Today, March 14, 2018, British physicist and cosmologist Stephen Hawking, one of the greatest scientists in history, died at the age of 76. Hawking had amyotrophic lateral sclerosis and died of complications from his disease. He had been diagnosed in 1963, when he was 21, and at the time was told he would live for just two more years.
Hawking graduated in physics in 1962 from University College, Oxford, and went on to become one of the best-known scientists in the field of cosmology. Throughout his career, he has won awards such as the Albert Einstein Medal, the Order of the British Empire and the Copley Medal of the Royal Society. He has published several articles and also science books for the general public, such as the acclaimed The Universe in a Nutshell, which has sold over 9 million copies. He married twice and had three children.
See below for six of Hawking’s greatest contributions to science.
1) Determined that the Universe began as a singularity
– (Samuel Leme/)
In 1970, Hawking published a study with colleague Roger Penrose proposing that, based on the General Theory of Relativity elaborated by Einstein, the Universe had to have started as a singularity. That is, it had to have started as a small point of infinite density.
Today, this hypothesis is widely accepted, but at the time, the subject still generated many doubts. Einstein had proposed that a body with a very large mass could collapse due to its own gravity, creating a black hole (a term coined later). This mass would collapse to a tiny point of very high density – a singularity. Hawking was basically proposing that the Big Bang was like a black hole collapsing in reverse.
2) He applied the second law of thermodynamics to black holes
Hawking determined that the total surface area of a black hole will never get smaller – it will only increase or stay the same. This rule is analogous to the second law of thermodynamics, which states that the entropy of a closed system only increases, never decreases.
3) Hypothesized that black holes can become extinct
The proposal for the previous item was overthrown by Hawking himself when he discovered that, due to quantum effects, black holes create and emit particles. With that, they lose mass and energy, which means that if they don’t gain mass due to another means, they will end up progressively decreasing until they cease to exist. But it is clear that this would be an extremely slow process: for a black hole with the same mass as the Sun to evaporate, it would take more time than the current age of the Universe.
This effect is called “Hawking radiation”, or “Bekenstein-Hawking radiation” when one takes into account that Hawking worked on a theory proposed by the Israeli scientist Jacob Bekenstein. It is perhaps Hawking’s greatest contribution to science.
4) Theorized how the Universe expanded and galaxies formed
One of Einstein’s greatest contributions with his General Theory of Relativity was the idea that the Universe had a beginning (although this term is controversial, as we will see in the next section), which allowed other scientists to formalize the concept of the Big Bang. Hawking thought about what came after the Big Bang, that is, about the moment when the Universe began to expand.
Building on a proposal presented by Alan Guth in 1980, Hawking proposed that the Universe expanded in the same way as bubbles form – several of them pop up at about the same time, but most pop immediately, or expand shortly before popping. With the Universe, it would be the same thing – some parts of it would have collapsed as soon as they appeared, when they were still microscopic, and others would have collapsed during the expansion. Other parts, however, kept growing until they became stable.
This passage of time, called by the scientist the “inflationary period”, was when variations in the intensity of the microwaves generated by the Big Bang, caused by quantum fluctuations, generated irregularities in the creation of the Universe. These irregularities mean that as the Universe expanded, some areas became denser than others and eventually collapsed (like bubbles) because of gravitational pull, spawning galaxies and stars.
5) Thought about what was before the Big Bang
The Hartle-Hawking State is a proposal made in 1983 by Hawking and Jim Hartle of the University of Chicago. It is very complicated to explain technically, but, in an extreme simplification, it tries to argue about what was “before” the Big Bang.
According to Hawking, if it were possible to travel back in time to the beginning of the Universe, it would be possible to reach a point where time did not yet exist. That’s because at the very high density point where it all began, called the singularity, the laws of physics still didn’t apply. Therefore, the idea of “time” did not exist. For us, it is difficult to understand this absence of time, since it is part of our lives and we are used to understanding the Universe as something that is aging. We got used to thinking of the Big Bang as a beginning. But, for Hawking, there was something before it happened.
Strictly speaking, whatever happened “before” the Big Bang cannot be measured (as already mentioned, because the laws of physics did not exist). Therefore, the idea of a “beginning” does not apply to the Universe. He’s always been there.
This idea that the Universe has no beginning is what is often called the “boundaryless proposal”, as it has no beginning either in time or in space. It’s a hypothesis about how the Universe began – there are others, of course – and, while it can’t be proven yet, it’s one of the most prominent ones on the subject.
6) He proposed a theory for everything
In 2006, Hawking and Thomas Hertog, a member of Cern (the laboratory that built the largest particle accelerator on the planet, the LHC) published a study with a pretty crazy hypothesis, but, according to them, possible to be proved. The two said that the Universe had several parallel beginnings. Most of them fell apart without creating a noticeable effect, but some merged and formed the Universe we know today.
This hypothesis is based on quantum physics. To understand, imagine a particle of light traveling from a light bulb to your eye. You imagine that the particle traveled in a straight line until it reached your retina, right? But to study the particle properly, quantum physics needs to predict all the ways the particle could reach its destination, including the possibility that it bounced off the walls before reaching your eye.
Admitting these possibilities is the only way to explain the strange properties of quantum particles, such as their apparent ability to be in two places at once. However, the big X of the issue is that only one of these possible behaviors becomes dominant, subjugating the others.
That’s what would have happened to the Universe: within a few seconds after the Big Bang, one of the hypotheses already became dominant, giving rise to the cosmos as we know it today. But in the early moments of the Big Bang, there were several possible hypotheses running at once, like several lanes of a racetrack.
Hertog and Hawking argue that this hypothesis can be proved by observing the radioactive microwaves that exist in the cosmos and that serve as a kind of record of the Big Bang. For the two scientists, their theory predicts the patterns in these microwaves, patterns that would be frozen records of this early quantum mixing.
This proposal combines with string theory, which proposes the existence of multiple Universes different from ours. The problem with string theory is that it doesn’t explain why we live in ours specifically. For Hertog and Hawking, there is an unknown factor, a kind of criterion, that explains why our Universe is the way it is and works the way it does. It was this factor that made our Universe the “chosen one” among the existing multiples and it is this factor that determines the way nature works, probably. This is the closest science has ever come to a “theory of everything”, that is, a theory that combines general relativity and quantum physics into something that applies to all things.