What Is Science?

There is an old parable — not sure if it comes from someone famous I should be citing, or whether I read it in some obscure book years ago — about a lexicographer who was tasked with defining the word “taxi.” Thing is, she lived and worked in a country where every single taxi was yellow, and every single non-taxi car was blue. Makes for an extremely simple definition, she concluded: “Taxis are yellow cars.”

Hopefully the problem is obvious. While that definition suffices to demarcate the differences between taxis and non-taxis in that particular country, it doesn’t actually capture the essence of what makes something a taxi at all. The situation was exacerbated when loyal readers of her dictionary visited another country, in which taxis were green. “Outrageous,” they said. “Everyone knows taxis aren’t green. You people are completely wrong.”

The taxis represent Science.

(It’s usually wise not to explain your parables too explicitly; it cuts down on the possibilities of interpretation, which limits the size of your following. Jesus knew better. But as Bob Dylan said in a related context, “You’re not Him.”)

Defining the concept of “science” is a notoriously tricky business. In particular, there is long-running debate over the demarcation problem, which asks where we should draw the line between science and non-science. I won’t be providing any final answers to this question here. But I do believe that we can parcel out the difficulties into certain distinct classes, based on a simple scheme for describing how science works. Essentially, science consists of the following three-part process:

  1. Think of every possible way the world could be. Label each way an “hypothesis.”
  2. Look at how the world actually is. Call what you see “data” (or “evidence”).
  3. Where possible, choose the hypothesis that provides the best fit to the data.

The steps are not necessarily in chronological order; sometimes the data come first, sometimes it’s the hypotheses. This is basically what’s known as the hypothetico-deductive method, although I’m intentionally being more vague because I certainly don’t think this provides a final-answer definition of “science.”

The reason why it’s hard to provide a cut-and-dried definition of “science” is that every one of these three steps is highly problematic in its own way. Number 3 is probably the trickiest; any finite amount of data will generally underdetermine a choice of hypothesis, and we need to rely on imprecise criteria for deciding between theories. (Thomas Kuhn suggested five values that are invoked in making such choices: accuracy, simplicity, consistency, scope, and fruitfulness. A good list, but far short of an objective algorithm.) But even numbers 1 and 2 would require a great deal more thought before they rose to the level of perfect clarity. It’s not easy to describe how we actually formulate hypotheses, nor how we decide which data to collect. (Problems that are vividly narrated in Zen and the Art of Motorcycle Maintenance, among other places.)

But I think it’s a good basic outline. What you very often find, however, are folks who try to be a bit more specific and programmatic in their definition of science, and end up falling into the trap of our poor lexicographic enthusiasts: they mistake the definition for the thing being defined.

Along these lines, you will sometimes hear claims such as these:

  • “Science assumes naturalism, and therefore cannot speak about the supernatural.”
  • “Scientific theories must make realistically falsifiable predictions.”
  • “Science must be based on experiments that are reproducible.”

In each case, you can kind of see why one might like such a claim to be true — they would make our lives simpler in various ways. But each one of these is straightforwardly false.

I’ve talked about the supernatural issue a couple of times before. Short version: if a so-called supernatural phenomenon has strictly no effect on anything we can observe about the world, then indeed it is not subject to scientific investigation. It’s also completely irrelevant, of course, so who cares? If it does have an effect, than of course science can investigate it, within the above scheme. Why not? Science does not presume the world is natural; most scientists have concluded that the world is natural because that’s the best explanation for what we observe. If you are ever confused about what “science” has to say about something, just ask yourself what actual scientists would do. If real scientists were faced with a purportedly supernatural phenomenon, they wouldn’t just shrug their shoulders because it wasn’t part of their definition of science. They would investigate it and try to come up with the best possible explanation.

