A Brief History of Time by Stephen Hawking
In the conclusion of the book, Stephen Hawking says (I am paraphrasing): “scientists have done a great job of explaining how the universe came to be and what it is today and how it works… but the most important question of why the universe exists at all is under-addressed by the scientific or philosopher community”
But he also helpfully points out that the “why question” rightfully is in the domain of the philosophers. Prior to the dizzying advancements in particle physics which require physicists to be first rate mathematicians who are perfectly at home using very advanced mathematics, philosophers “were” the scientists who contemplated the nature of the physical world (seen and unseen), physics, chemistry, astronomy, and all other sciences. Unfortunately, those days are long gone, and philosophers are reduced to asking different sorts of questions! They can still ask why the universe exists, but alas, they do not have the wherewithal to study the universe anymore and offer deep insights.
There is a goldilocks scenario (per Hawking: “If the rate of expansion one second after the big bang had been smaller by even one part in a hundred thousand million million, the universe would have re-collapsed before it ever reached its present size.”) that says everything happened in exactly the right sequence for the universe to come into being, for our very own Milky Way galaxy and the solar system to be created and ultimately lead to the creation of intelligent life such as ourselves, who could then ask the question: “why does the universe exist?” That, I found out, is called the anthropic principle vis-a-vis the origin of the universe. This allows a Creator to have played a role in the creation of our universe with say, the Big Bang, and the evolution according to fixed laws, most of which we understand now, and some that we still do not understand.
Hawking does a great job of explaining the big concepts — general and special relativity, quantum theory/quantum mechanics, black holes, and that Holy Grail of physics — how to reconcile Einstein’s theory of relativity (with all its implications for the visible universe) to quantum mechanics (with all its implications for invisible subatomic particles). One could even say that this is a case of “Relativity is Relativity and Quantum mechanics is quantum mechanics, and never the twain shall meet!” to borrow a phrase from Kipling.
The universe is an incomprehensibly large place, and whatever forces propelled the outward expansion of the universe at the Big Bang, they are still at play… bequeathing us a universe that continues to expand, in fact at an accelerating pace, according to most recent discoveries. The expansion of the universe was predicted by Einstein’s theory of relativity and was proved experimentally by Edwin Hubble in the 1920s. Interestingly enough, the universe is not only expanding, but it is also expanding uniformly in all directions. This was confirmed by the cosmic background microwave radiation that is all around us. A happy and accidental discovery of the signature of the early universe was the ticket to the Nobel prize for a couple of physicists, Arno Penzias and Robert Wilson in 1978!
Einstein’s theory of relativity predicts that there was a singularity (laws that govern the universe today do not apply at singularity) at the beginning of the universe aka the Big Bang. We have no idea what happened before the singularity. Relativity also predicts that the universe will reach a point when the deflationary forces eventually overcome the inflationary forces and the universe starts to contract, eventually to collapse into a singularity again — think about this, the entire observable universe with its billions of galaxies will contract and contract and contract until it is down to an infinitesimal speck that has infinite density in an outcome known as the Big Crunch. Hence, at the Big Bang and at the Big Crunch, the laws of physics as we know them cease to apply, and time has no meaning — time simply ceases to exist.
When we go from the laws governing the very big (“universe…relativity”) to the laws governing the very small (“subatomic particles…quantum theory”), you go from a system that is very deterministic to a system that is very probabilistic. Relativity predicts a Big Bang, the expansion of the universe for a long period of time, followed by a contraction, and eventually the Big Crunch. All very orderly, all well predicted and mostly verified by experimental observation. On the other hand, quantum theory does well with subatomic particles and in explaining electromagnetism, the so-called weak and strong nuclear forces, but is mostly silent on gravitational force. But there is a sense that quantum theory may help us to understand the singularity, or the boundary conditions of the universe better than relativity can.
Hawking suggests that if there is a defined beginning and a defined end to the universe, there is a role for a divine presence who might have planned this all out, after all. On the other hand, based on quantum theory, if we can prove that the universe has always existed with no defined beginning or end, and small imperfections in the uniformity of the early universe led to the creation of galaxies and stars and eventually human beings themselves, what role then for a creator? A weighty question? Without a doubt!
In the book, Hawking also spends a considerable amount of time discussing how black holes form and what their characteristics are; he formulated several theories, some of which are still being proven today. Black holes have always been a subject of popular interest, and conventional wisdom is that the gravitational pull of the black holes is so great that not even light cannot escape from it. Based on his extensive study of black holes, Hawking begged to differ… he theorized based on quantum principles of exclusion and uncertainty that even black holes have a “color” and that they emit radiation based on their temperature profile. As he explains in the book, if a curious astronaut, monitoring the development of a black hole were to irretrievably fall into it, he would be obliterated, and his personal history/time would come to an end. He would still achieve a dubious sort of immortality because the black hole would eventually radiate out the equivalent of the hapless astronaut’s mass into space as radiation. This is known as the Hawking Radiation and has recently been proven by observation.
Hawking also predicted that the second law of thermodynamics (the entropy of a closed system always increases) is honored by black holes. He predicted that when two black holes join their combined event horizon is larger than the sum of their individual event horizons. And this was also proved by observation recently when two black holes of each great than 20 solar masses joined together into a single black hole.
You might remember the excitement that accompanied the publication of the first ever pictures of a black a couple of years ago. The pictures showed an orange glow representing the event horizon of a black hole. That picture seemed to bring to life the event horizon that Hawking described in the book… the threshold where the effect of the gravitational pull of the black hole was just strong enough to hold light back from escaping… a pulsating and shimmering ring of light straining against the pull of the black hole.
At the beginning of this summary, we talked about the Holy Grail of physics — unification of relativity with quantum mechanics. That quest is still alive and well. There are many partial theories that fit certain conditions and satisfy certain assumptions, but until there is a way to combine general relativity with the uncertainty principle in a comprehensive way, there is still a long way to go. Per Hawking, combining general relativity with the uncertainty principle has already produced some remarkable results — black holes not being totally black, and the universe not having any potential singularities but being completely self-contained and without a boundary. On the flip side, this combination has created significant inconsistencies that need to be resolved to make the marriage of the two theories viable. These efforts toward unification continue apace with recent technological advances, (almost) unlimited computing power, improved experimental methods, and availability of massive infrastructure like the Large Hadron Collider. All of this has allowed scientists to look even deeper into subatomic particles.
On a closing note, a cursory glance at the current landscape of theoretical physics shows that there is a lively ongoing debate between the camps that believe in the primacy of relativity vs. the primacy of quantum mechanics. Science continues to march forward, and in Hawking’s view, a grand unification of the fundamental theories of physics is bound to happen within the lifetime of some of the people that are alive today. Given his deep insights on these matters, it might not be wise to bet against him.
