The Greatest Mind of this Generation
“It would not be much of a universe if it wasn’t home to the people you love.”
- Stephen Hawking
On the 14th of March 2018, Stephen Hawking, perhaps the greatest theoretical physicist the world has ever seen, died at the age of 76. He was an extraordinary man, and his accomplishments and legacy will live on for generations. His brilliance, courageousness and humour inspired people across the world.
But it’s not just Hawking’s ideas and theories that cause him to undoubtedly be the most recognisable figure in physics of this age; he holds an iconic status.
He wrote many books, all with huge impacts not just in science, but in the world. The most notable example being “A Brief History of Time” (published in 1988), selling more than 10 million copies. In addition, he has appeared in Star Trek, The Simpsons and The Big Bang Theory. His early life was the subject of the award-winning 2014 film The Theory of Everything. Furthermore, he was regularly consulted about some of the most prevalent scientific questions, ranging from time travel to alien life.
This combined with his fearless attitude and enlightening humour, made him not just a fantastic mind, but a cultural pillar of the world. He is someone that people don’t just look at as a theoretical physicist, but as a distinct symbol of ingenuity.
The Big Bang — where it all started
The initial period of Hawking’s career in research actually began with disappointment. He arrived at Cambridge University in 1962 to begin his PhD. Hawking chose the most famous British astrophysicist of the time, Fred Hoyle, as his supervisor. However, on his arrival to the University, he was informed that Hoyle had no room for another student — a polite way of saying Hawking didn’t make the cut.
Instead, he had to work with a physicist he had never heard of, Dennis Sciama. In fact, this was probably a great asset to Hawking, as Sciama was always around and eager to talk and postulate with Hawking, whereas Hoyle (being the famous scientist he was) was rarely present in the department. Furthermore, Hoyle opposed the concept of The Big Bang Theory, and would likely have discouraged Hawking from investigating the beginning of time, whereas Sciama was happy to allow Hawking to pursue his own scientific vision.
Singularities
Hawking was heavily studying the work of Roger Penrose. His main concept was that if Einstein’s general theory of relativity proved correct, then at the heart of every black hole there must be a singularity — a point where space and time themselves break down (i.e. where the mass and gravitational field are predicted to become infinite).
What Hawking had realised was (if it did prove correct) that this concept should hold true for the rest of the universe: the universe began in a singularity. Under Sciama’s encouragement, he was able to work out the maths and prove it.
However, Hawking, having a rounded and conscious view, was aware that general relativity described space and time on a large scale, and that quantum mechanics was required to take into account matter’s behaviour on a much smaller scale. He could see that the concept of a singularity at the universe’s origin signalled the need for quantum gravity, and thus a “theory of everything” that could unite quantum mechanics and general relativity.
Hawking looked at the situation literally: the initial idea of a singularity was at the centre of a black hole. Meaning, to understand the origin of the universe he must research black holes.
In the early 1970s, black holes were in need of strong investigation — theoreticians viewed them as just mathematical anomalies of general relativity and were reluctant to believe they could actually exist.
Thermodynamics: a wall to a deeper truth
One of the most well-established laws of nature, the second law of thermodynamics, states that the entropy of a system (level of disorder) always increases. All matter contains entropy, and problems arise when the following question is asked: what happens when matter is dropped into a black hole? Is its entropy lost with it? If indeed, the entropy is lost, then the net “amount of entropy” in the universe decreases — thus violating the second law of thermodynamics… see the issue?
However, Hawking confronted this dilemma with a similar styled mindset to that of Albert Einstein (in particular, when he developed his special theory of relativity). Rather than, like many closed-minded scientists, assuming “the idea” could not work, he just accepted that “the law” was broken. He was happy to disregard any concept that may stand in the way to a deeper understanding of the universe, and in this case: the second law of thermodynamics.
It appears that this fearless, daredevil-like way of approaching an issue is a common characteristic of the greatest thinkers.
How a disagreement led to a breakthrough
Like with Hawking’s supervisor situation, a seemingly negative occurrence led to perhaps his greatest breakthrough. In 1972, a Princeton University graduate, Jacob Bekenstein, proposed that the second law of thermodynamics should in fact apply to black holes — totally juxtaposing Hawking’s view. Interestingly enough, Bekenstein’s basis for his argument used one of Hawking’s own theories: the event horizon.
A black hole is said to hide its singularity with a boundary known as the event horizon. This boundary acts as a “point of no return” (anything that crosses it can never return to the outside). Hawking had shown that the area of a black hole’s event horizon will never decrease, and when matter falls into a black hole, this area increases.
