“A Brief History of Time” was published by the famous physicist Stephen Hawking in the late 1980s. It covers major scientific breakthroughs that lead to our current comprehension of the universe, including Stephen Hawking’s work on black holes and the Big Bang.
Fundamental questions are asked, like: How did our universe begin and why? What is time, and how do we perceive it? Why do we even exist?
Here are my key takeaways:
Black holes are formed when gravity surpasses all other forces.
The uncertainty principle contradicts determinism and is central to modern physics.
The anthropic principle as a justification for the formation of life.
Let’s dive into each!
There are four forces in the universe: the electromagnetic force, the weak nuclear force, the strong nuclear force, and gravity. Combined, they describe how particles interact with each other, energy, matter, and mass.
Among these forces, gravity is special. Some theories manage to convincingly unify the other three forces, but not gravity. Gravity is extremely weak compared to the others and can safely be ignored when looking at particle-scale situations. However, it is always attractive and can operate from any distance, making it overwhelmingly dominant in large-scale situations, like star systems.
The formation of black holes is one of those situations. As long as a star has “fuel to burn,” it can resist gravity that attempts to pull the star inward. When the star runs out of things to burn, it collapses. In certain cases, the gravity becomes so strong that it surpasses even the forces that separate atoms from each other and creates a point of infinite density: a singularity.
Hawking spent years studying the properties of black holes, culminating in the discovery that black holes, from which nothing—not even light—is supposed to escape, are emitting radiation. This radiation is now called Hawking radiation and has to do with the second principle of thermodynamics.
Today’s two main theories are Einstein’s Relativity and quantum physics. Both theories can only partially describe reality. Relativity describes large-scale events to a very high degree of precision, like the movement of stars or the GPS system. On the other hand, quantum physics describes particles and their interactions. To this day, these two theories are incompatible. Attempting to unify them leads to absurd results that are yet to be overcome.
Hawking’s work falls right in the middle: in black holes and during the formation of our universe, both gravitational forces and quantum effects are playing a major role. One of the core concepts of quantum physics is that it is not possible to know both the precise position and speed of a particle at the same time. This is called the uncertainty principle and is a fundamental limitation of what can be known. In fact, this principle is so important that it changed the meaning of scientific research, which is now described as “discovering truths within the bounds of the uncertainty principle.”
The principle invalidates determinism as it was originally formulated by Laplace. Knowing the initial conditions of a system as well as the rules that the system follows is not enough to predict its behavior. The behaviour is not random either, but rather follows a probabilistic model.
Discovering the laws of the universe is only part of the question. A deeper, more philosophical question is: Why? Why is the universe like this? Why is it so favorable to the development of life forms like us?
Universal constants, like the speed of light, the charge of an electron, or the mass of a neutron, need to have extremely precise values for our universe to exist. Any tiny change to these values would have catastrophic consequences, like leading to a quick implosion of the universe after the Big Bang or wouldn’t even make it possible for matter to be formed, let alone life.
So how lucky are we that these conditions are favorable in the first place? Were they carefully chosen by an all-knowing being? Are they the only possible values for these constants?
The anthropic principle states that since we are here to observe the universe, it is a requirement that the universe is favorable to life. It would not be possible for any observer to observe a universe improper to be observed.