The falsifiability question is a trickier one, to which I will not do justice here. It’s a charge that is frequently leveled against string theory and the multiverse, as you probably have heard. People who like to wield the falsifiability cudgel often cite Karl Popper, who purportedly solved the demarcation problem by stating that scientific theories are ones that could in principle be falsified. (Lenny Susskind calls these folks the “Popperazzi.”) It’s the kind of simple, robust, don’t-have-to-think-too-hard philosophy that even a scientist can get behind. Of course, string theory and the multiverse aren’t at all the kinds of things Popper had in mind when he criticized “unfalsifiable” ideas. His bugaboos were Marx’s theory of history, Freudian psychoanalysis, and Adlerian psychology. The problem with these theories, he (correctly) pointed out, was that they told stories that could be made to fit literally any collection of data. Not just “data we could realistically acquire,” but absolutely anything you could imagine happening in the world. That’s completely different from the examples of string theory or the multiverse, which clearly are saying something concrete about the world (the ultraviolet completion of quantum gravity, or conditions in the universe far outside our observable region), but to which we have no experimental access (or almost none). Of course, there’s also the issue that the demarcation problem is a lot trickier than naive Popperianism makes it out to be, but that’s another discussion. The right strategy, once again, is to look at what actual scientists would do or are doing. When faced with difficult problems concerning quantum gravity or the early universe, they follow precisely the outlined program: they invent hypotheses and try to see which one is the best explanation for the data. The fact that the data are relatively crude (the existence of gravity and gauge theory, the known cosmological parameters) doesn’t prevent it from being science.

Noah Smith (an economist) wrote an interesting post related to the “reproducibility” question. It’s another bugaboo, often raised by creationists who want to take jabs at evolution. As a working cosmologist, I know perfectly well that not all good science requires reproducible experiments. We haven’t made a Big Bang in the laboratory — yet. Few of the folks who emphasize reproducibility would go so far as to claim that cosmology (and much of astrophysics) doesn’t count as “science.” Instead, they say things like “Oh, but in cosmology you’re comparing data to theories that are developed here in Earth in response to laboratory experiments, so it’s a more complicated give-and-take.” Yes it is! What they should admit is that all of science involves this more complicated and subtle kind of give-and-take between theories and experiments.

Nothing in our three-step definition of science refers to “reproducibility” (any more than it refers to “naturalism” or “falsifiability”). The key feature of science is that it is empirical — progress is made by comparing multiple plausible theories to actual data — rather than rationalist/logical — deriving truths from reason alone. But when it comes to collecting those data, the only rule is “do the best you can.” Sometimes we’re lucky enough to be able to reproduce conditions exactly (Noah’s “Level Four”), but often we are not. What matters is that there are data, and that attempting to account for them is how we choose between various hypotheses that would have otherwise been plausible or at least conceivable. This might mean that some scientific questions are harder to decide than other ones, but that sounds like the least surprising conclusion in the world.

Some will object that this conception of science is too broad, and encompasses not only economics but also fields like history. To which I can only say, sure. I’ve never really thought there was an important distinction of underlying philosophy between what scientists do and what historians do; it’s all sifting through possibilities on the basis of empirical evidence.

Which is not to say that every worthwhile intellectual endeavor is a version of science in some way. Math and logic are not science, because they don’t involve steps 2 or 3. They are all about figuring out all possible ways that things could be, whether or not things actually are that way in our real world.

On the other hand, things like aesthetics and morality aren’t science either, because they require an additional ingredient — a way to pass judgment, to say that something is beautiful/ugly or right/wrong. Science doesn’t care about that stuff; it describes how the world is, rather than prescribing how it should be. You may think that there are objectively true statements one can make within these realms (“killing babies is wrong,” “Justin Bieber sucks”). But whether or not they are objectively true (they’re not, in any useful sense), they’re not scientific statements, in the way that “the universe is expanding” is a scientific statement. If they were, we could imagine worlds in which they were not true at all (“killing babies is good,” “Justin Bieber is awesome”). Those would be absolutely conceivable worlds, just not the ones in which we happened to live. And the knowledge of which world we lived in would have to come from collecting some data, just as that’s how we learned the universe is expanding.

