One Last Stab

By Sean Carroll | October 1, 2010 8:12 am

I’ve been too busy to contribute much to the laws of physics discussion, and now I’m about to hop on a plane to bluegrass country. But I am sincerely seeking the best way to make this point clear, so one more quick try. And I do appreciate the back-and-forth thus far; sometimes frustrating, but certainly very useful to me.

If you were to ask a contemporary scientist why a table is solid, they would give you an explanation that comes down to the properties of the molecules of which it is made, which in turn reflect a combination of the size of the atoms as determined by quantum mechanics, and the electrostatic interaction between those atoms. If you were to ask why the Sun shines, you would get a story in terms of protons and neutrons fusing and releasing energy. If you were to ask what happens when a person flexes a muscle, you would hear about signals sent through nerves by the transmission of ions across electromagnetic potentials and various chemical interactions.

And so on with innumerable other questions about how everyday phenomena work. In every single case, the basic underlying story (if that happens to be what you’re interested in, and again there are plenty of other interesting things out there) would involve the particles of the Standard Model, interacting through electromagnetism, gravity, and the nuclear forces, according to the principles of quantum mechanics and general relativity.

One hundred years ago, you would not have heard that story, because it hadn’t yet been put together.

But — here’s the important part — one thousand years from now, you will still hear precisely that same story.

There might be new layers underneath, but it won’t be necessary to refer to them to give a sufficient answer to the original question. There will certainly be much greater understanding of the collective behavior of these underlying particles and forces, which is where most of the great work in modern science is being done. And hopefully there will be a deeper story about why we have the laws we do, how gravity and quantum mechanics play together, how best to interpret quantum mechanics, and so on.

What there won’t be is some dramatic paradigm shift that says “Oops, sorry about those electrons and protons and neutrons, we found that they don’t really exist. Now it’s zylbots all the way down.” Nor will we have discovered new fundamental particles and forces that are crucial to telling the story of everyday phenomena. If those existed, we would have found them by now. The view of electrons and protons and neutrons interacting through the Standard Model and gravity will stay with us forever — added to and better understood, but never replaced or drastically modified.

I’m not actually trying to say something controversial. I think it is pretty unambiguously correct, once I actually say it clearly. But it’s something I think is not as widely appreciated as it really should be.

  • NewEnglandBob

    The problem is not with you or what you said, Sean.

  • Peter Morgan

    But are you certain, **certain**, that there’s no phlogiston in our models? I feel sure, from experience, that we will be able to tell a Whiggish history of how we were right all along, that both Newton’s theory of gravity and Einstein’s theory of gravity are true, but it seems at least equally intellectually honest to say that Newton’s theory was false in *some* sense. We go to considerable lengths to tell kids that weight is different from mass, a distinction that is part of the separation of Newton from earlier Physics; why do we bother if it doesn’t change anything?

    This is just the pessimistic metainduction, no big deal, some people think it’s a potent argument, others don’t. If someone finds good empirical evidence for string theory, or someone else proves that there are both big bang cosmological models and non-big-bang cosmological models that are consistent with any experimental evidence that satisfies some very natural set of conditions (thereby weakening empirical support for Big Bang Cosmologies), does such a thing change the world, for us, or not?

    I would say that if we use sledgehammers, such subtleties make no difference, but we are restricted to what we can achieve with sledgehammers, whereas we can achieve much more if we pay attention to subtlety and detail. It doesn’t seem right for me not to feel an earthquake when I first understand a small part of some subtlety that scientists spent decades or centuries discovering and inventing for us.

    However —I would say like you—, this is just repeating myself.

  • Non-Believer

    Heroic Sean. Its easier to give up but you won’t. And that is why eventually the human race may get educated and leave behind the idea that magical things are running the universe.

    I agree that our world is entirely explainable and what we already know will lead us to more understanding. It is not mysterious magic.

    I wonder if you think its possible that there will be a depth of understanding that the human brain is incapable of processing. I look at quantam physics today and I can hardly follow the basics. Many of the common illustrations of how it works have led me to errors in understanding. I am credited with an above average intelligence. Surely at some point there are concepts that our brains are not capable of coping with, even with extraordinary intelligence and years of study.

    Of course, there is the idea that we wouldn’t recognize our inability and would either adapt a solution or not realize those levels of reality exist.

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  • Sarang

    “If you were to ask a contemporary scientist why a table is solid, they would give you an explanation that comes down to the properties of the molecules of which it is made, which in turn reflect a combination of the size of the atoms as determined by quantum mechanics, and the electrostatic interaction between those atoms.”

    I guess there are two different interpretations of “why is a table solid?” — (a) why is it solid at such-and-such a temperature, (b) why is “solid” a meaningful concept, and what defines this concept? (a) is admittedly a microscopic question, (b) has nothing to do with microscopics. If I were to ask you why the acoustic phonon spectrum of a solid is linear at low frequencies and you tried to explain that it was because the stuff consisted of molecules which consisted of atoms, I think that would be a _terrible_ explanation.

  • Tevong

    For those fixated on the fact that giants in the past have been shown to be wrong so we shouldn’t be so confident of our own theories nowadays, the fact is Newton wasn’t wrong. His laws are still correct at describing things on everyday scales, just like classical electromagnetism isn’t invalidated by a deeper, more fundamental theory and we suddenly find all our generators and motors stop working the day quantum mechanics is discovered.

    I’ll repost the link to Asimov’s essay on the relativity of wrong here:

  • Keith

    Sean … Pace NewEnglandBob we have to somehow get people to read the words that are written and not the words they think (or would like to) have been written.

