Chapter 4
ARE YOU JUST A BAG OF ATOMS?
What Are You?
Some public speakers, I am told, cope with speech anxiety by picturing their audience naked. I don't know about you, but I'd rather not. apart into chemical elements (figure 7).
The human body is about 6i0 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.
If that doesn't work for you, maybe it helps to ponder the origin of your atoms. The universe didn't start out with chemical elements in place, except for hydrogen, which was created a few minutes after the Big Bang, because making the atomic nuclei for the chemical elements requires substantial pressure. Heavy elements could be generated only once stars began to form from hydrogen clouds under the pull of gravity. In these collapsing clouds, gravitational pressure eventually ignites nuclear fusion, which merges the cores of light nuclei to increasingly heavier ones.
But there comes a time when a star has fused everything it had to fuse. At the end of their lives, most stars dim calmly, but some of them collapse rapidly and subsequently explode, thereby becoming a supernova. The supernova explosion blows the star's interior out into the cosmos. Freed from the busy environment of the star, the released atomic nuclei then catch electrons and become proper atoms.
But even a supernova explosion doesn't entirely annihilate a star; it leaves behind a remnant that is either a neutron star or a black hole. Neutron stars are big blobs of nuclear matter, so dense they just barely escape collapsing to a black hole. The heaviest of the elements, such as gold and silver, can form only in a particularly violent environment, such as neutron star mergers. In these mergers, too, heavy nuclei are blown out and distributed throughout galaxies, where they catch electrons and become atoms.
Some of these atoms come together to form small molecules or even microscopic grains-stardust. The dust mixes into clouds of hydrogen and helium, which are still around from the Big Bang. And gravity continues its work. If the clouds get too dense, they will collapse again, give birth to new stars, solar systems, planets, and, potentially, life on these planets.
This process it not cyclic, and to our best current knowledge it cannot continue forever. At some point in the far future-estimated to be about a hundred trillion years from now-the universe's re-maiming nuclear fuel will be gone for good. This is one of the consequences of entropy increase, which we talked about in chapter 3. The universe can host life for only a limited amount of time.
But here we are, made of atoms that either came straight from the Big Bang or were thrown into interstellar space by stars in their final fit of anger. As the meme has it, we are made of stardust, children of the stars, and so on. Personally, I don't care much where my atoms came from, but at this point I have usually forgotten my speech anxiety.
More Is More
Does it take anything more than particles to make a conscious being?
I have found that many people reflexively reject the possibility that human consciousness arises from interactions of the many particles in their brain. They seem wedded to the idea that somehow something must be different about consciousness. And while the scientifically minded among them do not call it a soul, it is what they mean. They are looking for the mysterious, the unexplainable, the Extra that would make their existence special. They find it inconceivable that their precious thoughts are "merely" consequences of a lot of particles doing whatever the laws of nature dictate. Certainly, they insist, consciousness must be more than this. In a2019 survey, 75.8 percent of Americans subscribed to this idea of dualism-that the human mind is more than a complicated biological machine. In Singapore, the percentage of dualists was even higher: 88.3 percent.
If you are among the dualist majority, we have to make a deal be-fore we can move on. You put aside your belief that consciousness requires some Extra that physics doesn't account for and hear what I have to say. In return, I promise that if you, at the end of this book, still insist the human brain is exempt from the laws of nature, I'll let you get away with it.
Having said that, as a particle physicist by training, I have to in-form you that the available evidence tells us that the whole is the sum of the parts, not more and not less. Countless experiments have con-firmed 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.
Just as a country's history is a consequence of the behavior of its citizens and their interactions with the environment, so is the behavior of the citizens a consequence of the properties and interactions of the particles they are made of. Both are hypotheses that have with-stood any test they have been subjected to-so far. As a scientist, I therefore accept them. I accept them not as ultimate truths, for they may one day be revised, but as best current knowledge.
A lot of people seem to think it is merely a philosophical stance that the behavior of a composite object (for example, you) are determined by the behavior of its constituents-that is, subatomic particles. They call it reductionism or materialism or, sometimes, physicalism, as if giving it a name that ends in ism t will somehow make it disappear. But reductionism-according to which the behavior of an object can be deduced from ("reduced to," as the philosophers would say) the properties, behavior, and interactions of the object's constituents-is not a philosophy. It's one of the best-established facts about nature.