Sometimes the fact that science is not the only kind of respectable intellectual endeavor gets packaged as the statement that there are other “ways of knowing.” This is an unhelpful framing, since it could be true or false depending on unstated assumptions held by the speaker. Yes, mathematics is a different way of gaining true knowledge than science is, so at that minimal level there are different valid ways of knowing. But they are not merely different methods of getting at the truth, they are ways of getting at different kinds of truth. What makes science (broadly construed as empirical investigation) special is that it is the unique way of learning about the contingent truths that separate our actual world from all the other worlds we might have imagined. We’re not going to get there through meditation, revelation, or a priori philosophizing. Only by doing the hard work of developing theories and comparing them to data. The payoff is worth it.

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58 Responses to What Is Science?

  1. Luis Cejudo says:

    Your thoughts on Dennis Dutton “Beauty and Evolution”? I’m curious since your mention “aesthetics”. Many thanks and awesome blossom post.

  2. Sean Carroll says:

    Don’t really know anything about it.

  3. Meghan Chen says:

    To what extent would you consider science as related to, or even a subset of, art? The boundaries of what can be considered art is admittedly not very well-defined, however most art forms generally involve the generation of ideas that reflect some kind of symmetry, order and connection in our universe. Do you think science could be thought of as a more precise, empirical form of art?

  4. Noah Smith says:

    Great stuff.

    I do have one quibble. You say that theories that are in principle non-testable (like Marxian history) are conceptually distinct from theories that are in principle testable but non-testable given current technology (like string theory). I agree with that.

    However, it seems that some theories have the following interesting property: as evidence comes in, these theories can be tweaked to avoid contact with the evidence, without limit. The obvious example is a hypothesized new particle of very high mass. As our particle colliders increase in energy, and fail to find the particle, the theory can be tweaked to predict a mass for the particle just beyond the energy scale of our most powerful colliders. (Of course the theory also has to be tweaked to fit cosmological observations).

    Is such a theory testable? Well, each specific form of it is testable – those are the specific mass predictions that keep being falsified. But the general idea of the particle existing at some mass scale is not falsifiable, even in principle.

    What do we do with theories like this? As you know, this example is far from a silly hypothetical case… 😉

  5. Amelia says:

    Great article!

    Something that I’ve been thinking about for a while: Brian Greene talks about the possibility of an ‘Ultimate Multiverse’ in his book The Hidden Reality, where every possible mathematical formulation is realized as a law of physics in some universe out there. Would you consider this as more science or philosophy? Are conceptual ideas like this, that have no concrete basis in data, thought of as philosophical until someone finds at least a theoretical way we could go about proving its likelihood?

    Also, how far do you think science can go in terms of explanatory power? Is it likely that we end up with complete knowledge of the how and why of the most fundamental questions such as why there anything at all, why stuff is made up of the stuff it’s made up of, whether it be strings, branes, point particles, etc., or are these questions too metaphysical and irrelevant to the more pragmatic goals of science?

  6. Qu Quine says:

    Really great post, Sean. I am right in the midst of this very argument over at one of the religious web sites. I am working against how some use Scientism as a straw man attack. What you have here is going to be very helpful.



  7. Sean Carroll says:

    Noah– In the sense I was advocating, a parameterized set of models with a heavy particle with different possible masses would definitely count as legitimate scientific theories. Every example has definite empirical content (there’s a particle), and therefore so does the set of all such examples. The problem with such models is not that they aren’t testable (which I argue is a bit of a red herring), it’s that they become increasingly unnatural or contrived or unhelpful as more and more versions are ruled out. So using Kuhn’s criteria or something along those lines, people would gradually lose interest. But that would be an issue of “how do we decide between theories,” not “does this count as a theory at all.”

    Amelia– The question for such ideas is the same as for any other one; does it provide a good explanation for the data? Personally my feeling is “no,” since the best we could possibly do in such a situation is to ask what a “typical” situation would look like, and I don’t see much evidence that our universe is typical within such an ensemble. Even if it were, I’m not sure what the advantage of positing all those other possible realities is supposed to be.

