BOOK SUMMARY: A BRIEF HISTORY OF TIME BY STEPHEN HAWKING
Don’t you have time to read Stephen Hawking's A Brief History of Time? Or simply not able to grasp the complex concepts he explains? Then this summary is for you. I have tried my best to abridge the content in a simple way that everyone can comprehend (hoping so😤)
“Was there a beginning of time?”, “Could time run backwards?”, “Is the Universe infinite or does it have boundaries?”. This book is Hawking's attempt to address these complex questions.
In the first few chapters, Hawking discusses a short history of the universe and how we humans looked at it, in various ways, across different periods of time.
👉 Around 300BC, Aristotle believed that our earth is stationary and rest of the system – sun, moon and all stars were revolving around it. Later in the 2nd century AD, Ptolemy described a geocentric model mainly based on Aristotelian ideas, in which the planets and the rest of the universe orbit about a stationary earth in circular epicycles. He calculated that each planet moves in its own small circular path, while at the same time moving in a large circle around the Earth.
👉 Ptolemy’s Geocentric model was accepted by the world and stayed strong for the next 1300 years; until Nicolaus Copernicus explained the “Sun-Centric” model in AD1514. Great astronomers Kepler and Galileo also supported the sun-centric model.
👉 Soon in the 16th century, there was Sir Isaac Newton came up with his 3-laws of motion and the law of universal gravitation proved that “the universe might be infinite! and there can be many more planets and system apart from the sun, moon, and Earth!". Hawking refers this as the “real start” of modern physics and space study.
In the coming chapters, Hawking answers some of the basic questions like how did it Universe originate, how will it end, how is it structured, and is it finite or infinite? - by explaining two fundamental concepts: Theory of relativity and Quantum mechanics.
👉 A bouncing tennis ball in a running train would appear totally different from the person who’s sitting inside the train and to the one standing outside as the train passes. Likewise, Aristotle and Newton looked at time & speed as “absolute” but Albert Einstein proved that space, time & speed are always “relative” with his E = mc2 equation.
This “theory of relativity” was the major revolution in all our space sciences, made us to accurately analyze the distance & time a rocket would take to reach a planet. This also made us aware that the universe is bigger than what we thought so far.
👉 Then, the focus of the book moves towards the “ever-expanding universe” and “Blackholes”. Black holes are spots in space where gravity pulls so much that even light can not get out. Black holes can be big or small. Smallest blackholes can be as small as a tiny atom, and the bigger ones can be up to 20 times bigger than the Sun; these gigantic black holes are called “stellar”. (Now, you know why Christopher Nolan named his Sci-Fi drama as “Interstellar”)
👉 Upcoming chapters get deep into “cosmology” topics such as “entropy” and expand to “Big Bang” explosion - which is commonly believed to have been the birth of the universe. The universe originated as a very hot, small, and dense super-force - without no stars and planets. Then about 13.7 billion years ago, that magic ball exploded abruptly (thus the name "Big Bang💥💥"), into atoms, which eventually led to the formation of stars and galaxies!
Pretty much that’s the essence of this book, I do not want to go in-deep further. I know you’re yawning already😊).
Human’s universe exploration started with a “belief” that the Earth is sitting on the back of a giant tortoise👻, which sounds ridiculous today. In the same way, whatever we (our physicists & astronomers) believe about Universe today, may be seen as “absurd” in the future. Who do you say?
Note: This article is based on my OWN blogpost: http://www.tripsandbooks.com/2018/04/summary-brief-history-of-time-by.html