The genius work Stephen Hawking did as a student

Summary

Stephen Hawking’s PhD thesis, *Properties of Expanding Universes*, explores early cosmological theories, including the Big Bang, oscillating, and steady-state models. Written when he was 23, it tackles the expansion of the universe, the role of Einstein’s general relativity, and the mathematical evidence supporting a singular origin. Despite a diagnosis of motor neurone disease at 21, Hawking’s perseverance led him to complete the thesis, which later revolutionized our understanding of cosmology. Hawking’s decision to make his thesis publicly available inspired many to look up at the stars, illustrating his lifelong passion for the universe and science.

Takeaways

• 😀 Stephen Hawking's PhD thesis, titled 'Properties of Expanding Universes,' was publicly released in 2018, crashing the University of Cambridge website due to overwhelming interest.
• 😀 Hawking wrote his thesis in 1965 at the age of 23, before he became widely known, and even before he was confined to a wheelchair.
• 😀 Diagnosed with motor neuron disease at 21, Hawking was initially given only two years to live, but he later returned to his research after his condition stabilized.
• 😀 The thesis delves into the concept of the expanding universe, challenging static cosmological models like Einstein's original theory, which required a cosmological constant to maintain a stationary universe.
• 😀 Hawking explored three models of the universe's expansion: the Big Bang, the oscillating model, and the steady state model, which he critiqued in detail.
• 😀 The thesis is based on Einstein's general theory of relativity, which describes space and time as interconnected in a 'fabric' called spacetime.
• 😀 Chapter 1 critiques the Hoyle-Narlikar theory of gravitation, which proposes a steady state universe with continual creation of matter, a model that Hawking argued couldn't match observations.
• 😀 In Chapter 2, Hawking investigates how small variations (perturbations) in spacetime could explain galaxy formation, though modern science now attributes this to dark matter.
• 😀 Chapter 3 introduces the concept of gravitational radiation, or gravitational waves, a phenomenon predicted by Einstein but first observed in 2015 through LIGO experiments.
• 😀 The final chapter of Hawking's thesis introduces the concept of singularities in the universe, with a proof that the universe must have begun as a singularity, aligning with modern Big Bang theory and general relativity.

Q & A

What was the significance of Stephen Hawking's decision to release his PhD thesis publicly?

Stephen Hawking's decision to release his PhD thesis to the public marked a significant moment in both academic and popular science. It allowed many to access his early groundbreaking work on cosmology, which included his critiques of existing models like the steady state theory and his exploration of singularities. The release was so popular that it crashed the University of Cambridge website, indicating the widespread interest in his work.

How did Stephen Hawking’s personal challenges affect his PhD thesis work?

Stephen Hawking was diagnosed with motor neuron disease when he was 21, and doctors gave him only two years to live. This diagnosis led to a period of depression and disengagement from his work. However, with encouragement from his family and supervisor, Hawking returned to his research and completed his thesis, which became a testament to his resilience and determination.

What were the three models for the expansion of the universe discussed in Hawking's thesis?

Hawking's thesis discusses three models for the expansion of the universe: the Big Bang model, where the universe expands from a highly dense state; the oscillating model, where the universe goes through cycles of expansion and contraction; and the steady state model, where the universe remains constant and new matter is continually created to maintain its density as it expands.

What was Fred Hoyle's contribution to cosmology, and why was his steady state theory criticized by Hawking?

Fred Hoyle proposed the steady state theory, which suggested that the universe is infinitely old and unchanging, with new matter being created to preserve its constant density during expansion. Hawking criticized this model, demonstrating that it was mathematically inconsistent with observations, particularly the requirement for negative gravitational mass, a concept that had no empirical support at the time.

What is the significance of the concept of 'negative gravitational mass' in the steady state theory?

In the steady state theory, to keep the universe's density constant during expansion, new matter must be created. This would require particles to have 'negative gravitational mass,' a property that Hawking pointed out did not exist in the universe. This flaw in the theory contributed to its rejection in favor of the Big Bang model.

What is the 'C-field' in the context of the steady state theory?

The 'C-field' was a concept introduced by Hoyle and Narlikar to explain how new matter is created during the universe's expansion. This field was based on Richard Feynman’s ideas about fields in particle physics, specifically his theory involving interactions between pairs of particles. Hawking critiqued this concept in his thesis as part of his broader rejection of the steady state theory.

How did Hawking's work on perturbations contribute to our understanding of galaxy formation?

In his thesis, Hawking argued that small perturbations in space-time could not account for galaxy formation. However, modern cosmology has shown that galaxies do indeed form from such perturbations, aided by dark matter, which Hawking could not have predicted at the time of writing his thesis.

What is gravitational radiation, and how did it relate to Hawking's work?

Gravitational radiation, later known as gravitational waves, refers to ripples in space-time caused by massive objects like black holes. Hawking explored this concept in his thesis, although gravitational radiation had not been detected at the time. His work laid the groundwork for future research on this phenomenon, which was first observed in 2015.

What are singularities, and how did Hawking's thesis contribute to our understanding of them?

Singularities are points in space-time where gravitational forces are so intense that the laws of physics break down. In his thesis, Hawking extended Roger Penrose’s ideas on black hole singularities to the entire universe, proving that singularities are essential to the formation of the universe, leading to the Big Bang model.

How did Hawking use mathematical proofs in his thesis to challenge existing cosmological theories?

Hawking used rigorous mathematical proofs in his thesis to demonstrate that existing theories, such as the steady state model, were flawed. He showed that the universe must have originated from a singularity and that models without singularities led to logical contradictions, contributing to the eventual acceptance of the Big Bang theory.