    In following many of the comments on your posts I have been truly staggered — almost to the point of pulling out my remaining grey hair — that readers have totally failed to grasp that you are discussing the basic physics of our everyday world and experience of tables, cars, footballs and satellites, and not that of quantum entanglement, complex neurology, intricate photochemistry or a “grand unified theory of everything and its dog”.

  • Cosmonut

    Sean, with regards to:
    Nor will we have discovered new fundamental particles and forces that are crucial to telling the story of everyday phenomena. If those existed, we would have found them by now.
    What if you get some new force/laws which comes into play at the level of collective phenomena at the everyday level and is crucial for explaining them ? So, suppose you simulate something very complex using known physics and you find it doesn’t work out.
    With what confidence can we say that this can’t happen ?

    I agree with you that unlike a 100 years back, we can’t immediately point to an existing phenomenon – like the Sun shining – and show that it isn’t explained by known physics.
    But I guess, a hundred years back, the unexplained everyday phenomena were simpler to model, and hence, you could show more easily that your known physics failed.

    But nowadays, the unexplained frontier involves far more complex things like biological organisms, consciousness etc – so wouldn’t it be far more difficult to see if the known laws explain them adequately, or not ?

  • John

    Sean: “one thousand years from now, you will still hear precisely that same story”.

    That is the point. Obviously that will be the case for the (by now) trivial examples you quote. But for the unexplored everyday territories of the arrow of time, free will, consciousness, etc. this is very doubtful. I am not claiming these phenomena are outside the realm of physics, but they likely will require new insights at a fundamental level.

    Thousand years from now, long after the discovery of holographic zylbot dynamics, people will look back at these ignorant 21st century folks: how come they didn’t realize zylbots would solve all the quantumgravitational inconsistencies in their simplistic theories and give them a theory of consciousness at the same time?

    Zylbots are not hiding from us, we are just not clever enough (yet) to recognize them.

  • jpd

    i will give up after this, but
    re Tevong:
    Newton was right about a lot, but he was also wrong.
    alchemy was wrong.
    he thought it explained some things , but it was wrong.

  • PPK

    Sean: “What there won’t be is some dramatic paradigm shift that says “Oops, sorry about those electrons and protons and neutrons, we found that they don’t really exist. Now it’s zylbots all the way down.” Nor will we have discovered new fundamental particles and forces that are crucial to telling the story of everyday phenomena. If those existed, we would have found them by now. The view of electrons and protons and neutrons interacting through the Standard Model and gravity will stay with us forever — added to and better understood, but never replaced or drastically modified.”

    There may easily be as dramatic a paradigm shift in the future as any we had in the past, for example we could return to determinism, space and time could prove to not be fundamental, Lorentz invariance could prove to be an approximation, but most importantly there may be something completely new, something that we cannot even imagine now, just like QM and GR brought completely new qualities to physics.

    Fundamental particles and forces that are crucial to telling the story of everyday phenomena may also be discovered, until we can predict every last property from first principles there is certainly no reason to believe we found them all. For example there could be other weak fields present which influence outcomes of events which we so far take to be random. Or particles may turn out to have a complex which affects their behavior, and again there may be things which we cannot even imagine yet.

    Of course most of the laws which describe experiments will remain as they are today, but their status will change, they will be relegated to approximations.

  • Pieter Kok


    The original statement, The Laws Underlying The Physics of Everyday Life Are Completely Understood seems to make the silent assumption that these laws are microscopic, e.g., about quarks, photons, electrons, etc. Then there are the “emergent” laws that people bring up as counterexamples. If I understand you correctly, you argue that these are ultimately reducible to the well-known interplay between the fundamental building blocks I mentioned before.

    So far, so good. But then you use the phrase “completely understood”, which I take to mean that there exists an algorithm based on the underlying laws that can reproduce the emergent law. We then have to worry about the (technical) computational complexity of the algorithm. If the system consists of N particles, the algorithm must produce an output in poly(N) time. If the computational complexity scales exponentially the problem is intractable, and I would not consider such an algorithm a valid explanation of the emergent law. It is the same distinction between evanescent and propagating waves: in both cases the field amplitude is nonzero arbitrarily far from the source, but still we call only one solution “propagating”.

    You may object: but Nature is a computer that calculates the algorithm in poly(N) time. To which I counter: an explanation is a classical algorithm (because our mind operates in a classical way), but Nature is a quantum computer. If quantum computers are strictly more powerful than classical computers (i.e., if BQP > BPP), and if the emergent laws are in this class of problems, then I would say that your statement is false.

  • Aaron Wright

    Hi Sean,
    My sympathies for the “internetitude” you’re getting. I’ve read your posts but not all the comments. I have a couple of quick observations, if people are interested in more, I’ll put something up on my blog. First, you’re right that `we don’t understand the connection between the underlying laws and the macro behaviour’ doesn’t refute your points. Nevertheless, it is an answer to what I took to be your primary point: why don’t people make a big deal of our knowledge of this stuff? It’s a similar point to the observation that people deride Philosophy or English, etc. because it’s not practical.

    But, of course, it _is_ very practical…and here’s where I think you should look for people expounding on the incredible understanding we have of `basic’ physics: patent applications. That is, engineers and technologists rely on this understanding, say in designing a new waveguide/antenna for a cell phone.

    And maybe this goes some way to explaining the reactions your piece got. What people expect from physicists, especially physicists in the news / public / internet, is crazynewincrediblethingsthatblowyourmind. Physics reporting and popular books are often sensational. When you start to praise the calmer (still beautiful to us of course) physics, it’s like coming to a boxing match to find people playing chess.