Nevertheless, I am not a reductionist hard-liner. Our knowledge about the laws of nature is limited, much remains to be understood, and reductionism may fail in subtle ways I will discuss later. However, you have to learn the rules before you can break them.
And in science, our rules are based on facts. Fact is, we have never observed an object composed of many particles whose behavior falsified reductionism, though this could have happened countless times. We have never seen a molecule that didn't have the properties you’d expect, given what we know about the atoms it is made of. We have never encountered a drug that caused effects that its molecular com-position would have ruled out. We have never produced a material whose behavior was in conflict with the physics of elementary particles. If you say "holism," I hear "bullshit."
We certainly know of many things that we cannot currently predict, for our mathematical skills and computational tools are limited. The average human brain, for example, contains about a thousand trillion trillion atoms. Even with today's most powerful supercomputers, no one can calculate just how all these atoms interact to create conscious thought. But we also have no reason to think it is not possible. For all we currently know, if we had a big enough computer, nothing would prevent us from simulating a brain atom by atom.
In contrast, assuming that composite systems-brains, society, the universe as a whole-display any kind of behavior that does not derive from the behavior of their constituents is unnecessary. No evidence calls for it. It is as unnecessary as the hypothesis of God. Not wrong. But a scientific.
"ln case you find paraphrasing large numbers as confusing as I do, that’s about 1CP1,
This may come as a shock to some of you. Didn't Philip Anderson-a Nobel Prize winner! - claim the contrary when he coined the catch-phrase "More is different"? Indeed, he did. But just because a Nobel Prize winner said it does not mean it is correct.
Up until about fifty years ago, physicists described a system at different levels of resolution with different mathematical models. They would, for example, use one set of equations for water, then another set for its molecules, and yet another set for atoms and their constituents. These different mathematical models were independent of one another.
By the middle of the twentieth century, however, physicists began to formally connect these different models. I say formally because the mathematical derivations can in most cases not be executed yet; the calculations are just too difficult. But physicists now have a well-defined procedure to derive, say, the properties of water from the properties of atoms. This procedure is called coarse-graining, and while the mathematics is tough, the idea is conceptually simple.
Consider that you're describing a system at high resolution, meaning you take into account lots of fine structures at short distances. Imagine, for example, a topographic map, one that tells you not only where mountain ridges and valleys are but that goes all the way down to creases in the asphalt and pebbles in meadows. If you plan a hike, there is a lot of detail in this map that you do not need. To create a map that's better suited for your purposes, you could put, say, a hundred-yard grid on the terrain and use average values for each square of the grid. This would mean you'd discard information, but it would be information you wouldn't need.
Coarse-graining in physics is a more complicated version of this averaging; it's a method for discarding information you don't need. In physics, the size of the grid is often referred to as the cutoff, and the task is to write down an approximate model that is accurate enough at the resolution given by the cutoff, plus small corrections for the missing details. If you then throw away the small corrections below the cutoff for good, you have what physicists call an effective model. This model is not fundamentally correct-because, like your averaged topographic map, it is missing information-but it is good enough at the level of resolution you are interested in.
The best-known examples for effective models are bulk descriptions of gases and fluids in terms of aggregate quantities like temperature, pressure, viscosity, density, and so on. These descriptions average molecular details. There are many other effective models that we use in physics. It is typical of an effective model that the objects and quantities central to it are not the same as those in the underlying theory; they usually do not even make sense in the underlying theory. The conductivity of a metal, for example, is a property of materials that derives from the behavior of electrons. But it makes no sense to speak of the conductivity of an electron. Indeed, the whole concept of metal makes no sense if you are working with a model of subatomic particles. A metal is a certain arrangement of many small particles.
We say that such properties and objects, which play a key role in the effective theory but do not appear in the fundamental theory, a reemergent. An Emergent properties and objects can be derived from or reduced to something else. Fundamental is the opposite of emergent. A fundamental property or object cannot be derived from or reduced to anything else. Two other terms I will use in the following is that the more fundamental layers are the deeper ones, whereas the emergent ones are higher levels.
[["To be more precise, this case is called weak emergence. Philosophers distinguish it from strong emergence, which refers to the hypothetical case of a macroscopy system having properties that are not derivable from its constituents and their behavior. We'll talk more about strong emergence in chapter 6.]]
Pretty much everything we deal with in everyday life is emergent., a high-level property or object. The color of a material (high level) emerges from its atomic structure (deeper level). The potency of a drug (high level) emerges from its molecular composition (deeper level], and the molecular composition further emerges from the molecules' atomic composition (even deeper). The motion of a cell emerges from the arrangements and interactions of its molecules. The function of an organ emerges from that of its cells, and so on.
