With her popular blog Backreaction and first book Lost in Math， Sabine Hossenfelder has become one of the most prominent commentators on modern physics。 Unapologetic in her frank and acerbic — acidulous， even — commentary， she has definite and demonstrative views on physics and physicists。 （“I’m not exactly known for being nice，” she admits。） In Existential Physics， she tackles what physics says — and doesn’t say — about the Meaning of It All， including the nature of time， the origin of the univ With her popular blog Backreaction and first book Lost in Math， Sabine Hossenfelder has become one of the most prominent commentators on modern physics。 Unapologetic in her frank and acerbic — acidulous， even — commentary， she has definite and demonstrative views on physics and physicists。 （“I’m not exactly known for being nice，” she admits。） In Existential Physics， she tackles what physics says — and doesn’t say — about the Meaning of It All， including the nature of time， the origin of the universe， the existence of free will， and the “purpose” of existence。Meaning is not something those of an existential bent often look for in physics。 Indeed， physics is mostly seen as taking away meaning， showing us to be smaller and more insignificant in comparison to the larger universe at every turn。 Hossenfelder， however， forcefully believes physics does have a lot to say about our place in the universe。 Physicists， alas， aren’t much good at communicating that fact， allowing pseudoscience hucksters to co-opt and provide their own “meaning” to what science says， which is a disaster for both physics and the public by cloaking nonsense in the legitimacy of scientific “fact” and leading to confusion and misguided ideas。As she explores things such as free will and fine-tuning， Hossenfelder is always at pains to distinguish between the scientific， the unscientific， and the “ascientific。” As opposed to the unscientific， the ascientific are concepts and theories that are not， even cannot， be disproved by science。 But they also are not and cannot be proved by science， either。 They are simply oblivious to proper scientific method。 In such cases， Hossenfelder emphasizes that you can believe them， but you cannot prove them true。 Take the many-worlds interpretation of quantum mechanics。 This idea says that universes branch off with every flip of a coin， every quantum “decision” made， meaning there are infinite copies of you and everyone else。 But these universes are totally unobservable。 There is no proof， and never will be， that these universes are actually real。 The whole many-worlds interpretation can provide no observational proof of its validity。 It is functionally identical to many other interpretations， all producing the same testable results and thus no way to prove or disprove their correctness， that do not posit infinite universes。 You can therefore believe in an infinite fellowship of yourself， but you can never actually know there is such a fellowship。 What use， really， then， she asks， is the whole idea？My one and only major criticism of the book concerns the interview chapters Hossenfelder intersperses throughout: I wanted them to be longer and more numerous！ They’re fascinating discussions with various experts， but all seem to end before they really get going。 I was left unsatisfied and craving more。 Admirably frank in her professions of where physics is ignorant， and never claiming that it has all the answers， Hossenfelder nevertheless provides a vigorous argument for its power to illuminate and its relevance to humanity’s search for meaning in the universe。 I heartily recommend this book to any who are interested in the Big Questions。 。。。more