  8. Anonymous says:

    What’s an example of a testable (in principle) prediction made by current string theory? Suppose benevolent aliens provide us with a Planck scale collider–what do we see (per ST)?

  9. Sean Carroll says:

    If string theory is weakly coupled, there’s a well-understood cross-section at high energies that would deviate from the predictions of quantum field theory. (If the theory is strongly coupled, it’s harder to make reliable predictions, for obvious reasons.)

  10. Doc C says:

    Very nice description and delineation of how we do science, and ways we can use it.

    I think a harder question is how do we use science to help us to conduct our lives. We all use science in many of our daily activities. Are there areas of our lives that only science should be used to guide, and others for which it could or should be left aside? I suggest that part of the definition of science should include where it can be usefully applied in helping us to conduct our lives, and where it is insufficient or inadequate.

    In particular, can we apply science when we are faced with acting in the setting of absolute uncertainty? I don’t mean using it for setting odds or to improve risk management, I mean using it to create a sense of inner confidence that we are living life in a way that means not just something, but the right thing.

    If we could use science to determine exactly how our brains created consciousness, and how our consciousness affects our behavior, would we be better off, or would we just have changed the nature of our dilemma? And if science could not solve the dilemma, what would?

  11. Anonymous says:

    So it goes something like “ST counts as science because, if strings are weakly coupled, a conceivable experiment could provide sufficient evidence to favor ST over a very plausible alternative hypothesis (QFT).” I suppose I can buy that, since if we disqualify ST for not providing predictions (yet?) in the strong regime we would need to toss out QCD too, and QCD is definitely science.

    I agree, I think, that history and social sciences qualifying under this definition is ok–it’s just that those fields’ data is often of poor to useless quality as far as choosing between different hypotheses, making (3) borderline impossible so that in practice they aren’t scientific.

  12. Moshe says:

    Speaking of demarkation, I am confused about philosophy of science itself. Should I think about it as a science? So, for example, is the Popperian model of scientific activity to be judged against historical data, and if it fails to explain what scientists actually do (which I think it does), is it then falsified?

    In this context I am confused about the demarkation problem. Normally scientists don’t spend too much effort on achieving precise definition of their subjects. The question of “what is a star” or “what is a mammal” are not by themselves scientific questions. It is clear that to a certain extent those terms are arbitrary and they are only useful to the extent that they help organize and facilitate scientific activity. Why is the demarkation problem different? What insight would be lost if I define science as that activity which scientists engage in?

  13. Bee says:

    I think you might be able to improve your definition of science if you look at it from the systems perspective. It’s a process that increases our knowledge about the world. You have to work somewhat to define “knowledge” and “world” but roughly that’s it I think. Note the absence of any defining “method”. It doesn’t really matter just exactly what that process is as long as it works. However, time has taught us that there are certain procedures that work better than others, certain criteria that are generally useful etc etc. And that’s what we now call “science” in the narrow sense, increasing our knowledge about the world using certain procedures that have proved useful in the past.

    On the issue of falsifiablity, it’s a red herring because most theories aren’t strictly speaking falsifiable. They are what I called “implausifiable”. You constrain them so much that they become irrelevant and uninteresting.

  14. ph says:

    A great article Sean. I would like to know how theoretical science fits in to your definition. Consider inflation. When it was first conceived the fact that it could solve the monopole, horizon and flatness problem all in one stroke was considered “to good to be wrong”. Now let’s imagine there was no way to test inflation. Steinhardt actually argues this, but let’s just take it as hypothetical for the moment. Suppose there was no way to get any data to confirm or deny inflation. Would it count as science?
    I think we have to allow some room for theoretical plausibility. Of course empirical data is still the decider. But I think we all know that whilst a strong theoretical argument for something should not be considered conclusive in the absence of data, neither is it irrelevant to science. Similarly if something is totally illogical it isn’t going to make it to the list of reasonable hypothesis.
    I suggest science is an endeveour where hypothesis are tested via 1) theoretical plausibility and 2) empirical evidence. But where 2) is the decider. Something can be called a scientific fact if it has 1 and 2 or just a lot of good 2. But if only 1 it is not a scientific fact but neither is it “not science”. Perhaps it’s a first rung on the ladder of science. What do you think?