As the example of the coarse-grained topographic map illustrates, in the process of deriving emergent properties, we discard details that reside at short distances. This is why going from one level to the next higher one in the theory tower is a one-way street. You can derive the laws of hydrodynamics (which describe the motions off lids) from the theory of atoms. You cannot, however, derive the atomic theory from hydrodynamics. That's because in the derivation of the effective model you throw away information for good. This usually happens in the mathematics by taking some parameter to infinity or, equivalently, by discarding small corrections. In fact, that this theory tower is not a two-way street is why we cannot just deduce more fundamental laws from the laws we have. If we could, they wouldn’t be more fundamental! (So how do physicists discover more fundamental laws, then? We'll talk about this with David Deutsch in the next interview.)
In most cases, we currently cannot perform the mathematical calculations that would be necessary for coarse-graining. For example, no one can at present derive the properties of a cell from those of its atoms. Indeed, even predicting the properties of molecules is difficult, as the protein-folding problem illustrates. The math is just too difficult.
But it doesn't matter for our purposes whether or not we can actually perform the calculation that connects the deep level with the high level. We are interested here only in what we can learn from the structure of natural laws. Therefore, what matters is merely that, according to well-established theories, the deepest level determines what happens at the higher levels. If someone now claims that this isn’t so, they must at the very least explain how this can be. How can it be that a theory for, say, a metal does not follow from the theory forth collection of the metal's constituents? If you want to push this idea, that's the challenge you have to meet.
Emergent theories aren't of any less importance than fundamental ones. Indeed, they tend to be more useful exactly because they ignore irrelevant details. Emergent theories are in most cases the better explanations at their level of accuracy. But the only fundamental theories we currently know of-the currently deepest level-are the standard model of particle physics and Einstein's general relativity, which describes gravitation.
I will in the following refer to the areas of physics that study the fundamental laws as the foundations of physics. Everything else emerges from those fundamental laws, roughly in this order: atomic physics, chemistry, materials science, biology, psychology, sociology. Most physicists, myself included, don't think the currently fundamental theories will remain fundamental More likely, what's currently fundamental will turn out to be emergent from yet another, deeper level. ["The search for this deeper level was the subject of my previous book, Lost in Math, How beauty Leads Physics Astray, and I will not cover here in detail.]
In hindsight, it might seem patently obvious that scientific disciplines are tied together in this way. But this was not how scientists thought about nature for most of the previous century. Indeed, out-side the foundations of physics, you still find many who vehemently argue that all scientific disciplines are equally fundamental.
Now, to some extent this is quibbling over words. I use the term fundamental to mean "cannot be derived from another theory." Scientists in other disciplines sometimes think less fundamental implies less important, and then they're insulted. But physicists aren't trying to belittle other scientists by pointing out that everything is made of particles; it's just how it is.
I said I'd be honest with you, so I should add that some physicists still don't believe that natural laws are indeed reductionist. I don't have much to say about this except that I've laid out the evidence, and you can evaluate it yourself. The hypothesis that nature is reductionist is supported both by observational evidence-we find explanations for one level's functions by going to a deeper level, not the other way around-and recently by understanding some of the math behind it.
Having said that, I must address here a common misunderstanding about this layered structure of natural laws, namely that there seem to be examples contradicting it. Say you push a button that turns on a particle collider that collides two protons, which produces a Higgs boson. In that sequence, wasn't it your decision-i.e., an upper-level function-that caused an event on much shorter distances, hence violating the idea of this neatly ordered structure? Another common example is that of computer algorithms that switch transistors on and off while processing information. Isn't it the algorithm that you programmed-upper-level function-that controls the electrons? It isn’t hard to come up with an abundance of similar examples.
The misunderstanding in these cases is always the same. Just because it is useful to describe certain properties or behaviors of a system (you, a computer algorithm) in macroscopic terms (motives, computer code) doesn't mean the macroscopic description is more fundamental. It isn't. You could full well describe a computer, including its algorithms, in terms of neutrons, protons, and electrons. It would be a totally useless description, of course.
But if you wanted to prove reductionism false, you'd have to show that describing a system in macroscopic terms results in different pre-dictions than those you'd get from its microscopic description (and then do an experiment that demonstrates that the predictions from the microscopic description are wrong). No one has managed to do that. Again, it's not because that wouldn't have been possible. Maybe you can try to conceive of a world in which the behavior of atoms derives from that of the planets instead of the other way round, but for all we can tell, it's just not the case.
