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The Use of Fiction and Falsehood in Science

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Astrophysicist Neil deGrasse Tyson has some interesting and provocative things to say about religion in a recent interview. I tend to agree with Tyson that religions have a number of odd or even absurd beliefs that are contrary to science and reason. One statement by Tyson, however, struck me as inaccurate. According to Tyson, “[T]here are religions and belief systems, and objective truths. And if we’re going to govern a country, we need to base that governance on objective truths — not your personal belief system.” (The Daily Beast)

I have a great deal of respect for Tyson as a scientist, and Tyson clearly knows more about physics than I do. But I think his understanding of what scientific knowledge provides is naïve and unsupported by history and present day practice. The fact of the matter is that scientists also have belief systems, “mental models” of how the world works. These mental models are often excellent at making predictions, and may also be good for explanation. But the mental models of science may not be “objectively true” in representing reality.

The best mental models in science satisfy several criteria: they reliably predict natural phenomena; they cover a wide range of such phenomena (i.e., they cover much more than a handful of special cases); and they are relatively simple. Now it is not easy to create a mental model that satisfies these criteria, especially because there are tradeoffs between the different criteria. As a result, even the best scientists struggle for many years to create adequate models. But as descriptions of reality, the models, or components of the models, may be fictional or even false. Moreover, although we think that the models we have today are true, every good scientist knows that in the future our current models may be completely overturned by new models based on entirely new conceptions. Yet in many cases, scientists often respect or retain the older models because they are useful, even if the models’ match to reality is false!

Consider the differences between Isaac Newton’s conception of gravity and Albert Einstein’s conception of gravity. According to Newton, gravity is a force that attracts objects to each other. If you throw a ball on earth, the path of the ball eventually curves downward because of the gravitational attraction of the earth. In Newton’s view, planets orbit the sun because the force of gravity pulls planetary bodies away from the straight line paths that they would normally follow as a result of inertia: hence, planets move in circular orbits. But according to Einstein, gravity is not a force — gravity seems like it’s a force, but it’s actually a “fictitious force.” In Einstein’s view, objects seem to attract each other because mass warps or curves spacetime, and objects tend to follow the paths made by curved spacetime. Newton and Einstein agree that inertia causes objects in motion to continue in straight lines unless they are acted on by a force; but in Einstein’s view, planets orbit the sun because they are actually already travelling straight paths, only in curved spacetime! (Yes this makes sense — if you travel in a jet, your straightest possible path between two cities is actually curved, because the earth is round.)

Scientists agree that Einstein’s view of gravity is correct (for now). But they also continue to use Newtonian models all the time. Why? Because Newtonian models are much simpler than Einstein’s and scientists don’t want to work harder than they have to! Using Newtonian conceptions of gravity as a real force, scientists can still track the paths of objects and send satellites into orbit; Newton’s equations work perfectly fine as predictive models in most cases. It is only in extraordinary cases of very high gravity or very high speeds that scientists must abandon Newtonian models and use Einstein’s to get more accurate predictions. Otherwise scientists much prefer to assume gravity is a real force and use Newtonian models. Other fictitious forces that scientists calculate using Newton’s models are the Coriolis force and centrifugal force.

Even in cases where you might expect scientists to use Einstein’s conception of curved spacetime, there is not a consistent practice. Sometimes scientists assume that spacetime is curved, sometimes they assume spacetime is flat. According to theoretical physicist Kip Thorne, “It is extremely useful, in relativity research, to have both paradigms at one’s fingertips. Some problems are solved most easily and quickly using the curved spacetime paradigm; others, using flat spacetime. Black hole problems . . . are most amenable to curved spacetime techniques; gravitational-wave problems . . . are most amenable to flat spacetime techniques.” (Black Holes and Time Warps). Whatever method provides the best results is what matters, not so much whether spacetime is really curved or not.

