04/01/2021

Penrose's silence and the discoveries of black holes.

Imagem: Wikimedia Commons

Some say that silence can be the best answer to problems. For the mathematical physicist Roger Penrose, a brief moment of calm was enough to bring the scientific inspiration that changed our view of the universe. In 1964, during a meeting with his old friend and fellow British cosmologist Ivor Robinson, the two paused their lively conversation to cross the streets of London. At that moment, Penrose's mind traveled 2.5 billion light-years through the vacuum of outer space to the mass of a rotating quasar.

In his imagination, he fantasized about how gravitational collapse took over, pulling an entire galaxy ever closer to its center. And that brief, silent reflection led to the discovery that, last year, earned him the Nobel Prize in Physics .

Like many theoretical physicists who dedicated themselves to testing, exploring, and delving deeper into Albert Einstein's General Theory of Relativity, Penrose spent the 1960s studying the "singularity problem." The great challenge faced by specialists was to prove and test many of Einstein's predictions, especially regarding a "singularity" from which not even light could escape, known as a "black hole."

“People expected there to be a ricochet: that an object would collapse and spin around in a complicated way, and come back out again,” he told BBC Future . But discoveries have detected new, seemingly bright, distant, and very small cosmic objects, initially known as “quasi-stellar” and then shortened to “quasars.” As improbable as it seemed, each new observation pointed toward the idea that quasars were ancient galaxies about to collapse into singularities. Leading to the question: were singularities as improbable as everyone thought?

Cosmologists, astronomers, and mathematicians from all corners of the planet set out in search of a definitive theory to explain the nature of quasars. It was then that Penrose adopted a different approach from the others, seeking general solutions, basic principles, and essential mathematical structures. Although he rejected existing arguments, until Robinson's visit, the mathematical physicist had not reached a satisfactory conclusion.

It was in the silence of that afternoon in 1964, while crossing the London streets alongside his friend, that the necessary flash of inspiration Penrose needed came to him. All that energy, movement, and mass shrinking together would create an intense heat capable of emanating radiation at all wavelengths, in all directions. The smaller and faster it became, the brighter it would be. Mentally, he reached for his drawings on the blackboard and article sketches about those distant objects, trying to find the point that Russian researchers predicted where this cloud would explode again: such a point simply did not exist, and the collapse would continue unimpeded.

Upon exiting the center of densification, the object would shine with a light brighter than all the stars in the galaxy. In its depths, the light would bend at angles, distorting spacetime until all directions converged. It would eventually reach a point of no return. Light, space, and time would reach an endpoint: a black hole. At that instant, Penrose knew that a singularity didn't require any special circumstances. In our universe, they weren't impossible, but rather inevitable.

Upon reaching the other side of the street, Penrose's thoughts were interrupted, and he continued chatting animatedly with his friend. For the rest of the afternoon, he felt extremely cheerful, without fully understanding why. Until his mind drifted back to that crossing. The argument still needed refinement, but it worked. A gravitational collapse required only a few generic and easily attainable energy conditions to collapse into infinite density.

Today, at 89 years old, Penrose says he is pleased to have received the Nobel Prize in recognition of the discovery. “It’s a strange feeling. I’m just trying to get used to it. I’m flattered. (…) But, on the other hand, I’m trying to write three different papers at the same time, and that makes it more difficult than it was before,” he stated in a report .

Source: BBC