Brief Answers to the Big Questions is a wonderful collection of the late Stephen Hawking’s musings on the “Big Questions”. Not everyone will agree with all of his views, but it’s difficult not to be inspired by the cosmic journey Hawking transports you through, and the heartfelt optimism he has for the future of humanity.
For those who are familiar with Hawking’s writing, a lot of this book may feel repetitive. Each chapter is a self-contained essay on one out of ten “Big Questions”, each of which is something that Hawking has spoken publicly about in the past. While this format is a nice way to compile his thoughts, and gives a satisfying tour through his worldview and understanding of the universe, it does mean that some concepts are explained several times over. The book also doesn’t reveal anything particularly new. Anyone who’s read a different book by Hawking, or seen his TV show will recognise most of his arguments and explanations. This is the reason for a slightly lower content rating than might be expected, despite the fact that what Hawking does write about is captivating and esoteric.
It is however difficult not to gripped by Hawking’s prose and inspired by his optimism for the future. Hawking takes the reader on a spellbinding tour of a variety of sophisticated ideas in theoretical physics which often feels as colourful as a retelling of Lewis Carroll’s Alice in Wonderland. Hawking thrives especially in his defining topic – Black Holes, and explains the physics behind them in a wondrous, yet intuitive fashion.
Some of the most interesting ideas in the book include:
- The Black Hole Information Paradox: A black hole is characterised by only a few properties such as its mass and charge. This means that the same black hole can be formed by very different system so long as they have the same mass and charge. What this implies is that when a black hole is formed lots of information, about the original system that formed the black hole, is lost behind the event horizon. But when a black hole eventually evaporates, the particles it spews out via Hawking radiation bear no relation to what went in originally. So information seems to be lost irretrievably. This has major implications for determinisim in the universe. If information is lost, then it is not possible, even in principle, to predict the future of the universe.
- The Universe is Nothing: A particular view that Hawking has been a major proponent of is that the sum total of energy in the universe is zero. Hawking asserts that if we take all the positive energy and mass we see in the universe, then it balances out the negative energy intrinsic to expanding space – meaning that the universe contains no overall energy. Hawking suggests that this means nothing was needed to create the universe.
- Imaginary Time and the No-Boundary Proposal: One of the theorems Hawking was most famously involved with is the proof that the universe began in a singularity. At the time, Hawking himself, believed that he’d shown the universe had a beginning. Fast forward many years later and Hawking tried to prove the opposite! His “no-boundary” proposal claims that the universe has no boundary in imaginary time, meaning that the universe has no single-history. The mathematical details here make the idea much more compelling, but to avoid getting into them here the lack of a boundary in imaginary time means that the universe has an abundance of histories, and if all the histories occur, then the “initial conditions” of the Big Bang can take on any values. For Hawking, this suggests that no “fine-tuning” is needed for the boundary conditions of the universe, because there is no boundary!
- Comparing Biological Evolution with our Technological Revolution: Hawking talks about how slow the process of evolution in the current human species is, and compares it to our scientific knowledge and technology. Throughout the book, Hawking makes a passionate case for science education, part of his reasoning is that while evolution only gives us a useful “bit” (in the computing sense of the word) of information each year, the amount of information passed on in books and by society is billions of times faster. This means that in a technological sense, humanity is evolving far faster than it ever could biologically.
- Time Travel and Negative Energy: The only feasible method for travelling into the past would be to warp spacetime so much so that it formed a wormhole. This is not possible with ordinary matter – it bends spacetime the wrong way. What we’d need is a kind of matter with negative energy density. Matter like this would be extremely weird, but we know it can exist! The Casimir effect in quantum mechanics demonstrates that the virtual particles in empty space can be considered to have negative energy density.
Hawking explains a wide variety of sophisticated ideas in theoretical physics in an easy-to-understand way. Sometimes however, Hawking does say things that seem a little brazen to those more familiar with physics. He regularly assumes the existence of virtual particles popping in and out of space, when many physicists might quibble that the virtual particles are mathematical tools and not physical. He also fully endorses a realist interpretation of the Feynman path-integral formalism, in which quantum particles traverse all possible routes not just the one they actually appear to traverse. While this formalism produces the correct mathematical results, many physicists would not agree that the Feynman path-integral formalism is to be taken literally, some argue that it’s not even mathematically well-defined! It’s interesting that Hawking seems to endorse the path integral formalism but doesn’t mention anything about the Many-Worlds interpretation.
One of the highlights of the book though is Hawking’s rampant optimism, made all the more compelling given his remarkable personal life. Hawking paints an exciting picture of the future of humanity, but is keen to warn us of the dangers that accompany our technological ascension. Hawking makes a passionate plea for scientific education, and the need for humans to look beyond our existence on this planet. He warns that without proper risk-management and serious action to combat climate change, as well as other threats to the human race, we risk losing everything. But Hawking’s optimism shines through this and his hopeful message will inspire a new generation of scientists to shape the world around them for the better, and keep humanity on track for the stars.