  • Dreamer

    The view of electrons and protons and neutrons interacting through the Standard Model and gravity will stay with us forever — added to and better understood, but never replaced or drastically modified.

    While that may seem obvious to many, it is amazing how often people refuse to accept this simple fact — mostly by pseudoscientists and ID/creationists of course, who have a vested interest in the chance that firmly established scientific theory can still be overturned. Indeed, you will still find creationists who, somewhat astonishingly, quite seriously refuse to accept the majority of the last 100 years of physics — anything from Einstein onwards:


    But nowadays, the unexplained frontier involves far more complex things like biological organisms, consciousness etc – so wouldn’t it be far more difficult to see if the known laws explain them adequately, or not ?

    Is it mere coincidence that you are making the same argument for “something else” as the ID/Creationists do about the exact same two phenomena? While nothing is impossible, there doesn’t appear to be any good scientific reason why complexity requires an additional, as yet undiscovered, branch of physics. And even if there is one, it’s unlikely to provide any additional explanatory power for phenomena of the same scale as biological entities, any more than Einstein added to the calculation of the trajectories of WWII artillery.

  • Brian

    Zylbots is starting to sound like “physics of the gaps” …

  • Cody

    “For what was true yesterday would be true still, and new knowledge could not make old knowledge false,” J. Robert Oppenheimer

    It’s strange how much difficulty people have in understanding the convergent, tentative, and approximate constraints of science.

    I also don’t understand why people find consciousness so mysterious; if you’ve ever watched a dog hold it’s breath on a hot day to listen for a noise it thinks it heard (like a knock on the door), then you know why animals evolved sophisticated systems for decision making, and anyone who knows anything about head injuries is well aware of a brain’s sensitive reliance on physical structure, so it’s not like there is a soul or phlogiston or a thetan or something.

  • Richard L

    I just have to say that I agree with the Sean on this post… everyday stuff is quite easy to explain using the physics we know today – though I still seem to get some calculation error on my exams :/

    I like the message of this blog post, it’s something worth pondering on before falling asleep at night (to my experience, this is the best time to get good thinking done).

    What we can perceive with our senses, in our everyday experience, is explained by the physics we know today and nothing will change that. Be it light, warmth, sound or by tactile measures, our everyday physics is known.

    I’ll add that I disagree with all of the ‘literature students’ [see the link by other commentator to Asimov] and people stating that stuff like free will, consciousness and the mere existence of matter is everyday stuff… in what way is philosophy part of everyday experience? And as stated in an earlier blog-post (I think) – why won’t you add the financial sectors investments to that list? It’s pretty much the same as the question of free will…

  • spyder

    There are a number of people who wish to impose “what if” and “maybe/perhaps” contingencies on Sean’s original thoughts. It strikes me that human beings overcome “what if” problems of profound magnitude each and every day, simply by being human beings. The laws of everyday sciences and math propose numerous risks for drivers of automobiles. Yet we don’t suffer the debilitating argumentative deadlocks that keep us from accepting that the risks are part of the way we need to transport ourselves through time and space. We get into the autos and go forth, in very much the same way our ancestors got on horses, rode in wagons, or reined chariots.

    Likewise, we can say, with 100% certainty that the solid table will not levitate, but will stick to the floor.

  • Eric

    Slightly tangential question:

    So, if all everyday phenomena is satisfactorily explained, what justification is there for further basic physics research beyond scientists’ own intellectual understanding?

    Not to say that I dislike physics research; I’m starting my PhD in theoretical astrophysics next fall. But I wonder if we’re past the point where we can really say we’re providing a tangible benefit. A lot of people trot out the argument that we had no idea lasers would be useful and now we can’t live without them, but can we really make the same argument about dark matter and dark energy?

    *I* definitely want to know what dark matter is, but I don’t know if there’s any benefit to us finding out other than our own satisfaction.

  • Sam

    Cody said, “I also don’t understand why people find consciousness so mysterious…”

    Perhaps because they ask questions like “Is my perception of red the same as yours?” or “Why does light of wavelength 680 nm give rise to that (red) perception, while light of wavelength 480 nm gives rise to the perception of blue, and not the other way around?” or “Is the set of color perceptions I’ve already seen all that could be, or could some technology create an entirely different one?” It’s not at all obvious (to me) that answers to these (everyday?) questions will one day be provided by the standard model, GR, QM, or even SUSY. It may really require zylbot theory. [And please substitute “quale/qualia” for “perception/perceptions” if you prefer that jargon.]

  • Ricardo Massaro

    @Pieter Kok

    Suppose we’re able to build a quantum computer with only our current understanding of QM (i.e., with no new fundamental physics). Am I to understand that our current understanding of QM doesn’t “explain” how that quantum computer works (even though it was *built* using QM) just because it can factor integers exponentially faster than anything we can do classically?

    That doesn’t seem a very good definition of “explanation”.

  • Pieter Kok


    Our quantum computer can indeed behave in predictable (and useful) ways, such as in the case of factoring large numbers. But suppose that the quantum computer is producing some output based on what we feed as input, and we wish to work out the specific algorithm that is being computed. Even though we completely understand the underlying laws of quantum mechanics, and we built the machine ourselves, since the problem of characterizing the algorithm is intractable we cannot have a complete understanding of the patterns that emerge in the output, even in principle.