  15. Ron Murphy says:

    This seems like you’re talking about science after you have science in place. You really are talking yellow taxis.

    Personally I start with the cogito, and then come back up and (not having the desperate need that Descartes had to find God) figure out I can’t decide between materialism and solipsism. I can rule out most of Rationalisms and Idealisms and theologies, because they all push back to solipsism, if you bother to push hard enough.

    But this seems an entirely Rationalist approach – pure reason. That’s what the Cogito is, right? It seems the only way to start. But hold that thought. I’ll come back to pure reason.

    It seems the choice between solipsism and materialism, philosophically, is arbitrary. Until we start thinking about our senses. The material world slaps you across the face so often, feeling hungry, needing to drink, stubbing your toe, that it seems pretty persuasive. Dr Johnson may not have logically refuted solipsism (or Idealism) with “I refute it thus!”, but it’s still a persuasive though contingent inductive argument.

    Even if we (sorry, I) presuppose solipsism, it seems our (sorry, my) solipsist world still runs out this same way: my solipsist mind still insists, through the unavoidable figments of my solipsist imagination, that I need to eat, drink, and that you all do exist, even if only in my solipsist mind. So, why not just accept the material world at face value? What do we get if we accept that arbitrary choice?

    Well, we get sensing, and reasoning about our sensing: we get empiricism. But we soon learned, through the centuries of the Enlightenment, that the senses and our reasoning are flawed; not always reliable. Our early empirical investigations, our early ‘science’, may have been flaky, but it started to home in on ever better ways of getting around our human individual fallibilities.

    Then, when we do more ‘science’, and when we adopt ever more rigorous ways of doing it, we start to get consistent results. They are always contingent and are never pure logical proofs. Every valid logical argument relies on premises that must, in turn, be proved, …, and on into an infinite regress. Except for trivial tautologies and definitions, nothing is ever proved, no argument is ever ‘sound’.

    And yet the contingent science gives results. Evolution is a great result. It tells us that we are indeed material objects, with precursors that didn’t have brains, and hence no ability to reason the way we do. Heck, we are no more than collections of dynamic atomic elements, riding the crests and troughs of thermodynamic waves as the universe unfolds. Abiogenesis is implied, so all this is still contingent, sure. But really, is there any evidence of a ‘spark’ of life, or even a ‘spark’ of reason that would make humans different from other life forms, or life different from non-life? Anything that really is something totally different, anything non-material?

    We are material objects, and our brains are material systems. They acquire data; and all that data, learned from being a child, starts to make patterns in the brain. And those patterns have contexts that take on relationships that have at least some bearing on similar relationships with the material world outside the brain. Brains contextualise data to form meaning. Brains record data – they have memory. Brains process data – they think. They are decision making systems, they are computational, though in a very messy way.

    But all matter is computational in this context. A brain. A computer. A marble dropping down a marble cascade. A rock rolling down a hill ‘deciding’, by the unfolding of a sequence of causal events, if it should roll left or right of the tree before it. All aspects of the unfolding universe, using the model of causation, are causal consequences of dynamic events. Decision making, computation, is nothing more than outcomes of causal events. And that includes the activity of the brain.

    In this sense there is little difference, at the level of physics, between the senses and our reasoning. Our reasoning is just complex internal activity of neurons and stuff, while sensing is the same, but interfaced to the external world. Our ‘pure reason’ is yet more material activity. Empiricism, from this perspective, really is what we are dealing with here: animals reacting to the world they find themselves in. Components of animals, bits of stuff, neurons, reacts equal and opposite to the forces that drive them. When you consider the chemical interactions between neurons, that’s not significantly different from how an amoeba interacts with its environment. It’s chemical. It’s physical. It’s material.

