The tagline 'A Scientist's Guide to Life's Biggest Questions' grabbed my attention and made me buy this book by Sabine Hossenfelder, whose day job is studying quantum gravity at Frankfurt University.
The questions covered in Existential Physics are a mix of hard science (How did the universe begin? Are humans just bags of atoms or something more?) and speculation (Is the universe conscious? Do copies of us exist in a multiverse?) with some extra stuff that is a bit of both - hard speculation, if you will.
Along the way, there are some very interesting summaries of what we can say for certain, and some ideas that scientists advocate for that are, at best, ascientific, meaning there is just no way, now, to know.
The chapter on death and dying and how, on a human level, it illustrates entropy provided a me with a new take on the subject. Although there is no evidence for an "afterlife", and no workable scientific theory for one, the impression individuals make on the universe as "information" is never truly lost - unless it ends up in a black hole. Versions of us sort of might continue to exist, which is weirdly comforting.
I got a bit lost in the discussion about free will and determinism, which cropped up in a couple of places. I can accept that our universe is almost entirely predictable, if an observer had access to enough data and in that sense 'free will' as understood by most people doesn't actually exist. It's not a very intuitive way to approach things though - and Sabine acknowledges this and addresses the issue of holding people to account for their actions, whether those actions are pre-determined or not. There are a few similar diversions from physics into ethics throughout the book.
There is a small section of one of the later chapters that is probably the best precis I have ever read about artificial intelligence at this stage in the development of AI (pp207-210). Sabine outlines what is currently known about trying to create thinking machines and presents a convincing case that the first true AIs will be fragile and will struggle to survive.
"...artificial intelligences at first will be few and one of a kind, and that's how it will remain for a long time. It will take large groups of people and many years to build and train artificial general intelligences. Copying them will not be any easier than copying a human brain. They'll be difficult to fix when broken, because, as with the human brain, we won't beable to separate the hardware from the software. The early ones will die quickly for reasons we will not even comprehend."
That actually made me feel sad for the creations we might bring into being. Sabine also points out that these AIs will most likely be owned by people who are already rich and powerful and will reflect the ethics and interests of their masters. It's a very good point that I've not seen mentioned in other discussions of AI.
Another superb section is the interview with Zeeya Merali, which discusses whether it would be possible to bring another universe into existence. It's certainly doable in theory if beyond human current engineering ability in practice. But if a universe was created then it would separate off almost immediately, and develop detached from our universe. It could expand infinitely and sentient beings could evolve there and we would almost certainly never know, unless we discovered a way to observe other universes (which we can't do now, making the concept of a multiverse ascientific even though lots of scientists talk about it as established fact).
This leads to a discussion of ethics and morality - what responsibility would the creator(s) of that universe have towards any beings that lived in it? That's an ethical conundrum in its own right. It also opens up the possibility that if it's theoretically possible that we could create universes, then this universe may also have been created in a similar fashion. Not that there is any need for a creator based on what we observe about our universe, but a universe created in a lab would probably look the same as ours from inside.
Consciousness is a topic that crops up throughout the book. Trying to explain why humans have consciousness is really difficult - it's something that seems to be more than the sum of our parts (our constituent atoms) and if I understood what Sabine was saying, the observations of consciousness in complex combinations of atoms isn't something that could be predicted by just looking at those individual atoms. So, something currently unexplainable is going on.
The final section of the book is about whether there is any purpose to everything. Sabine concludes that the desire to understand the universe is a meaningful purpose in itself, and I found that a satisfying way to end the book.
I have read several 'popular science' books over the last few years. I found this harder than any I've read previously. The scientific terms come at the reader quickly and there were several occasions when I needed to re-read paragraphs. Some of the early chapters were particularly hardgoing, but I'm glad I powered through - either I got smarter as the book went on (unlikely) or the concepts were less bound up in mathematical theory so were easier to convey in words that a reader like me could grasp.
As a plus point, though, Sabine includes a 'Brief Answer' at the end of every chapter which summarises all that has been said before into three or four sentences. I found that very helpful clarifying what I had just read.
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