  • Ellipsis

    For the two everyday phenomena of the number of macroscopic dimensions we observe (i.e. 3+1), and the equivalence of inertial and gravitational mass, it is not at all clear that those two everyday phenomena should be just placed there by hand into axiomatic GR as they are presently, or if they are perhaps ultimately due to quantum gravity that we don’t understand as of yet. So, although I of course agree with you for the vast majority of everyday phenomena, there are those two exceptions to your statement that, if you maintain that your statement definitely holds even for those, you are not necessarily in agreement with physical consensus, which is that we don’t know yet.

  • Sean

    Cosmonut– The possibility of new long-range forces that respond nonlinearly to sources — i.e. were more than n times stronger for n particles than for one particle — is probably the most plausible loophole to the “we know all the forces” claim. But I don’t know of a way to make it actually work, though I’ve tried. It’s relatively easy to do the opposite — screen forces non-linearly — but sourcing them is not so clear. Of course, there’s zero evidence for such a phenomenon, but it’s worth thinking about.

    bittergradstudent — If gravitational waves are part of your everyday life, I’m not sure why you’re so bitter. That would make me a very happy grad student!

  • Cosmonut

    Hi Sean, thanks for your reply @24.

    Your posts on this subject got me thinking of this great passage I’d read in the Feynman Lectures and I managed to locate it today (its at the end of Chapter 41), and I reproduce a bit of it here.

    “The next great era of awakening of human intellect may well produce a method of understanding the qualitative content of equations. Today we cannot.
    Today we cannot see whether Schrodinger’s equations contains frogs, musical composers, or morality – or whether it does not. We cannot say whether something beyond is needed, or not. And so we can all hold opinions either way.”

    Thanks for the thought provoking topic.

  • ted

    Right Sean, but this is not your original argument. Before you argued that there were things in everyday life (let’s say 120) years ago that blatantly contradicted current Newtonian theory. Now you are saying that modern theories have more explanatory power – well duh!

    You say that we will have the same explanations 1000 years from now. Could be, but that kind of prediction is pretty cheap.

  • ted

    And ditto what Cosmo and Dick F said.

  • Cosmonut

    Is it mere coincidence that you are making the same argument for “something else” as the ID/Creationists do about the exact same two phenomena?

    Don’t know if its mere coincidence since the arguments are quite different.

    From what I know of the silly science/ religion wars going on in the US, the ID position is that scientific theory CAN’T explain such and such phenomenon, and hence it must be Jehovah at work.
    (although any person with sense can see that its actually Shiva :))

    So, in terms of Sean’s post, they claim to have the sort of counterexamples to phenomena explained by science, that were readily available 100 years back.

    If those claims really held up, that would cause a lot of excitement, I’m sure.
    But even if they did, the “Its Jehovah !” conclusion is not immediate at all.
    (The first step would surely be, “Its new physics !”)

    My argument was more on the lines of “How sure can we be that the known physics DOES explain very complex phenomena, given how tough it is to model the systems ?”.

    Anyway, Sean has grasped my point very well, so see his reply @24.

  • Marty

    If our best physical theories rely on postulates, does the fact that we formulate those postulates mean we understand what they postulate?

    One of the most ordinary attributes of the macroscopic world, and one that any person (educated or not) can observe, is that three spatial dimensions are sufficient to describe the relative positions of macroscopic objects. General relativity postulates a smooth differentiable manifold on which the metric can be determined if we know the stress-energy tensor over all of spacetime. The metric will have signature -+++, by assumption (and of course, because that is what agrees with observation). Since we have postulated 3 spatial dimensions, one time dimension, and a Lorentzian signature, does that mean we “understand” those facts? Sure, we observe that those postulates are apparently correct, at least macroscopically, but to say we “understand” those facts is contrary to what I think of as understanding.

    I think similar comments can be made about other parameters and postulates of our theories — do we understand them because we observe them, in the same sense that we understand gravity from general relativity?

  • wolfgang

    Once again Sean states the obvious (“it is close to impossible to find contradictions to the Standard Model with kitchen table experiments”) in such a way as to maximize opposition in comments to his blog post.
    Maybe Hiatus is not always such a bad thing 😎

  • Boaz

    Dreamer, in 14, emphasizes the quote about molecules interacting via the standard model.
    with Sean’s added caveat, “added to and better understood”.
    That seems important to add the caveat, because in a chemistry class, you really don’t study a Helium atom as a set of quantum fields, which are really wave functionals. One uses some kind of semi-classical approximation. In other words, one never really does the reduction to the lower level theory. Assumedly, the string theorists would like to study helium as string states.
    The standard model seems to be good for calculating S matrix elements, etc. so that we can compute the effects of collisions in the LHC and other colliders. But using it to describe chemistry seems quite hard. I wouldn’t go as far as to say its impossible, but I think that we cross domains from one theory to another with somewhat loose language. (I’m not clear whether the interpretation of wave functionals for bound states is really totally understood. Maybe I’m wrong.) Whether this way of talking about the relationships between different levels of phenomena will stick with us for 1000 years is not totally obvious to me.
    But I think its good for people to continue trying to connect these theories together and to do the reductions and connections as well as we can. Maybe we will find new interesting things in these attempts to formalize it more!

  • Ryan

    I have two questions I don’t think we have a sufficient understanding of the universe to answer;

    1) What generates the coherent behavior of large flocks of birds
    2) What is the nature of the process which generates (or embodies) consciousness

    My point isn’t to ask for specific answers, but to point out that I think there is a class of problem science is just beginning to consider; the issue of emergent dynamics and the behavior of partially chaotic systems.

