Sabine Hossenfelder has been known to piss off a few people, scientists and nonscientists included. That’s what makes her and her new book interesting. She is a German theoretical physicist, author, musician and YouTuber. She has strong opinions and is not afraid to voice them. Early in her book she provides a warning.


I want you to know what you are getting yourself into, so let me put my cards on the table up front. I am both an agnostic and a heathen. I have never been part of an organized religion and never felt the desire to join one. Still, I am not opposed to religious belief. Science has limits, and yet humanity has always sought meaning beyond those limits. Some do it by studying holy scripture, some meditate, some dig philosophy, some smoke funny things. That’s all fine with me, really. Provided that—and here’s the crux—your search for meaning respects scientific fact.


If your belief conflicts with empirically confirmed knowledge, then you are not seeking meaning; you are delusional. Maybe you’d rather hold on to your delusions. Trust me; I am sympathetic to that—but then this book is not for you. In the coming chapters, we will talk about free will, afterlife, and the ultimate search for meaning. It won’t always be easy. I myself have struggled with some of the consequences of what I know to be well-confirmed natural laws, and I suspect some of you will find it equally difficult.


You may think I exaggerate to make dry physics sound more exciting. Look, we all know I want this book to sell, so why pretend otherwise? But the main reason I issue this warning is that I am sincerely worried that this book may negatively affect some readers’ mental health. Occasionally someone contacts me, writing that they came across one of my essays, and now they don’t know hoe to go on with their life. They seem genuinely disturbed. What sense does life make without free will? What’s the point of human existence if it’s just a random fluke? How can you not freak out knowing that the universe might blink out any moment?


Indeed, some scientific facts are hard to stomach and, worse, there’s no psychologist who’ll be able to help. I know this because I’ve tried. But hang on. If you think it through, science gives more than it takes. In the end, I hope you will find comfort in knowing that you do not need to silence rational thought to make space for hope, belief, and faith.


Wow! I knew immediately after that warning that I simply had to read her book. And, I’m happy I did. I’ve read a lot of math and science books over the years. I even majored in math in college. I keep looking for the one book that will tell me everthing I want to know. Hossenfelder doesn’t answer every conceivable question. That’s too high a bar. But she does answer a surprising number. I’ll mention a few then let you decide if you want to read the book.


There are nine chapters with nine basic questions: (1) does the past still exist? (2) How did the universe begin? How will it end? (3) Why doesn’t anyone ever get younger? (4) Are you just a bag of atoms? (5) Do copies of us exist? (6) Has physics ruled out free will? (7) Was the universe made for us? (8) Does the universe think? (9) Are humans predictable?


The author answers these nine questions and several more that result from them with a minimum of complicated scientific concepts although you do need to put your thinking cap on to read this book.


Yes, Hossenfelder is German but she is not entirely devoid of humor.  For example: you shouldn’t trust physicists’ predictions for the end of the universe. You might just as well ask a fruit fly for a weather forecast.In other words, scientists can’t answer every question. As she said in the warning for her book: “science has limits, and yet humanity has always sought meaning beyond those limits.” She dismisses the idea that the universe was made for us, the “fine-tuning” argument, as follows: “Based on my prior belief that the constants of nature could have been anything, I am surprised they are what they are.” Big deal, she says, The statement “Based on my prior belief that I could have woken up being anything, I am surprised I’m human” likewise doesn’t mean I was ever likely you’d wake up being a verminous monster. More likely, you’ve read too much Kafka.


She manages to work in a few interesting references to authors and philosophers. For example, when discussing free will:


Our life is thus not, in Jorge Luis Borges’s words, a “garden of forking paths” where each path corresponds to a possible future and it is up to us which path becomes reality. The laws of nature just don’t work that way. For the most part, there is really only one path, because quantum effects rarely manifest themselves macroscopically. What you do today follows from the state of the universe yesterday, which follows from the state of the universe last Wednesday, and so on, all the way back to the Big Bang.


And she doesn’t wimp out when expressing her opinions: Personally, I would just say this means free will does not exist and put the case to rest. I feel encouraged in that because free will itself is an inconsistent idea, as a lot of people wiser than I am have pointed out before. For your will to be free, it shouldn’t be caused by anything else. But if it wasn’t caused by anything—if it’s an “uncaused cause,” as Friedrich Nietzsche put it—then it wasn’t caused by you, regardless of just what you mean by you. As Nietzsche summed it up, it’s “the best self-contradiction that has been conceived so far.” I’m with Nietzsche.


She goes on:


If free will doesn’t make sense, why, then, do many people feel it describes how they go about their evaluations? Because we don’t know the result of our thinking before we are done; otherwise, we wouldn’t have to do the thinking. As Ludwig Wittgenstein put it, “The freedom of the will consists in the fact that future actions cannot be known now.” His Tractatus is now a century old, so it’s not like this is breaking news.