The question of the reality of mental models in science is particularly acute with regard to mathematical models. For many years, mathematicians have been debating whether or not the objects of mathematics are real, and they have yet to arrive at a consensus. So, if an equation accurately predicts how natural phenomena behave, is it because the equation exists “out there” someplace? Or is it because the equation is just a really good mental model? Einstein himself argued that “As far as the laws of mathematics refer to reality, they are not certain; and as far as they are certain, they do not refer to reality.” By this, Einstein meant that it was possible to create perfectly certain mathematical models in the human mind; but that the matching of these models’ predictions to natural phenomenon required repeated observation and testing, and one could never be completely sure that one’s model was the final answer and therefore that it really objectively existed.

And even if mathematical models work perfectly in predicting the behavior of natural phenomena, there remains the question of whether the different components of the model really match to something in reality. As noted above, Newton’s model of gravity does a pretty good job of predicting motion — but the part of the model that describes gravity as a force is simply wrong. In mathematics, the set of numbers known as “imaginary numbers” are used by engineers for calculating electric current; they are used by 3D modelers; and they are used by physicists in quantum mechanics, among other applications. But that doesn’t necessarily mean that imaginary numbers exist or correspond to some real quantity — they are just useful components of an equation.

A great many scientists are quite upfront about the fact that their models may not be an accurate reflection of reality. In their view, the purpose of science is to predict the behavior of natural phenomena, and as long as science gets better and better at this, it is less important if models are proved to be a mismatch to reality. Brian Koberlein, an astrophysicist at the Rochester Institute of Technology, writes that scientific theories should be judged by the quality and quantity of their predictions, and that theories capable of making predictions can’t be proved wrong, only replaced by theories that are better at predicting. For example, he notes that the caloric theory of heat, which posited the existence of an invisible fluid within materials, was quite successful in predicting the behavior of heat in objects, and still is at present. Today, we don’t believe such a fluid exists, but we didn’t discard the theory until we came up with a new theory that could predict better. The caloric theory of heat wasn’t “proven wrong,” just replaced with something better. Koberlein also points to Newton’s conception of gravity, which is still used today because it is simpler than Einstein’s and “good enough” at predicting in most cases. Koberlein concludes that for these reasons, Einstein will “never” be wrong — we just may find a theory better at predicting.

Stephen Hawking has discussed the problem of truly knowing reality, and notes that it perfectly possible to have different theories with entirely different conceptual frameworks that work equally well at predicting the same phenomena. In a fanciful example, Hawking notes that goldfish living in a curved bowl will see straight-line movement outside the bowl as being curved, but despite this it would still be possible for goldfish to develop good predictive theories. He notes that likewise, human beings may also have a distorted picture of reality, but we are still capable of building good predictive models. Hawking calls his philosophy “model-dependent realism”:

According to model-dependent realism, it is pointless to ask whether a model is real, only whether it agrees with observation. If there are two models that both agree with observation, like the goldfish’s model and ours, then one cannot say that one is more real than the other. One can use whichever model is more convenient in the situation under consideration. (The Grand Design, p. 46)

So if science consists of belief systems/mental models, which may contain fictions or falsehoods, how exactly does science differ from religion?

Well for one thing, science far excels religion in providing good predictive models. If you want to know how the universe began, how life evolved on earth, how to launch a satellite into orbit, or how to build a computer, religious texts offer virtually nothing that can help you with these tasks. Neil deGrasse Tyson is absolutely correct about the failure of religion in this respect.  Traditional stories of the earth’s creations, as found in the Bible’s book of Genesis, were useful first attempts to understand our origins, but they have been long-eclipsed by contemporary scientific models, and there is no use denying this.

What religion does offer, and science does not, is a transcendent picture of how we ought to live our lives and an interpretation of life’s meaning according to this transcendent picture. The behavior of natural phenomena can be predicted to some extent by science, but human beings are free-willed. We can decide to love others or love ourselves above others. We can seek peace, or murder in the pursuit of power and profit. Whatever we decide to do, science can assist us in our actions, but it can’t provide guidance on what we ought to do. Religion provides that vision, and if these visions are imaginative, so are many aspects of scientific models. Einstein himself, while insisting that science was the pursuit of objective knowledge, also saw a role for religion in providing a transcendent vision:

[T]he scientific method can teach us nothing else beyond how facts are related to, and conditioned by, each other.The aspiration toward such objective knowledge belongs to the highest of which man is capabIe, and you will certainly not suspect me of wishing to belittle the achievements and the heroic efforts of man in this sphere. Yet it is equally clear that knowledge of what is does not open the door directly to what should be. . . . Objective knowledge provides us with powerful instruments for the achievements of certain ends, but the ultimate goal itself and the longing to reach it must come from another source. . . .