    In the end, science is no more than humans doing all that humans can do: empirically interact with their environment. What we call ‘science’ is just doing that more rigorously in order to compensate for the flaws in our empirical sensing, and out empirical ‘thinking’, our reasoning.

    Pure reason isn’t the thing philosophers have been making it out to be. It doesn’t exist; there is no pure mind. Philosophers have been suffering from the primacy of thought problem: their materialist empirical brains have mistakenly thought there was this really clever mind that could reason infallibly and think its way, by pure reason, to certainties about the world (and about gods and other stuff we sometimes make up).

    What about ‘other ways of knowing’? What other ways? This is what humans have: material bodies and brains; and this is what humans do: empirical interaction with the world. That’s it.

    Unless you want to reject all of science. Unless you really want to go all solipsistic. Good luck with that.

    I can live with the contingency of human knowledge acquisition through our empiricism, especially when we do it as rigorously as we can, when we figure out new ways to compensate for our flaws: science.

    That’s what science is to me. The variations on methodologies that Sean discusses are the meat and veg of it, and the icing on the cake of it. Humans do interaction; and in doing that they do knowledge acquisition; and in doing that rigorously they do science.

    In a way we only do science. We just do it as well as we can, in what we label as ‘science’. Or we do it badly, in poor science, or worse, by thinking we can reason our way to perpetual motion machines, or gods, without empirical evidence. Imagine that: a material empirical system thinks it can do without empiricism. Lol.

    Given the contingency, and the arbitrary choice of materialism instead of solipsism, I suppose I’m still talking yellow taxis, accepting the materialist view after making an arbitrary choice. But as contingent as it is, this still seems to hang together well compared to even more flaky ‘other ways of knowing’.

  16. Robin Hanson says:

    Your theory seems too broad in that it encompasses pretty much all human behavior. Most of the time most people are filtering various possible hypotheses about the world around them by their fit with the data they see. Even aesthetics and morality can be seen as science if you treat the data as our intuitions about what is pretty and moral. Surely people use the word “science” in a much more narrow way, so a good theory of science should account for that more narrow usage.

  17. Peter Erwin says:


    The example question you raise about “philosophy of science” — does the Popperian model explain what scientists actually do? — is more a question of “history of science”. And, like most other fields of history, this could in principle be amenable to empirical testing and falsifiability. (For example, I believe some historians of biology have argued that Thomas Kuhn’s model for scientific revolutions isn’t valid, at least in their field: very few of the “revolutions” in biology of the last one or two hundred years look much like Kuhn’s model — which is based mostly on a handful of examples in astronomy and physics.)

    But I strongly suspect that Popper was arguing at least as much from a normative point of view as from a descriptive one. In other words, the question he was interested in was not so much “How have scientists actually behaved in the past?” but “What aspect or aspects of how scientists have behaved is essential to true science, and is not present in pseudoscience?”

    Now, the latter could also be interpreted as: “How should scientists behave in order to make progress?” — something which is also in principle testable. For example, you could imagine setting up two or more otherwise identical societies, different in how they decided to practice science, and see if the one which prioritized Popper’s approach made more progress in science than the other(s). As a practical issue, of course, this is essentially impossible, probably more “impossible” than Planck-scale laboratory tests of string theory.

  18. John Lloyd-Jones says:

    I find the following to be the most useful explanation of “science”:

    Science is a body of knowledge and the process by which that knowledge is obtained and refined. “Knowledge” consists of two parts; observations and models. We construct models to fit our observations. A useful model is able to retrodict past observations and allow us to predict future observations.

    The lexicographer’s observations of vehicles led to a model where all yellow cars were taxis. This was a good model where she lived. It needed to be replaced with a better one once new observations (from other countries) were acquired.

  19. Shecky R says:

    There are not different ways of ‘knowing’… there are NO WAYS of knowing… but only different ways of believing. Science is a way of believing, and one that, on the surface at least, appears very productive (from a parochial human perspective); but hey, it could ALL be wrong… and we wouldn’t know it.

