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Stephen Hawking was one of the greatest theoretical physicists of the modern era. Best known for his popular media appearances and his long-standing battle with a debilitating disease, his real impact on posterity comes from his brilliant five-decade scientific career. Starting with his doctorate thesis in 1966 his pioneering work continued uninterrupted until his last paper in 2018, completed a few days before his death at the age of 76.
Hawking worked at the forefront of intellectual physics and his theories often seemed strangely distant as he formulated them. Yet, they are slowly gaining acceptance in the mainstream scientific audience, with new supporting evidence coming in all the time. From his breathtaking views of black holes to his explanation of the humble beginnings of the universe, here are some of his theories that have been substantiated … and others that are still pending.
The Big Bang wins
Hawking got off to a good start with his doctoral dissertation, written at a critical time when there was a heated debate between two rival cosmological theories: the Big Bang and the state of equilibrium. Both theories admit that the universe is expanding, but in the first it expands from an ultra-compact and super-dense state to a finite time in the past, while the second assumes that the universe is expanding forever, question constantly created to maintain constant density. In his thesis, Hawking showed that the steady state theory is mathematically contradictory. He argued instead that the universe started out as an infinitely small, infinitely dense point called a singularity. Today, Hawking’s description is almost universally accepted among scientists.
Black holes are real
More than anything else, Hawking’s name is associated with black holes – another type of singularity, formed when a star undergoes a complete collapse under its own gravity. These mathematical curiosities arose from Einsteingeneral theory relativity, and they had been debated for decades when Hawking turned his attention to them in the early 1970s.
According to an article by Nature, his stroke of genius was to combine Einstein’s equations with those of Quantum mechanics, transforming what was previously a theoretical abstraction into something that seemed able to actually exist in the universe. The final proof that Hawking was right came in 2019, when the Event Horizon Telescope obtained a direct image of the supermassive black hole that lurks at the center of the giant galaxy Messier 87.
Hawking radiation
Black holes get their name from the fact that their gravity is so strong that photons, or particles of light, shouldn’t be able to escape. But in his early work on the subject, Hawking argued that the truth is more subtle than this monochrome image.
By applying quantum theory – in particular, the idea that pairs of “virtual photons” can be created spontaneously from scratch – he realized that some of these photons seemed to be radiated by the black hole. Now called Hawking radiation, the theory was recently confirmed in a laboratory experiment at Technion-Israel Institute of Technology, Israel. Instead of a real black hole, the researchers used an acoustic analogue – a “sonic black hole” from which sound waves cannot escape. They detected the equivalent of Hawking’s radiation exactly according to the physicist’s predictions.
Black hole area theorem
In classical physics, entropy, or the disorder of a system that can only increase over time, never decreases. Along with Jacob Bekenstein, Hawking proposed that the entropy of a black hole be measured by the area of its surrounding event horizon.
The recent discovery of gravitational waves emitted by the fusion of pairs of black holes shows that Hawking was still right. Like Hawking told the BBC after the first such event in 2016, “the observed properties of the system are consistent with the black hole predictions I made in 1970 … the area of the final black hole is greater than the sum of the areas of the holes black initials. ” Following recent observations provided further confirmation of Hawking’s “area theorem”.
So the world is gradually catching up with Stephen Hawking’s astonishing predictions. But there are still a few that have yet to be proven in some way:
The information paradox
The existence of Hawking radiation creates a serious problem for theorists. It appears to be the only process in physics that removes information from the universe.
The basic properties of the material that were used to create the black hole seem to be lost forever; the radiation that comes out of them tells us nothing about them. This is the so-called information paradox that scientists have been trying to solve for decades. Hawking’s own take on the mystery, which was released in 2016, is that the the information is not really lost. It’s stored in a cloud of zero-energy particles surrounding the black hole, which he dubbed “soft hair.” But Hawking’s Hairy Black Hole Theorem is just one of many hypotheses that have been put forward, and to this day, no one knows the real answer.
Primordial black holes
Black holes are created from the gravitational collapse of pre-existing matter such as stars. But it is also possible that some were created spontaneously at the very beginning of the universe, shortly after the Big Bang.
Hawking was the first person to explore the theory behind such primordial black holes in depth. It turns out they could have virtually any mass, from very light to very heavy – although the smaller ones have not “evaporated” in any way due to Hawking’s radiation. One intriguing possibility considered by Hawking is that primordial black holes could constitute the mysterious black matter that astronomers believe permeates the universe. However, as Previously reported LiveScience, current observational data indicates that this is unlikely. Regardless, we currently have no observation tools to detect primordial black holes or to tell if they constitute dark matter.
The multiverse
One of the topics Hawking tinkered with towards the end of his life was the multiverse theory – the idea that our universe, with its Big Bang beginnings, is just one of the coexisting bubble universes.
Hawking was not happy with the suggestion, made by some scientists, that any ridiculous situation you can imagine must be happening right now somewhere in this infinite set. Thus, in its very last paper in 2018, Hawking sought, in his own words, to “try to tame the multiverse.” He proposed a new mathematical framework which, without completely doing without the multiverse, made it finite rather than infinite. But as with any speculation about parallel universes, we have no idea if his ideas are correct. And it seems unlikely that scientists will be able to test his idea anytime soon.
Timeline protection guess
Surprising as it may seem, the laws of physics – as we understand them today – do not prohibit time travel. Solutions to Einstein’s general relativity equations include “closed time curves“, which would effectively allow you to travel to your own past. Hawking was embarrassed by this because he felt that time travel raised logical paradoxes that simply should not be possible.
He therefore suggested that a currently unknown law of physics prevents the appearance of closed time curves – his so-called “timeline protection conjecture”. But “guesswork” is just a scientific language for “guessing,” and we really don’t know whether time travel is possible or not.
No creator
One of the most common questions cosmologists ask themselves is “What happened before the Big Bang?” »Hawking own view was that the question does not make sense. For all intents and purposes, time itself – as well as the universe and everything in it – started at the Big Bang.
“For me that means there is no possibility of a creator,” he said, and like Previously reported LiveScience, “because there is no time for a creator to have existed.” It’s an opinion that many people will disagree with, but one that Hawking has expressed many times throughout his life. It almost certainly falls into the “will never be solved one way or another” category.
Apocalyptic prophecies
During his later years, Hawking made a series of dark prophecies regarding the future of mankind that he may or may not be totally serious, BBC reported
These range from the suggestion that the elusive Higgs boson, or “God particle,” could trigger a vacuum bubble that would engulf the hostile universe alien invasions and artificial intelligence (AI) redemptions. While Stephen Hawking was right about so many things, we’ll just have to hope he was wrong about it.
Originally posted on Live Science.
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