Hossenfelder has good reasons to insist on clear scientific thinking. She reserves some of her sharpest criticism for famous popular science writers.


The reason I keep insisting physicists clean up their act and stop conflating belief with science is that their confusion is patently obvious to non-experts. Physicists from Brian Greene to Leonard Susskind to Brian Cox to Andrei Linde have publicly spoken about the multiverse as if it were best scientific practice. And because multiverse ideas attract a lot of media attention, this sheds a bad light on the capability of the scientific community to hold its members to high standards.


A prominent example for the damage that can result comes from 2016 Republican presidential candidate Ben Carson. Carson is a retired neurosurgeon who doesn’t seem to know much about physics, but what he knows, he must have learned from multiverse enthusiasts. On September 22, 2015, Carson gave a speech at a Baptist school in Ohio, informing his audience that “science is not always correct.” This is, of course, correct. But then he went on to justify his science skepticism by making fun of the multiverse:


And then they go to the probability theory, and they say, “But if there’s enough big bangs over a long enough period of time, one of them will be the perfect big bang and everything will be perfectly organized.” In an earlier speech, he cheerfully added, “I mean, you want to talk about fairy tales? This is amazing.”


… the point is, he [Carson] shows us what happens when scientists mix fact with fiction: non-experts throw out both together.


Hossenfelder’s book excels in simple explanations for some of the basic questions we have about life.


Why do we age?

The biological processes involved in aging and exactly what causes them are still the subject of research, but loosely speaking, we age because our bodies accumulate errors that are likely to happen but unlikely to spontaneously reverse. Cell-repair mechanisms can’t correct these errors indefinitely and with perfect fidelity. Thus, slowly, bit by bit, our organs function a little less efficiently, our skin becomes a little less elastic, our wounds heal a little more slowly. We might develop a chronic illness, dementia, or cancer. And eventually something breaks that can’t be fixed. A vital organ gives up, a virus beats our weakened immune system, or a blood clot interrupts oxygen supply to the brain. You can find many different diagnoses in death certificates, but they’re just details. What really kills us is entropy increase.


What are we made of?

The human body is about 60 percent water, so that makes my audience first of all a lot of oxygen and hydrogen. I imagine it floating away with a puff. Then, for each person, I have a big jar of carbon, a major constituent of proteins and fats. Carbon alone makes up about 18 percent of the human body, something like thirty pounds of an average adult. Then we have another gas, nitrogen (3 percent), a few smaller jars for calcium (1.5 percent) and phosphorus (1 percent), and tiny doses of potassium, sulfur, sodium, and magnesium. And that’s about it. That’s what humans are: pretty much indistinguishable collections of chemical elements.


Having said that, as a particle physicist by training, I have to inform you that the available evidence tells us that the whole is the sum of the parts, not more and not less. Countless experiments have confirmed for millennia that things are made of smaller things, and if you know what the small things do, then you can tell what the large things do. There is not a single known exception to this rule. There is not even a consistent theory for such an exception.


How long do our “parts” last?

A carbon-dating study in 2005 found that the average cell in the adult human body is only seven years old. Though some cells stay with us pretty much our whole life, skin cells are on average replaced every two weeks, and others (like red blood cells) are replaced every couple of months. We are, hence, physically less like the compact object our self-image suggests, and more like the ship of Theseus. In this 2,500-year-old mind twister, a ship of the Greek hero Theseus is put up in a museum. As time passes, parts of the ship begin to crumble or rot away, and bit by bit they are replaced with newer parts. A rope here, a plank here, a mast there. Eventually, none of the original pieces is left. “Is it still the same ship?” the Greek philosophers wondered.


What happens in the long run? How seriously should we take ourselves?

Our exploration of the world comes with the recognition of our own insignificance, and science has made this message only starker. The universe is big and we are small, merely some creatures crawling around on a medium-size rocky planet, one of an estimated 100 billion planets in one of about 200 billion galaxies in the visible universe. We quite literally don’t matter: most of the matter in the universe—about 85 percent—is dark matter, not the stuff we are made of, and in any case, whatever we achieve, it’ll be wiped out by entropy increase eventually.


Finally, she humbly admits neither scientists nor anyone else has all the answers.

But I want scientists to be mindful of the limits of their discipline. Sometimes the only scientific answer we can give is “We don’t know.”


Eventually, I think, we will have to accept some facts about our universe without scientific explanation, if only because the scientific method can’t justify itself.


What’s the meaning of life if there’s no purpose to it? I don’t intend to answer this question for you, not because I don’t think there’s an answer, but because I believe we all have to find our own answer. Let me just tell you how I personally think about it.


To get her answer and a whole lot more, read the book!