  20. David says:

    3. Where possible, choose the hypothesis that provides the best fit to the data.

    This doesn’t really capture the difference between science and mysticism. “God made it this way” will always be a hypothesis that fits the data better than any approximation from scientific models. This is the conundrum that led Popper to require falsifiability: a good scientific theory makes testable predictions.

    There is one more defining feature of scientific theory, which is reductionism. A scientific theory replaces a large collection of observations with a small set of underlying principles. There are several scientific theories which qualify on that criteria, while not making testable predictions.

  21. James Cross says:

    1- Think of every possible way the world could be. Label each way an “hypothesis.”

    We can think of many ways the world could be – for example, the God hypothesis – that cannot be proven or investigated. So there seems to be a need for step 2 that says to eliminate any hypothesis which cannot be investigated. You seem to address this in our supernatural discussion but not in your steps.

    “Science does not presume the world is natural; most scientists have concluded that the world is natural because that’s the best explanation for what we observe. ”

    I think that if something previously regarded as supernatural became proven it would be declared natural by scientists. Therefore, the supernatural is any hypothesis that is outside of currently accepted natural laws.

  22. Moshe says:

    Peter, I would be surprised to see any working academic taking a normative stance towards their subject of research, but I may be wrong. Certainly the aforementioned Popperatzi take that attitude, but I am not sure they include any working philosophers of science (for whom I understand Popper fell out of favors decades ago).

    But my main confusion was the demarcation question. Normally strict demarcation is not a profitable business, terms used in science are always somewhat blurry on the edges, if you will. On the other hand, this seems to be a central issue in the philosophy of science. I am curious to understand why, I am sure there are good reasons.

  23. Sean Carroll says:

    Moshe– “Science is what scientists engage in” is a pretty good working definition, but only if we agree on who is a scientist and who isn’t. Do astrologers count?

    Philosophy of science involves many different activities (unsurprisingly). Some of them are really just part of science — e.g. attempts to understand the measurement problem of quantum mechanics or the origin of the arrow of time. Many of them are “meta” — trying to decide what should count as science and what shouldn’t, how theories are chosen, etc. Part of that is historical/empirical and part of it is normative (what should count as science?).

    It’s true that philosophers generally care a lot more about definitions that scientists do. (Although don’t forget the fuss over defining what counts as a “planet.”) Mostly that’s because philosophers are seeking rigor and perfect clarity, whereas physicists are much happier to accept fuzziness and ambiguity as long as a theory basically works. Otherwise there’s no way physicists would treat the quantum measurement problem with such casualness.

  24. Moshe says:

    Thanks Sean. Clearly some sort of demarcation is necessary so that we all know approximately what we are talking about so we can have a meaningful discussion. But in the end isn’t the definition of our terms simply conventional? You can be perfectly precise in your definitions (as in math), but I don’t see any meaning in arguing what is the “right” definition.

    The planet story is an excellent example, because I did find that it is created a confusion as to what science really does. Unlike the impression created by that story, there is no god-given meaning to the word “planet”, and deciding that Pluto isn’t one was not a statement about the natural world. It is true that some definitions are more useful than others, and discovering more facts about the solar system made it clear that the previous definition of “planet” was not as useful as it was previously thought. But, saying that Pluto was thought to be a planet, but in the end turned out not to be, is misleading, I think.

  25. John Weil says:

    Some six months ago I sent Sean a copy of an essay I had written entitled (of all things) “What is Science”. I’m sure he gets a hundred such essays every day, so mine disappeared without any response, understandably.

    But with today’s blog topic, I guess I must subject you all to what I have written. Here it is:


    Scientists and philosophers often refer to the “laws of nature”, which are regarded as basic properties of the universe. The use of these terms is misleading and leads to important misunderstandings. These “laws” are a human endeavor, not a property of the universe. In a similar vein, science is often viewed as a quest to discover these laws of the universe. This view makes two completely unwarranted assumptions: that the universe follows “laws” as we know them, and that we are capable of understanding them.