To make clear these fundamental ends and valuations, and to set them fast in the emotional life of the individual, seems to me precisely the most important function which religion has to perform in the social life of man.

Now fundamentalists and atheists might both agree that rejecting the truth of sacred scripture with regard to the big bang and evolution tends to undermine the transcendent visions of religion. But the fact of the matter is that scientists never reject a mental model simply because parts of the model may be fictional or false; if the model provides useful guidance, it is still a valid part of human knowledge.

The Role of Imagination in Science, Part 3

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In previous posts (here and here), I argued that mathematics was a product of the human imagination, and that the test of mathematical creations was not how real they were but how useful or valuable they were.

Recently, Russian mathematician Edward Frenkel, in an interview in the Economist magazine, argued the contrary case.  According to Frenkel,

[M]athematical concepts and ideas exist objectively, outside of the physical world and outside of the world of consciousness.  We mathematicians discover them and are able to connect to this hidden reality through our consciousness.  If Leo Tolstoy had not lived we would never had known Anna Karenina.  There is no reason to believe that another author would have written that same novel.  However, if Pythagoras had not lived, someone else would have discovered exactly the same Pythagoras theorem.

Dr. Frenkel goes on to note that mathematical concepts don’t always match to physical reality — Euclidean geometry represents an idealized three-dimensional flat space, whereas our actual universe has curved space.  Nevertheless, mathematical concepts must have an objective reality because “these concepts transcend any specific individual.”

One problem with this argument is the implicit assumption that the human imagination is wholly individualistic and arbitrary, and that if multiple people come up with the same idea, this must demonstrate that the idea exists objectively outside the human mind.  I don’t think this assumption is valid.  It’s perfectly possible for the same idea to be invented by multiple people independently.  Surely if Thomas Edison never lived, someone else would have invented the light bulb.   Does that mean that the light bulb is not a true creation of the imagination, that it was not invented but always existed “objectively” before Edison came along and “discovered” it?  I don’t think so.  Likewise with modern modes of ground transportation, air transportation, manufacturing technology, etc.  They’re all apt to be imagined and invented by multiple people working independently; it’s just that laws on copyright and patent only recognize the first person to file.

It’s true that in other fields of human knowledge, such as literature, one is more likely to find creations that are truly unique.  Yes, Anna Karenina is not likely to be written by someone else in the absence of Tolstoy.  However, even in literature, there are themes that are universal; character names and specific plot developments may vary, but many stories are variations on the same theme.  Consider the following story: two characters from different social groups meet and fall in love; the two social groups are antagonistic toward each other and would disapprove of the love; the two lovers meet secretly, but are eventually discovered; one or both lovers die tragically.  Is this not the basic plot of multiple stories, plays, operas, and musicals going back two thousand years?

Dr. Frenkel does admit that not all mathematical concepts correspond to physical reality.  But if there is not a correspondence to something in physical reality, what does it mean to say that a mathematical concept exists objectively?  How do we prove something exists objectively if it is not in physical reality?

If one looks at the history of mathematics, there is an intriguing pattern in which the earliest mathematical symbols do indeed seem to point to or correspond to objects in physical reality; but as time went on and mathematics advanced, mathematical concepts became more and more creative and distant from physical reality.  These later mathematical concepts were controversial among mathematicians at first, but later became widely adopted, not because someone proved they existed, but because the concepts seemed to be useful in solving problems that could not be solved any other way.

The earliest mathematical concepts were the “natural numbers,” the numbers we use for counting (1, 2, 3 . . .).  Simple operations were derived from these natural numbers.  If I have two apples and add three apples, I end up with five apples.  However, the number zero was initially controversial — how can nothing be represented by something?  The ancient Greeks and Romans, for all of their impressive accomplishments, did not use zero, and the number zero was not adopted in Europe until the Middle Ages.

