Title: A Brief History of Time
Author: Stephen Hawking
Genre: Non-Fiction, Science, Physics, Universe
Published: 1988
BookMarks
"We see the universe the way it is because we exist" : Anthropic principle
“A Brief History of Time” by Stephen Hawking, tries to answer the fundamental questions regarding the universe, like, how vast is it? what is it made of? Did it have a beginning? What was there at beginning? Can time move backwards? And will a single unified theory be able to describe everything about the universe?
Two questions, lying on the opposite sides of the spectrum, that have always intrigued humans – from earth to sun to galaxy to the universe - how vast is it and what lies beyond the limits? And what is the basic building block of all matter – from grains to molecules to atoms to electros/protons/neutrons to quarks, how much smaller does it get?
Now this is one subject, where science needs imagination to formulate theories which have to match up to the observations. It has been almost four decades since the publication of the book, but some of the theories are still at conjecture stage.
Some of the interesting takes from the book.
On Earth - Earth is a medium-sized planet orbiting around an average star in the outer suburbs of an ordinary spiral galaxy which is itself only one of a million million galaxies in the observable universe.
On the Model of the Universe - Since the beginning of civilization, the model of the universe has constantly evolved from Ptolemy & Aristotle to Copernicus, Galileo, Kepler and Newton and Edwin Hubble. In this evolution of the understanding of universe, critical roles have been played by eclipse on moon, the North Star, the moons of Jupiter and as the story goes "an apple".
On the Beginning
- Need of a "First Cause" - Within the universe every event can be explained as being caused by previous events. This the existence of universe itself could only be explained if it had a beginning.
- Another theory states - Time is a property of the universe and did not exist before the beginning of universe. General theory of relativity breaks down at the point of big bang. Also, events before the big bang have no consequences to the scientific model of the universe. Hence time had a beginning at the big bang.
- Many people do not like the idea of time having a beginning as it implies divine intervention. Meanwhile the Catholic Church accepted the Big Bang model and has officially pronounced it to be in accordance with the Bible.
- "What did God do before he created the universe? He was preparing hell for people who asked such questions" - St. Augustine
On Theory
- A theory has to satisfy two requirements - describe a large class of observations on the basis of a model and must make definite predictions about results of future observations
- Eventual goal of science is to provide a single theory that describes the whole universe. At present there are two partial theories - general Theory of relativity (for large objects) and quantum mechanics (for the nano ones). And these two are inconsistent with each other.
On Space and Time
- Fundamental postulate of the theory of relativity - the laws of science should be the same for all freely moving observers no matter what their speed.
- Speed of light was calculated by observing the Eclipses of Jupiter's moons
- Theory of relativity ended the concept of absolute time
- A metre defined as distance travelled by light in 0.0000000003335640952 second as measured by a caesium clock - also corresponding to the distance between two marks on a platinum bar in Paris.
- An event is something which happens at a particular point in space and at a particular time.
- In general relativity, bodies always follow straight lines in four dimensions but appear to move along curved paths in three dimensions. Objects move along geodesics (the shortest distance between two points on any surface)
- Space and time are dynamic quantities. When a body moves out a force acts, it affects the curvature of space and time and in turn the structure of space-time affects the way in which bodies move and forces act. Space and time affect and are affected by everything that happens.
On the Expanding Universe
- The farther a galaxy is, the faster it is moving away
- The boundary condition of the universe is that it has no boundary.
On The Uncertainty Principle - Particles have a quantum state - a combination of position and velocity
As per Aristotle, Gravity - brings things down and Levity - lifts things up
On Black Holes - Black holes are one of the few cases where a theory was developed in great detail as a mathematical model before there was any evidence from observations that it was correct.
Overall, an interesting book which tries to summarize some of the toughest concepts for the ordinary reader. Also, one of those books which definitely need multiple re-reads for better understanding.
And the funniest take personally – We often hear, mathematics is the language of science, and here is a book in English on the universe with only a single equation, “E=mc2” mentioned in the introduction. Hawking says as per the publishers, every equation reduces the potential readers by half!