    Our ancestors found that living in an unpredictable, ever-changing world was very difficult. So they sought to observe regularities in the world about them that enabled them to predict some portion of the future with sufficient accuracy to make their lives more comfortable and comforting. Yes, it is predictability that we crave, not conservation laws or symmetries or any other universal property. We need to reduce the unpredictability of life to make it possible for us to survive and then to do more than just survive.

    Thus we seek ways of predicting some part of the future. The all-important sun sets in the evening and we do not panic since we have observed on many occasions that it will rise the next morning. In the same way we look for other types of prediction that will make our life easier by reducing the uncertainties of the future. We may need to predict the behavior of a particle in a field, or the strength of a structural material. If, along the way, we find apparent conservation laws or other universalities, so much the better, but these are helpful tools along the way to our real goal which is, always, predictability.

    The universe is what it is. It can do any damn thing that it wants to without regard to our “laws” or “principles”. It has repeatedly shown humankind that it has the capability and the inclination to do things that seem simply irrational in our eyes. The properties of atoms, which at first appeared to be small versions of the solar system, are dramatically different from what was expected based on our experience with the solar system in astronomy. A whole new branch of science, quantum physics, another human (and uncomfortable) representation of reality, had to be created to give orderliness to our view of the atomic world. There are many such examples.

    So we observe and then describe what we have observed, in the language of our experiences and, often, in mathematics. But we have not deduced a “law of nature”. We have, instead, proposed a law of humankind that is a useful approximation to what the universe is doing over the range of the set of observations from which the law was derived. Often this “law” is regarded as a Law of Nature, extending to regions far beyond that which was observed, but this is a mistake. The law is humankind’s law, not a law of the universe, and nature is not bound to obey it in any way. If the law is well founded on observation and describes reality over some significant range, it can be highly useful. But, again, it is not a law of the universe, and we should not be surprised at all when it is incorrect outside of the range over which it was originally validated. Sometimes, extending our deduced laws far beyond their confirmed range is the best we can do, having no other alternative, but we need to remember that the universe itself is not obliged to respect our extrapolation.

    Sometimes we find that we need to have more than one human law to describe adequately a full range of experience and/or experiment. This range can be over an extent of physical parameters, or of circumstances, or of any other variable(s) bearing on our observations. Quantum field theory and gravity each successfully describe the behavior of nature over large but non-overlapping ranges. While we strive to find some “theory of everything” that will correctly predict behavior over the entire range, we should have no a priori expectation that such a theory exists and should not be surprised when the attempts at unification fail.

    But it is not just a range of parameters (for example, dimensions in the case of gravity and quantum theory) that can delimit the effectiveness of our scientific theories. Our laws can also be limited by the situation in which our observations of nature are conducted. Both electromagnetic waves and matter show properties which we associate with both waves and particles, depending on the type of observation we make. In each case, waves or particles, we have developed a set of predictive laws based on our experience with waves or particles in other realms of observation, and we find it helpful to apply these laws to our new observations, choosing whichever one seems to fit the case at hand. But it seems likely that electromagnetic waves and particles are neither waves nor particles, but something more profound and complex which is not represented in our human experience and which does not show directly in our measurements. It is a perfect case of the blind men and the elephant – some feel “waves”, some feel “particles”, but no one feels “elephant”.

    The Uncertainty Principle, which stands up well to experimental experience, may be another example of the imperfectness of the fit of our “laws” to reality. We may have been approximating nature with the wrong variables – perhaps we have been trying to characterize the behavior of “foot” when it actually “trunk”. Perhaps this principle is an expression of the inaccuracy of our laws at the extremes of range at which it matters.

    Science is about prediction. Science is our human attempt to find predictability in nature by fitting to it various experiential (and often mathematical) tools to give us the ability to predict in some realm of our activities. It is not some mystical quest to find something that we believe is out there. It is a bald, human attempt to make order out of a universe that may well be far messier than we can comprehend.

    John W. Weil