To make sense of this tower of theories, note that the function of a composite object does not derive merely from its constituents. One also has to know the interactions of the constituents and the correlations between them, i.e., one needs the full microscopy information. Quantum entanglement, in particular, is really a type of correlation-it links particles together-but even though it can span macroscopic distances, it's still a property defined on the fundamental level. We will talk more about entanglement later, but let us note for now that it doesn't contradict reductionism.
In summary, according to the best current evidence, the world is reductionist: the behavior of large composite objects derives from the behavior of their constituents, but we have no idea why the laws of nature are that way. Why is it that the details from short distances do not matter over long distances? Why doesn't the behavior of protons and neutrons inside atoms matter for the orbits of planets? How come what quarks and gluons do inside protons doesn't affect the efficiency of drugs? Physicists have a name for this disconnect-the decoupling scales-but no explanation. Maybe there isn't one. The world has to be some way and not another, and so we will always be left with un-answered why questions. Or maybe this particular why question tells us we're missing an overarching principle that connects the different layers.
One Bit at a Time
If you're at all like me, you probably think of yourself as a physically compact, localized object, feet at one end, head at the other. That intuitive self-image, however, isn't rooted in reality.
Our bodies' physical composition constantly changes. We swap some of the particles we're made of for new ones each time we breathe, drink, or eat. After all, that's how we grew to this size to begin with. Throughout our lives, we repurpose atoms that previously belonged toother animals, plants, soil, or bacteria, atoms that were created in the Big Bang or by stellar fusion. 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. From this ancient debate comes the saying "No man ever steps in the same river twice, for it's not the same river and he's not the same man," which is usually attributed to Heraclitus," [Though Heraclitus didn't actually write that is a quote in which word after word has been replaced until none of the original words remain sill, she same quote? The answer is left as an exercise for the roader.]
As so often, the answer depends on how you define the terms in the question. What do you mean by the ship and what do you mean by the same? It's only once you have defined these expressions that you’ll be able to answer the question-and there are many different answers. Don't worry; I have no intention to roll up 2,500 years of philosophy-I'll get back to physics in a moment-but credit where credit is due: the old Greeks realized long ago that an object's constituents aren't the only thing that's relevant about it. Even after you have exchanged all the pieces of the ship, its construction plan-the information you need to build it-remains the same. Indeed, you could define information as what doesn't change about the ship when you replace its parts.
It's similar for humans. Humans are made of particles, and the behavior of those particles determines our behavior. But that reduction isn’t what makes humans or any complex structure-interesting. What makes them interesting are the emergent higher-level proper-ties: Humans walk, talk, and write books. Some of them reproduce. Others fly to the moon. Jars of chemicals don't do that. The relevant property of humans is not our constituents. It's the way the constituents are arranged; it's the information you need to build a human, the information that tells you what it can do.
I don't mean just your genetic code, for your genes alone aren’t sufficient to define the person you are today. I mean all the necessary details that specify the way each part of your body, each single molecule, interacts with any other. That includes the countless little (and big) experiences that left marks in your brain, traces of the food you’ve eaten and air you've breathed, legacies of past illnesses, scars, and bruises. What makes you you are this entire arrangement. Your you-ness, whatever exactly it is, emerges from the configuration of the particles you are constituted of. For all we currently know, these properties could emerge in different ways.
The Canadian scientist and philosopher Zenon Pylashyn illustrated this nicely with a thought experiment in 1980. Imagine you’re going about your usual day-to-day thinking, maybe wondering whether it's time for a coffee. Now, suppose someone takes away one of your neurons and replaces it with a silicon chip. The silicon chip is designed so it responds to input and output from the rest of your brain identically to the replaced neuron. The chip performs the exact same function that the neuron did previously, and it seamlessly connects to the other neurons. Does that change anything about your personality? Do you maybe suddenly forgo coffee and ask for tea? No. Why would it make a difference? After all, nothing changed about the way your brain processes information. Good. Then swap the next neuron with a chip. And the next. That way, one by one, your brains replaced by silicon chips, until it's all silicon chips. Are you still the same person?
