarius A* is 100 times more energetic than the Large Hadron Collider (LHC) at CERN, Geneva, the world’s largest and most powerful particle accelerator,” he added.
When Srivastava asked 1999 Physics Nobel laureate Gerard ‘t Hooft if there was mass inside a blackhole, he told him that all the action of a black hole is on the surface.
“And this is what our team proved—we came to the conclusion that there is no mass at the centre of a black hole. The Hawking-Penrose theorems state that the laws of physics break down at the centre, and since there is no mass in the middle of a black hole, these colossal mammoths do not suffer the anomalies dictated by the theorems,” Srivastava said.
“I found it most satisfying that our results about black holes were almost the same as those by ‘t Hooft, one of our greatest living theoretical physicists, albeit using very different means.”
Black holes or ‘bright holes’?
Srivastava believes black holes should ideally have been called “bright holes”. To explain why, he cited the work of the HAWC collaboration, which tried to find out what generates high-energy photons from the centre of Sagittarius A*.
“It interpreted that such photons are generated through the interaction between gaseous particles near the surface of Sagittarius A* and PeVatron protons on its surface,” Srivastava said.
“The energy of these photons is about 100 times less than that of the protons, or equal in energy to the protons of CERN’s LHC. But the collaboration did not know how and why such PeVatron protons are generated on the surface of the black hole,” Srivastava said.
He argued that since high-energy photons are emitted from the black hole, it should be termed a ‘bright hole’.
Quoting Rutherford, often called the father of nuclear physics, Srivastava said physics is the mother of all sciences. To Rutherford’s remark, “In science, there is only physics. Everything else is stamp collecting.” Srivastava added, “When used well, physics enriches any field—and is itself made richer in return.”
(Edited by Sanya Mathur)
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