Outer Limits of Reason (47 page)

Karl Popper and Falsifiability

Noticing the problems of induction and the other problematic aspects of the scientific processes, Karl Popper formulated a description of the way science really works. He agreed with Hume and the others that the problem with induction makes it impossible to verify a scientific theory. In contrast, it is relatively easy to show that a scientific theory is
incorrect
. All you have to do is find one instance where the theory is shown to be false. If a theory implies some phenomena and if observation shows that these phenomena do not happen, then we have no recourse but to conclude that the theory is false. In the notation of this book,

Theory ⇒ false phenomena

means the theory is false. Popper felt that rather than trying to verify a theory, scientists should try to show it is false.

Popper was influenced by Eddington's famous experiment with a solar eclipse, which we discussed in 
section 7.3
. He was seventeen years old in 1919 when the experiment showed that Newton's notion that space is a flat place where phenomena take place is not true. Eddington showed that large objects like the sun will bend light and that Newton's notion of space needs to be abandoned. Einstein's theory of general relativity was seemingly “more correct.” Popper was awed by the fact that after hundreds of years of following Newton, scientists were willing to abandon Newton's ideas because they were shown not to work this one time. He sharply contrasted this with theories in politics, morality, and religion, where a doctrine is held by its believers despite much evidence showing it is false.

This ability of science to be shown to be incorrect—in other words, the fact that science is
falsifiable
—was for Popper the defining property of science. It is the demarcation between science and other disciplines. Science makes predictions that can be shown to be wrong by observation. He described disciplines that do not make falsifiable predictions as
pseudosciences
and felt they do not reach the lofty status of science. Popper's primary examples of pseudosciences were Marxism and psychoanalysis. These two influential intellectual movements made many predictions about politics, economics, and human nature. However, whenever their predictions turned out to be false, Marxists and psychoanalysts were always able to show how their theories really explained these abnormalities. In a sense, a pseudoscience is too powerful since every outcome of any experiment and every phenomenon can be explained by it. It is only in real science where some prediction can be wrong and show that an entire theory is wrong and must be discarded.

For Popper, science progresses by making falsifiable conjectures and predictions. Scientists then go out and check these conjectures and predictions by doing experiments. If the experiments show that the conjectures are false, the scientists move on to other conjectures. However, if the experiments do not show the conjectures are false, this does not mean the theory is true. Rather, this only shows that the theory has not been falsified . . . yet.

Not everyone takes Popper's ideas to heart. People have argued whether this is really the way that science progresses. Most scientists are very happy with the probabilistic solution to the problem of induction and freely use other methodologies to select different theories. Once a theory is selected, it is usually felt to be confirmed if there is enough evidence showing it is correct. In real life scientists do not wait around until their theories are falsified.

Another criticism of Popper is that falsifiability is not the be-all and end-all that he makes it out to be. While it is used by many scientists, there are times when it does not work so well. As we will see in the next section, when Urbain Leverrier (1811–1877) looked at the motion of the newly found planet Uranus, he saw certain irregularities that did not fit well with the laws of Newton. An orthodox Popperian would have advised Leverrier to abandon Newton's laws and look for other laws. Luckily Leverrier ignored such hypothetical advice and held onto the laws of Newton. Instead of discarding Newton's laws of planetary motion, he used them to find another planet that caused Uranus to veer off course. Science is a complicated process.

Popper's ideas bring to light another problem in the philosophy of science: How does a researcher tell if a new and radical idea is right or is crazy? Is this new idea visionary or is it simply cuckoo? Obviously one should go out and perform experiments to test the idea. However, what if the idea cannot be tested or if the results of experiments are inconclusive? At what point should a theory no longer be considered radical and start being considered the truth? When should a theory be considered a quack theory? At one time most scientists believed in substances called ether and phlogiston. Planetary epicycles were once common knowledge. And yet these ideas turned out to be false. In contrast, at one time the ideas advanced by Copernicus, Pasteur, and the Wright brothers were considered totally insane, while now they are legitimate science. While it is true that most quacks remain quacks, nevertheless, the history of science has taught us that our ability to differentiate good science from bad science is not perfect.

Let's say we have two different theories that explain a certain phenomenon. How are we to tell which is the correct theory? This is the case when there are two different-shaped pegs that fit into the same hole. Which one belongs there? Obviously if there is any experiment or observation that falsifies one theory then it is to be discarded. Does that mean the other one is true? Perhaps there are other theories besides these two theories. Before any are falsified, what are we to do? This is a limitation to our ability to know the laws of nature. It is a limitation to reason.

Popper's definition of science makes the goal of achieving absolute truth through the scientific method unachievable. More importantly, for our purposes, what it shows is that what we think we know about the universe is not necessarily true. It simply has not been falsified yet. While it could very well be that the scientific theories that we currently do have are, in fact, the ultimate truth, it could also be that our current theories will one day be falsified. We simply do not know. Our theories could be the truth and could just be another tentative stage in the development of science.

We will never know even if we do have the right answer. Eddington's experiment did not show that Einstein's theory of general relativity is the correct theory. It simply showed that Newton's theory did not work well for large objects like the sun. Whether or not Einstein's theory is correct is something we do not know. If it is incorrect, then it might one day be shown to be false. In contrast, if it is correct, Popper offers no method for us to know this. We are constantly in a state of waiting to be falsified. For Popper, all scientific knowledge is provisional and not absolute.

Thomas Kuhn and Paradigms

In 1962, Thomas S. Kuhn (1922–1996) published one of the most influential books in the philosophy of science.
The Structure of Scientific Revolutions
changed the way people think about science and how it progresses. According to Kuhn, science takes place within a paradigm—that is, a group of ideas and language used by all the researchers in that field. The science that is done within such a paradigm is termed
normal science
. The community of scientists who are working within that paradigm will accept this science and agree with it. This is how the vast majority of science is done.