Negative numbers were also controversial at first.  How can one have “negative two apples” or a negative quantity of anything?  However, it became clear that negative numbers were indeed useful conceptually.  If I have zero apples and borrow two apples from a neighbor, according to my mental accounting book, I do indeed have “negative two apples,” because I owe two apples to my neighbor.  It is an accounting fiction, but it is a useful and valuable fiction.  Negative numbers were invented in ancient China and India, but were rejected by Western mathematicians and were not widely accepted in the West until the eighteenth century.

The set of numbers known explicitly as “imaginary numbers” was even more controversial, since it involved a quantity which, when squared, results in a negative number.  Since there is no known number that allows such an operation, the imaginary numbers were initially derided.  However, imaginary numbers proved to be such a useful conceptual tool in solving certain problems, they gradually became accepted.   Imaginary numbers have been used to solve problems in electric current, quantum physics, and envisioning rotations in three dimensions.

Professor Stephen Hawking has used imaginary numbers in his own work on understanding the origins of the universe, employing “imaginary time” in order to explore what it might be like for the universe to be finite in time and yet have no real boundary or “beginning.”  The potential value of such a theory in explaining the origins of the universe leads Professor Hawking to state the following:

This might suggest that the so-called imaginary time is really the real time, and that what we call real time is just a figment of our imaginations.  In real time, the universe has a beginning and an end at singularities that form a boundary to space-time and at which the laws of science break down.  But in imaginary time, there are no singularities or boundaries.  So maybe what we call imaginary time is really more basic, and what we call real is just an idea that we invent to help us describe what we think the universe is like.  But according to the approach I described in Chapter 1, a scientific theory is just a mathematical model we make to describe our observations: it exists only in our minds.  So it is meaningless to ask: which is real, “real” or “imaginary” time?  It is simply a matter of which is the more useful description.  (A Brief History of Time, p. 144.)

If you have trouble understanding this passage, you are not alone.  I have a hard enough time understanding imaginary numbers, let alone imaginary time.  The main point that I wish to underline is that even the best theoretical physicists don’t bother trying to prove that their conceptual tools are objectively real; the only test of a conceptual tool is if it is useful.

As a final example, let us consider one of the most intriguing of imaginary mathematical objects, the “hypercube.”  A hypercube is a cube that extends into additional dimensions, beyond the three spatial dimensions of an ordinary cube.  (Time is usually referred to as the “fourth dimension,” but in this case we are dealing strictly with spatial dimensions.)  A hypercube can be imagined in four dimensions, five dimensions, eight dimensions, twelve dimensions — in fact, there is no limit to the number of dimensions a hypercube can have, though the hypercube gets increasingly complex and eventually impossible to visualize as the number of dimensions increases.

Does a hypercube correspond to anything in physical reality?  Probably not.  While there are theories in physics that posit five, eight, ten, or even twenty-six spatial dimensions, these theories also posit that the additional spatial dimensions beyond our third dimension are curved up in very, very small spaces.  How small?  A million million million million millionth of an inch, according to Stephen Hawking (A Brief History of Time, p. 179).  So as a practical matter, hypercubes could exist only on the most minute scale.  And that’s probably a good thing, as Stephen Hawking points out, because in a universe with four fully-sized spatial dimensions, gravitational forces would become so sensitive to minor disturbances that planetary systems, stars, and even atoms would fly apart or collapse (pp. 180-81).

Dr. Frenkel would admit that hypercubes may not correspond to anything in physical reality.  So how do hypercubes exist?  Note that there is no limit to how many dimensions a hypercube can have.  Does it make sense to say that the hypercube consisting of exactly 32,458 dimensions exists objectively out there somewhere, waiting for someone to discover it?   Or does it make more sense to argue that the hypercube is an invention of the human imagination, and can have as many dimensions as can be imagined?  I’m inclined to the latter view.

Many scientists insist that mathematical objects must exist out there somewhere because they’ve been taught that a good scientist must be objective and dedicate him or herself to the discovery of things that exist independently of the human mind.  But there’re too many mathematical ideas that are clearly products of the human mind, and they’re too useful to abandon merely because they are products of the mind.