    It’s true that we know why the birds are ‘solid’ and that the brain uses electrical impulses somehow, but this isn’t the same as having a rigorous understanding of the qualitative difference between a thousand birds flying randomly and a thousand birds making instantaneous and coordinated decisions about which direction to fly in.

  • Gordon

    1. I would postulate that it is like an array of cellular automata and a local phenomenon and is not instantaneous but seems so. Each bird reacts to the bird in front of it or in its visual field, so if the bird in front turns to the left, it does, and the effect ripples almost instantaneously through the flock.

  • Gordon

    2. Not known yet. Christof Koch is working on it:

    The Quest for Consciousness, a Neurobiological

  • felix

    Completely explaining everyday phenomena so what? Everyday phenomena are dull anyway. When can we fly to Proxima Centauri, a mere distance of 4 light-years away? Science is not ended by understanding everyday phenomena. Science is about doing the incredible things that go far beyond everyday experience.

  • Ricardo Massaro

    @Pieter Kok

    But doesn’t that imply that our current understanding of physics can’t completely understand classical computers either? Consider this: it’s possible to build a (classical) circuit implementing a 3SAT problem such that we can’t answer in polynomial time whether the circuit will ever output “1”.

    It seems that your requirement for “complete understanding” is unattainable a priori — regardless of the complexity of the universe.

  • Paddy

    Paul Dirac said much the same thing in 1929 (but more carefully phrased, natch):

    The fundamental laws necessary for the mathematical treatment of a large part of physics and the whole of chemistry are thus completely known, and the difficulty lies only in the fact that application of these laws leads to equations that are too complex to be solved.

    But I still think Sean is being naive at a number of levels.

    For a start, scientists have been pretty smug about their explanations of everyday life for centuries, if not millenia (Epicurus would have told you a nice story about tables being made of atoms, back in 300 BC). And in many cases, especially since about 1700, they would not have been wrong; it’s just that their explanation would have had fewer “layers” than Sean’s stories. Chemists didn’t go around 100 years ago worrying that they didn’t understand the chemical bond; they took it as a given and celebrated the fact that they could use it to understand the properties of molecules. By 1929 Dirac could celebrate that chemistry had been “explained”, but his explanation would have been less “fundamental” than Sean’s: he was thinking of standard non-relativistic QM. If you’d asked Lord Kelvin in 1890 he could have explained why a table is solid in terms of chemical bonds, elasticity etc. Unlike Dirac’s unsolvable equations and Sean’s just-so stories, Kelvin’s explanation would have included some physical laws you could actually use to design a table that didn’t collapse under its own weight. So actually, the laws Sean is celebrating are neither applicable to everyday situations, nor truely fundamental. (Which is not to say that they can’t be used to help design some marvellous gadgets).

    Secondly, I’m a bit sceptical that we are stuck with electrons for ever and no paradigm shift will change that. Arguably the concept of “electrons” is already long out of date, at least insofar as it implies that electrons are unproblematic distinct objects.

    Finally, there are the emergent laws like the second law of thermodynamics and evolution by natural selection. It is not that we don’t understand where these laws come from: in both those cases the explanation is very clear. But the point is, it has nothing to do with the “fundamental” laws of electrons et al. Entropy would increase in almost any universe, even if we radically changed the fundamental laws, e.g. by replacing field theory with cellular automata. Organisms will evolve under selective pressure any time you have almost-but-not-perfect inheritance, irrespective of how you implement that. Arguably, that makes these laws much more fundamental than QFT or whatever TOE is eventually discovered. And there are very likely other emergent laws which are directly relevant to everyday life that we havn’t figured out yet. Turbulence may well be a case in point.

  • Frank

    This blog mentions the arrow of time as counterexample to Sean’s wefigureditallout claim.

    Any comments?

  • Pieter Kok


    In both counterexamples you start with the algorithm. But I am trying to say that the nature of an explanation goes the other way: you start with the phenomena (i.e., the output of the quantum computer) and the basic laws of quantum mechanics (i.e., a universal set of quantum gates). To find an explanation of the phenomena in terms of the basic laws means you have to uncover the algorithm. You will have to use experimentation, in the form of comparing input states with output states. You may be lucky/inspired in a particular case and hit upon an algorithm that seems to work, but there is no “meta-algorithm” that will uncover the algorithm you are looking for efficiently. I would say that in this sense the phenomena are not completely understood.

    The other way around is a different case: in order to find a factoring algorithm you already have a complete specification of what the algorithm should accomplish. Remarkably, this allows you to actually prove that a given algorithm (Shor’s) does what you want it to do.

    This is slightly different from my original comment (#12), so thanks for bringing up these arguments. Even if this is not the last word in the matter (this is the Internet, after all), I strongly believe that we should treat “explanations” in a computational sense, with all the machinery of computational complexity theory that comes with it. I think this will eventually also bring about a shift in the underlying assumption that the fundamental laws are always microscopic.

  • Nullius in Verba


    What if you have two new forces that exactly cancel one another out, and screen only one of them?

    Say you gave all matter a slight net positive charge that exactly counterbalanced gravity, as well as an electric dipole moment? The electrostatic repulsion would cancel the gravity, and you would see no force between particles. But in large clouds of matter, the dipole moment would shield the electrostatic repulsion, while leaving the gravity alone.

    Or did I misunderstand?