Bekenstein’s postulation was that, to preserve the second law of thermodynamics, perhaps the area of the horizon is itself a measure of entropy? Meaning that, when matter falls into a black hole and crosses the event horizon, its entropy is not lost as the event horizon area increases. Thus, the net “amount of entropy” in the universe would not decrease, meaning the second law is not broken.
Hawking immediately disliked this idea and was said to be angry that his work had been used in such a flawed concept. He went to the extent of getting together with colleagues Brandon Carter and James Bardeen to disprove Berkenstein’s theory. Instead, he discovered the precise mathematical relationship between entropy and a black hole’s event horizon. Rather than disproving the concept like he intended, he had confirmed it with confidence — becoming his greatest and most important breakthrough.
Hawking radiation
Hawking did not want to accept that thermodynamics must be taken into account when considering black holes. He explained that anything that has entropy also has a temperature, and anything that has a temperature can radiate. He admitted that, to begin with he had made the mistake in only taking general relativity into account: believing that nothing can escape the grip of a black hole. The realisation of this mistake led him to taking quantum mechanics into account. Quantum mechanics states that particle-antiparticle pairs are constantly appearing out of empty space, but annihilate each other and disappear rapidly after. Hawking deduced that when this occurs at an event horizon, the pair can be separated — one particle crosses the horizon and is lost, while the other escapes (thus meaning they can never meet again and annihilate), leaving the black hole as radiation. The randomness of quantum creation, and therefore this process as a whole, is what leads to the “randomness of heat” (entropy).
Due to the very nature of black holes, and the fact that any measurable ones are huge distances away, it is almost impossible to test Hawking’s prediction. Despite this lack of experimental confirmation, “nearly every expert believes he was right” and “most physicists would agree that Hawking’s greatest contribution is the prediction that black holes emit radiation”, as explained by Sean Carroll, a theoretical physicist at the California Institute of Technology.
The theory of everything: a unification of physics
The entropy equation Hawking had developed (with the initial spark from Bekenstein), known as the Bekenstein-Hawking entropy equation, represents more than just a mathematical equation for a particular topic in physics: it is the unification of the most significant physical disciplines. It contains: Newton’s constant (with gravity), Planck’s constant (with quantum mechanics), the speed of light (with Einstein and relativity), and the Boltzmann constant (with thermodynamics). This unification in a single, elegant mathematical equation was the first hint at a “theory of everything”, where all physics is unified.
Although this solved the entropy problem, it gave birth to the black hole information loss paradox. This is the concept that if a black hole can radiate, it will eventually evaporate and cease to exist. And if this does occur, what happens to the “information” (matter) that fell into it? If the information also ceases to exist then quantum mechanics is violated, and if it escapes then Einstein’s theory of relativity is violated.
Essentially, in addition to hinting at an elegant unification of physics, Hawking had created a battle: separating the laws of physics, forcing physicists to pick a side (a battle which continues to this day). In fact, he eventually sided with the argument that information is indeed lost, despite the violation of quantum mechanics. It wasn’t until 2004 (after results emerging from string theory had managed to convince the majority of theoretical physicists that information is not lost) that Hawking gave in and dramatically announced his updated view at a conference in Dublin: black holes cannot lose information.
To this day, the quest for quantum gravity continues. Many famous physicists agree that the single biggest clue for the existence of this unification of physics is Hawking radiation, thus making Stephen Hawking a revolutionary figure in science.
The physical battle
In addition to all of the above, Hawking continued to push the boundaries of theoretical physics at an extraordinary rate, and the way he managed to do it given the physical war he was waging, is a representation of how inspirational he is.
In the year of 196 (the same year he “didn’t make the cut” to be one of Fred Hoyle’s students), Hawking was diagnosed with amyotrophic lateral sclerosis. This is a degenerative motor neurone disease that, over time, causes a person to lose control of their own muscles. Further emphasising that Hawking’s career did not have the best start, he was told this disease would leave him with two years to live.
Amazingly, this did not prove true. Hawking went on to live for a further 56 years. Physical and mental, what he overcame was unprecedented. His mind remained sharp, and so he continued to explore physics with new, fascinating approaches to problem solving and calculations. For example, rather than writing out complicated equations, he would use his mind to reimagine them in a geometric form.
Cultural stardom
The combination of Hawking’s work: his revolutionary discoveries, theories, and publications that gave a breath of fresh air to theoretical physics; personality: his daredevil attitude, humorous character, and unrelenting drive for a deeper understanding; and the fact that he discovered and achieved all that he did whilst being burdened with an oppressive motor neurone disease, makes Stephen Hawking a scientific legend and cultural icon. He will never be forgotten.
Originally published at http://thephysicsfootprint.com on March 6, 2022.