However, normal science is not the only story. As time goes on, certain anomalies will be found within the working paradigm. While these anomalies will not be ignored, scientists will nevertheless stick to the paradigm and make only minor changes to the ideas present in the paradigm. They will try to fix up and slightly modify the paradigm rather than transform it. With more time, these anomalies will build up into a massive crisis. There will be something wrong with the paradigm and a revolutionary change must be made. This is what Kuhn calls
revolutionary science
. The paradigm will change and this change has come to be known as a
paradigm shift
. At first the revolutionary scientists will be shunned by their peers. They will be speaking a different language and will have a different worldview. The new paradigm will seem strange and perhaps even unreasonable. However, it will explain more and have fewer anomalies than the old one. Eventually the new paradigm will gradually be accepted by the scientists in the field.

After some time, the revolutionary new paradigm will become the normal paradigm and all the new or flexible workers in the field will work in this paradigm. Their science will become the new orthodoxy. Eventually certain anomalies will be found with this paradigm and this process will go on and on. Throughout the development of a certain field, there will be long periods of normal-science equilibrium, punctuated
¹⁶
by revolutionary paradigm shifts.

There are many examples of such paradigm shifts. The paradigmatic example is the shift from the Ptolemaic geocentric system to Copernicus's heliocentric system. This revolution took hundreds of years until it became the new paradigm. Another revolution was the change from Newton's worldview to Einstein's general relativity in the early twentieth century. The change from classical mechanics to quantum mechanics was also a major paradigm shift. An example from biology is Louis Pasteur's germ theory. In all these cases, there was a major change from an old point of view to a new one.

Another major idea in Kuhn's work is his notion of
incommensurability
between two paradigms. He felt that since there are different languages and different worldviews, it is virtually impossible for people who accept different paradigms to communicate. Some philosophers go further and say that it is wrong to compare different paradigms. Why should we say that one is more scientific or more rational than another? Each paradigm works for its own time.

Kuhn came to some of these ideas by studying the works of Aristotle. He realized that from the point of view of a Newtonian scholar, Aristotle is totally wrong and a bad physicist. But if you look at Aristotle's physics from the point of view of a scholar in Aristotle's time, he was doing very good physics that was worthy of the two millennia in which he was admired. Kuhn writes: “Might not the fault be mine rather than Aristotle's, I asked myself. Perhaps his words had not always meant to him and his contemporaries quite what they meant to me and mine.” Kuhn realized that he had to look at the context that Aristotle was working in: “The central change cannot be experienced piecemeal.” One has to look at the larger picture in order to appreciate Aristotle.
¹⁷

Kuhn's book
¹⁸
was considered . . . dare we say it? . . . revolutionary. Its most controversial thesis was that science is not a search for some deep-seated notions of truth. Rather, they work within a social structure. During the normal-science phase, they pose and answer questions based on the current paradigm. Their beliefs are formed by an educational process that unquestionably accepts the correctness of a particular paradigm. From this point of view, one can ask if there is a search for truth when one does normal science or if we are simply working within a culturally constructed paradigm. This was taken further by some philosophers to mean that science was on equal footing with some less scientific fields.

Another problem posed by philosophers is the rationality of paradigm changes. Within normal science, it is quite rational to see the next step. But when the entire paradigm has to be discarded for a new one, there is no set rational way to find a new paradigm. Some philosophers believe that a paradigm shift is essentially an irrational process. If one were to believe this, then science is no longer a reasonable quest to understand the universe we live in. Rather, its main changes are not ruled by reason.

What about progress in science? If one takes incommensurability seriously, then the notion that science progresses as time goes on is in doubt. Some people have, in fact, taken this position and do not believe that the science based on current paradigms is in any way better than the science based on previous paradigms. Here I have to take exception and criticize such ideas. There most definitely is scientific progress. Newton's system is better than Aristotle's system and, in turn, Einstein's system is better than Newton's system. Later systems explain more phenomena than earlier systems. Later systems explain phenomena better. No matter what some philosophers say, we will never abandon the heliocentric view and return to geocentrism.

Truth is another topic that is important to Kuhn, his followers, and some of his critics. Most people would say that as time goes on, our scientific theories might not be exact, but we are getting closer and closer to something we might call
the truth
. This truth does not live within some paradigm, but it is in some sense “out there” and does not depend on the paradigm scientists use to understand it. However, there are philosophers who disagree with this standard view. They say that there is no underlying truth and one can only view the physical world through the prism of some type of paradigm. Such philosophers argue that every paradigm until now has been wrong and there is no reason to believe that the current paradigm is somehow the correct view of the world. They would say that science is not progressing toward anything. Rather, as it changes paradigms, it is simply moving away from its past. The idea that there is a fixed set of ideas in the world independent of some paradigm was dubious to Kuhn. He felt that objective truth does not really exist. (While I cannot prove that these ideas about the ultimate nature of reality are wrong, I, and probably most scientists, find such ideas to be simply false.)

The End of Science

There is a feeling among some researchers that the work of scientists over the past few centuries has revealed all the mysteries of our universe and the job of science will be complete very soon. Scientists today have understood and described all the known forces that run the universe. They have unified most of them and shown how they are really the same force. They have explained the wonders of the different chemicals and their interactions. It has been demonstrated how the different materials in the universe are made of the same types of subatomic particles and what happens when they combine. Large parts of human and animal physiology are very clear to us. In short, we seem to know a lot of what makes the universe tick. These thinkers feel that in a little while all scientists will have to do is to “dot the i's and cross the t's.” There won't be any major scientific question that will remain open.