  • Sean Peters

    I’m a latecomer to the laws of physics debate here, but having read it all now from the beginning – come on, Sean. You make a very strong claim – we already know everything – and then qualify it to death with “in our everyday experience”, and “not in the details of how it all plays out”, etc. So you’ve made a claim that appears to say a lot more than it actually does, and then are all surprised that people get confused? You’re blaming readers because they didn’t pay enough attention to the fine print?

    Sure, people should have read this more carefully. And if they had, the reaction would most likely have been a big yawn, as you are not really claiming much of anything once all the qualifications have been incorporated. As an illustration, it’s just as true that the everyday experience of people in 1776 was pretty much completely explained by Newton – sure, there were some more accurate measurements to be taken of moving bodies that might have changed things, and there were some hints that all was not well in the world of thermodynamics, and there was that troubling electricity to be explained, but guess what – that’s far outside the everyday world of 1776.

    And the state of science in 200 BC pretty much completely described the everyday world then, too. Of course, objects in motion tend to slow down and come to rest – that’s plainly observable. And obviously, the earth is the center of the universe and other bodies orbit it. Sure, detailed measurements of inertia still had to be done, and there were those difficult epicycles to work out in the orbits of planets and moons, but guess what – that’s far beyond the everyday world of 200 BC.

    In reality, it seems that you wanted to make a very sweeping claim but couldn’t support it, so you watered it down with qualifications until it was meaningless. And then blamed readers for not picking up on the qualifications. Usually I really like your writing, but this whole line of argument is unbelievably weak.

  • David Derbes

    Sean is surely correct about this, but a little voice tells me that the universe may have secrets we haven’t figured out about some ordinary, everyday things that, a hundred years from now, people will be surprised we didn’t know. Are we going to have a deeper understanding of Coulomb’s Law? I doubt it. Will there be a qualitatively different understanding of what protons are, or what electrons are, or of the nature of light? Unlikely.

    Still, there isn’t, as far as I know, a really good understanding of friction. Can the coefficient of friction between, say, smooth pure copper and smooth pure carbon, be calculated?

    Admittedly it was more than a long and fruitful century ago, but Kelvin thought we had *all* of physics understood at the turn of the last century, apart from the small clouds of black body radiation and the nature of the luminiferous aether. And we know how that turned out. Sean is saying that there aren’t any more clouds with respect to *everyday* physics. In my opinion only a fool would bet against him.

  • John

    @Sean Peters

    It’s not just that the abundance of fine print in Sean’s argument that confuses people.

    When Sean uses the words “for the first time in history” he simply misrepresents the history of science. With all the fine print in effect, Sean could have made the same we-figured-it-all-out statement in the middle ages (as you correctly point out).

  • Avon

    Sean’s attitude is the real holdup on real science – we have to wait for all of the old scientist fossils to die off. After they’ve spent their entire professional life barking up the wrong tree, do you expect them to change their minds gracefully?

    Evolution is stumbling badly, and we’re left with creationism as the only alternative?

    What about the standard model of the universe? Standard model expansion is speeding up and slowing down like a car stuck in stop-and-go traffic. The vast majority of the universe is made up of dark, negative energy (which no-one has ever seen) and dark matter (which no-one has ever seen). Those of us with less-than-advanced degrees see a forest, not trees.

    Does any-one out there have any idea why gravity works? Or why quantum mechanics works? What about light or electricity or time? We have NO IDEA why the most elementary concepts in physics do what they do. Currently all we have is empirical knowledge of the universe around us, the engineers are doing all of the work while the theorists sit around and espouse nonsense, while telling us they have all the answers.

    Real science is done by ordinary people who reject the dogma of the “standard model” and objectively study the data, realize the connection, and tell somebody. Win the vaunted Nobel prize? More likely they will be professionally burnt at the stake.

  • Russ Abbott

    It maybe that the today’s physics provides a model of a platform upon which explanations of everyday experience can be built. But it seems to me that two clarifications are needed.

    1. We don’t understand completely how that platform works. For example the platform includes gravity as one of its primitive elements. Are you really satisfied simply to say that we understand the everyday phenomenon of gravity because gravitational phenomena fit the model we have built for it? There are many phenomena for which we can build descriptive models even though we don’t understand how they work.

    2. Think of some computer program whose inner workings you don’t understand. That computer program produces some phenomena. Although it’s true that the computer program executes on a computer whose elementary operations we do understand, is it really useful to say that just because we understand the underlying machine we understand how the phenomena themselves come about? It may be the case that our current model of fundamental physics is sufficiently powerful that mechanisms using that physics can bring about the sorts of complex phenomena people (including you) have cited, etc. If that’s what you want to say, then ok. But that dismisses an awful lot that we don’t understand. Point 1 then goes on to say that we don’t even fully understand how that model works.

    Perhaps it might be better to say that modern physics provides a description of a level of complexity that (a) is unlikely to change much and (b) is sufficient to serve as a platform for implementing most of what we see in our everyday lives. But (a) we don’t fully understand how that platform itself works, and (b) we don’t fully understand the workings of many of the phenomena that are built upon that platform.

  • Jiav


    Very interesting series of post. Please count me in 3. You’re too presumptuous. New physics might be required to understand consciousness.

    While I’m deeply believing that’s not true, I will consider presomptuous to take for granted that no new physics is requiered to understand consciousness. Or, to clarify, to understand my own inner world.

