**HOW STEPHEN HAWKING REDEFINED COSMOLOGY**

**By Devansh Marwaha**

Stephen Hawking, arguably the icon of science in the 21st Century, shook up the world of cosmology with his renowned publications; “A Brief History of Time” being the first. His tenacity and persistence to change the world, despite his diagnosis of amyotrophic lateral sclerosis (ALS), was what made his lectures, books, theories and headlines so ground-breaking.

His scientific story began with Einstein. Einstein’s formulation of gravity revealed that particularly large satellites, such as stars, could collapse under their own gravity, forming a singularity. A singularity is a point where spacetime is infinitely curved, but scientists weren’t sure if they existed and had no way to prove this. In the 1960s, it was discovered by Roger Penrose at Birkbeck, University of London that singularities weren’t just possible but inevitable in space and that they would go on to form black holes. This string of discoveries stimulated fascination in many scientists fascinated by black holes, including Stephen Hawking.

At this time, Hawking had just arrived at the University of Cambridge having completed a degree in University College, Oxford, to complete research in cosmology and complete a PhD at Trinity Hall. Here, he met Roger Penrose, the mathematician who had delivered lectures on the inevitability of black holes. The two of them initially met when Penrose was giving a lecture at the University of Oxford on singularities, and Hawking (as a member of the audience) asked a variety of astute and awkward questions at the end. In an interview Penrose specifically said:

“He obviously knew the weak points in what I was saying. It was clear he was someone to contend with.”

Many believe his first discovery, with Penrose, was the establishment of the Big Bang Theory. However, the theory was already in motion for debate when Hawking started looking into it (late 1960s) and it the theory at the time was:

“the idea that the universe began as a tiny speck that subsequently expanded”

Hawking realised the similarity between the reference of the “tiny speck” and a singularity. He and Penrose worked on the proving how the Earth was created by looking at time in reverse and comparing it to the collapse of black hole backwards. By 1970 they had published their findings, which stated that the theory of relativity implied the universe must have started with a singularity (the Big Bang.)

The next cosmological development stemmed from Hawking’s deterioration from his motor neurone disease – ALS. Around 1975, his condition was severe, and the laborious nature of his actions made him realise a fundamental of black holes: they can only increase in size (and mass) not decrease, the way his condition only got worse by progression. Though this seems obvious, scientists were relatively clueless about the properties of black holes, so, this revelation was strikingly similar to the theory that entropy (a measure of disorder) can also only increase in space. When Jacob Bekenstein, declared that the similarity was no coincidence, and that the area of a black hole was actually a measure of its entropy, Hawking set out to prove him wrong. Then the revelation came to Hawking. Black holes must be hot and radiating heat in order to have entropy. This became conventionally known as “Hawking Radiation”.

Following this leap in our understanding of physics, Hawking went on establish the vanishing of black holes – due to their emission of radiation they would eventually disappear, but the large black holes would take longer than the existence of universe, so the smaller ones would be the only black holes which could “explode” near the end of their life cycle, releasing the energy of a million one megaton hydrogen bombs. Furthermore, in 1982 Hawking theorised how quantum fluctuations, during the inflation of the universe’s matter, might have caused galaxies to exist.

From here, the severity of Stephen’s condition led to limitations in his scientific theories. Despite this, he developed the wave function of the universe in 1983 and made numerous other scientific contributions with a small sensor which helped him communicate, activated by just a small muscle in his cheek which was all he could move. Therefore - as we mourn his death (14.03.14), commemorate how he catalysed responses to degenerative disease, and reflect on his scientific breakthroughs – we can safely say that Stephen Hawking made his dent in the universe.