As with Theseus's ship, it depends on how you define you and the same. In some sense, you arguably aren't the same person, because you’re now made of different physical components. Yet the physical components aren't what we care about. What we care about is the arrangement of the components. It's the functions they perform that make you interesting. In that sense, you haven't changed. You can still perform the same functions, you're still as interesting as you used to be.
But are you really the same? That's where physics becomes relevant. It's one thing to write that you can replace a neuron with a silicon chip without altering the brain's function whatsoever. Whether that’s actually possible is another question entirely. The phrase he same in Pylyshyn's thought experiment implicitly assumes it is possible to replace neurons with chips, not just so the differences are unnoticeably small, but so there are no differences. This strong assumption is necessary for the argument to work. If I replaced one molecule of your coffee with one molecule of tea, it would taste the same to you; it's an unnoticeably small difference. But if I kept replacing molecule after molecule, eventually you would notice. A large number of unnoticeably small changes can eventually become noticeably large change. How do we know that's not what's going on in the neuron replacement?
The obvious answer is that we don't know, because no one's done it. Still, we can ask what is possible according to all we know about physics. Is it possible to replace a neuron with something else so the substructure-silicon or carbon-makes no difference? Yes, it's possible because, as we discussed in the previous section, scales decouple. We can ignore the details on short distances for the emergent behavior on large distances. And this also means you can swap the short-distance physics for another one, neurons for chips, or yet something else, and it wouldn't make a difference, as long as the emergent behavior is the same.
Of course, as always, it could be that something is wrong with the theories we currently use and that this argument therefore fails for reasons we don't yet know of. The physicist and Nobel Prize winner Gerard 't Hooft, for example, has argued that the observations we attribute to quantum randomness are really due to noise that is as yet unaccounted for, arising from new phenomena at short 'distances. If that is so, the decoupling of scales could fail. Maybe 't Hooft is right, but so far, his idea is pure speculation.
I should mention for completeness that it isn't entirely clear at present whether our brains are the sole home of our identity, but this complication doesn't matter for the argument. Studies have shown, for example, that at least some aspects of human cognition are embodied; that is, they rely on input from other body parts, such as the heart or guts. That may be bad news for people who've had their head Frozen in the hope of being resurrected, but it isn't relevant to the question whether your constituents can be replaced by physically different parts. If swapping neurons in the brain doesn't entirely move your cognition to u silicon basis, then just imagine that the rest of your body is also being replaced.
The information that makes you you can be encoded in many different physical forms. The possibility that you might one day upload yourself to a computer and continue living a virtual life is arguably beyond present-day technology. It might sound entirely crazy, but it’s compatible with all we currently know.
>> THE BRIEF ANSWER
You, I, and everything else are made of small constituent particles, and whatever large objects like us do is a consequence of what their many small constituents do. However, the characteristic features of a creature or object are the relations and interactions among their many constituent particles, not the particles themselves. For all we currently know, it is therefore possible to exchange the physical substrate of a being or object with something else. So long as this replacement maintains the characteristic relations and interactions, it should also maintain function, including consciousness and identity.
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(Genesis 1:27) So God created mankind in his own image,
in the image of God he created them;
male and female he created them. (Genesis 1:27)
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(Genesis 2:7) Then the Lord God formed a man[a] from the dust of the ground and breathed into his nostrils the breath of life, and the man became a living being. (Genesis 2:7)
DNA: 
DNA, or deoxyribonucleic acid, is the molecule that carries genetic instructions for the development and function of living organisms, passed down through generations. It is a double helix structure, like a twisted ladder, composed of nucleotide bases (Adenine, Thymine, Guanine, and Cytosine) that form the rungs of the ladder. The sequence of these bases encodes biological information and instructions for making proteins, which are essential for an organism's traits and functions.
Function
Genetic Information: DNA contains the complete set of genetic information for an organism, essentially the "blueprint" for its development and daily operations.
Protein Synthesis: Segments of DNA called genes provide instructions for making specific proteins, which carry out various functions in the body.
Inheritance: DNA is passed from parents to offspring, ensuring that traits are inherited.
Structure
Double Helix: DNA consists of two long strands that are twisted around each other, forming a shape known as a double helix.
Backbone: Each strand has a backbone made of alternating sugar (deoxyribose) and phosphate molecules.
Nucleotide Bases: Attached to the sugars are four types of nucleotide bases: adenine (A), guanine (G), cytosine (C), and thymine (T).
Base Pairing: Adenine always pairs with thymine, and cytosine always pairs with guanine, forming the rungs of the DNA ladder.
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