    “We can’t be sure that the motion of the planets isn’t governed by hard-working angels keeping them on their orbits, in the metaphysical-certitude sense of being “sure.” That’s not a criterion that is useful in science. ”

    I don’t want to be rude in anyway, but the truth is that I think you miss the point here. It’s not about a metaphysical-certitude sense of being sure, it’s about the fact that known physic seems to be able to explain behavior with no need for consciouness or inner life. Sure, one possibility is that certain configuration of information will be proven to equate inner life. But another possibility is that behavior need no inner life to be explained by known physics. Conversely, that means that known physic might have nothing to say on what is the inner life we all experienced.

    “What would be a refutation of my claim that we understand the laws underlying everyday phenomena? Easy: point to just one example of an everyday phenomenon that provides evidence of “new physics” beyond the laws we know.”

    So I count inner life as everyday phenomena for which known physics says nothing yet, and for which we should not be too fast to rejecte the need for new physics.

    Not that I believe it, but we should be more cautious than Maxwell was.


  • Boaz

    @Avon, 44-
    This seems a bit harsh to say that Sean’s attitude is holding up science… and really disrespectful to scientists to call the old folks fossils…
    Why would you say that real science is done by those who reject the standard model? The standard model has a lot of success. People who accept the standard model are clearly also making much progress and teaching us much about the world.
    I think Sean goes wrong in wanting physics to cover more territory than it really does. He does give the qualification that “the physics” of every day life is explained. So its not that everything is explained, only physics. This is a bit of a tricky loophole, though, if you haven’t said a bit more clearly what physics is- in new contexts, 1000 years from now.
    What is physics? And how unified of a discipline is it really? What are its limitations, as currently defined? These are the grey areas I’d be interested in Sean going into a bit more depth on. (Sorry, perhaps I should read his book first, before criticizing!) Or maybe just finding a slightly different way of discussing it, so that other disciplines are given respect and seen how they fit into physics.

  • JimV

    Yes, friction (nanotribology) is understood, based on the Standard Model, with the usual problem of solving very large systems of simultaneous PDE’s on the macro level.

    I’m firmly with those who see consciousness as a non-problem. In my case (can’t speak for the rest of you), billions of neurons are churning through lots of possibilities before I write each word of this sentence. I have no nerves which monitor their actions, so the results seem to arrive out of nowhere, but someday a giant super-computer with as many registers as I have neurons will be able to think as well or poorly as I do.

    In mechanical engineering we have an problem with certain welds known as “hydrogen cracking”. It turned out that quantum mechanics predicts a particular shape of hydogen bonds which explains this problem. (It took several weeks of computer work to do the calculations.)

    There are still a lot of calculations and worthwhile research to be done, but I agree with Sean – a thousand years form now there will still be hydrogen cracking if weld electrodes aren’t kept dry, and it will still be explained by quantum mechanics acccording to the Standard Model. We may or may not have the giant computers then, depending on whether our civilization keeps progressing or not.

    Yes (according to my humble opinion), there will be things we can never figure out because we aren’t smart enough, just as chimpanzees will never figure out the Standard Model.

    There is sort of a catch-22 here. Since there is no magic, just emergent behavior out of complex physical laws, it follows that emergent creatures like ourselves have lots of limitations which we would rather not acknowledge.

  • Brian Fies

    Sean, I’m with you 99% of the way. But on my bookshelf I’ve got this set of Encyclopedia Britannicas from 1892 whose “Astronomy” article has pages and pages on solar spectroscopy and not one sentence attempting to explain what causes spectral lines or, indeed, how the sun shines at all. Understandable–they didn’t know fusion, they hadn’t even figured out the electron yet!–but it’s striking that there’s not a hint that such questions were significant or even worth asking. Similarly, I had an upper division astrophysics course (in the early ’80s) in which the topic of galactic missing mass came up and the prof shrugged it off as a trivial rounding error for the math guys to clean up rather than a hint that most of the universe was missing. So I always wonder: what fundamental thing sitting right in front of us are we overlooking today? What questions are we not even thinking to ask? Could a new physics of dark matter/energy or something we don’t even know we don’t know change our understanding of *everything*? It seems plausible, especially on the order of centuries. I think it unlikely, but protons, neutrons and electrons could turn out to be shadows on the cave wall that simply aren’t needed to explain reality four or five centuries from now.

  • Sorbit

    The examples (table, sun etc.) are quite trivial as mentioned above. Your original claim was much stronger and now you seem to have considerably qualified it. You did good by doing this.

  • bete noir

    Easy: point to just one example of an everyday phenomenon that provides evidence of “new physics” beyond the laws we know. Something directly visible that requires a violation of general relativity or the Standard Model. That’s all it would take, but there aren’t any such phenomena.

    Whereas I mostly agree with you, on behalf of all contrarians in this world here’s my attempt at a counterexample of the kind you describe. There’s an everyday phenomenon that is, to say the least, not well understood: mass. We know the masses we experience in our everyday lives are related to confinement and chiral symmetry breaking in QCD, but don’t know exactly how those happen.

    Now, imagine that 100 years from now somebody would be able to give an explanation for confinement and chiral symmetry breaking in QCD as simple and intuitive as Einstein’s explanation of the photoelectric effect. Wouldn’t that explanation deserve the title of “basic law of Nature”? I think it would. So, people living in the next century would rightly say “Well, that guy Sean Carroll didn’t really know the most basic law of everyday life, how ordinary baryonic matter has mass.”

  • Slide2112

    ugh. Always a dissapointing moment here at CV. Wood builds a beautiful home so why consider anything else?

  • Boaz

    @bete noir, 51
    But, it sounds like you’re saying that the explanation would still be in terms of QCD, so it doesn’t violate the standard model.

