All the predictions spot on (or nearly so) by Stephen Hawking

All the predictions spot on (or nearly so) by Stephen Hawking

The great scientist has left us for three years, and many theories he elaborated in life are still in the experimental phase. Here are the ones that turned out to be correct

(Photo: Jemal Countess / Stringer / Getty Images) On March 14, 2018, over three years ago, the great English scientist Stephen Hawking, one of the most important theoretical physicists of the age, left us modern. As happened with Albert Einstein (and several other scientists), many of his theories only passed the sieve of experimental proof after his death; and many others are still waiting to be tried. Hawking's scientific career began with his doctoral thesis, published in 1966, and ended a few days before his death, with the publication of his latest article: Over half a century of theories and predictions in the most advanced fields of physics and astrophysics, including the thermodynamics of black holes, the description of the Big Bang, the theorization of gravitational singularities and much more. has put together a short list of Hawking's theories that have been validated to date and those that still remain hypotheses at the moment. Let's see them together.

Long live the Big Bang

As we said, Hawking's career began with his doctoral thesis, published at a time of heated debate in the scientific community about two opposing cosmological theories , that of the Big Bang and that of the so-called steady state. Both theories agreed that the Universe was expanding, but the first postulated that the origin of the expansion was an ultra-compact and super-dense state, existing at a precise time in the past, while the second assumed that the 'Universe had always been expanding, with the continuous creation of new matter to keep its density constant. Hawking showed that the steady state theory is not mathematically consistent, and postulated that the Universe as we know it today originated in an infinitely small and dense point, a so-called singularity. His theory is now almost unanimously accepted by the rest of the scientific community.

Black holes are out there

Hawking's name is closely associated with the theory of black holes, another type of singularity that is formed when a star, exhausted the fuel that triggers the reactions of nuclear fusion, collapses under the action of its own gravity. The existence of black holes derives directly from Einstein's theory of general relativity, and their real existence was in doubt more or less until the early 1970s, when Hawking became interested in the problem. In an article published in Nature, the British scientist combined Einstein's equations with those of quantum mechanics, showing that black holes, hitherto considered a pure "mathematical abstraction", could actually exist in the Universe. The final proof of the correctness of Hawking's theory only came in 2019, when the Event Horizon Telescope was able to photograph a supermassive black hole at the center of the giant galaxy Messier 87.

Hawking radiation

Black holes are so called because their gravitational field is so strong that nothing, not even photons, the particles that make up light, can escape it. Or almost: applying a law of quantum mechanics, which postulates that a pair of "virtual photons" can spontaneously be created in a vacuum, Hawking theorized that some of these photons could also have been created outside a black hole (the so-called radiation of Hawking). Years later, scientists at the Technion-Israel Institute of Technology in Israel studying an acoustic analogue of black holes (an object that does not allow sound waves to escape) detected the equivalent of Hawking radiation in sound, exactly where and how. predicted by the British physicist.

The black hole area theorem

More black holes. In classical thermodynamics, entropy is defined as the measure of the "disorder" of a particular system, and the second principle argues that entropy can only increase over time. Working with colleague Jacob Bekenstein, Hawking proposed a method to calculate the entropy of a black hole from a measurement of its area: the observation of gravitational waves emitted by two coalescing black holes, in 2016, once again allowed to prove Hawking's intuition was right. "The properties of the black holes we observed," he told the BBC at the time, "are consistent with my 1970 predictions: the area of ​​the final black hole is greater than the sum of the areas of the initial black holes." Thank you, Stephen.

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Astronomy Black holes Physics Space Stephen Hawking globalData.fldTopic = "Astronomy, Black Holes, Physics, Space, Stephen Hawking"

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