    We say the table is made of atoms, and the atoms are made of protons, neutrons and electrons, and the protons and neutrons are made of quarks. And we can rearrange those basics in our accelerators and predict the results. We understand some aspects of the standard model, and so we say that we understand the table.

    I think this way of looking at things would say that the future mass law (or explanation) is not a basic law of nature. Or at least, the standard model rules are the underlying story.

    This line of thinking is certainly important in order to support particle physics, cosmology and other “basic” research. Once one gives up on finding practical results from one’s research, you do have to have explain why other people should support you in what you do. Being part of a generally healthy intellectual adventure and attempt to come to terms with our world is certainly one approach to interact with other people. But if it comes across as, “our theory is the best, it underlies everything, and no, I can’t really explain it to you”. Then its hard to keep people’s interest and support. And not just non-scientists. Chemists who mainly rely on non-relativistic quantum mechanics, and a lot of other stuff, or biologists who use some physics concepts, and some other stuff may also not want to support basic physics research if its not relevant to what they do.

  • bete noir

    But you still cannot tell me how matter gets a mass.

  • bete noir

    To be more explicit: yes, of course, in my hypothetical example the answer would still be in terms of the SM. It obviously couldn’t be otherwise. But not necessarily in terms of quarks and gluons, and that’s the point. The relevant degrees of freedom may be completely different. Just like in the photoelectric effect the relevant degrees of freedom are not the electromagnetic fields, but the photons.

    Hand-waving arguments about chairs made of atoms will not cut it. We do not know the origin of baryonic mass.

  • Boaz

    But how is this different from say high TC superconductivity? Ok, not exactly an every day phenomenon. But the basic elements that give rise to it- the “mechanism” behind it, isn’t understood.
    I’d guess there’s still things about turbulence that aren’t understood, and other weather phenomenon.
    The point in understanding such a thing is to find the right degrees of freedom. Find a few basic element that work together in a certain way, and show that the phenomenon you’re interested in comes out of that. With weather phenomenon, one expects that some fluid mechanics equations may be sufficient. Sean is saying we can do it all “using” the standard model and general relativity, and you seem to agree. The photoelectric effect was different in that photons were not really a part of the existing E&M, classical mechanics, etc of the time. It seemed quite hard to say what this photon thing was. And it really only made a bit more sense with quantum mechanics.
    Maybe you’re saying that in some sense the solution to the mass problem would use such weird degrees of freedom, that in some sense they really wouldn’t fit into the standard model all that well?

  • Phillip Helbig
  • bete noir

    But how is this different from say high TC superconductivity? Ok, not exactly an every day phenomenon.

    Exactly, I didn’t mention high-Tc superconductivity because it’s not part of our everyday experience (yet).

    Maybe youu2019re saying that in some sense the solution to the mass problem would use such weird degrees of freedom, that in some sense they really wouldnu2019t fit into the standard model all that well?

    A good example is low-Tc, BCS superconductivity. Explaining it didn’t require drastically changing QED, say at the Lagrangian level. But it did require extending it non trivially. The notion of dynamical breaking of U(1) gauge symmetry by an electron-pair condensate may seem familiar now, but it was very tough to figure out at the time BCS did. It is a non-trivial, non-perturbative extension of our notion of QED.

    Similarly, our understanding of baryonic mass will doubtlessly happen in the context of QCD, but it will probably require a similar non-trivial extension of our notion of what QCD is in the non-perturbative regime. Whether it will involve some kind of duality, holographic formulation, topological degrees of freedom, whatever, we don’t know yet. But then, that means we still don’t know what the fundamental physical law is that governs mass generation in ordinary matter.

    (Or, to be precise, the generation of 90% of the mass of baryonic matter. About 10% or so comes from quark masses, and for those we do not even know what the microscopic law is. Maybe the SM Higgs mechanism, or something else. The LHC will tell, hopefully.)

    (By the way, that’s another counter example to Sean’s statement. We do not know what microscopic law gives rise to about 10% of our own mass. And no, it’s not beer.)

  • Boaz

    Good points, bette noir.
    I guess your distinction gets at what we mean by a fundamental physical law.
    In the case of low-Tc superconductivity, would we say that the fundamental law is the BCS mechanism, or is it QED?
    It seems to me that the basic theories (classical E&M, QED, stat-mech…) are kind of like tool kits out of which to build more specific theories/models. And they may even come in different forms, like we have Lagrangians or Hamiltonians or forces for classical mechanics. And we have wave functions, or matrix operators or Wigner functions for quantum mechanics.
    I think things like axiomatic quantum field theory aren’t very popular because we like to have a little bit of wiggle room in our basic theories so we can mold them to fit the phenomena we actually want to describe.
    With string theory, we could say that it hasn’t been very easily able to describe the standard model, so it hasn’t been widely used. But they have tried to use it to describe condensed matter and nuclear physics phenomena.

  • Boaz

    I guess this comment thread is done, but here’s a philosophy thesis I’ve been trying to read that formalizes the “More is Different” idea that would say that the microphysics laws aren’t the only fundamental ones. I think it might put the claim of bette noire on stronger grounds- that different degrees of freedom may imply new laws. He goes into a lot about symmetry breaking.


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Cosmic Variance

Random samplings from a universe of ideas.

About Sean Carroll

Sean Carroll is a Senior Research Associate in the Department of Physics at the California Institute of Technology. His research interests include theoretical aspects of cosmology, field theory, and gravitation. His most recent book is The Particle at the End of the Universe, about the Large Hadron Collider and the search for the Higgs boson. Here are some of his favorite blog posts, home page, and email: carroll [at] .


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